Boston, Mass. -- The two jet streams that flow over West Africa during the summer months may contribute to the extended drought that has plagued this already semi-arid area, according to Penn State researchers.
"We are trying to explain the West African drought, in part, by looking at the correlations between precipitation and the jet streams," says Colleen Mikovitz, graduate student in meteorology in the College of Earth and Mineral Sciences.
The area affected by drought since the 1970s is the Sahel, a savannah area lying just south of the Sahara Desert. Countries in the Sahel include Ghana, Niger, Senegal, Sierra Leone, Liberia and Burkina Faso, where the rainy season usually runs between May and September.
"While the drought that began 30 years ago continues, we are looking at data from 1979 through 1994," Mikovitz told attendees today (June 3) at the spring meeting of the American Geophysical Union meeting in Boston, Mass. "It appears that there is a correlation between the strength of the jet streams in this area and precipitation."
Two jet streams flow over the Sahel, the African Easterly Jet, which originates over the continent and the Tropical Easterly Jet, which originates over the Indian Ocean and is part of the circulation pattern of the Indian Monsoon. The Tropical Jet is higher and flows at about 40,000 feet above the Earth's surface and the African Jet is at about 10,000 feet.
Mikovitz and Dr. Gregory S. Jenkins, assistant professor of meteorology, looked at the average precipitation per year and the long-term averages and compared them with the patterns of the jets. They found that the Tropical Easterly jet was mostly weaker during the dry periods.
"The pattern with the African Easterly jet was not as clear, but tends to be slightly stronger especially during very dry years," says Mikovitz. "There seems to be some connection between the jets and precipitation."