Modeling and Observational Studies of Shallow Cumulus Convection Over the Indian Ocean: Aerosol and Meteorological Effects on Diurnal Cycles

Without the impact of large-scale forcing, the simulated diurnal cycles of turbulence and cloudiness were characterized by significant daytime reductions and midday minima. Periodic pulsations with a dominant time period of between 0.8 and 3 h driven by turbulent eddies were superimposed on the diurnal cycles. Simulation results show that the principal cause of the daytime reductions was not the diurnally varying surface fluxes or the cloud radiative effects, but rather the gaseous absorption of solar radiation mainly due to water vapor and ozone. Depending on its direction and magnitude, large-scale vertical motion either enhanced or reduced cloudiness, producing a much different pattern of diurnal variations from the one driven by gaseous absorption.