On the flip side, the clouds may inhibit the formation of tropical cyclones in the Caribbean.
Prospero said lower rainfall in West Africa presumably causes more dust, which reduces sunlight, lowers water temperatures and cuts evaporation, all factors in cyclonic formation.
While experts disagree about the changes in the dust clouds over the decades, all agree this year's cloud was remarkable.
Mojena said the dust arriving in Cuba has risen 10-fold in the last 30 years after severe droughts in northern Africa, though Omar Torres, a specialist in atmospheric physics at the NASA Goddard Space Flight Center in Maryland, said satellite studies since 1980 do not show increased Sahara dust emissions beyond normal seasonal variability.
Even so, "this year's advancement all the way to Wyoming was totally unexpected," Torres said. "I never saw anything like that in recent years."
Science Writer Seth Borenstein in Washington and Associated Press writers Peter Orsi in Havana and Danica Coto in Puerto Rico contributed.
Andrea Rodriguez on Twitter: www.twitter.com/ARodriguezAP
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