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Hurricane Erin and the SAL in 2001

Contributed by Jason Dunion

The Saharan Air Layer (SAL) is an 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