Abstract:

Substantial evidence from proxies suggests that South Asian monsoon variations in the past are due to variations in Earth’s orbit. These variations modulate the amount of solar radiation incident and, thus, the energy available to run the monsoon system. Proxies and model simulations indicate that the land and ocean monsoons respond differently to the changes in Earth’s orbit. In this talk, I will underscore two critical differences between land and ocean monsoons that lead to this asymmetry in their response. Firstly, the surface energy flux over the ocean counters the changes in insolation. Therefore, it determines the evolution of net energy input into the atmosphere. Over land, net surface energy flux is insignificant, and the net energy input is driven by insolation. Secondly, the dominant terms in the moist static energy budget are different over land and ocean. This is due to the profile of vertical velocity. Over land, it is bottom-heavy, and over the ocean, it is top-heavy. Thus, changes in insolation are only a trigger, and the final response of the monsoon depends on the local energetics.