The impact of Saharan Air Layer on tropical cyclone genesis and intensification

Recent research results have suggested that the Saharan Air Layer (SAL) may alter the intensity of Atlantic Tropical Cyclone (TC) activity. The alteration occurs through a variety of dynamical and thermodynamical processes, including the following: the entrainment of dry, stable air into storms, which promotes evaporatively driven downdrafts in TCs; the maintenance of a midlevel easterly jet due to warm SAL air, which increases vertical shear; the enhancement of pre-existing trade wind inversions in the Atlantic, which stabilizes the atmosphere; and the interactions between dust and cloud/radiation, which modifies TC development as well as environment instability and moisture/energy budgets.

The purpose of this work is to study the impact of SAL on TC genesis and intensification in terms of its warm and dry air, vertical shear induced by mid-level easterly jet, and Saharan dust through a suite of numerical investigations. To achieve the goal, an on-line tracer model, which includes the calculation of dust, has been developed based on the Weather Research and Forecasting (WRF) model. Numerical simulations for Tropical Storm Florence (2006) were performed and preliminary results will be presented.