REMOTE SENSING: Wind and Rainfall over the Tropical Atlantic
Researchers at the Department of Meteorology University of Maryland use novel satellite based wind and rainfall products to study the wind and freshwater forcing of the tropical ocean. Bi-weekly wind and rainfall oscillation in the West African Monsoon. Enhanced spatial and temporal resolution of the satellite sensors provides better insight into the instraseasonal time scales. With the QuikSCAT scatterometer winds and rainfall estimates from the Tropical Rainfall Measuring Mission (TRMM) we have observed a new type of intraseasonal, biweekly oscillation in the West African Monsoon. This oscillatory regime preceeds rainy season in subSaharan West Africa that begins in boreal summer and whose arrival is of critical importance for local economies.
Two-day average surface winds and rainfall obtained from scatterometry and TRMM microwave measurements are illustrated above. The left panel shows 16-18 May. The right panel shows 21-23 May. Rates exceeding 0.5 mm/hr are shaded. Note the rapid change in direction and rainfall pattern. This pattern has switched back by 30 May. This oscillation in rainfall occurs in conjunction with monsoonal wind patterns and is particularly noticeable in the zonal wind field. It is also associated with a cooling of surface temperature and a reduction in zonal surface pressure gradient. Together the phasing of these variables implies feedback cycle acting between the monsoonal winds and their clouds, soil moisture and surface temperature. For more details go to rainfall