The Relative Impacts of the SAL Relative Humidity and Dust Loading upon Tropical Cyclone Development

Studies have shown that tropical cyclones (TCs) can be substantially modified in terms of their intensity and formation when intersecting with the Saharan Air Layer (SAL). The SAL is a low- to mid-level dry, dusty air mass flowing westward off the western coast of Africa out across the Atlantic Ocean. These characteristics (easterly jet, dry air and dust loading) of the SAL can interact with a developing TC in complex manners thus motivating the study of TC-SAL encounters. Debate over whether the SAL augments or diminishes the development of TCs still exists today.

The goal of this study is to gain an enhanced understanding of the relative importance of the impact from two SAL characteristics, namely the dry air layer and the dust loading, when a TC comes into contact with the SAL. The Regional Atmospheric Modeling System, a cloud-resolving model with a sophisticated microphysics scheme, has been employed to create a realistic reproduction of the 2006 Tropical Storm Debby (TS Debby) encounter with a SAL event near the Cape Verde Islands. Sensitivity tests have been conducted in which the dust loading and moisture content of the observed SAL have been systematically varied in the simulation environment. Preliminary results show that influences from both dust and dry air lead to variations in cyclone strength. The relative significance of these effects will be quantified and presented. It is felt that the results of this research will improve our understanding of the relative importance of aerosol and environmental controls on the development of tropical cyclones.