Effect of Surface Fluxes versus Radiative Cooling on Tropical Deep Convection

Abstract:

The effect of turbulent surface fluxes is contrasted with that of the radiative cooling rate on tropical deep convection in a series of idealized cloud-system resolving simulations with parameterized large scale circulations. Two methods of parameterizing the large scale dynamics are used; the Weak Temperature Gradient (WTG) approximation and the Damped Gravity Wave (DGW) method.

It is found that, when stating with moist initial conditions, an increment in surface fluxes produce more precipitation than equal amount of increment of column-integrated radiative cooling. A simple scaling argument based on the normalized gross moist stability is introduced.

When starting with dry initial conditions, the atmosphere in WTG exhibits multiple equilibria of a wet and a dry states for a wide range of net energy input to the atmospheric column. The persistence of the dry state lasts longer when surface fluxes are perturbed, in the time mean as well as in the time evolution. The DGW method, however, shows no multiple equilibria.