On the evolution of the northern Bay of Bengal Dome.

The climatologically averaged sea surface height anomaly (SSHA) during the summer monsoon in the Bay of Bengal (BoB) shows two prominent negative anomalies, one in the southern BoB and another in the northern BoB. The occurrence of negative SSHA observed in the southern BoB has been extensively studied and is linked to Sri Lanka Dome (SLD), whereas negative SSHA observed in the north has received less attention. A pronounced thermal dome develops in the northern BoB with its mean position between 86-89^oE and 16-19^oN, as shown by the doming of isotherms. We refer to this oceanic thermal dome as the northern BoB Dome (NBD). The present study focuses on the evolution of the NBD using observation and a coupled OGCM-biogeochemical model. The formation of NBD occurs during the summer monsoon (May - September), at a time when the wind stress curl is positive. Interestingly, the cyclonic curl is positive in the entire northern BoB, yet the negative SSHA is confined to a small region. Our analysis shows that strong stratification in the northern BoB inhibits the entrainment of the cooler-nutrient-rich subsurface waters to the surface during the event of dome formation. Consequently, the mixed-layer temperature in the NBoB region stays above the temperature criteria for active convection (>28 ^oC). Further, the inhibition of entrainment of nutrients causes the NBD region to be lower in productivity than the SLD region, as seen in chlorophyll distribution. We compare the NBD's heat and nutrient budget with the SLD and show that the near-surface stratification differences make the two domes distinct from each other.