Earth and Climate Science

Dr. Vishal Dixit
Postdoctoral research scholar, TU Delft, Netherlands,

Abstract

Water is a unique molecule in the earth system. Though it is most abundant on the earth’s surface as oceans, it’s miniscule presence (0.25%) in the atmosphere as water vapor and clouds has a fundamental impact in establishing earth’s climate and driving air circulations.  Water stands out from other gases due to its unique properties: 1. It’s ability to interact with radiation over broad spectrum, 2. its ability to change phase while suspended and 3. its lower molecular weight relative to the air. These properties prove crucial in controlling earth’s hydrological cycle. Moreover, these properties also introduce enigmatic feedbacks between clouds and air circulations on multiple spatio-temporal scales. The scientist leading World Climate Research Program hold incomplete understanding of these feedbacks responsible for our poor estimations of future climate change.

The processes controlling east-west oriented large-scale tropical cloud bands (Intertropical convergence zone, ITCZ) are the “fundamental puzzle” that we need to solve to get better resolution on this cloud-circulation coupling enigma.  In this talk, I will discuss three different flavors of cloud-circulation coupling relevant to the tropical rain-bands and connect them to the previously discussed properties of water. In the first, I will present climate model experiments that demonstrate that small changes to the boundary layer turbulence over the Saharan desert can induce large migrations of African monsoons rainfall over the desert. In the second, I will show how local cloud radiative effects themselves can modify the latitudinal width of the ITCZ in a climate model. Finally, I will briefly discuss ongoing work using cloud resolving and large eddy simulations to investigate how cumulus friction active in subtropical shallow clouds may change the turning of trade winds and hence might change the ITCZ.