PHILADELPHIA -- A 'historic' outbreak of Saharan dust that is clogging the atmosphere from western Africa to the Caribbean and potentially posing health threats could make it as far as the Midwest.
While the phenomenon is an annual occurrence, "This dust episode has a huge spatial extent," said Andrea Sealy, a meteorologist with the Caribbean Institute for Meteorology and Hydrology, in Barbados.
And for the time being at least, it is yielding a collateral benefit to property owners on the Gulf and Atlantic Coast, and to U.S. taxpayers. All that dust suppresses storms in the subtropical Atlantic, one of the world's most-productive hurricane-spawning grounds.
This particular outbreak could well be among the largest of the last 60 years, said Frank D. Marks, director of the government's Hurricane Research Division, who is familiar with the orange-tinted fallout that has descended upon his car in years past.
He described the outbreak that started last week as a "very opaque or dense plume." It is known as the Saharan Air Layer, or SAL, but it isn't all sand.
The primary source is the Sahara, which is roughly the size of the 48 contiguous states covered by unimaginable amounts of sand.
If there is such thing as a sand harvest, Sahara has one at the end the dry winter, said Marks. In June, monsoon winds carry sand and particulate matter into the atmosphere where it is transported westward by upper-air winds, generally in three- to five-day intervals.
By taking the high road, the dust can avoid the chaotic currents near the surface where we live and breathe, he said, adding that some of the larger particles won't make the entire 4,500-mile trip, give or take a few hundred miles.
The heaviest concentrations typically are in a 2- to 2.5-mile layer that begins about a mile above the surface, said Jason Dunion, a SAL specialist with the National Oceanic and Atmospheric Administration.
The aerosol ingredients can be eclectic, says Andrea Sealy, whose institute is affiliated with the World Meteorological Organization. She said studies have looking at what else is up there making the trips, "such as various bacteria" and "camel dung; live locusts have survived the journey in the past as well.