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Subject: A17) What is the Saharan Air Layer (SAL) ?
How does it affect tropical cyclones ?
![](sal2.jpg)
Hurricane Erin and the SAL in 2001
Contributed by Jason Dunion
The Saharan Air Layer (SAL) is a mass of very dry, dusty air which
forms over the Sahara Desert during the late spring, summer, and early
fall and usually moves out over the tropical Atlantic Ocean. The SAL
usually extends between 5,000-20,000 ft (1500-6000 m)
in the atmosphere and is associated with large amounts of mineral dust,
dry air (~50% less moisture than a typical tropical sounding), and
strong winds (~25-55 mph or ~10-25 m/s).
The SAL has been shown to have significant negative impact on tropical
cyclone intensity. Its dry air can act to weaken a tropical cyclone
by inhibiting updrafts in the storm, while its strong winds can
substantially increase the vertical wind shear in and around the storm
environment. It is not yet clear what effect the SAL's dust has on
tropical cyclone intensity, though some studies have suggested that it
too may have a negative impact on intensification.
The SAL can cover an area the size of the continental U.S. and has
been tracked as far west as the Caribbean Sea, Central America, and
the Gulf of Mexico. Real-time satellite imagery for tracking the SAL
can be found here.
References:
-
Dunion, J.P., and C.S. Velden, 2004: The impact of the Saharan Air
Layer on Atlantic tropical cyclone activity. Bull. Amer. Meteor.
Soc., vol. 85 no. 3, 353-365.
Last updated September 21, 2004
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