Saharan Dust Processing and Transport by Atlantic Tropical Cyclones

The Saharan Air Layer (SAL) is a dry, dusty air mass flowing westward at low to mid levels off the western coast of Africa out across the Atlantic Ocean. Developing tropical cyclones (TC) occasionally intersect with the SAL. Studies have shown that TC-SAL interactions can substantially impact the intensity and formation of the affected storms. As the SAL influences the encroaching storm, the storm in turn will modify the characteristics of the SAL bringing in moisture and redistributing the dust. The redistribution of dust can have significant impact on radiative forcing and therefore is of importance in the context of changing climates.

This study examines how tropical cyclones affect the amount of dust removed from the atmosphere and the vertical redistribution of dust. The Regional Atmospheric Modeling System (RAMS), a cloud-resolving model with a sophisticated microphysics scheme, has been employed to create a realistic reproduction of the 2006 Tropical Storm Debby encounter with a SAL event near the Cape Verde Islands. Passive tracers were added to RAMS and initialized to match the SAL dust distribution to separate the effects of microphysical processing of dust (e.g., nucleation and scavenging) from those of dust transport. Preliminary results indicate that both microphysics and dynamics play significant roles in the redistribution of SAL dust during TC-SAL interaction. It is felt that the results of this research will contribute to our understanding of the impact that deep convective storms have on the redistribution of mineral dust in the atmosphere.