Keywords: Bay of Bengal, Sea Level Height Anomaly (SSHA), Chlorophyll a pigment concentration, Empirical orthogonal function, Variability.

 INTRODUCTION The Bay of Bengal, located in the western part of the north Indian Ocean is a tropical basin. It is land locked in the north at around 30°N and to the south it is open to the Indian Ocean. To the west it is bounded by the Indian land mass, while to the east it is bounded by the East Asian land mass. It is only the southern part of the Bay of Bengal that is open to the Indian Ocean. During summer, the heating of Asian land mass generates large land-sea pressure difference, which drives the southwesterly (summer) Monsoon winds. In contrast, during winter the Asian land mass is much colder than the ocean which drives the northeasterly (winter) monsoon winds. The southwesterly winds are strong (10 m/s), while the northeasterly winds are weak (5 m/s). During summer the moist southwesterly monsoon winds bring a large amount of precipitation to the Bay of Bengal. The surface currents in the Bay of Bengal also show a seasonal reversal. This reversal in the surface current is most prominently seen in the coast currents along the east coast of India. The East India Coastal Current (EICC) moves southward during the winter monsoon transporting warm low salinity waters from the head of Bay of Bengal towards the equator. The same current changes its direction during the summer monsoon transporting high salinity waters of the Arabian Sea in the northward direction. In addition to the reversal of the coastal currents, the currents in the open Bay of Bengal also change their direction. For example, the north equatorial current in the Bay of Bengal moves westward in winter while in summer it moves from west to the east. (Wyrtki 1971) presents initial information of Bay of Bengal waters and (Prasanna Kumar et al. 1993) described the seasonal and inter-annual sea surface height variations using TOPEX/POSEIDON altimeter data. [Varkey et al., 1996; Singh et al., 2015] shows the seasonal variation and circulation in the Bay of Bengal. Recent studies have been examined the surface circulation and mesoscale features in the Bay of Bengal and (Benny and Mizuno 2000) described the Kelvin and Rossby waves in the Bay of Bengal. Life cycle of eddies along the western boundary of the Bay of Bengal and their implication is well explained by Nuncio et al. in (2012).