NASA MODIS Image of the Day: February 9, 2012 – Dust storm off West Africa
Strong winds continued to blow a cloud of dust off the coast of West Africa in early February 2012.
Only the day before, dust shrouded much of the coastline of West Africa, Mauritania and Senegal, obscuring parts of both the land and the ocean from view.
By the time the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Aqua satellite passed over the region on February 7, the dust over the coastline had moved west,most thickly covering the Atlantic Ocean and Cape Verde Islands. Although images collected by MODIS are static, wind can leave distinct visible clues as to its strength and motion. The most notable clue in this image is the pattern of swirls in the dust near the Cape Verde Islands. These swirling eddies begin where the wind strikes the Cape Verde Mountains, and stretch to the southwest on the leeward side of the islands, in line with the prevailing northeasterly wind. Such patterns are created when a strong wind collides with an immobile buff body. The airflow at the point of impact is impeded, and air must flow turbulently in order to pass the body. Behind the body, the air flow swirls in symmetric patterns. Such disturbed airflow is normally invisible, since air itself cannot be seen. When clouds cover a turbulent area, the disturbed patterns can cause striking patterns in the clouds. In this case, the air is heavily laden with dust, and the airflow patterns are clearly painted in a palette of tan and blue.
