P40  The Impacts of Saharan Air Layer on the Atlantic Tropical     Storms: A Case Study using WRF/Chem

Zhang, Yongxin, Zhiquan Liu, Craig Schwartz, Hui-Chuan Lin, and Xiang-Yu Huang, National Center for Atmospheric Research

The Saharan air layer (SAL) is an intensely dry, warm and dust-laden air layer that often overlies the cooler and more-humid surface air of the Atlantic Ocean. It originates in the Saharan Desert region of North Africa and extends from the surface upwards several kilometers. Its occurrence during the late spring through early fall largely coincides with the Atlantic hurricane season.

Observational and analytic studies have shown that the SAL suppresses the activity of Atlantic tropical storms through the following mechanisms: (a) the SAL introduces dry and stable air into the storm, which promotes convectively driven downdrafts in the storm, and (b) the SALŐs midlevel easterly jet can enhance the vertical wind shear, which helps to suppress the development of the storm, and (c) the SAL strengthens the preexisting trade wind inversion, which acts to stabilize the environment.

This work applies the fully coupled chemistry within WRF (WRF/Chem) and examines the interaction of the SAL with Atlantic tropical storms. Hurricane Earl that developed out of a tropical wave on August 25 and disappeared on September 6, 2010 after making landfall, will be used as an example. Key questions that will be addressed in this work include: (a) whether or not WRF/Chem can resolve the basic features of the SAL, and (b) what are the physical and chemical processes through which the SAL exerts influence on the activity of Atlantic tropical storm.