The effect of vapor buoyancy on tropical atmospheric circulations

Abstract:

The molar mass of water vapor is smaller than that of dry air, making humid air lighter than dry air even at the same temperature, pressure and volume. This vapor buoyancy effect is often considered much smaller than thermal buoyancy, so its impact on large-scale circulations is not well studied. However, recent studies proposed that vapor buoyancy can make cold air rise in the tropical free troposphere using a theoretical model and a 2D cloud-resolving model (Yang and Seidel 2020; Seidel and Yang 2020). This surprising result suggests that vapor buoyancy has a profound impact on tropical circulations. Here we use reanalysis data and an idealized 3D general circulation model (GCM) to further test the hypothesis. We will also perform sensitivity experiments to investigate how vapor buoyancy affects the Hadley circulation, tropical precipitation, and the width of the intertropical convergence zone, which has substantial implications on the tropical radiative balance.