Trends and Interannual Variability of Winds and Turbulent Heat Flux in the Indian Ocean Sector of Southern Ocean during 2000-2009

Abstract

Using satellite-based wind and sea surface temperature (SST) observations, linear trend and inter-annual variability of wind stress, turbulent heat flux ( Q ) and wind stress curl are addressed for the Indian Ocean sector of the Southern Ocean (ISO, 0°E - 155°E) for the period 2000-2009. The analysis reveals that spatial mean of Q varies between 70 and 73 Wm -2 in the austral summer and winter, respectively, while the mean wind stress is nearly same at 0.22 Nm -2 for both seasons. The anticyclonic curl dominates the ISO, which increases from 0.15 × 10 -7 to 0.35 × 10 -7 Nm -3 during the austral summer. The detrended box-mean time series of Q , wind stress, and wind stress curl exhibits a decreasing trend of –6.3 ± 1.6 Wm -2· decade -1 , -0.012 ± 0.004 Nm -2· decade -1 and -0.48 ± 0.6 × 10 -8 Nm -3· decade -1 , respectively. The Empirical Orthogonal Function (EOF) analysis was carried out to study inter-annual variability. EOF-1 of Q captures 25% of the total variance, which mimics the austral summer pattern; its time coefficient is highly and negatively correlated with a 2-month lagged Nino3.4 SST index (r =-0.8 at 95% confidence). EOF-1 of wind stress accounts for 35% of the total variance and its time coefficient is strongly correlated with the Antarctic Oscillation (r= 0.86 at 95% confidence). EOF-1 of wind stress curl captures 15% of the total variance; its time coefficient is correlated to the Nino3.4 SST index (r= 0.65 at 95% confidence) with the former lagging the latter by two years. The repercussions of the weakening trends of the climatic parameters on the air-sea interaction and ocean circulation are highlighted.