Deceleration of Isentropic Overturning Circulation In Tropics: Implications for Mechanical Efficiency of Moist Convection in a Warming Climate

This research investigates the isentropic overturning circulation in Tropics responding to the warming climate using idealized simulation. This idealized setting applies a rotating Boussinesq atmosphere with simplified thermodynamics for phase transitions. We mimic tropical atmospheric conditions under varying lapse rates and radiative cooling. This approach allows us to investigate the behavior of moist convection as surface temperatures increase.

Our study reveals that under climate change scenarios, the mechanical efficiency of moist convection increases, corresponding with a deceleration in the isentropic overturning circulation. In our model, we conceptualize moist convection as heat engines transporting the warm and humid air parcels to a cold and dry sink. The mechanical efficiency of moist convection increases to compensate the decline in both the mass flux and energy flux corresponding to the warming in the surface. A deeper analysis reveals that, the turbulent activities near the lower boundary is suppressed preventing the efficiency loss due to turbulent mixing. In particular, an increased aggregation of moist convection in a warming climate acts to protect the convective core from external dry air mixing, thereby preserving its efficiency.