Cloud-Resolving Large-Eddy Simulation of Tropical Convective Development and Surface Fluxes

Cloud-resolving large-eddy simulations (LES) on an 500x500 km scale periodic domain coupled to a thermodynamic ocean mixed layer are used to study the effect of large scale moisture convergence M on the convective population and heat and moisture budgets of the tropical atmosphere. Several simulations were run with M representative of the suppressed, transitional, and active phases of the Madden-Julian Oscillation (MJO). Increasing M leads to more organized convective systems with generation of surface cold pools having increased winds and higher surface fluxes. Overall surface evaporation decreases as large-scale moisture convergence increases, and is only a minor component of the water budget for convective conditions representing the active phase of the MJO. Cold pools generated by evaporation of precipitation under convective conditions are gusty, with roughly double the wind speed of their surroundings. Enhanced surface evaporation due to cold pool gusts is up to 40% of the mean, but has a small effect on the total moisture budget in comparison with the imposed large-scale moisture convergence. The effects of precipitation and cloud shading on sea-surface temperature, while significant, do not appear to change convective activity.