Main features of rain drop size distributions observed in Benin, West Africa, with optical disdrometers

Abstract : As part of the African Monsoon Multidisciplinary Analysis (AMMA) field campaign, rain Drop Size Distribution (DSD) measurements were carried out in Benin, in the Sudanese climatic zone, with optical disdrometers, over 3 rainy seasons. The observed DSDs are well modelled by a gamma distribution, with the value of the shape parameter (μ) close to 5. The average normalized intercept parameter (N0*) is close to 103 mm−1m−3. After classification of the convective and stratiform spectra, it is shown that for a given rain rate the proportion of the bigger drops is higher in the stratiform spectra, consistent with the observed occurrences of ‘N0 jumps' within the squall lines. Specific reflectivity-rain rate (Z-R) relationships were derived for the whole data set, for the squall lines and for the convective and stratiform regions.