1B.1
The generation of intense convection over West Africa during the summer monsoon season.
Dan C. Collins, Georgia Institute of Technology, Atlanta, GA; and P. J. Webster
The generation of intense convection over West Africa during summer monsoon is tied to temporal and spatial variability of surface conditions. During the northward spring migration of the ITCZ and summer monsoon, the covariance of surface air temperature, soil moisture and pressure fields influences the generation of convection through atmospheric instabilities. The variability of West African monsoon precipitation is examined through wavelet analysis identifying the synoptic, intraseasonal and seasonal bands. Statistical analysis shows that the location and strength of atmospheric convection are tied to the spatial distribution of soil moisture and the variability of surface air temperature and pressure at both intraseasonal and seasonal timescales. At intraseasonal timescales the northward extent of convection is tied to land-surface conditions and periodic chaotic changes in the easterly jets and convective activity. Differential heating of the atmospheric column due to both the land-sea contrast and moisture availability are believed to be important to the generation of the African monsoon circulation on seasonal timescales, while meridional soil moisture variability may play a significant roll in generating and maintaining convective precipitation. Previous studies have indicated a relationship between the meridional distributions of moist static energy and the onset and strength of the West African monsoon. The influences of zonal and meridional gradients of surface air temperature, pressure and soil moisture anomalies are examined. The role of inertial instability and the location of zero absolute vorticity associated with zonal pressure gradients are considered as a possible factor in the northward extent of convection. Orography plays a significant role in the intensification of the monsoon over West Africa. A mesoscale circulation model is used to examine the relative impacts of soil moisture and orography to the generation and maintenance of convection over the West African monsoon region, and the strength and location of convection associated with zonal pressure gradients.
Session 1B, CONVECTION, waves, and precipitation I
Monday, 3 May 2004, 8:30 AM-10:15 AM, Napoleon I Room
Next paper