Developing high spatial resolution daytime cloud climatologies for Africa

MODIS visible imagery has been used to develop a short-period climatology of cloudiness for the African continent at approximately 250m spatial resolution. The MODIS imagery, from satellite overpasses at ~ 1030 and 1330 Local Time, are used to produce frequencies of visible clouds that provide a good estimate of mid-day cloudiness. Though our means fields are based on only about 5 years of data, they depict strong mesoscale controls on the mean cloudiness. Over much of Africa these controls are independent of season and are evident in the monthly means of any year. Most patterns can be explained as the effects of diurnally-driven circulations associated with sloping topography or land-water contrasts. Some regions with frequent cloudiness reflect the interaction of the prevailing winds with topography. This cloud climatology should be of value to all forecasters in Africa who wish to understand better their regional and local climatology.