Trends and Interannual Variability of Satellite-Based Wind and Sea Surface Temperature over the Southern Ocean in the Recent Decade

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DOI: 10.4236/ijg.2015.62009    3,548 Downloads   4,625 Views  Citations

ABSTRACT

Using satellite-based 10-m surface wind (SW), wind stress (WS) and sea surface temperature (SST) anomalies, trends and inter-annual variability during 1993 and 2008 over the Southern Ocean (SO) are addressed. The climatological mean (16 years average) indicates that negative wind stress curl diminished (enhanced) between 40°S and 60°S zonal strap region coincide with weak (strong) SW and warm (cold) SST anomaly during January (July). Annual climatology indicates that strong region of SW divides warmer waters northward with positive wind stress curl (WSCL) and colder waters southward with negative WSCL. The time series anomalies are smoothened with a 12-month running mean filter. The filtered area-mean time series anomalies of zonal and meridional component of SW and SST have linear trends of -0.0005 ± 0.0003 m/s/decade, 0.0012 ± 0.0002 m/s/decade and -0.00005°C ± 0.0001°C/decade, respectively. The SW anomalies show an increasing trend of 0.0013 ± 0.0002 m/s/decade, with the meridional (zonal) component exhibiting an increasing (decreasing) trend. The meridional component plays a critical role in heat transfer through atmospheric circulation. The WS and wind stress divergence exhibit increasing trends whereas wind stress curl shows a decreasing trend. The SST fluctuates close to zero with repeated high and low peaks at an interval of 2 - 3 years. We address the interannual variability by performing EOF analysis on SW, WS, WSCL and SST anomalies which have been passed through a 12-month running mean filter. EOF-1 spatial pattern portrays low variances south of 40°S in SW between 25°E and the Drake Passage whereas in WS it is confined to Pacific Ocean sector of the SO. EOF-2 pattern exhibits high variability along the ACC, which is pronounced in the central Indian sector of the SO in SW and Pacific Ocean sector of the SO in WS. The time coefficient (SW, WS and WSCL) of EOF-1 (EOF-2) is correlated with reversed (actual) Antarctic Oscillation (AAO) index. The EOF-1 of SST shows high variance in the Indian sector south of 55°S and in the south Pacific sector of the SO. The corresponding time coefficient function indicates an inverse relationship with AAO index. EOF-2 of SST shows dipole structure of high variance in the Pacific Ocean sector of the SO; high positive variance is also evident in Indian sector. The time coefficient of EOF1 (EOF-2) is correlated with reversed AAO (Nino 3.4) index, with the earlier (latter) leading the former by 4 (9) months. Based on the EOF analyses, it can be inferred that AAO and Nino indices play an important role in modulating SW and SST changes in the SO.

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Pednekar, S. (2015) Trends and Interannual Variability of Satellite-Based Wind and Sea Surface Temperature over the Southern Ocean in the Recent Decade. International Journal of Geosciences, 6, 145-158. doi: 10.4236/ijg.2015.62009.
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