alx-ai/arxiv_papers · Datasets at Hugging Face

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ow as a
function of latitude during 1996 { 2006. Each curve corresponds to a dierent
year as indicated on the right. To improve lisibility, years 1997 and above are
shifted by multiples of 10 m s1. The blue curves until 2002 show the advection of
supergranulation as measured by time-distance helioseismology (Gizon & Rempel
2008) and MDI full-disk data (2 { 3 months per year). The red curves from 2001
are averages (from the surface down to 7 Mm) of the meridional
ow inferred by
ring-diagram analysis and GONG data (Gonz alez Hern andez et al. 2008). The
ring-diagram values are multiplied by a factor of 0 :8 to ease the comparison. Note
the local maximum moving towards the equator, from 25in 1996 to 10in 2006.50 Gizon, Birch & Spruit
Figure 21: Solar cycle variations of the meridional and zonal
ows in the near-
surface layers. ( Top) Time residuals of the meridional
ow after subtraction of
the average meridional
ow for 1996{2006 (from Figure 20 ). The color scale
is in units of m s1. The rst eleven years (the observations) are extrapolated
into the future by tting the eleven-year periodic component. The thick black
curves represent the mean latitude of activity estimated from Mount Wilson mag-
netograms. ( Bottom ) Time residuals of the zonal
ows after subtraction of the
mean rotational velocity for the period 1996{2002, followed by the eleven-year
periodic component. Flows are deduced from the advection of the supergranula-
tion in MDI time-distance divergence maps (Gizon & Rempel 2008). The color
scale is in units of m s1.Local Helioseismology 51
Figure 22: Farside imaging. ( a) Ray-path diagram for 2+2 skip farside imag-
ing (Lindsey & Braun 2000). Waves seen leaving (arriving) at the pupils on the
visible surface of the Sun travel in the direction of the yellow (green) arrows.
The waves skip from the solar surface once before, and once after, reaching the
focal point on the farside of the Sun. Active regions located at the focal point
induce small phase shifts into the waves. ( b) GONG farside images (lighter yel-
low background) combined with magnetograms of the front side (darker yellow
background) covering a 12 day period each. Each full-Sun map is plotted as a
function of Carrington longitude (latitude in a co-rotating frame) and latitude.
The active region NOAA 9503 (August 2001) is seen to form on the farside of
the Sun and then rotate onto the visible disk. Courtesy of Charles Lindsey.52 Gizon, Birch & Spruit
10 FLARE-EXCITED WAVES
The excitation of solar oscillations by a
are was rst observed by Kosovichev &
Zharkova (1998) using MDI data. Since then, many other examples have been
found (e.g. Donea et al. 2006). Figure 23 shows a summary of some observa-
tions of the waves generated by the
are of 15 January 2005. In this example,
the location of the wave source (as estimated from helioseismic holography) is
seen to nearly coincide with the hard x-ray emission as seen by the RHESSI
spacecraft. The seismic waves are rst seen about twenty minutes after the hard
x-ray emission and propagate outwards according to the time-distance relation
(Figure 6a). In addition to exciting local waves, solar
ares are also observed to
put energy into the the very low degree global modes Karo & Kjeldsen (2008).
The details of the physical mechanism responsible for the wave excitation are
not clear. Two main suggestions have been high-energy electrons (Kosovichev
2007) and the Lorentz forces (Hudson, Fisher & Welsch 2008) due to the recon-
guration of the magnetic eld during the
are. Lindsey & Donea (2008) discuss
the competing mechanisms in detail. Additional observations and modeling ef-
forts are needed in order to test these proposals.
11 FUTURE OBSERVATIONS
11.1 Solar Dynamics Observatory
The Helioseismic and Magnetic Imager (HMI) is designed to deliver ideal data for
local helioseismology. HMI is one of several instruments onboard NASA's Solar
Dynamics Observatory (SDO) to be
own this year in a geosynchronous orbit.
HMI will transmit 4086 4096 pixel Doppler images of the Sun at the cadence of
one image every 50 s or better. It will combine high spatial resolution (1 arcsec)
and full spatial coverage, with a very high duty cycle over a nominal mission
duration of ve years. This combination will make possible the local helioseis-
mic analysis of regions closer to the limb (less foreshortening), in order to study
higher solar latitudes and the evolution of magnetic active regions as they rotate
from limb to limb across the solar disk. In addition to Dopplergrams, HMI will
provide images of the three components of the vector magnetic eld, providing
important information for the interpretation of helioseismic data. A stated goal
of HMI/SDO is the subsurface detection of the magnetic eld before it emerges at
the surface, leading to reliable predictive capability (Kosovichev & HMI Science
Team 2007). In combination with observations from the Atmospheric Imaging As-
sembly (AIA), a set of four SDO telescopes designed to provide an unprecedented
view of the lower corona, HMI and local helioseismology will help establish rela-
tionships between the internal structure and dynamics of the Sun and the various
components of magnetic activity in the solar atmosphere. SDO instruments willLocal Helioseismology 53
Figure 23: Flare-excited waves in Active Region NOAA 10720 on 15 January
2005. ( a) MDI/SOHO magnetogram (color background) with RHESSI X-ray
emission averaged over the period 00:41:33{00:42:34 UT (12{25 keV contours at
10, 20, 30, 40, 50, 60, and 80 per cent of the maximum
ux). Three hard X-ray
sources are observed. The green dot shows the location of the helioseismic source
(Moradi et al. 2007). Courtesy of Alina Donea and Hamed Moradi. ( b) Sequence
of events. High-energy electrons accelerated in the solar
are interact with the
lower atmosphere, producing hard X-ray emission (observed by RHESSY) and
shocks leading to an initial hydrodynamic impact in the photosphere (observed
by SOHO/MDI). Raw SOHO/MDI Dopplergrams reveal an expanding seismic
wave about 20 min after the initial impact. The dashed curve shows a theoretical
time-distance curve for helioseismic waves. Figure and caption from Kosovichev
(2006). With kind permission of Springer Science and Business Media.
generate a total data
ow of about 1 :5 TB/day, which represents a real challenge
for the ground segment in terms of data storage, processing, and analysis.
The instrumental design of HMI is similar to MDI's, except for the choice of
the absorption line. Using a combined Lyot-Michelson lter system, HMI will

ow as a

function of latitude during 1996 { 2006. Each curve corresponds to a dierent

year as indicated on the right. To improve lisibility, years 1997 and above are

shifted by multiples of 10 m s1. The blue curves until 2002 show the advection of

supergranulation as measured by time-distance helioseismology (Gizon & Rempel

2008) and MDI full-disk data (2 { 3 months per year). The red curves from 2001

are averages (from the surface down to 7 Mm) of the meridional

ow inferred by

ring-diagram analysis and GONG data (Gonz alez Hern andez et al. 2008). The

ring-diagram values are multiplied by a factor of 0 :8 to ease the comparison. Note

the local maximum moving towards the equator, from 25in 1996 to 10in 2006.50 Gizon, Birch & Spruit

Figure 21: Solar cycle variations of the meridional and zonal

ows in the near-

surface layers. ( Top) Time residuals of the meridional

ow after subtraction of

the average meridional

ow for 1996{2006 (from Figure 20 ). The color scale

is in units of m s1. The rst eleven years (the observations) are extrapolated

into the future by tting the eleven-year periodic component. The thick black

curves represent the mean latitude of activity estimated from Mount Wilson mag-

netograms. ( Bottom ) Time residuals of the zonal

ows after subtraction of the

mean rotational velocity for the period 1996{2002, followed by the eleven-year

periodic component. Flows are deduced from the advection of the supergranula-

tion in MDI time-distance divergence maps (Gizon & Rempel 2008). The color

scale is in units of m s1.Local Helioseismology 51

Figure 22: Farside imaging. ( a) Ray-path diagram for 2+2 skip farside imag-

ing (Lindsey & Braun 2000). Waves seen leaving (arriving) at the pupils on the

visible surface of the Sun travel in the direction of the yellow (green) arrows.

The waves skip from the solar surface once before, and once after, reaching the

focal point on the farside of the Sun. Active regions located at the focal point

induce small phase shifts into the waves. ( b) GONG farside images (lighter yel-

low background) combined with magnetograms of the front side (darker yellow

background) covering a 12 day period each. Each full-Sun map is plotted as a

function of Carrington longitude (latitude in a co-rotating frame) and latitude.

The active region NOAA 9503 (August 2001) is seen to form on the farside of

the Sun and then rotate onto the visible disk. Courtesy of Charles Lindsey.52 Gizon, Birch & Spruit

10 FLARE-EXCITED WAVES

The excitation of solar oscillations by a

are was rst observed by Kosovichev &

Zharkova (1998) using MDI data. Since then, many other examples have been

found (e.g. Donea et al. 2006). Figure 23 shows a summary of some observa-

tions of the waves generated by the

are of 15 January 2005. In this example,

the location of the wave source (as estimated from helioseismic holography) is

seen to nearly coincide with the hard x-ray emission as seen by the RHESSI

spacecraft. The seismic waves are rst seen about twenty minutes after the hard

x-ray emission and propagate outwards according to the time-distance relation

(Figure 6a). In addition to exciting local waves, solar

ares are also observed to

put energy into the the very low degree global modes Karo & Kjeldsen (2008).

The details of the physical mechanism responsible for the wave excitation are

not clear. Two main suggestions have been high-energy electrons (Kosovichev

2007) and the Lorentz forces (Hudson, Fisher & Welsch 2008) due to the recon-

guration of the magnetic eld during the

are. Lindsey & Donea (2008) discuss

the competing mechanisms in detail. Additional observations and modeling ef-

forts are needed in order to test these proposals.

11 FUTURE OBSERVATIONS

11.1 Solar Dynamics Observatory

The Helioseismic and Magnetic Imager (HMI) is designed to deliver ideal data for

local helioseismology. HMI is one of several instruments onboard NASA's Solar

Dynamics Observatory (SDO) to be

own this year in a geosynchronous orbit.

HMI will transmit 4086 4096 pixel Doppler images of the Sun at the cadence of

one image every 50 s or better. It will combine high spatial resolution (1 arcsec)

and full spatial coverage, with a very high duty cycle over a nominal mission

duration of ve years. This combination will make possible the local helioseis-

mic analysis of regions closer to the limb (less foreshortening), in order to study

higher solar latitudes and the evolution of magnetic active regions as they rotate

from limb to limb across the solar disk. In addition to Dopplergrams, HMI will

provide images of the three components of the vector magnetic eld, providing

important information for the interpretation of helioseismic data. A stated goal

of HMI/SDO is the subsurface detection of the magnetic eld before it emerges at

the surface, leading to reliable predictive capability (Kosovichev & HMI Science

Team 2007). In combination with observations from the Atmospheric Imaging As-

sembly (AIA), a set of four SDO telescopes designed to provide an unprecedented

view of the lower corona, HMI and local helioseismology will help establish rela-

tionships between the internal structure and dynamics of the Sun and the various

components of magnetic activity in the solar atmosphere. SDO instruments willLocal Helioseismology 53

Figure 23: Flare-excited waves in Active Region NOAA 10720 on 15 January

2005. ( a) MDI/SOHO magnetogram (color background) with RHESSI X-ray

emission averaged over the period 00:41:33{00:42:34 UT (12{25 keV contours at

10, 20, 30, 40, 50, 60, and 80 per cent of the maximum

ux). Three hard X-ray

sources are observed. The green dot shows the location of the helioseismic source

(Moradi et al. 2007). Courtesy of Alina Donea and Hamed Moradi. ( b) Sequence

of events. High-energy electrons accelerated in the solar

are interact with the

lower atmosphere, producing hard X-ray emission (observed by RHESSY) and

shocks leading to an initial hydrodynamic impact in the photosphere (observed

by SOHO/MDI). Raw SOHO/MDI Dopplergrams reveal an expanding seismic

wave about 20 min after the initial impact. The dashed curve shows a theoretical

time-distance curve for helioseismic waves. Figure and caption from Kosovichev

(2006). With kind permission of Springer Science and Business Media.

generate a total data

ow of about 1 :5 TB/day, which represents a real challenge

for the ground segment in terms of data storage, processing, and analysis.

The instrumental design of HMI is similar to MDI's, except for the choice of

the absorption line. Using a combined Lyot-Michelson lter system, HMI will