The Effects of Dust–Radiation–Cloud Interactions on the Development of an MCS over North Africa

The study evaluates the impact of dust-radiation-cloud interaction on storm development using the WRF-Dust model. An MCS that developed over North Africa during 5-6 July 2010 was selected for this study, primarily because (1) it developed near a moderate dust plume, and (2) CloudSat and CALIPSO passed through the storm after it reached maturity, providing useful vertical profiles of backscatter and cloud information for model verification. To study both the dust direct and indirect effects, four numerical experiments were conducted that differed only in whether or not they simulated dust-radiation and/or dust-cloud interactions. The results showed that the overall pattern of the dust distribution and the MCS of interest were well captured in all the experiments. However, the MCS is characterized differently by the inclusion of different dust physical processes.

The combined results from all four experiments suggest that the dust direct effect has a greater impact on the MCS’s development than the dust indirect effect. Regardless of whether the inclusion of the dust-cloud interaction, the experiments that accounted for the dust-radiation interaction show delays in the MCS development, longer storm lifetimes, and elongated anvil/stratiform clouds. On the other hand, the dust indirect effect affects the MCS development differently depending on whether dust-radiation effects were also simulated. When only the dust-cloud interaction is activated, time delay in hydrometeor growth, convective invigoration, and long-lasting cloud particles are shown, which follows the classical theory for the aerosol indirect impact. However, when both dust-cloud and dust-radiation interactions are activated, the dust indirect effect alters its typical role and magnifies the dust direct impacts. This illustrates the complex nonlinearity of dust-radiation-cloud interactions in general.