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Communication incl. Poster: BibTeX citation key:  Moumounib
Moumouni, S., Gosset, M. & Houngninou, E. 2009. Study of the variability of rain Drop Size Distributions over different temporal scales and its impact on the Z-R relationship, based on AMMA observations in Benin. Work presented at Third International AMMA Conference, July 20—24, at Ouagadougou, Burkina Faso.
Added by: Devic 2009-09-08 16:17:04    Last Edited by: roussot 2009-11-23 20:40:21
Categories: Water cycle
Keywords: Precipitation
Creators: Gosset, Houngninou, Moumouni
Publisher: African Monsoon Multidisciplinary Analyses (Ouagadougou, Burkina Faso)
Collection: Third International AMMA Conference

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As part of the African Monsoon Multidisciplinary Analysis (AMMA) field campaign, rain Drop Size Distribution have been measured in Benin during three rainy seasons. This data is used to characterize rainfall microstructure for MCSs representative of the soudanian climate and to illustrate the effect of Drop Size Distribution (DSD) variability on radar measurements. The sensitivity of the coefficients in the relationship between radar reflectivity (Z) and rain rate (R) is analyzed at several scales: i) within the convective systems, between the convective and stratiform regions, ii) from system to system and also iii) within the West African region.
Within the convective systems a clear difference is found between the convective and the stratiform areas. For similar rain rates, the spectra in the convective region are narrower and with lower mean diameters, as observed before in Africa or other Tropical Squall lines. The climatological Z-R relationships derived for the convective rain (Z=343 R1.38), is different from the one derived for the stratiform rain (Z=468 R1.39) or for the whole data set (Z=433 R1.33). For organized squall lines, the prefactors vary even more, with a factor 2 between the convective and the stratiform region. We find however that applying two different climatological Z-R, according to the region of the storm, does not improve substantially the rain estimation. The storm to storm variation of the DSD properties is very high. No physical explanation was yet established to explain or predict it. It induces a strong variability in the Z-R relationship fitted on individual even. The prefactor varies between 200 and 900 within the entire data set (93 events). Using event-adjusted, rather than global Z-R reduces by about 40% the uncertainty on the event rain amount and by 30% the uncertainty on the rain rates. Storm to storm adjustment of the Z-R relationship, using for instance the available gages network is thus recommended.
Last Edited by: roussot