Comparison of long-term variability of Sea Surface Temperature in the Arabian Sea and Bay of Bengal

Long-term variability of Sea Surface Temperature (SST) in the Arabian Sea (AS) and Bay of Bengal (BoB) during 1880-2010 is examined using all the available data sets of monthly SST, wind speed, incoming solar radiation, cloud cover, long wave radiation, latent heat flux, net surface heat flux and surface currents. SST time series reveal an upward (increasing) trend (warming) after 1940 in both the basins. Wavelet analyses of the SST time series reveal that AS SST is controlled by semi-annual and annual forcing while the BoB SST is influenced predominantly by annual forcing. The SST responses in both the basins are in phase to the climatic events such as El Niño, La Niña and Indian Ocean Dipole, but a stronger impact is noticed in the AS SST. The climatic events affected the seasonal peaks of SST warming (April-May) and cooling (August-September) in both the basins. Time series of SST anomaly also showed in phase responses to the climatic events and an upward trend from 1960 to 2010 in both the basins. Long-term decreasing trends observed in surface wind speed, latent heat flux and advective process via the weakened surface currents, together with the long-term increasing trend in P − E (Precipitation, P minus Evaporation, E) contributed to the SST warming trend in both the basins. In association with the upward trend in P − E, the Simple Ocean Data Assimilation (SODA) Reanalysis Sea Surface Salinity time series exhibited freshening (a decreasing trend) and enhanced the salinity stratification in the BoB, thus modulated the BoB SST warming. These cumulative processes led to the warmer SSTs in the BoB compared to that in AS.