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correlation was also detected at the Bahamas area, which was characterized as a “hot |
spot” for the formation of MHWs (Figure 7). Relatively low correlation coefficients were |
computed over the Straits of Florida, and especially west of 83◦ W and east of 81◦ W, with |
very weak correlation along the northern Straits and the EFS (Rp < 0.80). The lower values |
mainly occurred over the area where the FC flows, controlling the distribution of physical |
properties (see Section 4.2). The lowest correlation coefficients (Rp < 0.75) were computed at |
the coastal area north of Miami Beach (26◦ N). The lag (in days) between the two parameters |
is around 5 days (Rp = 0.90; Figure 10c). Once the seasonal cycle is removed, the interaction |
between them is more direct, showing smaller correlation (Rp = 0.57) with a 3-day lag |
(Figure 10e). The agreement between the two parameters confirms that the effect of the |
atmospheric temperature on the ocean sea surface temporal and spatial evolutions also |
holds for the nearshore and coastal study areas. This effect varies among different marine |
Water 2022, 14, 3840 17 of 28 |
regions because of other environmental factors, both atmospheric (e.g., wind speed) and |
oceanic (e.g., river plumes, lateral fluxes, vertical mixing, general circulation). |
Water 2022, 14, x FOR PEER REVIEW 19 of 31 |
Figure 10. Horizontal distribution of Pearson correlations coefficients (Rp) derived between (a) the |
daily Sea Surface Temperature (SST; satellite observations) and air temperature (ERA 5), and (b) the |
SST and wind speed (ERA5) data over the entire study area and period (1982–2021). Cross correlation between SST and air temperature, and SST and wind speed with (c,d), and without (e,f) the |
seasonal cycle, respectively. The y- and x-axes represent the Pearson correlation coefficients and lag |
(days) between each pair of timeseries, respectively. |
The wind speed also contributes to the variability of the SST, showing negative Pearson coefficients (counter-correlation) over all areas (Figure 10b). High SST anomalies usually coincide with weak wind anomalies throughout the study period. The strongest impact of the wind on SST was detected over the broader Miami area (25–26° N) with correlation coefficients close to −0.40. The majority of the Straits of Florida showed correlation |
coefficients around −0.35, while the smallest values were computed for the Bahamas, |
where the air temperature effect is stronger (Figure 10a). Relatively weak correlation (Rp |
= −0.29) was also detected along the western coast of Florida and north of the Florida Keys. |
Generally, the impact of the wind on SST is weaker and more spatially homogenous compared to the air temperature effect. The general correlation coefficient, derived from all |
daily values is approximately Rp = −0.43 and reveals the same small lag (~3 days) for |
Figure 10. Horizontal distribution of Pearson correlations coefficients (Rp) derived between (a) the |
daily Sea Surface Temperature (SST; satellite observations) and air temperature (ERA 5), and (b) the |
SST and wind speed (ERA5) data over the entire study area and period (1982–2021). Cross correlation |
between SST and air temperature, and SST and wind speed with (c,d), and without (e,f) the seasonal |
cycle, respectively. The y- and x-axes represent the Pearson correlation coefficients and lag (days) |
between each pair of timeseries, respectively. |
The wind speed also contributes to the variability of the SST, showing negative Pearson |
coefficients (counter-correlation) over all areas (Figure 10b). High SST anomalies usually |
coincide with weak wind anomalies throughout the study period. The strongest impact |
of the wind on SST was detected over the broader Miami area (25–26◦ N) with correlation |
coefficients close to −0.40. The majority of the Straits of Florida showed correlation coefficients around −0.35, while the smallest values were computed for the Bahamas, where the |
air temperature effect is stronger (Figure 10a). Relatively weak correlation (Rp = −0.29) was |
Water 2022, 14, 3840 18 of 28 |
also detected along the western coast of Florida and north of the Florida Keys. Generally, |
the impact of the wind on SST is weaker and more spatially homogenous compared to the |
air temperature effect. The general correlation coefficient, derived from all daily values is |
approximately Rp = −0.43 and reveals the same small lag (~3 days) for seasonal (Figure 10d) |
and non-seasonal (Figure 10f) timeseries. The correlation coefficient of the non-seasonal |
correlations, which is derived from variations related to extreme events is smaller and |
equal to −0.25. |
The mean monthly evolution of the SST (seasonal cycle removed) at specific coastal |
areas (insert maps in Figure 8) shows statistically significant increasing trends for all |
regions (pvalues < 0.01; Figure 11). The respective air temperature anomalies (seasonal |
cycle removed) reveal a similar variability to the SST anomalies, leading to high positive |
correlation coefficients (Rp > 0.60). |
Water 2022, 14, x FOR PEER REVIEW 20 of 31 |
seasonal (Figure 10d) and non-seasonal (Figure 10f) timeseries. The correlation coefficient |
of the non-seasonal correlations, which is derived from variations related to extreme |
events is smaller and equal to −0.25. |
The mean monthly evolution of the SST (seasonal cycle removed) at specific coastal |
areas (insert maps in Figure 8) shows statistically significant increasing trends for all regions (pvalues < 0.01; Figure 11). The respective air temperature anomalies (seasonal cycle |
removed) reveal a similar variability to the SST anomalies, leading to high positive correlation coefficients (Rp > 0.60). |
Figure 11. Monthly evolutions, without the seasonal cycle, of the Sea Surface Temperatures (SST |
anomaly, black line, °C), air temperature (red line in upper panels; °C) and wind speed (red line in |
lower panels; m/s), averaged over: (a,g) All Regions (entire study domain); (b,h) Miami Beach; (c,i) |
Biscayne Bay; (d,j) North Key West; (e,k) South Key West; (f,l) Tampa Bay, over the 1982–2021 period (areas marked in Figure 8). The linear trends and the Pearson correlation coefficients (Rp) for |
each case are shown. The asterisks (*) indicate statistically significant correlations of 99%. |
The stronger impact of air temperature was observed at areas where the effects of the |
Gulf’s mesoscale ocean dynamics are weaker, such as Tampa Bay in the west Florida coast |
(Figure 11f), and Key West (Figure 11d,e). The general correlation is around 0.84 (Figure |
11a) but the Miami Beach and Biscayne Bay areas are characterized by significantly |
weaker correlations (Rp < 0.65; Figure 11b,c). The latter showed slightly stronger correlation between the measured atmospheric temperature at Buoy FWYF1 and SST (Figure |
12a). The respective correlation between the SST and the air temperature is weaker in Miami Beach (Rp = 0.81; Figure 12b). The correlation without the seasonal cycle in Biscayne |
Bay (Rp = 0.40) is double than the respective correlation in Miami Beach (Rp = 0.20). The |
linear regression between the two variables is closer to the x = y identity line for the enclosed basin of Biscayne Bay. This suggests that factors other than atmospheric conditions |
also control the processes impacting SST and MHW there (see Section 4.2). It is noted that |
these Pearson coefficients are derived from monthly means and, therefore, the general |
value (Figure 11a) is different from the one derived from daily values to estimate the lag |
between the two time series (Figure 10e; Rp = 0.57). The wind speed interannual trends are |
negative at all areas with smaller correlation coefficients between the wind speed and the |
SST anomalies compared to the ones correlating air temperature with SST. These coefficients are similar between the coastal areas, in agreement with the spatial distribution |
presented in Figure 10b. The highest values at central EFS were derived for Miami Beach, |
where the air temperature conditions showed the weakest impact on SST among all study |
coastal areas. Moreover, very strong decreasing trends of wind speed were computed for |
both Miami Beach and Biscayne Bay, contributing to the increasing interannual trends of |
SST. |
Figure 11. Monthly evolutions, without the seasonal cycle, of the Sea Surface Temperatures (SST |
anomaly, black line, ◦C), air temperature (red line in upper panels; ◦C) and wind speed (red line in |
lower panels; m/s), averaged over: (a,g) All Regions (entire study domain); (b,h) Miami Beach; (c,i) |
Biscayne Bay; (d,j) North Key West; (e,k) South Key West; (f,l) Tampa Bay, over the 1982–2021 period |
(areas marked in Figure 8). The linear trends and the Pearson correlation coefficients (Rp) for each |
case are shown. The asterisks (*) indicate statistically significant correlations of 99%. |
The stronger impact of air temperature was observed at areas where the effects of |
the Gulf’s mesoscale ocean dynamics are weaker, such as Tampa Bay in the west Florida |
coast (Figure 11f), and Key West (Figure 11d,e). The general correlation is around 0.84 |
(Figure 11a) but the Miami Beach and Biscayne Bay areas are characterized by significantly |
weaker correlations (Rp < 0.65; Figure 11b,c). The latter showed slightly stronger correlation |
between the measured atmospheric temperature at Buoy FWYF1 and SST (Figure 12a). |
The respective correlation between the SST and the air temperature is weaker in Miami |
Beach (Rp = 0.81; Figure 12b). The correlation without the seasonal cycle in Biscayne Bay |
(Rp = 0.40) is double than the respective correlation in Miami Beach (Rp = 0.20). The linear |
regression between the two variables is closer to the x = y identity line for the enclosed |
basin of Biscayne Bay. This suggests that factors other than atmospheric conditions also |
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