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.