Evolution characteristics and mechanisms of the spring warm pool in the Bay of Bengal

Knowledge of spring warm pool in the Bay of Bengal (BoBWP) is key for further understanding the climate variability in this region and beyond, but little is known about the BoBWP climatological state and the related mechanisms. In this study, we investigate the spatial structure and evolution of the BoBWP using daily Optimum Interpolation SST data from 1982-2022 in combination with multi-source data. Our analysis shows that the BoBWP is located in the central bay (6 degrees-13 degrees N) with a thickness around 20 m similar to 40 m. Composite analysis indicates that the BoBWP emerges in early April, peaks in early May and dissipates in early June. During the developing period, the net heat flux dominates the formation of spring warm pool through significant air-sea coupling processes, and induces the warming rate of 0.27 degrees C/10d in the mixed layer, which is far larger than the contribution of oceanic dynamical processes (0.01 degrees C/10d). During the decaying period, the net heat flux also plays a dominant role, with a cooling rate of -0.21 degrees C/10d, meanwhile ocean dynamical processes contribute to the cooling of the warm pool with a rate of -0.01 degrees C/10d. Additionally, the SST and the area of the BoBWP are significantly correlated with ENSO (r=0.66 and 0.73, p=0.05). During El Nino decaying year, the BoBWP primarily expands in a southward direction, with a 75% increase in area. Conversely, during La Nina decaying year, the BoBWP almost disappears, with a 52% decrease.