Modeling Studies of the Radiative and Cloud Microphysical effects of the Saharan Dust on Tropical Convections

The Saharan dust aerosols potentially affect various tropical weather systems in the tropical Atlantic region. Numerical experiments are carefully designed using the Weather Research and Forecasting model coupled with chemistry (WRF-Chem) to investigate the radiative and cloud microphysical effects of the Saharan dust aerosols on tropical convections over East Atlantic Ocean. The one-month long simulations show that the dust direct radiative effect warms up the low-level air but increases the stability resulting in reduced cloud cover underneath the maximum dust layer. When the direct and indirect effects are considered together, dust aerosols downshift the cloud droplet size distribution. The cloud cover is reduced below the maximum dust layer but enhanced above it. The direct radiative forcing of dust aerosols is -13.66 and -11.25 W/m² at the surface and at the top of the atmosphere, respectively. When the indirect effects are included, the net radiative forcing of dust becomes -8.14 and -5.03 W/m².

The impact of dust aerosols on the precursor of Hurricane Earl (2010) is also studied. Although the overall impact of dust aerosols is small even for a weak storm, including dust aerosols in the model reduces the forecast errors.