During the Indian summer monsoon, the most notable variability in the tropical Indian Ocean is the northward- propagating monsoon intraseasonal oscillation (MISO). MISO involves important air-sea interactions, but it not fully understood. In our study, we noticed two clear regions in the Bay of Bengal (BoB) with intraseasonal changes in ocean heat content (OHC) that happen over the season. Just like how sea surface temperature (SST) behaves, the increase in OHC also moves northward and leads the start of MISO by about 10 days. Our detailed analysis shows that the ocean dynamics, rather than surface heat fluxes, are the main reason for these changes in OHC, especially the vertical advection. This vertical movement brings heat deeper into the southern BoB, but the heating stays close to the surface in the northern BoB. Besides the downwelling linked to MISO, waves caused by wind play a key role in making the two OHC regions different. Thus, these discoveries help us understand better how the air and sea interact during MISO.   
 

monsoon intraseasonal oscillation;ocean heat content;vertical advection