Studies of the Hadley Circulation with an Idealized Moist GCM

We present results from a series of studies that address the range of effects that moist convection can have on the Hadley circulation. We study this in a simplified moist GCM, which makes idealizations such as a zonally symmetric aquaplanet surface, gray radiative transfer, and a simplified Betts-Miller convection scheme. By changing convection scheme parameters, the Hadley cell and ITCZ precipitation can change significantly, meaning no theory of the Hadley circulation is possible in this model without considering the effect of convection.

An important diagnostic that determines how convection can influence the Hadley circulation is the gross moist stability (GMS), which is defined as the energy transport per unit mass transport of the circulation, and is therefore a measure of the efficiency of the Hadley cell. We show that the GMS is determined by properties of the convection scheme, such as how penetrative the scheme is. When the GMS is smaller, the Hadley cell is less efficient and a stronger mass flux is required to keep temperatures flat in the upper troposphere. The GMS is shown to be important for many additional aspects of the tropical general circulation, including the sensitivity of the mass flux and precipitation distribution to imposed energy fluxes. We also discuss work on scalings for the strength and width of the Hadley cell as a function of moisture content and temperature gradients.