Jeudi 29 juin à 14h sur le site de l'UPMC.

Salle de réunion 411, tour 45-46, 4e étage.

Giovanni A. Dalu de IBIMET CNR, Rome, Italie

Theory for the dynamics of a Saharan dust cloud

Sudden Saharan desert dust storms generate dust clouds over North Africa. In this region of prevailing easterly winds, these clouds migrate westwards floating in the lower half of the troposphere. The diabatic dust warming (DDW), due to the solar radiation absorption, drives an upper anticyclone and a lower anticyclone.
The dust cloud dynamics are analyzed in terms of the solution to a two-layer Gill model, and the cloud latitudinal migration is analyzed in terms of potential vorticity balance. Results show that the latitudinal narrow and longitudinal long dust clouds migrate further northwards than lat-lon wide-short clouds. This northwards migration is larger for clouds originated in a more northern position. An ambient easterly winds can displace the dust cloud over the Atlantic in ten days, reducing its northwards displacement.
The impact on the dust cloud trajectory due to the presence of a lower frictional Ekman layer and of the Saharan heat low (SHL) are also analyzed. Results show that the latitudinal displacement increases in the presence of the Ekman pumping and that dust clouds originated to the south (north) of the SHL have a smaller (larger) northwards displacement.