When the winds of winter sweep across West Africa, temperatures drop and skies turn yellow. Prevalent from November to March, the harmattan is a desert wind that blows across the Sahara Desert from the northeast or the east, usually as a result of a high pressure system over the northwestern Sahara. Harmattan winds pick up dust and darken skies.
A harmattan dust storm was blowing on February 28, 2014, when the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite acquired this image. The yellow dust was concentrated largely over the Cape Verde Islands, where the mountain topography created swirling eddies and triangular wakes in the dust cloud. West Africa frames the right edge of the image, and distinct plumes of dust moved west from Senegal and Mauritania.
The dust storm had a long reach. By March 4, a faint yellow haze lingered over the Caribbean.
The storm is not unusual in its reach. Hundreds of millions of tons of dust blow out of Africa every year, reaching the Atlantic, Caribbean, and Gulf of Mexico. The dust fertilizes ocean waters, feeding plankton growth, but it may also carry fungus and disease-causing microorganisms that damage coral reefs. On land, the dust is a health hazard when inhaled, and it has been found to carry chemical contaminants, including pesticides.
NASA image courtesy Jeff Schmaltz, LANCE/EOSDIS MODIS Rapid Response Team at NASA GSFC. Caption by Holli Riebeek.