Indirect and semi-direct effects of aerosols on the local water and energy budget of the Indian Ocean region are examined by modeling how the inclusion of aerosols affects the macrophysical (e.g., cloud cover) and microphysical properties (e.g., liquid water paths) of trade wind cumuli, their diurnal cycle, and the related cloud radiative forcing using the cloud-resolving, anelastic, nonhydrostatic Eulerian/semi-Lagrangian EULAG model. Model simulations are initialized using vertical profiles of temperature, moisture, and velocities measured by dropsondes during the Indian Ocean Experiment (INDOEX) and surface fluxes estimated using sea surface temperatures estimated from the microwave imager (TMI) on board the Tropical Rainfall Measuring Mission (TRMM) satellite. Aerosol properties are determined using estimates of their microphysical and optical properties obtained during INDOEX. The dependence of the modeled properties on surface fluxes of heat and moisture, on aerosol absorptive properties, on cloud condensation nuclei concentrations, and on the vertical distribution of aerosols is investigated. Results are interpreted by examining vertical profiles of longwave and shortwave heating induced by the aerosols.

The simulations are evaluated against estimates of cloud cover obtained by a multi-channel radiometer (MCR) during INDOEX. Because flight tracks in INDOEX were designed to sample both pristine and polluted clouds on north-south legs to and from the Indian subcontinent, the results can be interpreted in the context of observed aerosol effects on cloud properties.