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several anomalies in the neutrino sector are pointing towards the existence of a new (sterile) neutrino state with a mass around 1 ev. the solid experiment is located at the sck•cen br2 research reactor in belgium and will investigate this possibility. using the large flux of anti-neutrino generated in the reactor, it will collect a high statistics sample of inverse beta decay (ibd) events. these will be used to study the energy and distance dependence of the neutrino flux, which in turn will be used un-ambiguous support or reject the evidence of sterile neutrinos being the cause of these anomalies. the measurement is challenging as one has to operate a detector very close to the high radiation environment of a nuclear reactor and on the surface with little overburden to shield against cosmic rays. solid is employing a new technology combining pvt (cubes of 5x5x5 cm3) and 6lif:zns(ag) scintillators (sheets 250 μm thickness) to face these challenges. the highly segmented detector is read out by a network of wavelength shifting fibres and mppcs, which allows for a precise localization of the ibd reaction products. neutrons captured in the 6li can be easily separated from electromagnetic particles (e+, γ), which are absorbed in the pvt, due to the different response of the respective scintillators. the 1.6-tons detector was installed towards the end of 2017 and is taking date since early 2018. we will describe the detector design, the experimental setup at br2 and the detection principle. this will be followed by a first look at the data. | solid: search for oscillations with a lithium-6 detector at the sck•cen br2 reactor |
the numi off-axis electron neutrino appearance (nova) experiment can detect muon neutrinos and measure their disappearance via oscillation between the near and far detectors. we will present recent results of muon neutrino disappearance analysis on 50% higher statistics then previous published results. better signal selection algorithm, based on deep neural network inspired by progress in computer vision community, is described. improved detector simulation and re-tuned cosmic rejection and energy estimation algorithms as well as a new fit in four hadronic energy fraction populations are performed. the data allows us to make the joint world best measurement of δm232 . | muon neutrino disappearance at nova |
prospect, the precision oscillation and spectrum experiment, is a reactor antineutrino experiment at a very short baseline. the prospect detector consists of a segmented 6li-doped liquid scintillator deployed at the onrl high flux isotope reactor (hfir) with minimal overburden (< 1 m.w.e.). this location provides one of the shortest baselines for a high-statistics measurement of reactor antineutrinos and the opportunity to test hard-to-reach regions of dark matter phase space. this talk will describe the data analysis to search for boosted dark matter in the prospect data. | cosmic ray boosted dark matter at prospect - experimental analysis |
the dune experiment is part of the next generation of neutrino oscillation experiments that seek to definitively answer key questions in the field. it will utilize liquid argon time projection chambers (lartpcs) enabling sub-mm spatial resolutions for unprecedented sensitivity. as part of prototyping designs for such a detector, in particular the single-phase (sp) and dual-phase (dp) technologies, two protodune detectors were built at the cern neutrino platform. protodune-sp was commissioned in fall 2018, with test beam data taken immediately after that. a key component of the lartpc energy calibration is the drift electron lifetime which corrects the charge attenuation caused by drift electrons captured by impurities. in this talk, i shall describe the analysis for measuring electron lifetimes with the prm system and using that to perform a run-by-run calibration of the lartpc charge response. this is a complementary analysis to the cosmic ray tagger (crt)-based measurement of the lifetime within the tpc volume and has important implications for dune where the crt-based methods will be more challenging due to the lack of cosmic statistics. | measurement of electron lifetime by the lar purity monitoring system at protodune-sp |
the 4 10 kt liquid argon time projection chambers (lar-tpcs) of the future dune experiment will enable precise measurements of the oscillation parameters and the discovery of cp violation for leptons, thanks to their excellent 3d imaging capabilities coupled with a high-resolution calorimeter. one or more modules of the dune detector may exploit a dual phase (dp) lar-tpc that, relying on the extraction of the charge produced in the liquid volume and its subsequent multiplication in argon gas, will increase the expected granularity and energy resolution. this poster summarizes the analysis technique under development for particles identification and energy reconstruction in dune-dp, and its preliminary validation using cosmic ray data from the cern 4 t demonstrator. it is shown also the status of protodune-dp, the dual-phase prototype of the dune detector, scheduled to take data in fall 2018, that will assess the potential of dual phase the technology for future neutrino detectors. | energy reconstruction in dune-dp |
nova is a long-baseline neutrino oscillation experiment, designed to make precision neutrino oscillation measurements using νμ disappearance and νe appearance. it consists of two functionally equivalent detectors and utilizes the fermilab numi neutrino beam. nova uses a convolutional neural network for particle identification of νe events in each detector. as part of the validation process of this classifier's performance, we apply a data-driven technique called muon removal. in a muon-removed electron-added study we select νμ charged current candidates from both data and simulation in our near detector and then replace the muon candidate with a simulated electron of the same energy. in a muon-removed decay-in-flight study we remove the muonic hits from events where cosmic muons entering the detector have decayed in flight, resulting in samples of pure electromagnetic showers. each sample is then evaluated by our classifier to obtain selection efficiencies. our recent analysis found agreement between the selection efficiencies of data and simulation within our uncertainties, showing that our classifier selection is generally robust in νe charged current signal selection. | data-driven cross checks for electron neutrino selection efficiency in nova |
orca (oscillations research with cosmics in the abyss) is a megaton-scale cherenkov neutrino detector currently under construction by the km3net collaboration, at a depth of 2450m in the mediterranean sea. atmospheric neutrinos cross the earth along a wide range of baselines, undergoing matter effects which enhance neutrino oscillations in the few gev energy range with a dependence on the neutrino mass ordering (nmo). the orca design consists of a dense configuration of multi-pmt optical modules, exploiting the excellent optical properties of deep seawater to reconstruct both cascade events (mostly νe {ν_e} ) and track events (mostly νμ ν_μ) down to a few gev. orca is expected to measure the nmo with a median significance greater than 3σ σ after a few years of operation. this contribution focuses on the methods and results of the sensitivity studies for the measurement of the mass ordering as well as oscillation parameters (θ23 θ_{23} , δm2 δ m^2 ). | sensitivity of orca to the neutrino mass ordering and oscillation parameters |
atmospheric neutrinos are produced by cosmic ray interactions in the atmosphere. these neutrinos have been used to study neutrino oscillations. i will discuss the neutrino oscillation studies with atmospheric neutrinos. | atmospheric neutrinos |
the deep underground neutrino experiment is a next-generation long-baseline neutrino oscillation experiment based on liquid argon time projection chamber technology. dune-s single-phase prototype protodune-sp at cern finished its two-year phase-1 running in july 2021, successfully collected test-beam and cosmic ray data. a key aspect of lartpc calibration is the lifetime of drift electrons. a purity monitor is a miniature tpc measuring the lifetime of electrons generated from the photocathode via the photoelectric effect. it enables continuous monitoring of the detector status, especially when filling the cryostat and when liquid argon recirculation systems operate. the purity monitoring system in protodune-sp phase-1 monitored liquid argon purity throughout its entire lifetime. it is essential to the experiment's successful commissioning, operation, and data taking. this poster discusses the design, implementation, and results of purity monitors and plans. | purity monitoring for protodune-sp |
the module-0 demonstrator is a ton-scale single-phase liquid argon time projection chamber (lartpc) operated as a prototype for the dune liquid argon near detector (nd-lar). based on the argoncube design concept, module 0 features true 3d pixelated charge readout, an advanced high-coverage photon detection system, and a low-profile resistive-shell field cage. here we show the analysis of a cosmic ray dataset acquired with this detector, operated at the university of bern in the spring of 2021. we demonstrate detector capabilities including the performance of the charge and light readout systems and signal matching between the two, detector purity and response uniformity. we will also compare the data to a microphysical detector simulation, performed with highly-parallelized gpu algorithms. this successful prototype validates key aspects of the design of the liquid argon near detector (nd-lar) for the deep underground neutrino experiment (dune), a future experiment that will address open issues in neutrino physics, such as the measurement of the charge-parity violating phase in neutrino oscillations and the determination of the neutrino mass ordering. | demonstration of a novel, ton-scale, single-phase lartpc with pixelated readout |
the large-scale water-based liquid scintillator (wbls) detector is a new opportunity for the neutrino community to accomplish competent long-baseline neutrino oscillation and unprecedented low-energy neutrino measurements. several table-top wbls detection systems have been implemented at bnl and lbnl. it is critical to advance further with a mid-scale demonstrator to understand and tune the wbls property and stability. a 1-ton detector located at bnl instrumentation building, equipped with 58 pmts (30 on the bottom and 28 on the wall) and muon scopes, was built in 2022. various liquid materials were developed and filled sequentially. the performance and stability of wbls for cosmic muons and an alpha source were measured. in this presentation, the latest experiment's status and the physics results will be shown. | results from 1-ton wbls testbed at bnl |
the deep underground neutrino experiment (dune) is a next-generation long-baseline neutrino oscillation experiment based on liquid argon time projection chamber (lartpc) technology. dune's single-phase (sp) prototype protodune-sp (pd-sp) at cern finished its two-year phase-1 running in july 2021, successfully collected test-beam and cosmic ray data. a key aspect of lartpc calibration is the lifetime of drift electrons, which corrects the charge attenuation caused by drift electrons captured by impurities. a purity monitor is a miniature tpc measuring the lifetime of electrons generated from the photocathode via the photoelectric effect. it enables continuous monitoring of the detector status, especially when filling the cryostat and when liquid argon recirculation systems operate. the purity monitoring system in protodune-sp phase-1 (pd-sp-i) monitored liquid argon purity throughout its entire lifetime. it is essential to the experiment's successful commissioning, operation, and data taking. i will discuss the design, implementation, and results of purity monitors in pd-sp-i and future plans. | purity monitoring for protodune-sp |
the deep underground neutrino experiment (dune) will address open issues in neutrino physics such as the measurement of the cp-violating phase in neutrino oscillations and the neutrino mass ordering. the module-0 demonstrator is a single-phase liquid argon time projection chamber (lartpc) operated as a prototype for the dune liquid argon near detector (nd-lar). based on the argoncube design concept, module-0 features a novel 80k-channel pixelated charge readout and advanced high-coverage photon detection system. the module-0 demonstrator was operated with cosmic rays in spring 2021, collecting a dataset of 25 million events. performance of the charge readout system will be presented. supported by doe de-sc0010113. | charge readout system in dune liquid argon near detector module-0 |
we study the model with three right-handed neutrinos which masses are smaller than the weak scale ${\cal o}(10^2)$ gev (called as the $\nu$msm). the model can explain the origin of neutrino masses by the seesaw mechanism, offer a candidate of dark matter and realize the baryogenesis via neutrino oscillation. the seesaw mechanism at such energy scales can induce phenomenon which are observable by experiments. as an example, we discuss the lepton universality of charged kaon decays in this model. it is shown that the heavy neutral leptons accounting for the neutrino masses and the cosmic baryon asymmetry can give a significant correction to the lepton universality, and that the deviation from the standard model prediction can be large as ${\cal o}(10^{-3})$ which will be probed by near future experiments. | probing baryon asymmetry of the universe by using lepton universality |
the deep underground neutrino experiment (dune) is a next-generation long base-line neutrino experiment, which aims to answer some of the fundamental questions about the universe. dune will measure the oscillation probabilities of neutrinos and antineutrinos at unprecedented precision to quantify the charge-parity (cp) violation in the leptonic sector, which will shed light on the matter-antimatter asymmetry in the universe. these measurements require a precision detector calibration that constrains the uncertainties from relevant detector response parameters. however, traditional calibration methods are insufficient due to the lack of abundant cosmic ray muons at the deep underground location, therefore new techniques must be developed to meet the calibration requirements. one of the main energy scale and resolution calibration strategies for dune is the pulsed neutron source (pns.) this device will inject quasi-monoenergetic neutrons into the detector modules, where their capture signatures can be used as a standard candle for energy scale and resolution calibration. in this talk, i will present the recent prototyping effort for the pns system including tests performed at the south dakota school of mines neutron lab. the basic calibration concept and the characterization results will also be discussed. | development of the pulsed neutron source for dune detector calibration |
the deep underground neutrino experiment (dune) is a leading-edge experiment for long-baseline neutrino oscillation studies, neutrino astrophysics and nucleon decay searches. protodune-dual phase (dp) is a 6 × 6 × 6 m3 liquid argon time-projection-chamber (lartpc) operated at the cern neutrino platform in 2019-2020 as a prototype of the dune far detector. in protodune-dp, the scintillation and electroluminescence light produced by cosmic muons in the lartpc is collected by photomultiplier tubes placed up to 7 m away from the ionizing track. in this paper, we present the performance of the protodune-dp photon detection system, comparing different wavelength-shifting techniques and the use of xenon-doped lar as a promising option for future large lartpcs. the scintillation light production and propagation processes are analyzed and compared to simulations, improving understanding of the liquid argon properties. | scintillation light detection in the 6-m drift length protodune dual phase liquid argon tpc |
the no νa experiment is a νe appearance neutrino oscillation experiment at fermilab. it identifies the νe signal by the electromagnetic (em) showers induced by the electrons in the final state of neutrino interactions. cosmic muon induced em showers, dominated by bremsstrahlung, are abundant in no νa far detector. we use the cosmic muon-removal technique to get pure shower sample from cosmic data. the large cosmic-em sample can be used to characterize the em signature and provides valuable checks of the mc simulation, reconstruction, pid algorithm, and calibration across the no νa detector. fermilab. | cosmic muon-removal technique for no νa experiment |
recently, the idea of using neutrino oscillations to measure the hubble constant was introduced. we show that such a task is unfeasible because for typical energies of cosmic neutrinos, oscillations average out over cosmological distances and so the oscillation probability depends only on the mixing angles. | using neutrino oscillations to measure h0? |
the km3net experiment is a next-generation neutrino telescope, consisting of two separate detection structures, organised as arrays of light sensors, and immersed in the depths of the mediterranean sea. the two detectors are the oscillation research with cosmics in the abyss (orca detector), located off the coast of france and the astrophysics research with cosmics in the abyss (arca detector), off the coast of sicily. identical in the design but differing by scale, these two detectors observe neutrino interactions in the sea water through cherenkov light produced by the interaction products at different energy ranges. specifically, orca aims at detecting atmospheric neutrinos to study their oscillation parameters, while arca will focus at higher energies on astrophysical neutrinos and the characterisation of their sources. among the latter topic, fast radio bursts (frb) are good candidates for multi-messenger emissions due to the huge energy involved in their burst. i will present the method and criteria of a multi-messenger analysis intended to search for spatial and temporal coincidences of astrophysical neutrino signals from km3net with frbs. the search uses a frb catalogue of around 800 sources among which 14 occured in the period ranging from january 2020 to march 2021, and were visible from the km3net site. | multi-messenger observations with the km3net telescope: search for high energy neutrinos coinciding with fast radio bursts |
several anomalies in the neutrino sector are pointing towards the existence of a new (sterile) neutrino state with a mass around 1 ev. the solid experiment is located at the sck•cen br2 research reactor in belgium and will investigate this possibility. using the large flux of anti-neutrino generated in the reactor, it will collect a high statistics sample of inverse beta decay (ibd) events. these will be used to study the energy and distance dependence of the neutrino flux, which in turn will be used un-ambiguous support or reject the evidence of sterile neutrinos being the cause of these anomalies. the measurement is challenging as one has to operate a detector very close to the high radiation environment of a nuclear reactor and on the surface with little overburden to shield against cosmic rays. solid is employing a new technology combining pvt (cubes of 5x5x5 cm3) and 6lif:zns(ag) scintillators (sheets 250 μm thickness) to face these challenges. the highly segmented detector is read out by a network of wavelength shifting fibres and mppcs, which allows for a precise localization of the ibd reaction products. neutrons captured in the 6li can be easily separated from electromagnetic particles (e+, γ), which are absorbed in the pvt, due to the different response of the respective scintillators. the 1.6-tons detector was installed towards the end of 2017 and is taking date since early 2018. we will describe the detector design, the experimental setup at br2 and the detection principle. this will be followed by a first look at the data. | solid: search for oscillations with a lithium-6 detector at the sck•cen br2 reactor |
now 2016 is the 9th workshop of a series started in 1998 in amsterdam. since the year 2000, this international workshop takes place in otranto (lecce, italy). now is locally organized by the infn sections and depts. of physics of bari and lecce, and is one of the few "major conference series" recognized by inspires in the field of neutrino physics, https://inspirehep.net/info/conferences/series the aim of the workshop is: to discuss neutrino oscillation physics, in particular current experimental data and their theoretical interpretation; to outline future investigations of neutrino masses and mixings; and to explore the links with various research fields in astroparticle physics and cosmology. the structure of the workshop includes five sessions, with plenary and parallel talks on several topics of current interest. the sessions for the now 2016 edition are: session i - oscillation parameters: present session ii - oscillation parameters: future session iii - multimessenger astrophysics session iv - neutrino masses, states and interactions session v - particle physics in the cosmos the now 2016 proceedings have been edited by antonio marrone (u. of bari and infn, bari), alessandro mirizzi (u. of bari and infn, bari), and daniele montanino (u. of salento and infn, lecce). for further information see the now website, http://www.ba.infn.it/now | neutrino oscillation workshop |
sox (short distance neutrino oscillations with borexino) is a new experiment that takes place at the laboratori nazionali del gran sasso (lngs) and it exploits the borexino detector to study the neutrino oscillations at short distance. in different phases, by using two artificial sources 51cr and 144ce-144pr, neutrino and antineutrino fluxes of measured intensity will be detected by borexino in order to observe possible neutrino oscillations in the sterile state. in this paper an overview of the experiment is given and one of the two calorimeters that will be used to measure the source activity is described. at the end the expected sensitivity to determine the neutrino sterile mass is shown. | the sox experiment in the neutrino physics |
pair-instability supernovae (pisne) are an exotic class of supernovae which, in addition to being fascinating in its own right (its very existence is a topic of debate), may be important for many areas of astrophysics (early stellar populations, galaxy/chemical evolution, cosmic reionization, etc.). at present, pisne are one of the three proposed mechanisms for explaining superluminous supernovae, though one major drawback is that pisn models predict longer rise times to peak luminosity than seen in observations of superluminous supernovae. model rise times can be reduced by having shallower progenitor envelopes and/or outward mixing of radioactive material during the explosions. here, we present explosions and light curves for four progenitor models, with relatively shallow envelopes, that span the pisn mass range. our light curves exhibit significantly shorter rise times than other pisne light curves. in addition, we investigate the effects of a multidimensional treatment during the explosive burning phase of pisne, including the first such treatment in 3d. we find a small amount of outward mixing of radioactive ni-56 that increases with the number of dimensions, however this mixing is insufficient to significantly alter the light curve rise time. we find significant mixing between the silicon and oxygen rich layers, especially in 3d, that may affect model spectra and should be investigated in the future. finally, we present the neutrino signals expected from our most massive and least massive pisn models. accounting for neutrino oscillations, we compute the expected event rates for current and future neutrino detectors. | multidimensional pair-instability supernova simulations and their multi-messenger signals |
in mountainous landscapes such as the central alps of europe, the bedrock topography is one of the most interesting subjects of study since it separates the geological substratum (bedrock) from the overlying unconsolidated units (ice). the geometry of the bedrock topography puts a tight constraint on the erosional mechanism of glaciers. in previous studies, it has been inferred mainly from landscapes where glaciers have disappeared after the termination of the last glacial epoch. however, the number of studies with a focus on the structure beneath active glaciers is limited, because existing exploration methods have limitation in resolution and mobility. the eiger-μ project proposes a new technology, called muon radiography, to investigate the bedrock geometry beneath active glaciers. the muon radiography is a recent technique that relies on the high penetration power of muon components in natural cosmic rays. specifically, one can resolve the internal density profile of a gigantic object by measuring the attenuation rate of the intensity of muons after passing through it, as in medical x-ray diagnostic. this technique has been applied to many fields such as volcano monitoring (eg. ambrosino et al., 2015; jourde et al., 2016; nishiyama et al., 2016), detection of seismic faults (eg. tanaka et al., 2011), inspection inside nuclear reactors, etc. the first feasibility test of the eiger-μ project has been performed at jungfrau region, central swiss alps, switzerland. we installed cosmic-ray detectors consisting of emulsion films at three sites along the jungfrau railway tunnel facing aletsch glacier (jungfraufirn). the detectors stayed 47 days in the tunnel and recorded the tracks of muons which passed through the glacier and bedrock (thickness is about 100 m). successively the films were chemically developed and scanned at university of bern with microscopes originally developed for the analysis of physics experiments on neutrino oscillation. the analysis of muon absorption rate enabled us to image a three-dimensional boundary shape between dense granite bedrock (∼ 2.7 g/cm3) and light ice part (∼ 0.8 g/cm3) in the very uppermost part of aletsch glacier. this is the first application of muon radiography to cryogenic science. further measurements are presently ongoing to image inside a much larger edifice of eiger glacier, which straddles on the western flank of the famous eiger mountain. references: ambrosino et al. (2015), j. geophys. res. solid earth, 120, 7290-7307. jourde et al. (2016), scientific reports, 6, 33406. nishiyama et al. (2016), pure appl. geophys., doi:10.1007/s00024-016-1430-9. tanaka et al. (2011), earth planet sci. lett., 306, 156-162. | bedrock topography beneath uppermost part of aletsch glacier, central swiss alps, revealed from cosmic-ray muon radiography |
utilizing powerful nuclear reactors as antineutrino sources, high mountains to provide ample shielding from cosmic rays in the vicinity, and functionally identical detectors with large target volume for near-far relative measurement, the daya bay reactor neutrino experiment has achieved unprecedented precision in measuring the neutrino mixing angle θ13 and the neutrino mass squared difference |δm2ee|. i will report the latest daya bay results on neutrino oscillations and light sterile neutrino search. | recent results from daya bay |
the opera experiment was designed to observe νμ→ντ oscillations through τ appearance on the cern neutrino to gran sasso (cngs) beam over a baseline of 730 km. opera was a hybrid experiment composed of lead plates and emulsion layers acting as a target for neutrino interactions. the experiment was complemented with electronic detectors: scintillator strips used as target trackers and muon spectrometers. a review of the opera final results is presented in this paper. | results from the opera experiment in the cngs beam |
danss is a highly segmented detector, which contains 2500 one meter long plastic scintillator strips. the danss detector is placed under an industrial reactor of the kalininskaya nuclear power plant. the distance to the core is varied on-line from 10.7 to 12.7 m, and the primary task of the experiment is a search for short-distance neutrino oscillations. this work contains results of the cosmic muons study based on the data obtained with the danss detector. in order to achieve these results, the specific algorithm of muon track reconstruction with 97 % efficiency was developed. we also present some preliminary results on the annual variability in the flux of cosmic muons, an evaluation of the < ethrcosθ > parameter and the correlation coefficient. | cosmic muons measurements in the danss experiment |
nova is a long-baseline neutrino oscillation experiment with functionally identical, segmented, tracking calorimeter near and far detectors. the detectors lie 14.6 mrad off-axis from the fermilab numi beam, with a well-defined peak in neutrino energy at 2 gev. the absolute calibration of the energy scale of the detectors is a major systematic uncertainty in long-baseline oscillation search in nova. neutrino detectors make use of some standard candles for absolute energy calibration. stopping muon energy distributions, michel electron energy distributions, and invariant π0 mass are among them. in this talk, we cover nova's use of a new method to identify π0 with cosmic origins in the nova far detector. we employ a computer vision based particle identifier using convolutional neural networks (cvn) to identify π0s, complementing an existing strategy to identify π0 from the neutrino beam using more traditional methods in the near detector. registered for phd at cochin university of science and technology, india and doing research in nova experiment at fermilab. | π0 mass reconstruction in nova far detector. |
from a cosmological perspective, scalar fields are well motivated dark matter and dark energy candidates. several possibilities of neutrino couplings with a time-varying cosmic field have been investigated in the literature. in this work, we present a framework in which violations of lorentz invariance (liv) and $cpt$ symmetry in the neutrino sector could arise from an interaction among neutrinos with a time-varying scalar field. furthermore, some cosmological and phenomenological aspects and constraints concerning this type of interaction are discussed. potential violations of lorentz and $cpt$ symmetries at present and future neutrino oscillation experiments such as icecube and km3net can probe this scenario. | neutrino lorentz invariance violation from cosmic fields |
neutrino oscillation experiments have provided compelling evidence for nonzero neutrino masses. the simplest and arguably most plausible explanation for the smallness of neutrino masses consists in adding to the particle spectrum of the standard model heavy right-handed neutrinos, with a majorana mass term that breaks lepton number by two units. notably, the out-of-equilibrium decay of the heavy neutrinos in the very first stages of our universe could also provide an explanation to the observed cosmic matter-antimatter asymmetry. here, we review the mechanism of leptogenesis through the decay of heavy right-handed neutrinos and its connection to low energy neutrino experiments. | leptogenesis from heavy right-handed neutrino decay |
the india-based neutrino observatory (ino) is a proposed underground facility located in india that will primarily house the magnetised iron calorimeter (ical) detector to study atmospheric neutrinos produced by interactions of cosmic rays with earth's atmosphere. the physics goal is to to make precision measurements of the neutrino mixing and oscillation parameters through such a study. we present here the results from detailed simulations studies, as well as a status report on the project. in particular, we highlight the sensitivity of ical to the open issue of the neutrino mass ordering, which can be determined {\it independent of the cp phase} at ical. | india based neutrino observatory, physics reach and status report |
operating 40 km off the coast of france since 2007, the antares detector is the largest deep-sea neutrino telescope in the northern hemisphere with an instrumented volume of more than 0.01 cubic kilometers. it consists of an array of 885 photomultipliers detecting the cherenkov light induced by charged leptons produced by neutrino interactions in and around the detector. the primary goal of antares is to search for astrophysical neutrinos in the tev-pev range. this comprises generic searches for any diffuse cosmic neutrino flux as well as more specific searches for astrophysical galactic and extragalactic sources. the search program also includes multi-messenger analyses based on time and/or space coincidences with other cosmic probes. the antares observatory is sensitive to a wide-range of other phenomena, from atmospheric neutrino oscillations to dark matter annihilation. in this contribution, recent results from the antares neutrino telescope will be presented. | recent results from antares |
the particle showers produced in the atmosphere due to the interactions of primary cosmic particles require a thorough understanding in the backdrop of searches for rare interactions. while the showers encompass the physics of strong, weak and electromagnetic interactions, the very first interactions are strong interactions producing hadronic showers which could introduce uncertainties in the estimates of particle yields. in this work, we made a comprehensive study of air shower simulations using various combinations of hadronic models and particle transport code of the corsika package. the hadronic particles, mostly pions and kaons decay to muons which are the most abundant charged particles on earth. the primary proton and helium distributions are taken as power law which are scaled to match the measured flux in balloon experiments at the top of atmosphere. the shower simulation includes production, transport, and decays of secondaries up to the ground level. in this study, we focus on the bulk of the spectra and particles which is computationally intensive and hence parallel processing of events is done on computer cluster. we provide a way to normalize the simulation results to be compared with the ground-based measurements namely, single and multiple muon yields and their charge ratios as a function of zenith angle and momentum. this provides a basis for comparisons among the six model combinations used in this study and the differences are outlined. most of the hadronic models in corsika produce the bulk ground based measurements fairly well. we use one of the best model combinations to quantitatively predict the absolute and relative yields of various particles at ground level as well as their correlations with primaries and with each other. the leptonic ratios are obtained as a function of energy and zenith angle which are important inputs for the neutrino oscillation physics. | cosmogenic particles at ground level and their correlations with primary particles |
being the primary source of energy in the solar corona, the magnetic field plays a dominant role in driving solar eruptions and heating the coronal plasma. however, direct measurement of coronal magnetic field suffers from several limitations, and is extremely difficult to obtain. using observations from the coronal multi-channel polarimeter, we derived the spatial distribution of plasma density and phase speed of the prevalent transverse magnetohydrodynamic wave in the corona, which allows us to map the coronal magnetic field strength. such measurements of the global coronal magnetic field provide critical information to disentangle different initiation mechanisms of solar eruptions and unveil the physical processes of coronal heating. | magnetoseismology for the solar corona: from10 gauss to coronal magnetograms |
solar probe plus (spp), currently in phase d, will be the first mission to fly into the low solar corona, revealing how the corona is heated and the solar wind and energetic particles are accelerated, solving fundamental mysteries that have been top priority science goals since such a mission was first proposed in 1958. the scale and concept of such a mission has been revised at intervals since that time, yet the core has always been a close encounter with the sun. the primary science goal of the solar probe plus mission is to determine the structure and dynamics of the sun's coronal magnetic field, understand how the solar corona and wind are heated and accelerated, and determine what mechanisms accelerate and transport energetic particles. spp uses an innovative mission design, significant technology development and a risk-reducing engineering development to meet the spp science objectives. in this presentation, we provide an update on the progress of the solar probe plus mission as we prepare for the july 2018 launch. | solar probe plus: a nasa mission to touch the sunmission status update |
in this work we present recent results from high-resolution direct numerical simulations and a phenomenological model that describes the radial evolution of reflection-driven alfven wave turbulence in the solar atmosphere and the inner solar wind. the simulations are performed inside a narrow magnetic flux tube that models a coronal hole extending from the solar surface through the chromosphere and into the solar corona to approximately 21 solar radii. the simulations include prescribed empirical profiles that account for the inhomogeneities in density, background flow, and the background magnetic field present in coronal holes. alfven waves are injected into the solar corona by imposing random, time-dependent velocity and magnetic field fluctuations at the photosphere. the phenomenological model incorporates three important features observed in the simulations: dynamic alignment, weak/strong nonlinear aw-aw interactions, and that the outward-propagating aws launched by the sun split into two populations with different characteristic frequencies. model and simulations are in good agreement and show that when the key physical parameters are chosen within observational constraints, reflection-driven alfven turbulence is a plausible mechanism for the heating and acceleration of the fast solar wind. by flying a virtual parker solar probe (psp) through the simulations, we will also establish comparisons between the model and simulations with the kind of single-point measurements that psp will provide. | on the radial evolution of reflection-driven turbulence in the inner solar wind in preparation for parker solar probe |
low first ionisation potential (fip) elements show enriched abundances in the slow solar wind and coronal loops compared to photospheric values. turbulence is likely to be a key physical mechanism to explain these abundances. turbulent mixing is indeed essential to prevent gravitational settling of heavy elements. moreover, the average turbulent lorentz force, the ponderomotive force, could explain the preferential lifting of low fip ions in the upper chromosphere and transition region. in this talk, we use unidimensional models of the solar atmosphere, to compute the turbulent properties around the transition regions in several regimes. we use the incompressible (or reduced) mhd formalism with the shell-atm code, and show that the turbulent field is consistent with both coronal heating and significant fip fractionation. then, we use the compressible mhd code pluto, and compare the turbulent properties of the two models. in particular, we look at the effect of chromospheric shocks on the propagation of alfvén waves near the top of the chromosphere that may act to modify wave properties in the ionisation region of heavy elements. this work has been funded by the erc project slow source - dlv-819189 | fip fractionation in the turbulent solar chromosphere and corona: incompressible and compressible models |
the solar wind is a unique laboratory to study the turbulent processes occurring in a collisionless plasma with high reynolds numbers. a turbulent cascade is a process that transfers the free energy contained within large scale fluctuations into the smaller scales and it is considered as the most important mechanisms responsible for heating of the solar corona and solar wind. the paper analyzes power spectra of solar wind velocity and magnetic field fluctuations that are computed in the frequency range around the break between inertial and kinetic scales. the study uses measurements of the bright monitor of the solar wind (bmsw) on board the spektr-r spacecraft with a time resolution of 32 ms complemented with 10 hz magnetic field observations from the wind spacecraft propagated to the spektr-r location. the statistics based on more than 42.000 individual spectra show that: (1) the spectra of both quantities can be fitted by two power-law segments; (2) the median slopes of parallel and perpendicular fluctuations of velocity and magnetic field components are different; (3) the break between mhd and kinetic scales as well as the slopes are mainly controlled by the ion beta parameter. these experimental results are compared with high-resolution 2d hybrid particle-in-cell simulations. in spite of several limitations, the model results agree well with the experimental findings. we discuss differences between both observations and simulations in relation to the role of important physical parameters (e.g., ion beta, temperature anisotropy, collisional age, fluctuation amplitude of the magnetic field) determining the properties of the turbulent cascade. | power spectral density of magnetic field and ion velocity fluctuations from inertial to kinetic scales |
the white light images from the large-angle and spectrometric coronagraph (lasco) c2 and c3 have shown small-scale periodic plasmoid releases from the tip of the helmet streamers. the density and velocity of these blobs show similarities with the slow solar wind. there are various scenarios proposed to comprehend the release mechanism for these plasmoids. most widely accepted explanations include interchange reconnection and significant proton coronal heating at the streamer tip. a three-dimensional global coronal model will be used to examine this intermittent blob release over a several day period. we use the new real time version of alfven wave solar model (awsom-r) to decrease the computational costs. in awsom-r, the global magnetohydrodynamic (mhd) equations for the lower corona are solved along one-dimensional magnetic field line threads. the alfven wave dissipation is partitioned into coronal heating of protons and electrons. we study how this heat partitioning affects plasmoid formation. we investigate the size and periodicity of the streamer blobs for carrington rotation 2109 (12 april 2011-09 may 2011) by constructing synthetic white light images from the time-dependent model and comparing our results with observations. | examining the release mechanism of intermittent streamer blobs |
the photosphere, transition region, and corona are host to a plethora of small, bright, transient phenomena, collectively known as bright points, or brightenings. given their ubiquity and frequency, bright points are likely an important signature of plasma heating and/or transport mechanisms. we present a novel and efficient wavelet-based method that automatically detects and tracks the evolution of a large set of bright points in solar imagery, from sdo, iris and sst. co-locating bright points across simultaneous multi-instrument observations of the photosphere, transition region, and corona enables a more comprehensive study of their characteristics. a statistical analysis of their characteristics such as occurrence rates, lifetimes and sizes are given, along with a more detailed study of individual events. through the study of a statistically significant set of bright points we attempt to place constraints on the underlying physical mechanisms. | an automated method to detect, track and characterise bright points in multi-instrument solar imagery. |
the new vacuum solar telescope is the most important facility of the fuxian solar observatory in china. based on the high spatial and temporal resolution nvst observations, we investigate the solar activities in the chromosphere and obtain some new results. (1) observations of a flux rope tracked by filament activation (yang et al. 2014a). the filament material is initially located at one end of the flux rope and fills in a section of the rope. then the filament is activated and the material flows along helical threads, tracking the twisted flux rope structure. the flux rope can be detected in both low temperature and high temperature lines, and there exists a striking anti-correlation between the hα and euv lines, which could imply some mild heating of cool filament material to coronal temperatures during the filament activation. (2) fine structures and overlying loops of homologous confined solar flares (yang et al. 2014b). at the pre-flare stage, there exists a reconnection between small loops. during the flare processes, the overlying loops, some of which are tracked by activated dark materials, do not break out. these direct observations may illustrate the physical mechanism of confined flares, i.e., magnetic reconnection between the emerging loops and the pre-existing loops triggers flares and the overlying loops prevent the flares from being eruptive. (3) magnetic reconnection between small-scale loops (yang et al. 2015). we report the solid observational evidence of magnetic reconnection between two sets of small-scale loops. the observed signatures are consistent with the predictions by reconnection models. the thickness and length of the current sheet are determined to be about 420 km and 1.4 mm, respectively. the reconnection process contains a slow step and a rapid step. we suggest that the successive slow reconnection changes the conditions around the reconnection site and disrupts the instability, thus leading to the rapid approach of the anti-parallel loops and resulting in the rapid reconnection.references:yang, s. h., et al. 2014a, apjl, 784, l36yang, s. h., et al. 2014b, apjl, 793, l28yang, s. h., et al. 2015, apjl, 798, l11 | solar activities observed with the new vacuum solar telescope |
context. magnetic bright points (mbps) are small, bright, and conspicuous magnetic structures observed in the solar photosphere and are widely recognized as tracers of magnetic flux tubes. previous studies have underscored the significance of mbps in elucidating the mechanisms of coronal heating. the continuous advancement of solar telescopes and observation techniques has significantly enhanced the resolution of solar images, enabling a more detailed examination of mbp structures. in light of the growing availability of mbp observation images, the implementation of large-scale automated and precise mbp segmentation methods holds tremendous potential to facilitate significant progress in solar physics research.aims: the objective of this study is to propose a deep learning network called mbp-transcnn that enables the automatic and precise pixel-level segmentation of mbps in large quantities, even with limited annotated data. this network is designed to effectively handle mbps of various shapes and backgrounds, including those with complex features.methods: first, we normalized our sample of mbp images. we then followed this with elastic deformation and rotation translation to enhance the images and expand the dataset. next, a dual-branch encoder was used to extract the features of the mbps, and a transformer-based global attention mechanism was used to extract global contextual information, while a convolutional neural network (cnn) was used to extract detailed local information. afterwards, an edge aware module was proposed to extract detailed edge features of mbps, which were used to optimize the segmentation results. focal loss was used during the training process to address the problem of the small number of mbp samples.results: the average values of precision, recall, f1, pixel accuracy, and intersection over union of the mbp-transcnn are 0.976, 0.827, 0.893, 0.999, and 0.808, respectively. experimental results show that the proposed mbp-transcnn deep learning network can quickly and accurately segment the fine structure of mbps. | a deep learning approach for automated segmentation of magnetic bright points in the solar photosphere |
this paper poses the problem of studying the role of large-scale electric currents propagating in the upper layers of the solar atmosphere in processes of coronal heating of the sun. for detecting and calculating the magnitude of the large-scale electric current, data on the distribution of the components of the magnetic field vector in the photosphere provided by the helioseismic and magnetic imager (hmi) on board the solar dynamics observatory (sdo) were used. photoheliograms of the sun's corona in the ultraviolet radiation channels at 131, 171, 193, and 211 å provided by the atmospheric imaging assembly (aia/sdo) were used to estimate the temperature in the corona above active regions (ars). the dynamics of the large-scale current and the average temperature in 9 regions with different levels of flare activity of the corona above the ars have been studied and charts of the spatial distribution of the temperature in the corona above the ars have been constructed. the following results have been obtained: 1. heating of the coronal matter owing to ohmic dissipation of large-scale electric currents proceeds in a stationary regime. 2. the increase in the average temperature in the corona above an ar during solar flares to <log t ¯>=6.3 -6.5 (2.0-3.2 mk) is caused, not only by heating of coronal structures by large-scale electric currents, but also by other processes at coronal elevations. 3. for the noaa 11899 and 12494 regions a reduction in the average temperature of the corona to <log t ¯>=5.7 (0.5-0.6 mk) was observed with a simultaneous drop in the values of the large-scale electric current to zero. these observations indicate that the mechanism for heating of the corona by ohmic dissipation of electric currents is shut off at zero values (within the computational errors) of the large-scale electric current. 4. in the noaa regions 12192 and 12371, when constructing charts of the temperature distribution in the corona outside flare events, hot structures with temperatures ≥ 10 mk were observed outside the flare events which appear to mark the location of the channel of a large-scale electric current at coronal elevations. for the noaa region 12192 this assumption is confirmed by a numerical simulation carried out in 2016. | large-scale electric currents in coronal heating processes above active regions on the sun |
magnetic switchbacks in the solar wind have been observed over a wide range of heliocentric distances in both the solar equatorial plane and at high latitudes. these structures consist of a perturbation or fold in the local magnetic field, leading to local inversion in the radial component of the field, as well as an enhancement in the radial plasma speed over the background flow. the correlation between the velocity and magnetic field components is consistent with large amplitude alfvén waves propagating away from the sun, suggesting an important role in transporting energy out into the heliosphere. since the launch of parker solar probe (psp), in-situ observations within 0.3 au for the first time have revealed an increased occurrence rate, larger amplitudes, and tendency of switchbacks to cluster in patches separated by quieter radial field intervals. these discoveries have generated significant interest in these structures and in particular their origin, which remains unsolved. psp observations show that patches of switchbacks have spatial scales of order of granulation cells in the solar photosphere, and exhibit enhanced ion temperatures and α-particle abundances over the background plasma. in this talk, i will provide an overview of the observational properties of switchbacks and patches from the first 10 solar encounters and how they provide clues about their source mechanisms deeper in the solar atmosphere. i will also discuss the potential implications for solar wind acceleration and coronal heating. | magnetic switchbacks from an observational perspective |
alfvén wave turbulence has emerged as an important heating mechanism to accelerate the solar wind. the generation of this turbulent heating is dependent on the presence and subsequent interaction of counter-propagating alfvén waves. this requires us to understand the propagation and evolution of alfvén waves in the solar wind in order to develop an understanding of the relationship between turbulent heating and solar wind parameters. in this paper we aim to study the response of the solar wind upon injecting monochromatic single frequency alfvén waves at the base of the corona for various magnetic flux tube geometries. we use an ideal magnetohydrodynamic (mhd) model using an adiabatic equation of state. an alfvén pump wave is injected into the quiet solar wind by perturbing the transverse magnetic field and velocity components. the alfvén waves were found to be reflected due to the development of the parametric decay instability (pdi). further investigation revealed that the pdi was suppressed both by efficient reflections at low frequencies as well as magnetic flux tube geometries. | flux tube dependent propagation of alfvén waves in the solar corona |
shocks ahead of coronal mass ejections (cmes) can accelerate solar wind plasma to high energies. ions heavier than protons can be used as tracers for the associated heating and acceleration mechanisms in the solar wind plasma. helium, as measured by the ace and wind satellites, is studied in a series of shocks associated with cmes. the heating seen in helium after the shock passage is compared to the proton heating in the each shock. the orientation of the shock normal to the magnetic field is also examined, as the structure of the shock can be oriented differently from one spacecraft to the next possibly explaining the variations in heating. a discussion of the scale factor of the structure of the shock and its influence on heating is discussed. | multi-spacecraft measurements of heavy ions at interplanetary shocks in front of coronal mass ejections |
in this paper, we characterize transverse oscillations as either alfvénic or landau-type in an incompressible non-ideal magnetohydrodynamic (mhd) fluid. we consider shear viscosity and magnetic diffusivity as dissipation mechanisms to derive a general dispersion relation for the incompressible mhd waves. the solutions of this dispersion relation for k as a function of ω - denoting by the source for any value of θ up to which magnetic tension acts as restoring force and dominates over internal friction forces - result in four roots, as follows. two roots, which have a high phase velocity $c_{\rm a}\cos\theta $ are identified as almost undamped propagating alfvén waves. the other two roots, which have a phase velocity $(2c_{\rm a}\cos\theta)/(\sqrt{\eta/\nu} + \sqrt{\nu/\eta})$, result in alfvénic-type disturbances of a much shorter decay length than the wavelength. in contrast, when internal frictional forces start dominating over magnetic tension (i.e. for the propagation perpendicular to the background magnetic field, where the tension in the magnetic field becomes zero), the solutions of the dispersion are akin to landau-type transverse oscillations. transverse waves of this type were initially reported by landau in an ordinary viscous fluid. however, our study corresponds to mhd visco-resistive fluid. the prediction for these lateral propagating transverse waves to be of landau type may be very useful to explain the heating of observed filamentary structures across the magnetic field on a very small spatial scale in the solar coronal plasma, wherein the heating rate is directly proportional to the operating frequency of the driver, while its damping length is inversely proportional to the square root of the frequency. | transverse oscillations of the incompressible mhd mode in the visco-resistive plasmas: an explanation of alfvénic to landau-type characteristics |
over most perihelion segments of the parker solar probe (psp) orbit (inside about 20 solar radii) the integrated science investigation of the sun-energetic particle instrument-lo (isois/epi-lo) observed significant non-dispersive intensities of ~100-1500kev 4he, o, mg, si, and fe, both close to and distant from the heliospheric current sheet (hcs), as determined in the psp fields and sweap instrument data. the ion angular distributions are strongly anisotropic away from the sun, and sometimes appear to be consistent with a conic distribution about the ~radial magnetic field, though to date this has not been resolved. inside the hcs, the ion intensities are typically lower than in regions adjacent to it. the observations are consistent with continuous perpendicular heating of the ions closer to the sun on open magnetic field lines, over many hours (and large distances in apparent source surface longitudes). given the apparently broad source surface connections and local minima inside the hcs, we argue that the hot ion source is not the hcs itself. based on the shape of the ion spectra and the higher energies reached by higher z (and higher charge state) ions, we suspect a heating mechanism that involves wave-particle interactions. | near-continuous coronal heavy ion acceleration observed on parker solar probe at perihelion |
the acceleration of the solar wind, particularly from open flux tubes, remains an open question in solar physics. countless physical processes have been suggested to explain all or parts of the coupled problem of coronal heating and wind acceleration, but the current generation of observations have been so far unable to distinguish which mechanism(s) dominates. in this project, we consider heating by alfvén waves in a three-dimensional, time-dependent reduced magnetohydrodynamics model. this model solves for the heating rate as a function of time due to the twisting and braiding of magnetic field lines within a flux tube, which is caused by alfvén waves generated at the single footpoint of the flux tube. we investigate three specific structures commonly found in the corona: 1) an open flux tube in a coronal hole, 2) an open flux tube on the edge of an equatorial streamer, and 3) an open flux tube directly neighboring an active region. we present the time-dependent heating rate, power spectra of fluctuations, and the time-averaged properties of the solar wind arising from each magnetic structure. we compare the time-averaged properties from the present modeling with previous results from a one-dimensional, time-steady code (cranmer et al. 2007) to better calibrate the physics in the lower-dimensional code and get a better understanding of the intricate role that bursty, transient heating from alfvén-wave-driven turbulence plays in the acceleration of the solar wind from different magnetic structures. | time-dependent modeling of solar wind acceleration from turbulent heating in open flux tubes |
observations and modeling shows that in the solar chromosphere the temperature rises from a minimum of below 4,000 k to over 6,000k. this rapid change occurs for reasons that remain a mystery but may prove essential to allowing energy to flow from the solar surface upward toward the corona. we will present the results of a set of massively parallel simulations and analytical theory showing that conditions in the coolest parts of the chromosphere will easily drive a previously unidentified thermal plasma instability that develops rapidly into turbulence. this meter-scale turbulence will modify the conductivities, temperatures, and energy flows through the chromosphere with important consequences for heating. this research should help us evaluate this thermal instability as a mechanism to convert neutral flow and turbulence energy into electron thermal energy in the quiet sun. | simulations reveal a new thermally-driven plasma instability in the solar chromosphere |
observations of active region (ar) coronae in different euv wavelengths reveal the presence of various loops at different temperatures. to understand the mechanisms that result in hotter or cooler loops, we study a typical bipolar ar, near solar disk center, which has moderate overall magnetic twist and at least one fully developed sunspot of each polarity. from aia 193 and 94 a images we identify many clearly discernible coronal loops that connect opposite-polarity plage or a sunspot to a opposite-polarity plage region. the aia 94 a images show dim regions in the umbrae of the spots. to see which coronal loops are rooted in a dim umbral area, we performed a non-linear force-free field (nlfff) modeling using photospheric vector magnetic field measurements obtained with the heliosesmic magnetic imager (hmi) onboard sdo. after validation of the nlfff model by comparison of calculated model field lines and observed loops in aia 193 and 94 a, we specify the photospheric roots of the model field lines. the model field then shows the coronal magnetic loops that arch from the dim umbral area of the positive-polarity sunspot to the dim umbral area of a negative-polarity sunspot. because these coronal loops are not visible in any of the coronal euv and x-ray images of the ar, we conclude they are the coolest loops in the ar. this result suggests that the loops connecting opposite polarity umbrae are the least heated because the field in umbrae is so strong that the convective braiding of the field is strongly suppressed.from this result, we further hypothesize that the convective freedom at the feet of a coronal loop, together with the strength of the field in the body of the loop, determines the strength of the heating. in particular, we expect the hottest coronal loops to have one foot in an umbra and the other foot in opposite-polarity penumbra or plage (coronal moss), the areas of strong field in which convection is not as strongly suppressed as in umbrae. many transient, outstandingly bright, loops in the aia 94 a movie of the ar do have this expected rooting pattern. | evidence of suppressed heating of coronal loops rooted in opposite polarity sunspot umbrae |
we aim to develop a diagnostic method for the coronal heating mechanism in active region loops. observational constraints on coronal heating models have been sought using measurements in the x-ray and euv wavelengths. statistical analysis, using euv emission from many active regions, was done by fludra and ireland (2008) who studied power-law relationships between active region integrated magnetic flux and emission line intensities. a subsequent study by fludra and warren (2010) for the first time compared fully resolved images in an euv spectral line of ov 63.0 nm with the photospheric magnetic field, leading to the identification of a dominant, ubiquitous variable component of the transition region euv emission and a discovery of a steady basal heating, and deriving the dependence of the basal heating rate on the photospheric magnetic flux density. in this study, we compare models of single coronal loops with euv observations. we assess to what degree observations of individual coronal loops made in the euv range are capable of providing constraints on the heating mechanism. we model the coronal magnetic field in an active region using an nlff extrapolation code applied to a photospheric vector magnetogram from sdo/hmi and select several loops that match an sdo/aia 171 image of the same active region. we then model the plasma in these loops using a 1d hydrostatic code capable of applying an arbitrary heating rate as a function of magnetic field strength along the loop. from the plasma parameters derived from this model, we calculate the euv emission along the loop in aia 171 and 335 bands, and in pure spectral lines of fe ix 17.1 nm and fe xvi 33.5 nm. we use different spatial distributions of the heating function: concentrated near the loop top, uniform and concentrated near the footpoints, and investigate their effect on the modelled euv intensities. we find a diagnostics based on the dependence of the total loop intensity on the shape of the heating function and discuss its range of applicability for loops of different length. | diagnostics of coronal heating in solar active regions |
more than four decades have passed since a link between solar wind magnetic sector boundary structure and mid-latitude upper tropospheric vorticity was discovered (wilcox et al., science, 180, 185-186, 1973). the link has been later confirmed and various physical mechanisms proposed but apart from controversy, little attention has been drawn to these results. to further emphasize their importance we investigate the occurrence of mid-latitude severe weather in the context of solar wind coupling to the magnetosphere-ionosphere-atmosphere (mia) system. it is observed that significant snowstorms, windstorms and heavy rain, particularly if caused by low pressure systems in winter, tend to follow arrivals of high-speed solar wind. previously published statistical evidence that explosive extratropical cyclones in the northern hemisphere tend to occur after arrivals of high-speed solar wind streams from coronal holes (prikryl et al., ann. geophys., 27, 1-30, 2009; prikryl et al., j. atmos. sol.-terr. phys., 149, 219-231, 2016) is corroborated for the southern hemisphere. a physical mechanism to explain these observations is proposed. the leading edge of high-speed solar wind streams is a locus of large-amplitude magneto-hydrodynamic waves that modulate joule heating and/or lorentz forcing of the high-latitude lower thermosphere generating medium-scale atmospheric gravity waves that propagate upward and downward through the atmosphere. simulations of gravity wave propagation in a model atmosphere using the transfer function model (mayr et al., space sci. rev., 54, 297-375, 1990) show that propagating waves originating in the thermosphere can excite a spectrum of gravity waves in the lower atmosphere. in spite of significantly reduced amplitudes but subject to amplification upon reflection in the upper troposphere, these gravity waves can provide a lift of unstable air to release instabilities in the troposphere thus initiating convection to form cloud/precipitation bands (prikryl et al., ann. geophys., 27, 31-57, 2009). it is primarily the energy provided by release of latent heat that leads to intensification of storms. these results indicate that vertical coupling in the atmosphere exerts downward control from solar wind to the lower atmospheric levels influencing tropospheric weather development. | is tropospheric weather influenced by solar wind through atmospheric vertical coupling downward control? |
the characterization of planetary exospheres today, relies on the development of a highly efficient ionization source, due to the scant neutral molecules (n < 108 cm -3) present in diffuse planetary coronae. these tenuous atmospheres provide insight on to physical processes known to occur such as: space weathering, magneto-atmosphere interactions, as well as atmospheric escape mechanisms, all of which are being heavily investigated via current 3d monte carlo simulations (turc et al. 2014, leblanc et al. 2016 in prep) at latmos. validation of these studies will rely on in-situ observations in the coming decades. neutral detection strongly depends on electron-impact ionization which via conventional cathode-sources, such as thermal filaments (heated up to 2000 k), may only produce the target ionization essential for energy-measurements with large power consumption. carbon nanotubes (cnts) however are ideal low-power, cold cathodes, when subject to moderate electric fields (e ~ 1 mv / m). we present our current device, a small cnt chip, of emission area 15 mm2, emitting electrons that pass through an anode grid and subsequent electrostatic analyzer. the device currently extracts hundreds of µamperes with applied external voltages ~ -150 volts, approaching minimum power consumption < 0.1 watts. the 3d modeling of field effect electrons ionizing a standard influx of neutrals is shown, using the multiphysics suite comsol. to better anticipate the species an ideal in-situ spacecraft equipped with such an ionization source would observe, we discuss europa's exosphere. europa's environment is largely shaped by the jovian plasma sputtering the icy regolith with heavy ions and electrons (kev < e < mev), producing predominately molecular oxygen (johnson et al. 2002). | towards a carbon nanotube ionization source for planetary atmosphere exploration |
impulsively generated, large-amplitude slow magnetoacoustic waves are often detected in active region coronal loops, associated with small non-eruptive solar flares. such a kind of loop oscillations were first discovered with the soho/sumer spectrometer, so often called "sumer" oscillations. recently, a similar phenomenon manifested as longitudinal intensity oscillations in terms of apparent sloshing motions along the flaring loop was detected by sdo/aia and hinode/xrt, and interpreted as standing or reflected propagating slow-mode waves. explorations of wave excitation and damping mechanisms have demonstrated their significance in potentially determining the transport coefficients, heating function, and nonuniform structuring by coronal seismology, as well as in understanding the mechanisms for quasi-periodic pulsations (qpps) often observed in solar and stellar flares. in this presentation, we first summarize the wave and thermal properties of seven longitudinal oscillation events observed by sdo/aia. the phase shifts and amplitude relationships between plasma temperature and density evolutions will be used to estimate the transport coefficients for thermal conduction and compressive viscosity based on linear theory and 1d mhd simulations. then we show our recent results in studying the excitation and damping mechanisms for standing and reflected propagating slow-mode waves using a 2d arcade loop model considering the density and temperature structures constrained by observed physical parameters. finally, the simulation results based on a 3d bipolar ar model will be compared and discussed. our results suggest that the modified transport coefficients such as significantly enhanced viscosity and suppressed thermal conduction help understanding the quick transition of an initial reflected propagating slow wave into a fundamental standing mode with strong damping in a hot loop at about 10 mk. | observation and modeling of standing and reflected propagating slow-mode waves in flaring coronal loops |
the solar chromosphere, the thin layer of the sun's lower atmosphere separating the photosphere from the corona, is the site of numerous complex physical processes. studying the structure and dynamics of chromospheric magnetic fields is a step toward understanding the heating mechanisms of the solar atmosphere and the origins of the solar wind. we present results from two-dimensional simulations of magnetic reconnection in the solar chromosphere using a multi-fluid model. this approach allows decoupling of the plasma and neutral components in the fluid which is necessary for modeling chromospheric magnetic fields. we seek to isolate effects of the hall effect and recombination by turning these terms on and off to explore how each individually affects chromospheric magnetic reconnection. we discuss the differences that arise amongst these cases both qualitatively through visualizing the simulation and quantitatively through measurements of the reconnection rate at the simulation origin. | recombination and the hall effect in simulations of chromospheric magnetic reconnection |
more than 70 years of the space-borne solar exploration clearly shows that extreme ultraviolet (euv) wavelengths are very useful for observations of the solar transition region and corona. because of this, almost all of the current and future solar space missions have euv payloads. unfortunately, china has never sent a solar euv spectrometer to space so far, which significantly restricts the chance for chinese solar physicists to have original discoveries and breakthroughs. now it is the right time to develop our own payloads and contribute to space exploration of solar physics. in the paper, the characteristics of solar irradiance as well as the common optical elements at euv wavelengths are introduced firstly. the history, current status and future perspectives of solar euv spectroscopic observations are systematically reviewed, including the instrument designs and major scientific achievements. three major types of spectroscopic observations are focused on, i.e., full-disk integrated irradiance measurements, low-speed spectroscopic imaging observations with a certain spatial resolution and two-dimensional fast spectroscopic imaging. then, a three-step development strategy is proposed to start chinese solar euv spectroscopic observations in space. the scientific objectives, observational requirements and candidate schemes of each step are discussed. moreover, a solar euv imager working at a wavelength that has never been done before is suggested. once the above explorations are successfully implemented, major advances towards our understanding of many unsolved solar mysteries will be made, including the accurate speed estimation of coronal mass ejections and forecast of their arrival times at the earth, the origin of solar wind and coronal heating mechanism, as well as the generation mechanism of solar eruptions. it will significantly elevate the level of key technologies involved in ultraviolet space explorations, too. | 太阳极紫外光谱探测的历史与展望', '太阳极紫外光谱探测的历史与展望', 'current status and future perspectives of solar spectroscopic observations at extreme ultraviolet wavelengths. |
investigating the differential emission measure (dem) of solar microflares provides an important constraint to understand complex magnetic energy releases and coronal heating mechanisms. the distribution of hot coronal plasma at higher temperatures (above 5 mk) during microflares is often loosely constrained, chiefly due to lack of high sensitivity measurements covering the wide range of temperatures observed. the focusing optics x-ray solar imager (foxsi) sounding rocket experiment performs direct imaging and spectroscopy of the sun in hard x-rays, in the energy range 4 to 20 kev. foxsi uses direct focusing grazing incidence x-ray optics, the first of its kind for dedicated solar observations, and offers better sensitivity for temperatures above 5 mk. we present an overview of microflare heating observed during the foxsi-2 flight on 2014 december 11 at 19:13 ut, from ar 12230, which indicates emission beyond 10 mk. brightening in extreme ultraviolet (euv) and soft x-rays (sxr) is also seen for this event from the coordinated observations using the atmospheric imaging assembly (aia) onboard sdo and x-ray telescope (xrt) onboard hinode. the aia and xrt observations provide a broad temperature coverage and are poorly constrained at the hotter end. we will demonstrate the recovery of the dem using foxsi-2 hxr data in conjunction with hinode/xrt and sdo/aia that offers unprecedented temperature coverage and produce a more constrained dem than is possible with typically available observations. we will highlight the significance of foxsi observations and discuss the energetics involved in the microflare heating. | constrained differential emission measure of microflare heating observed with foxsi-2, hinode/xrt and sdo/aia |
energy dissipation mechanism for weakly collisional or collisionless plasma is of principal importance for particle heating. depending on plasma conditions, different energy dissipation proxies emerge, including third-order law, j·e (the work done by the field on particles), -(p·∇)·u (pressure-strain interaction), etc. it is now understood that these channels for energy transfer, to a great extent, are correlated with coherent structures. by performing scale-dependent spatial filtering on the vlasov equation, we can extract information at prescribed scales and introduce several energy transfer functions. this approach affords a path to assess the relative importance of different transfer channels at all scales ranging from mhd to kinetic scales. it depicts that the energy exchange through j·e occurs at large scales, while the energy conversion from fluid flow to internal through -(p·∇)·u dominates at small scales. these two conversions are bridged by the scale-to-scale energy transfer. | scale dependence of energy transfer in turbulent plasma |
recent observational, theoretical, and experimental work strongly suggest that the damping of alfvén waves is responsible for the heating of solar coronal holes. in order to experimentally investigate potential damping mechanisms, we have performed a series of experiments at the large plasmadevice (lapd) at the university of california, los angeles. under experimental conditions scaled to approximate coronal holes, we have studied the propagation of alfvén waves propagating through a gradient parallel or perpendicular to the magnetic field in both the kinetic regime (electron thermal speed ≫ alfvén speed) and inertial regime (electron thermal speed ≪ alfvén speed). in the recent laboratory experiment of kinetic alfvén wave, it is observed that, in the presence of the gradient in the alfvén speed, the damping mechanism is not sufficient to explain the energy reduction in the plasma. in order to better understand the reduction in wave energy through the gradient, we are carrying out an analysis of alfvén wave propagation in the inertial regime. here we report results for alfvén waves in the inertial regime propagating through a parallel gradient. this work is supported, in part, by grants from the nsf solar-terrestrial program under grant ags-1834822 and the u.s. department of energy, office of science, office of fusionenergy science under award numbers de-sc0016602 and de-sc0021261. the experiments were performed at the basic plasma science facility (bapsf), which is supported by the doe and nsf, with major facility instrumentation developed via an nsf award ags-9724366. | experimental investigation of alfvén wave propagation in an inhomogeneous plasma |
in this talk, i will show our recent results on 3d simulations of coronal loops driven with transverse waves at the footpoints. we find that the transverse waves convert to turbulence via the kelvin-helmholtz instability (for standing waves) or uniturbulence (for propagating waves). the latter is turbulence generated from the interaction of the driven propagating waves with the counterpropagating waves which are generated in-situ because of the plasma structure. both of these turbulence generation mechanisms lead to fully turbulent loops, which allow for efficient energy dissipation and heating. | driven transverse waves lead to turbulent coronal loops and heating |
black hole accretion disks in x-ray binaries (xrbs) phenomenologically display two different x-ray emission states: a soft state with a low-energy thermal peak and a subdominant non-thermal component, and a hard state with a broad spectrum peaking in hard x-rays. the latter is of great interest from a plasma physics perspective, as the hard x-rays are believed to be powered by some form of plasma heating in the magnetized corona. the energization mechanism is not established, and one likely possibility is that it is fueled by the large-scale magnetic reconnection resembling solar flares. we perform 2d particle-in-cell simulations of magnetic reconnection that self-consistently follow the production of hard x-rays. our simulations follow ab-initio compton scattering of seed photons in the reconnection region and include photon-photon pair creation, which affects the high-energy tail of the spectrum. we investigate the reconnection layer of a moderate optical depth and a high compactness parameter relevant to xrb coronae, and find that it is capable of producing the observed hard-state spectrum of cyg x-1. | ab-initio comptonization in reconnecting current sheets of x-ray binary coronae |
the physics behind the heating of the solar corona and the acceleration of the fast solar wind from coronal holes (predominantly open field regions of the solar corona) is not well understood. recent observations of large-amplitude counter-propagating alfvén waves at the base of coronal holes suggest that the outward and the inward waves interact nonlinearly to generate turbulence which heats and accelerates the plasma. however, the mechanism of generating inward alfvén waves is yet to be fully established. most theories within the mhd framework invoke partial reflection of outward alfvén waves from gradients in the alfvén speed to explain the inward waves. to date, though, no experiment has reported the detection of a reflected alfvén wave in an experimental arrangement relevant to coronal holes. we have performed new experiments to detect a reflected wave from an alfvén speed gradient under conditions scaled to match coronal holes. the experiments were conducted in the large plasma device at the university of california, los angeles. our results show that the reflected alfvén wave energy increases as the ratio of the wavelength to the gradient scale length increases. the results of the experiments are presented. this work was supported by us doe frontier plasma science program funded by contract number de- ac0209ch11466. d.w.s. and m.h. were supported by the doe grant de-sc0021261. the experiments were performed at the basic plasma science facility (bapsf), supported by the doe and nsf, with major facility instrumentation developed via an nsf award ags-9724366. | study of alfvén wave reflection to address the solar coronal heating problem |
euv observations of active region (ar) coronae reveal the presence of loops at different temperatures. to understand the mechanisms that result in hotter or cooler loops, we study a typical bipolar ar, near solar disk center, which has moderate overall magnetic twist and at least one fully developed sunspot of each polarity. from aia 193 and 94 å images we identify many clearly discernible coronal loops that connect plage or a sunspot of one polarity to an opposite-polarity plage region. the aia 94 å images show dim regions in the umbrae of the sunspots. to see which coronal loops are rooted in a dim umbral area, we performed a non-linear force-free field (nlfff) modeling using photospheric vector magnetic field measurements obtained with the heliosesmic magnetic imager (hmi) onboard sdo. the nlfff model, validated by comparison of calculated model field lines with observed loops in aia 193 and 94 å, specifies the photospheric roots of the model field lines. some model coronal magnetic field lines arch from the dim umbral area of the positive-polarity sunspot to the dim umbral area of a negative-polarity sunspot. because these coronal loops are not visible in any of the coronal euv and x-ray images of the ar, we conclude they are the coolest loops in the ar. this result suggests that the loops connecting opposite polarity umbrae are the least heated because the field in umbrae is so strong that the convective braiding of the field is strongly suppressed. | suppression of heating of coronal loops rooted in opposite polarity sunspot umbrae |
we simulate the temperature profiles along coronal loops measured with aia dem tomography and field-line extrapolation by nuevo et al (2013). by varying the strength and nature of the heating mechanism, we modeled steady-state, gravitationally stable loops that have temperature profiles with local maxima below the loop apex. because these loops have negative vertical temperature gradients over much of their length, they have been called 'down loops' and were seen to exist primarily in equatorial quiet regions near solar minimum. in our models, the amount of heat deposited in the loop is attributed to two sources: (1) the dissipation of alfvén waves in a turbulent cascade, and (2) the dissipation of compressive waves over a variable length. the compressive waves are generated in a nonlinear process by which some fraction of the alfvén waves undergo mode conversion instead of contributing directly to the heating process. we found that when a large percentage (> 99%) of the alfvén waves underwent this conversion, the heating was greatly concentrated at the base of the loop and stable 'down loops' were created. in some cases, we found loops with three extrema that are gravitationally stable. we map the full parameter space to explore which conditions lead to which loop types, and we demonstrate that the simulated characteristics of the loops - including magnetic field strength, pressure, and temperature - are consistent with values measured by nuevo et al. (2013). for more details see schiff & cranmer (2016). | explaining inverted temperature loops in the quiet solar corona with magnetohydrodynamic wave mode conversion |
the solar wind undergoes significant heating as it propagates away from the sun, however the exact mechanisms heating the plasma are not yet fully understood. identifying the physical mechanisms responsible for this heating is fundamentally important to describe the solar corona and solar wind. parker solar probe and solar orbiter will provide a wealth of data from an unexplored region to quantify the heating contribution of proposed mechanisms including stochastic heating as a function of the heliocentric distance. as a preparation for these upcoming missions we study stochastic heating at 1 au. stochastic heating occurs when the motion of ions becomes chaotic as the amplitude of electromagnetic field fluctuations at scales comparable to the ion gyroscale exceed a critical value. under these conditions, the magnetic moment of ions is not conserved, allowing for diffusion across magnetic fields, consequently leading to perpendicular heating of the ions. we analyze over a decade of wind observations using previously proposed techniques and show that the nature of stochastic heating in various subsets of the solar wind is in qualitatively good agreement with predictions, focusing on the critical amplitude of magnetic fluctuations where stochastic heating starts operating. in the second part of this study, we repeat the analysis using a new approach and we demonstrate that our technique yields results, which are in excellent agreement with predictions and rely on fewer assumptions than previous methods. our technique allows us to study in detail how the turbulent energy is partitioned between ions and electrons. this novel analysis will be useful for studying data from parker solar probe and solar orbiter to determine what mechanisms heat the solar wind. | a new approach to study stochastic heating in the solar wind with implications for parker solar probe and solar orbiter |
quasi-periodic density fluctuations appear ubiquitous in the regions where the solar wind forms and accelerates. the origin of these fluctuations is still debated and could result from a number of physical processes including rising mhd waves, periodic impulsive heating or continual magnetic reconnection. the recent analysis of deep-field imaging campaigns carried out with the stereo cor-2 instrument highlight the omnipresence of density fluctuations with length scales of approximately 1 solar radius in both fast and slow solar winds. we use the time-dependent magneto-hydrodynamic model multi-vp of the solar wind to explore the mechanisms at play in the low corona that could produce such density fluctuations higher up in the atmosphere. we first test the idea that impulsive and periodic heating above the transition region in the corona could lead to density fluctuations higher up in the atmosphere. we investigate how such density fluctuations can be transmitted out in the solar wind beyond the sonic point. we present synthetic imagery that will help the future analysis of remote-sensing data that will be acquired by parker solar probe, solar orbiter and the polarimeter to unify the corona and heliosphere (punch) missions over the next decade. part of this work was funded by the european research council through the project slow_source - dlv-819189 | transient coronal heating as a source of density fluctuations imaged by stereo and future space missions |
a long-standing problem in solar physics is the observation of anomalous heating in the solar corona and in solar flares. this heating is often heuristically attributed to magnetic reconnection, but the precise thermalization mechanism has not been identified. in various other reconnection situations such as the magnetosphere and the laboratory, a similar strong, fast anomalous ion heating that cannot be explained by classical mechanisms has also been routinely observed. we explain these ubiquitous observations by showing that stochastic ion heating not only is intrinsic to collisionless reconnection but furthermore is sufficiently fast and strong to account for the observed anomalous ion heating. the critical element of our explanation is that in typical magnetic reconnection geometry, the magnetic field reconnects but the electron canonical circulation vector, a function of the magnetic field, does not reconnect. by exploiting the perpetual connectedness of the electron canonical circulation, the in-plane electric and magnetic fields are approximated and then demonstrated to satisfy the ion stochastic heating condition. the calculation is verified by an electron fluid simulation while computation of test particle orbits and comparisons to experiments provide further support for the validity of this heating mechanism. | stochastic heating as the ubiquitous fast ion heating mechanism in magnetic reconnection |
coronal heating mechanisms are notoriously difficult to constrain with current observations. we present new observations from an instrument designed to measure a critical diagnostic of the frequency heating events in active regions. the marshall grazing incidence x-ray spectrometer (magixs) is a sounding rocket mission that aims to observe the soft x-ray solar spectrum (0.6 2.5 nm) with both spatial and spectral resolution. this wavelength range has several high temperature and abundance diagnostics that can be used to infer the coronal heating frequency. magixs will observe the sun through a 12 x 33 slot, producing ``overlappograms, where the spatial and spectral information are overlapped and must be unfolded. in this presentation, i will report on the magixs launch and data collection and provide preliminary analysis of magixs observations. | preliminary results from the marshall grazing incidence x-ray spectrometer (magixs) |
turbulent cascade transferring the free energy contained within the large scale fluctuations of the magnetic field, velocity and density into the smaller ones is probably one of the most important mechanisms responsible for heating of the solar corona and solar wind and thus the turbulent behavior of these quantities is intensively studied. however, the temperature is also highly fluctuating quantity but behavior of its variations is studied only rarely. there are probably two reasons, first the temperature is tensor and, second, an experimental determination of the temperature variations requires knowledge of the full velocity distribution with a time resolution and such measurements are scarce. to overcome this problem, the bright monitor of the solar wind (bmsw) on board the spektr-r spacecraft uses the maxwellian approximation and provides the thermal velocity with 32 ms time resolution. we use these measurements and complement them with 10 hz magnetic field observations from the wind spacecraft propagated to the spektr-r location and analyze factors influencing the shape of the temperature power spectral density. a special attention is devoted to mutual relations of power spectral densities of different quantities like parallel and perpendicular temperature, magnetic field and velocity fluctuations and their evolution in course of solar wind expansion. | spectra of temperature fluctuations in the solar wind |
the solar wind is a unique laboratory to study the turbulent processes occurring in a collisionless plasma with high reynolds numbers. a turbulent cascade—the process that transfers the free energy contained within the large scale fluctuations into the smaller ones—is believed to be one of the most important mechanisms responsible for heating of the solar corona and solar wind. the paper analyzes power spectra of solar wind velocity, density and magnetic field fluctuations that are computed in the frequency range around the break between inertial and kinetic scales. the study uses measurements of the bright monitor of the solar wind (bmsw) on board the spektr-r spacecraft with a time resolution of 32 ms complemented with 10 hz magnetic field observations from the wind spacecraft propagated to the spektr-r location. the statistics based on more than 42,000 individual spectra show that: (1) the spectra of both quantities can be fitted by two (three in the case of the density) power-law segments; (2) the median slopes of parallel and perpendicular fluctuation velocity and magnetic field components are different; (3) the break between mhd and kinetic scales as well as the slopes are mainly controlled by the ion beta parameter. these experimental results are compared with high-resolution 2d hybrid particle-in-cell simulations, where the electrons are considered to be a massless, charge-neutralizing fluid with a constant temperature, whereas the ions are described as macroparticles representing portions of their distribution function. in spite of several limitations (lack of the electron kinetics, lower dimensionality), the model results agree well with the experimental findings. finally, we discuss differences between observations and simulations in relation to the role of important physical parameters in determining the properties of the turbulent cascade. | power spectral density of magnetic field and ion velocity fluctuations from inertial to kinetic ranges |
we investigate abundance variations of heavy ions in coronal loops. we develop and exploit a multi-species model of the solar atmosphere (called irap"s solar atmospheric model: isam) that solves for the transport of neutral and charged particles from the chromosphere to the corona. we investigate the effect of different mechanisms that could produce the first ionization potential (fip) effect. we compare the effects of the thermal force and of the ponderomotive force. the propagation, reflection and dissipation of alfvén waves is solved using two distinct models, the first one from chandran et al. (2011) and the second one that is a more sophisticated turbulence model called shell-atm. isam solves a set of 16-moment transport equations for both neutrals and charged particles. protons and heavy ions are heated by alfvén waves, which then heat up the electrons via collision processes. we show preliminary results on composition distribution along a typical coronal loop and compare with typical fip biases. this work was funded by the european research council through the project slow_source - dlv-819189. | simulating the fip effect in coronal loops using a multi-species kinetic-fluid model |
the large-scale solar wind speed distribution varies in time in response to the cyclic variations of the strength and geometry of the magnetic field of the corona. semi-empirical predictive laws (such as in the widely-used wsa law) parametrise the asymptotic solar wind speed via simple parameters describing the geometry of the coronal magnetic field. in practice, such scaling laws require ad-hoc corrections and empirical fits to in-situ spacecraft data, and a predictive law based solely on physical principles is still missing. i will discuss improvements to this kind of laws based on the analysis of very large samples of wind acceleration profiles in open flux-tubes (both from mhd simulations and potential-field extrapolations), and show that flux-tube expansion effectively control the locations of the slow and fast wind flows (as in wsa), but that the actual asymptotic wind speeds attained - specially those of the slow wind - are also dependent on field-line inclination. i will furthermore present a new solar wind model - multi-vp - which takes a coronal magnetic field map as input (past data or forecast), and computes a collection of solar wind profiles (1 to 30 rsun) spanning a region of interest of the solar atmosphere (up to a full synoptic map) at any instant desired in quasi-real time, while keeping a good description the plasma heating and cooling mechanisms. multi-vp provides full sets of inner boundary conditions for heliospheric propagation models (such as enlil; see https://stormsweb.irap.omp.eu/doku.php?id=windmaptable), bypassing the need to rely on semi-empirical approaches. i will fully discuss the predictive capabilities of the model (synthetic imagery and in-situ time series) and its suitability to real-time space-weather applications. this is work is supported by the fp7 project #606692 (helcats). | new stratagies for modelling and forecasting the background solar wind |
on 2 july 2019, a total solar eclipse was visible across south america. because the corona is a million times fainter than the photosphere, total solar eclipses provide vital opportunities to make coronal observations essential for providing insight into mechanisms behind coronal heating and the solar wind. an international team of 25 scientists, engineers, technicians and students (the solar wind sherpas) dispersed into 4 teams across chile and argentina to make white light, spectroscopic, and several narrow band (ar x, fe ix, fex, fe xi, fe xiii, fe xiv, and ni xv) observations of the solar corona. with support from nsf, four undergraduates from underserved populations (one from the university of hawai'i and three from bridgewater state university (bsu) in massachusetts) were part of the expedition team. the goal for including undergraduates was to expose them to field work in eclipse science, help them network with professionals in the field, and better prepare them for careers in solar physics. this research experience has already had a positive impact on these students' opportunities and preparation for future research work. eclipse expedition travel support for students and m. arndt was provided by nsf ags-1834662 awarded to the university of hawaíi, institute for astronomy. bsu students received summer stipends through bsu's atp program as well as the massachusetts nasa space grant consortium. a bsu cars grant provided additional travel support for m. arndt. | the south american total solar eclipse of 2 july 2019: an opportunity for undergraduate engagement in research |
the evolution of the solar wind from the corona to the earth and throughout the heliosphere is a complex interplay between local micro kinetics and large scale expansion effects. these processes in the solar wind need to be separated in order to understand and distinguish the dominant mechanism for heating and acceleration of the solar wind. with the upcoming launch in 2018 of parker solar probe and the launch of solar orbiter after, addressing the local and global phenomena will be enabled with in situ measurements. parker solar probe will go closer to the sun than any previous mission enabling the ability to examine the solar wind at an early expansion age. this work examines the predictions for what will be seen inside of the 0.25 au (54 solar radii) where parker solar probe will take measurements and lays the groundwork for disentangling the expansion and collisional effects. in addition, methods of thermal plasma data analysis to determine the stability of the plasma in the parker solar probe measurements will be discussed. | understanding non-equilibrium collisional and expansion effects in the solar wind with parker solar probe |
space weather forecasting requires precise estimation of the arrival time of eruptive events, which typically propagate through and interact with the solar atmosphere and solar wind. therefore, the arrival time estimation depends on the accuracy of modelling the solar atmosphere and the complex interactions. for instance, the euhforia 2.0 project expects an accurate and efficient coronal model that covers the region from the surface of the sun up to 0.1au, serving as the inner boundary condition for the heliospheric model.based on the open-source code coolfluid, we have developed a fully implicit mhd coronal model. the model has been validated by data-driven coronal simulations, and the fully implicit temporal solution significantly accelerates the numerical simulations. more physical mechanisms, e.g., the heating term(s), and numerical techniques, e.g., high-order schemes, are being developed to improve this model further. in this work, we specifically focus on the numerical flux schemes (lax-friedrichs, hll, etc.) of the finite-volume mhd solver used by the coronal model, and evaluate their performance and impact on the coronal simulations. both the internal structures and the quantities at the outer boundary are quantitatively compared.this research has received funding from the european union's horizon 2020 research and innovation programme under grant agreement no. 870405 (euhforia 2.0). | evaluations of numerical flux schemes of a coronal mhd model |
we present new results towards the explanation of the chromospheric-heating problem and the solar-wind origin, using a two-fluid model that takes into account the collisional interaction between ions (protons) and neutrals (hydrogen atoms). our aim is to further reveal the mechanism behind chromospheric heating and plasma outflows. we simulate and analyse the propagation and evolution of alfvén waves in the partially ionised solar chromosphere, consisting of ions + electrons and neutral fluids. the simplified model chromosphere is permeated by a vertical, uniform magnetic field. we perform numerical simulations in the framework of a quasi-1.5-dimensional (1.5d), two-fluid model in which alfvén waves are excited by a harmonic driver in the transverse component of the ion and neutral velocities, operating in the chromosphere. in the case of a small-amplitude driver, alfvén waves are weakly damped, and for the chosen wave periods of a few seconds, alfvén waves manage to propagate through the chromosphere and enter the solar corona. non-linear alfvén waves excited by a large-amplitude driver cause significant chromospheric heating and plasma outflows. we thus conclude that two-fluid alfvén waves with larger amplitudes can contribute to chromospheric heating and plasma outflows, which may result higher up in the solar-wind origin. | monochromatic two-fluid alfvén waves in the partially ionised solar chromosphere |
coronal holes are regions of the sun's atmosphere with open magnetic field lines that extend into interplanetary space. these regions are ≍ 200 times hotter than the underlying photosphere. recent observations of damping of alfvén waves in coronal holes suggest that a wave driven process may be responsible for the temperature rise[1,2]. the mechanism of this wave damping is unknown. we have explored the effectiveness of a longitudinal gradient in alfvén speed in reducing the energy of propagating alfvén waves under conditions scaled to match those in coronal holes. the experiments were conducted in the large plasma device[3] located at the university of california, los angeles. our results[4] show that the energy of the transmitted alfvén wave decreases as the inhomogeneity parameter, 𝜆/𝐿a, increases. here, 𝜆 is the wavelength of the alfvén wave, and $𝐿_{a}$ is the scale length of the alfvén speed gradient. for gradients similar to those in coronal holes, the waves are observed to lose a factor of ≍ 5 more energy than they do when propagating through a uniform plasma without a gradient. contrary to theoretical expectations, this reduction in the energy of the transmitted wave is not accompanied by observation of a reflected wave. nonlinear effects causing reduction in wave energy are ruled out as the amplitude of the initial wave is too small and the wave frequency well below the ion cyclotron frequency. decrease of alfvén wave energy due to mode coupling is unlikely, as no other mode is present. since the total energy must be conserved, it is possible that the reduced wave energy is being deposited in the plasma. these results pertaining to coronal holes are presented. | understanding the role of alfvén waves in heating solar coronal holes through laboratory experiments |
collisionless magnetic reconnection, which converts the magnetic energy into the kinetic energy of plasma particles via the heating or acceleration, has been believed widely to be able to explain various eruptive phenomena such as solar flares and geomagnetic storms. however, the microphysical mechanism of anomalous resistivity in the collisionless magnetic reconnection is still an unsolved fundamental problem. among the many physical mechanisms of anomalous resistivity generation, chaos-induced resistivity based on the chaos of the charged particle orbits near the magnetic neutral point is not the most popular formation mechanism, but its microscopic physical picture is the clearest. this paper first briefly reviews the early research and physical model of the chaos-induced resistivity in collisionless magnetic reconnection region, introduces the recent research progress of the chaos-induced resistivity, and expounds the future research direction of the chaos-induced resistivity. | chaos-induced resistivity in collisionless magnetic reconnection region |
the solar wind is a unique laboratory to study the turbulent processes occurring in a collisionless plasma with high reynolds numbers. a turbulent cascadethe process that transfers the free energy contained within the large scale fluctuations into the smaller onesis believed to be one of the most important mechanisms responsible for heating of the solar corona and solar wind. the paper analyzes power spectra of solar wind velocity and magnetic field fluctuations that are computed in the frequency range around the break between inertial and kinetic scales. we use the spacecraft moving around 1 au (wind, spektr-r) and compare the analysis with similar results from the spacecraft in other places of the heliosphere (parker solar probe, solar orbiter). these experimental results are compared with high-resolution 2d hybrid particle-in-cell simulations, where the electrons are considered to be a massless, charge-neutralizing fluid with a constant temperature, whereas the ions are described as macroparticles representing portions of their distribution function. in spite of several limitations (lack of the electron kinetics, lower dimensionality), the model results agree partly with the experimental findings. we discuss differences between both observations and simulations in relation to the role of important physical parameters (e.g., ion beta, temperature anisotropy, collisional age, fluctuation amplitude of the magnetic field) determining the properties of the turbulent cascade in different heliospheric locations. | variations of power spectral density of magnetic field and ion velocity fluctuations through the heliosphere |
the focus of many investigations on coronal wave heating has been to scrutinise the role of transverse (i.e. kink) modes; examining their damping by resonant absorption and the transfer of energy to alfvén modes. subsequently, the alfvén modes are then subject to phase mixing and this leads to plasma heating. more recently, a non-linear mechanism for energy transfer has also been proposed, the so called uni-turbulence. due to the ease with which they have been observed, the rapidly damped standing kink modes in active regions have spawned numerous studies investigating the role of resonant absorption in the observed damping. however, their counterparts in the quiet sun, the propagating kink waves, have received little attention. here i will discuss the results from a large-scale study of kink wave damping in the quiet sun. we find convincing evidence that the damping of the kink waves is significantly weaker than in active regions and suggests that resonant absorption/phase mixing/uni-turbulence are not important mechanisms for wave-based heating of the quiescent sun. i will also discuss the physical reason we suspect is behind this result and what it tells us about the fine-scale structure of the quiescent corona. | is phase mixing important in the quiet sun? |
the parker solar probe, launched in 2018, will reach a radial distance of about 9.8 rsun below the alfven surface, and has completed 7 orbits around the sun. one of the main objectives of the psp mission is to answer the outstanding questions about how the solar corona plasma is heated to millions of degrees kelvin, and how the solar wind is accelerated near the base of the solar corona. various heating mechanisms have been proposed, but one that is gaining increasing credence is related to the dissipation of low frequency magnetohyrodynamic (mhd) turbulence. so far, two kinds of turbulence transport models have been developed based on the incompressible mhd and nearly incompressible (ni) mhd phenomenologies. in the former turbulence model, the nonlinear interaction between counter propagating alfven waves produces quasi-2d turbulence, which dissipates and heats the solar corona. in the latter turbulence model, the quasi-2d turbulence is produced by the magnetic carpet and is the dominant component. when advecting through the solar corona, the dissipation of quasi-2d turbulence heats the solar corona to millions of degrees kelvin, and drives the solar wind from a subsonic to a supersonic speed. in this talk, we compare the ni mhd turbulence model results with the fast and slow solar wind flows of psp. the heating of electrons and protons in the fast solar wind flow along the trajectory of psp will also be discussed. | turbulence transport modeling and parker solar probe (psp) measurements |
the student thermal energetic activity module (steam) will explore how solar coronal plasmas are heated in flares and active regions by measuring the abundances of elements with low first ionization potential (fip) using soft (0.5-10 kev) and hard (5-30 kev) x-rays to distinguish signatures of reconnection-based coronal heating mechanisms. typically, coronal abundances of low-fip elements (e.g. mg, si, fe, ca) are enhanced by a factor of 4 above chromospheric values. measuring the abundances of low fip elements for various ions of these elements at different temperatures provides insight into the coronal or chromospheric origins of the heated plasma. x-ray emissions, including spectral lines and continuum, provide the most direct signatures of hot coronal plasma. a combination of hard and soft x-ray spectrometers will be used to measure incident photons and their energies within solar active regions. steam will utilize forward modeling with bremsstrahlung and atomic emission databases to fit physical parameters such as temperature and elemental abundance to observed spectral data. these elemental abundances allow steam to infer the origin of plasma for flares and active regions. steam is a student payload hosted on one of the punch small explorer spacecraft with an expected launch in late 2023 and 2-year prime mission. steams spectral observations of solar flares and active regions in soft and hard x-rays during the rising phase and maximum of solar cycle 25 will measure a wide range of activity to help constrain potential coronal heating mechanisms. steam is in the preliminary design phase and completing critical trade studies. we will present the steam science motivation, design, current progress, and future outlook. | student thermal energetic activity module (steam) x-ray spectrometer on the punch small explorer |
the development of a detailed understanding of turbulence in magnetized plasmas has been a long standing goal of the broader scientific community, both as a fundamental physics process and because of its applicability to a wide variety of phenomena. turbulence in a magnetized plasma is the primary mechanism responsible for transforming energy at large injection scales into small-scale motions, which are ultimately dissipated as heat in systems such as the solar corona and wind. at large scales, the turbulence is well described by fluid models of the plasma; however, understanding the processes responsible for heating a weakly collisional plasma such as the solar wind requires a kinetic description. we present the first fully kinetic eulerian vlasov-maxwell study of turbulence using the gkeyll simulation code. we focus on the pristine distribution function dynamics that are possible with the eulerian approach. we also present the signatures and form of dissipation as diagnosed via field-particle correlation functions. | <p>a full eulerian vlasov-maxwell study of turbulent dynamics and dissipation |
on the day-side of the earth magnetopause, the existence of magnetic reconnection has been proven by in-situ observations. interacting with the solar wind, the loop-like magnetic field on magnetopause breaks and releases energy to accelerate particles that result in magnetic substorms. in analogy with this process, during solar eruptions, the reconnection downflow carrying multiple magnetic islands can also induce magnetic reconnection on the loop top.to investigate the loop top magnetic reconnection (ltmr) processes, we perform high-resolution 2.5-dimensional mhd simulations of a post-eruption current-sheet (pecs) under the high-lundquist-number coronal environment. the fast reconnection scheme triggered by the plasmoid instability produces various downflow magnetic islands. it's found that ltmrs are of frequent occurrence when the small-scale magnetic islands encounter the loop-top field, and the ltmr rates are of the same order as in the pecs. the ltmr plays a key role in the formation of the flare loop. in the early phase, the flare loop is enlarged via the accumulation of multiple small-scale plasmoids merging with each other via reconnection. the flare loop finally evolves into a multi-layer structure involving three notably distinct parts, the stable cool kernel with high density, the low-density hot loop showing quasi-periodic oscillations, and the above-loop-top region where ltmr happens. steady magnetic loop structure and supersonic downflow are important conditions for the formation of terminal shocks (tss). according to our simulations, the violent plasmoid instability of pecs shatters the downflow into pieces. although supersonic downflows do form, they are relatively short and can only interact with the above-loop-top region. meanwhile, hit by intermittent downflows and magnetic islands, the above-loop-top region shows significantly anisotropic turbulent characteristics, which further hampers the formation of tss. our results thus imply that the ltmr might provide another important mechanism for particle acceleration and loop-top heating, and it can be more important than tss, especially for high lundquist-number conditions. | 2.5d mhd simulation of the evolution of magnetic islands toward flare loops |
the multi-slit solar explorer (muse) is a proposed nasa midex mission, currently in phase a, composed of a multi-slit euv spectrograph (in three narrow spectral bands centered around 171å, 284å, and 108å) and an euv context imager (in two narrow passbands around 195å and 304å). muse will provide unprecedented spectral and imaging diagnostics of the solar corona at high spatial (~0.5 arcseconds), and temporal resolution (down to ~0.5 seconds) thanks to its innovative multi-slit design. by obtaining spectra in 4 bright euv lines (fe ix 171å, fe xv 284å, fe xix-xxi 108å) covering a wide range of transition region and coronal temperatures along 37 slits simultaneously, muse will for the first time be able to ``freeze" (at a cadence as short as 10 seconds) with a spectroscopic raster the evolution of the dynamic coronal plasma over a wide range of scales: from the spatial scales on which energy is released (<0.5 arcsec) to the large-scale often active-region size (~ 170 arcsec x 170 arcsec) atmospheric response. we use advanced numerical modeling to showcase how muse will constrain the properties of the solar atmosphere on the spatio-temporal scales (<0.5 arcsec, <20 seconds) and large field-of-view on which various state-of-the-art models of the physical processes that drive coronal heating, solar flares and coronal mass ejections (cmes) make distinguishing and testable predictions. we describe how the synergy between muse, the single-slit, high-resolution solar-c euvst spectrograph, and ground-based observatories (dkist and others) can address how the solar atmosphere is energized, and the critical role muse plays because of the multi-scale nature of the physical processes involved. we focus on how comparisons between muse observations and theoretical models will significantly further our understanding of coronal heating mechanisms. this is a companion paper to cheung et al. (2021), also submitted to sh-17. | probing the physics of coronal heating with the multi-slit solar explorer (muse) |
hard x-rays (hxrs) provide a key diagnostic for energy release during a solar flare, as hxrs are emitted from flare-accelerated electrons and strongly heated flare plasma. in the case of a solar eruptive event, a flare is associated with the eruption of a coronal mass ejection (cme); though it is largely understood that reconnection is important for the eventual release of the cme, the triggering mechanism for the eruption and its relationship to flare energy release remains under debate. in this study, we leverage the optimal viewing geometry of the solar terrestrial relations observatory (stereo) relative to the solar dynamics observatory (sdo) and the reuven ramaty high-energy solar spectroscopic imager (rhessi) during 2010-2013 to provide simultaneous measurements of cme evolution, magnetic reconnection, and flare energy release for 12 solar eruptive events. we analyze the relative timing of these phenomena, focusing on event onset and fast-varying features, or bursts, in the time profiles to improve our understanding of particle acceleration mechanisms and the connections between flare and cme energization. notably, this study has identified two events with rarely-studied rhessi hxr flares occurring outside of active regions, which can provide additional insight on how the magnetic configuration affects the evolution of eruptive events. | investigating energy release during solar eruptive events with rhessi, stereo, and sdo |
two competing fundamental hypotheses are usually postulated in the solar coronal heating problem: heating by nanoflares and heating by waves. in the latter it is assumed that acoustic and magnetohydrodynamic disturbances whose amplitude grows as they propagate in a medium with a decreasing density come from the convection zone. the shock waves forming in the process heat up the corona. in this paper we draw attention to yet another very efficient shock wave generation process that can be realized under certain conditions typical for quiet regions on the sun. in the approximation of stationary dissipative hydrodynamics we show that a shock wave can be generated in the quiet solar chromosphere-corona transition region by the fall of plasma from the corona into the chromosphere. this shock wave is directed upward, and its dissipation in the corona returns part of the kinetic energy of the falling plasma to the thermal energy of the corona. we discuss the prospects for developing a quantitative nonstationary model of the phenomenon. | on an efficient shock wave generation mechanism in the quiet solar transition region |
drift waves are generally known to be present abundantly in plasmas which feature density gradients. in fusion devices, the drift wave mode triggers turbulence generally hindering the device's capability; in the earth's magnetosphere, the drift wave mode is most frequently present as the lower hybrid drift instability affecting current sheet stability and causing premature magnetic reconnection. studying the behaviour of drift waves in the environments of the solar chromosphere and the corona has been, however, hindered by two main factors; observationally, our current measurements do not allow for resolving such high-frequency small-scale structures and numerically, only a few plasma solar plasma codes are capable of separately resolving ion and electron dynamics, especially on small length scales. based on the limited previous research however, these waves could be a great candidate for at least partly explaining the coronal heating problem due to the fact that they are universally unstable and capable of dissipating heat and do not require a trigger mechanism beyond a simple density gradient. in this contribution, we review the nature and effects of drift waves in space plasmas and summarize past solar drift wave research. afterwards, we present our own results obtained with the fusion code gene (gyrokinetic electromagnetic numerical experiment), adjusted to model solar corona, which allowed us to estimate the nature, frequency and growth rate of drift waves in solar plasma conditions. | the role of drift waves in solar plasma |
we present numerical results from high-resolution fully kinetic simulations of plasma turbulence under the near-sun conditions encountered by parker solar probe during its first perihelion, characterized by a low plasma beta and a large level of turbulent fluctuations. the recovered spectral properties are in agreement with those from psp observations and recent high-resolution hybrid simulations just below the ion characteristic scales, i.e., the spectrum of the magnetic field exhibits a steep transition region with a spectral index compatible with -11/3. when the electron scales are reached a spectral break is observed and the spectrum steepens while still showing a clear power law. we discuss theoretical predictions for such a spectral behavior, based on a two-fluid model which assumes that a self-similar energy transfer across scales is occurring, without the need to include any kinetic process. we also analyse the role of magnetic reconnection and the statistics of reconnection events, as well as signatures in the proton and electron distribution functions hinting at mechanisms for energy dissipation. the results of this work represent a step forward in understanding the processes responsible for particle heating and acceleration and therefore on the origin of the solar wind and coronal heating. furthermore, they allow for reliable predictions for future spacecraft missions investigating electron-scale physics in low-beta plasmas. | fully kinetic simulations of electron-scale plasma turbulence in the inner heliosphere: a pathfinder for future spacecraft missions |
collisionless plasmas in space often evolve into turbulence by exciting an ensemble of broadband electromagnetic and plasma fluctuations. such dynamics are observed to operate in various space plasmas such as in the solar corona, the solar wind, as well as in the earth and planetary magnetospheres. though nonlinear in nature, turbulent fluctuations in the kinetic range (small wavelengths of the order of the ion inertial length or smaller) are believed to retain some properties reminiscent of linear-mode waves. in this paper we discuss what we understand, to the best of our ability, was peter gary's view of kinetic-range turbulence. we call it the gary picture for brevity. the gary picture postulates that kinetic-range turbulence exhibits two different channels of energy cascade: one developing from alfvén waves at longer wavelengths into kinetic alfvén turbulence at shorter wavelengths, and the other developing from magnetosonic waves into whistler turbulence. particle-in-cell simulations confirm that the gary picture is a useful guide to reveal various properties of kinetic-range turbulence such as the wavevector anisotropy, various heating mechanisms, and control parameters that influence the evolution of turbulence in the kinetic range. | the gary picture of short-wavelength plasma turbulence—the legacy of peter gary |
coronal heating remains one of the main unsolved problems in the solar physics. to identify the physical mechanisms responsible for heating the coronal plasma, we need to clarify where and how this heating occurs, and how the heating process is related to local and global properties of the magnetic field and plasma. the thermal radio emission, which is produced in strong magnetic fields of active regions due to the gyroresonance mechanism, is a promising tool for diagnosing the heating process. in this report, we analyze multiwavelength imaging radio observations of two solar active regions (ar 12827 and ar 12924) obtained in the test mode by the recently constructed siberian radioheliograph, in the frequency ranges of 3-6 and 6-12 ghz, respectively. we compare the observed radio maps with synthetic images (produced using the gx simulator numerical tool) based on the extrapolated magnetic field and the thermal plasma structure determined by a hydrodynamic model within a range of parametric heating laws; we search for the model that would provide the best agreement with the observations at all available radio frequencies. the obtained results do not directly match any of the widely discussed heating models; on the other hand, they (together with our previous analysis of the nobeyama radio observations at 17 ghz) provide an additional dimension to probing the coronal plasma and thus can offer clues for development of a more advanced coronal heating model. | diagnosing coronal heating in solar active regions with multiwavelength radio observations |
physical quantities, such as ion temperature and non-thermal velocity, provide critical information about the heating mechanism of the million-degree solar corona. we provide new constraints to ion temperatures using euv line widths, only assuming that the plasma non-thermal velocity is the same for all ions. we measured ion temperatures at the polar coronal hole boundary observed in 2007 by hinode/eis and soho/sumer. the temperatures of ions with the charge to mass ratio (z/a) less than 0.20 or greater than 0.33 are much higher than the local electron temperature. the measured ion temperature first decreases with the z/a to 0.25 and then increases with the charge-to-mass ratio. we ran the alfvén wave solar model-realtime (awsom-r) and the spectrum module to validate the ion temperature diagnostic technique and to help interpret the results. we suggest that the widths of hot lines in the coronal hole (e.g., fe xii, fe xiii) are also affected by the solar wind bulk motions along the line of sight. we discussed the factors that might affect the line width fitting, including the instrumental width and non-gaussian wings in some bright sumer lines that can be fitted by a double-gaussian or a kappa distribution. our study confirms the presence of preferential heating of heavy ions in the coronal holes and provides new constraints to the coronal heating models. | estimating ion temperatures at the polar coronal hole boundary |
solar flares result in an increase of the solar irradiance at all wavelengths. while the distribution of the flare fluence observed in coronal emission has been widely studied and found to scale as f(e) ~ e^{-\alpha}, with \alpha slightly below 2, the distribution of the flare fluence in chromospheric lines is poorly known. we used the solar irradiance measurements observed by the sdo/eve instrument at a 10s-cadence to investigate if there is a dependency of the scaling exponent on the formation region of the lines (or temperature). we analyzed all flares above the c1 level since the start of the eve observation (may 2010) to determine the flare fluence distribution in 16 lines covering a large range of temperature, several of which were not studied before. our results show a small downward trend with the temperature of the scaling exponent of the pdf, going from above 2 at lower temperature (a few 10^4 k) to about1.8 for hot coronal emission (several 10^6 k). however, because colder lines also have smaller contrast, we could not exclude that this behavior is caused by including more noise for smaller flare for these lines. we discuss the method and its limits and tentatively associate this possible trend to the different mechanisms responsible for the heating of the chromosphere and corona during flares. | on the variation of the scaling exponent of the flare fluence with temperature |
we suggest a novel mechanism of a coronal mass ejection based on the electron weibel instability [1] of an anisotropic distribution of hot (up to multi-kev) electrons in the presence of an external magnetic field. namely, we show that, under certain conditions in the solar or stellar coronal arches, the weibel-type instability can lead to a fast generation of a small-scale quasi-magnetostatic turbulence and a considerable deformation of the total magnetic field. it occurs if, for some reason, a sufficiently high degree of electron anisotropy arises in the arches and a saturated magnetic field of the instability is greater than or of the order of the initial magnetic field of the arches. we derive the approximate analytical formulae for a growth rate, a suppressing external magnetic field and a wave number range of the weibel electron instability in a homogeneous collisionless bi-maxwellian plasma with an axis of the highest temperature directed along the external magnetic field and with an optimal wave vector of the weibel perturbations lying in a transverse direction. we carry out typical estimates of the aforementioned values for coronal arches with a plasma density ∼ 1010 - 1012 cm-3, a magnetic field from tens to hundreds gauss and a weibel-instability scale from sub- to several meters. we find the necessary energy content and degree of anisotropy of hot electrons required for an explosive increase of the energy density of the weibel quasi-magnetostatic turbulence up to the value comparable to the energy density of the coronal magnetic field during a time period less or of the order of the hot-electron injection time ∼ 1 - 100 s. as a result, a fast growth of the transverse particle temperature and a simultaneous strong decay of the plasma conductivity along the coronal magnetic field are expected. also, an accompanying small-scale magnetic-field reconnection process and a turbulent ion flow will follow and destroy the magnetic and kinetic pressure balance. we carry out two- and three-dimensional pic-simulations of the nonlinear development of the aforementioned weibel instability by means of the epoch code for a wide range of parameters of the relatively cold coronal plasma and the hot anisotropic fraction of injected electrons in the presence of the external magnetic field of the order of the saturated (self-generated) magnetic field. this modeling demonstrates a formation of a large number of the small-scale current filaments and supports strongly the suggested weibel mechanism of the coronal mass ejection, at least for an indicated class of the coronal arches with a fast electron heating expected under well-known conditions in an atmosphere of the stars of the late-type spectral classes. however, a numerical simulation of the long-term nonlinear stage of the weibel instability in a magnetized collisionless plasma with a long enough and powerful injection of hot electrons into a region of a large scale comparable with the transverse size of a coronal arch is still a challenging problem. the analytical investigation of the weibel instability process in the presence of an external magnetic field was supported by the russian science foundation, project no. 21-12-00416. the numerical analysis of the nonlinear stage of this process was supported by the russian foundation for basic research, grant mk no. 18-29-21029. simulations were carried out in the joint supercomputer center of the russian academy of sciences. 1. kocharovsky vl. v., kocharovsky v. v., martyanov v. y., tarasov s. v. analytical theory of self-consistent current structures in a collisionless plasma // phys. usp. 2016. v. 59, n. 12. p. 1165-1210. doi: 10.3367/ufne.2016.08.037893. | weibel-instability mechanism of a coronal mass ejection: analytical results for the growth rate and pic-modeling of the nonlinear stage in the presence of an external magnetic field |
george fisher has worked in solar physics and astronomy for over 40 years. he will review contributions made by him and his collaborators to understanding the dynamics of the atmosphere during solar and stellar flares. he will then describe research on the dynamics of magnetic fields in the solar interior, using thin flux tube models as well as mhd simulation. he will then discuss constraints on coronal heating mechanisms from combined magnetic field and x-ray observation. finally, he will describe the efforts that he and collaborators have made to develop "data-driven" models of the solar atmosphere, focusing on inversion techniques to determine velocity fields from a sequence of images, and to find the electric field in the photosphere from the temporal evolution of magnetic fields observed there. | understanding the dynamics of magnetic field and plasma in the interior and atmosphere of the sun |
we present the spatially resolved absolute brightness of fe x, fe xi and fe xiv coronal emission lines observed during the 2019 july 2 total solar eclipse between 1.08 and 3.0 rsun. the topology is that of a classic solar minimum corona, with a dipole field dominance showcased by large polar coronal holes and two wide equatorial streamer belts. the fe xi line is found to be the brightest line followed by fe x and fe xiv (in disk bsun units). all lines vary in brightness between streamers and coronal holes; while fe xiv has the largest variation, fe x remains rather uniform with latitude. the fe line ratios are used to infer the relative ionic abundances and electron temperature (te) throughout the corona, yielding values from 1.2 mk in coronal holes up to 1.7 mk in the core of streamers. the line brightnesses and inferred te values are compared to the psi magnetohydrodynamic (mhd) model prediction of the eclipse. the mhd model predicts the fe lines rather well in the coronal streamers but underestimates the brightness of the fe lines in coronal holes. the mhd model generally underestimates the te values, especially in polar open field regions, pointing to a slightly insufficient heating mechanism and/or limitations in the modeling approach. | inferences of the absolute brightness of fe x, xi and xiv, and the electron temperature from the 2019 total solar eclipse |
gravity induced resonant emission (gire) has been proposed as the mechanism of coronal heating; here we are comparing this with multi photon ionisation (mpi) in laser. we find both are same, except electron damping as a pre-phase mechanism to initiate mpi in gire. a high intensity laser field used for mpi, but in gire, this happens at resonance condition when the larmour radii of the particles are same. the temporal compression of photons is achieved by grating devise, but in gire, this is done by field deficit created due to the loss of electrons at resonance condition and this loss is compensated by photo electrons emitted during mpi. fig.1 (a) \& (b) are plots of mpi in laser and resonance condition of gire, shows absolute resemblance except the wider range of frequency spectrum in gire. | multi photon absorption in gravity induced resonant emission |
the student thermal energetic activity module (steam) is a student-built and operated instrument aboard the punch/nfi spacecraft. expected to launch in mid-2025 with a 2-year prime mission, steam will observe near the maximum of solar cycle 25. steam aims to increase understanding of coronal plasma heating mechanisms using measured abundances of elements with low first-ionization potentials (fip). the relative abundances of low-fip elements (e.g., fe, mg, ca, si) are increased in the corona by 4 times above typical chromospheric values. the abundances of these elements thus provide insight into the origins of heated plasma in flares and active regions. emission from these low-fip elements will be measured using both soft (0.5-10 kev) and hard (5-30 kev) x-ray spectrometers that measure energies of incident photons with resolutions of <0.3 and <1 kev respectively. these x-rays, including spectral lines and continuum, provide the most direct signatures of hot coronal plasma. on-ground preflight calibration using radioactive isotope sources fe-55, zn-65, ba-133, cd-109, and am-241 was performed to determine the spectrometer gain and offset values, spectral resolution, and attenuation of x-rays through the filters. spectral data collected in flight will be fit to models incorporating both bremsstrahlung and atomic emission lines to estimate both the temperature and elemental composition of the observed plasma. steam will explore the energetic processes and origins of plasma in the corona that provide the source regions of solar wind outflows that punch will observe. together, these two missions will provide a better understanding of the processes between the corona and the heliosphere. punch is currently in phase c. the steam flight model is currently being built, with an expected delivery in march 2023. we will present the steam science motivation, design, current progress, and future outlook. | steam - understanding origins of coronal plasma through elemental abundances in x-ray spectra |
plasma-neutral coupling (pnc) in the solar atmosphere concerns the effects of collisions between charged and neutral species’. it is most important in the chromosphere, which is the weakly ionized, strongly magnetized region between the weakly ionized, weakly magnetized photosphere and the strongly ionized, strongly magnetized corona. the charged species’ are mainly electrons, protons, and singly charged heavy ions. the neutral species’ are mainly hydrogen and helium. the resistivity due to pnc can be several orders of magnitude larger than the spitzer resistivity. this enhanced resistivity is confined to the chromosphere, and provides a highly efficient dissipation mechanism unique to the chromosphere. pnc may play an important role in many processes such as heating and acceleration of plasma; wave generation, propagation, and dissipation; magnetic reconnection; maintaining the near force-free state of the corona; and limiting mass flux into the corona. it might play a major role in chromospheric heating, and be responsible for the existence of the chromosphere as a relatively thin layer of plasma that emits a net radiative flux 10-100 times greater than that of the overlying corona. the required heating rate might be generated by pedersen current dissipation triggered by the rapid increase of magnetization with height in the lower chromosphere, where most of the net radiative flux is emitted. relatively cool regions of the chromosphere might be regions of minimal pedersen current dissipation due to smaller magnetic field strength or perpendicular current density. this talk will discuss pnc from an mhd point of view, and focus on the basic parameters that determine its effectiveness. these parameters are ionization fraction, magnetization, and the electric field that drives current perpendicular to the magnetic field. by influencing this current and the electric field that drives it, pnc directly influences the rate at which energy is exchanged between the electromagnetic field and particles. in this way, pnc can have a strong influence on the energetics of a process that involves the conversion of magnetic energy into particle energy, which subsequently appears as radiation, waves, bulk flow, and heating. | basic properties of plasma-neutral coupling in the solar atmosphere |
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