Philippe Chambon, Fabrice Duruisseau, Eric Wattrelot and Jean-François Mahfouf
Within the 4D-Var ARPEGE global data assimilation system in operations at Meteo-France, only clear-sky microwave observations are presently used. A new framework is currently under investigation to assimilate as well microwave observations in cloudy and rainy areas. This method is developed in the frame of the Megha-Tropiques satellite mission to improve rainfall forecasts of Tropical convection. It is called 1D-Bay+4D-Var and corresponds to a two-step process: (i) a Bayesian inversion algorithm to retrieve profiles of temperature and humidity from the microwave radiances, (ii) the 4D-Var assimilation of these retrieved profiles. The 1D-Bay+4D-Var method is an alternative to both 1D-Var+4D-Var and direct all-sky assimilation ; it has been successfully used in operations for the assimilation of radar reflectivities at Meteo-France since 2008. Preliminary results of assimilation of the radiances from the SAPHIR microwave sounder onboard Megha-Tropiques will be presented. In particular, the impacts of assimilating cloudy and rainy observations on tropical winds and precipitation forecasts will be discussed.