On the use of advanced microwave sounding Unit-A and -B measurements for studying the monsoon variability over West Africa
Eymard, L. ; Karbou, F. ; Janicot, S. ; Chouaib, N. ; Pinsard, F.
The advanced microwave sounding unit (AMSU) -A and -B sensors provide observations of humidity and temperature that are relevant for meteorological and climate studies. The use of these observations in numerical weather prediction models has increased in the past 10 years because of some improvements in data assimilation. However, an appropriate use of AMSU measurements apart from assimilation context is rather difficult and depends for the most part on how successfully the instrumental characteristics are accounted for. In particular, atmosphere humidity and temperature variations can be completely hidden by features because of the effect of the observation zenith angle. In this paper, 8 years of AMSU-A and -B observations have been corrected from the observations zenith angle effect and have been used to study temperature and humidity variations over West Africa. Comparisons have been made between AMSU observations and selected atmospheric fields from European Centre for Medium-Range Weather Forecasts analyses as well as outgoing longwave radiation estimates. It has been found that observations from AMSU-A channel 5 can be used to monitor the heat low evolution and that AMSU-B observations from channels 3 and 5 are well adapted to study the humidity variations in direct link with the African monsoon from intraseasonal to interannual scales.
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