Understanding the Response of Tropical Ascent to Warming Using an Energy Balance Framework.

Previous work has established that warming is associated with an increase in dry static stability, a weakening of the tropical circulation, and a decrease in the convective mass flux. Using a set of idealized simulations with specified surface warming and superparameterized convection, we find support for these previous conclusions. We use an energy and mass balance framework to develop a simple diagnostic that links the fractional area covered by the region of upward motion to the strength of the mean circulation. We demonstrate that the diagnostic works well for our idealized simulations and use it to understand how changes in tropical ascent area and the strength of the mean circulation relate to changes in heating in the ascending and descending regions. We show that the decrease in the strength of the mean circulation can be explained by the relatively slow rate at which atmospheric radiative cooling intensifies with warming. In our simulations, decreases in tropical ascent area are balanced by increases in nonradiative heating in convective regions. Consistent with previous work, we find a warming‐induced decrease in the mean convective mass flux. However, when we condition by the sign of the mean vertical motion, the warming‐induced changes in the convective mass flux are nonmonotonic and opposite between the ascending and descending regions. Plain Language Summary: The circulation of the atmosphere is expected to weaken in a future warmer climate. Despite an expected increase in precipitation, studies show that the average strength of stormy updrafts (as measured by the average speed of the updrafts multiplied by their area) will also decrease. We use simulations with realistic representations of storms to test these ideas and derive an equation that may help us better understand how the strength of the circulation is linked to changes in its energy balance. Key Points: The ascending area narrows as the heating there increases relative to the cooling in the sinking airThe circulation weakens with warming because radiative cooling increases more slowly than stabilityEnhanced vertical moisture gradients and stratiform heating support decreased ascent area [ABSTRACT FROM AUTHOR]