Comparing satellite and surface rainfall products over West Africa at meteorologically relevant scales during the AMMA campaign using error estimates

International audience Monsoon rainfall is central to the climate of West Africa and understanding its variability is a challenge for which satellite rainfall products could be well suited to contribute to. Their quality in this region has received less attention than elsewhere. The focus is set on the scales associated with atmospheric variability and a meteorological benchmark is set up with ground-based observations from the AMMA program. The investigation is performed at various scales of accumulation using four gauge networks. The seasonal cycle is analyzed using 10-day averaged products, the synoptic scale variability using daily means and finally the diurnal cycle of rainfall is analyzed at the seasonal scale using composite and at the diurnal scale using 3-hourly accumulations. A novel methodology is introduced that accounts for the errors associated with the areal-time rainfall averages. The errors from both satellite and ground rainfall data are computed using dedicated techniques that come down to an estimation of the sampling errors associated to these measurements. The results show that the new generation of combined IR/MW satellite products is describing the rain variability similarly to ground measurements. At the 10-day scale, all products reveal high regional and seasonal skills. The day-to-day comparison indicates that some products perform better than others, while all of them exhibit high skills when the African Easterly Waves spectral band is considered. The seasonal variability of the diurnal scale as well as its relative daily importance is only captured by some products. Plans for future extensive intercomparisons exercise are briefly discussed