Thursday, 13 January 2005
Annual Cycle and Interannual Variability in the Sahel rainfall based on the CPC African Rainfall Estimates Climatology (ARC)
The performance of the Climate Prediction Center (CPC) Africa RFE Climatology (ARC) is evaluated through the study of the annual cycle and the interannual variability in the West African rainfall. ARC is a climatological dataset based on daily Meteosat rainfall estimates (RFE) going back to 1982. The RFE data set used in ARC consist of Meteosat infrared satellite data at a resolution of 0.1 degree merged with ground-based Global Telecommunications System (GTS) rain gauge. It is a three step procedure. First, three-hourly Meteosat IR cloud top temperature data are converted to a standard GOES Precipitation Index (GPI) by assigning a 3 mm rainrate to each pixel colder than 235 K. Then, the GPI at each grid point is compared to rain gauge data at corresponding lat-lon positions to determine the error at each point. An interpolation technique is then used to blend the GPI with the gauge data. The gauge data help to determine the magnitude of the precipitation fields. In this study, we compare the ARC with several other data sets including GTS data, CMAP, and GPCP. Preliminary results show that for the period from 1995 to 2003, the ARC reproduces the annual cycle in the Sahel rainfall adequately. However, only about 2/3 of the intensity of the rains is captured suggesting that ARC tends to underestimates rainfall in the Sahel. The possible sources of this underestimation are discussed. On the other hand, ARC depicts the interannual variability in the Sahel rainfall very well. This suggests that it is a valuable data set for evaluating high resolution model data.