I have noticed in some of the daily summaries for Hurricane tracking that there is a lot of saharan dust coming off of Africa. What causes this? Is there not a lot of rain with the storms coming off Africa into the Atlantic?
Posted August 11, 2007
MIKE MOSS SAYS: Jason, While there is some rainfall with systems developing over Africa and traveling west to emerge over the eastern Atlantic, what sometimes happens is that the rains are principally located over the Sahel region just south of the Sahara, but the storms induce increased pressure gradients over the desert regions just to their north, increasing the wind speeds to levels required to loft sand and dust which is then transported westward as part of a hot, dry "Saharan Air Layer." This kind of air and the dust that it entails have become the subject of considerable research interest due to its tendency to negatively impact tropical cyclone development and intensification. There appears to be a significant inverse relationship between the intensity and frequency of dust transport out of the Sahara, and the intensity and frequency of hurricanes forming in the eastern Atlantic. Reasons for this include dust intercepting sunlight and cooling Atlantic waters below, dust absorbing sunlight and warming air aloft so as to decrease the vertical temperature lapse rate and associated instability that helps power storms, and the fact that the Saharan air is very dry, which can rob developing systems (and sometimes established hurricanes) of energy if the dry air becomes entrained into the cyclone. Some researchers think enhanced dust levels in 2006 helped quash what had been expected to be an active season, while others note the rapid development of an unforecast El Nino pattern, which is unrelated to the dust but is also a notable negative factor for Atlantic hurricane formation.