RESUME / ABSTRACT  




Assimilation of Precipitation at the Meteorological Service of Canada

par/by


Godelieve Deblonde





A one-dimensional variational (1D-Var) scheme to assimilate passive microwave brightness temperatures (e.g. from the SSM/I, TMI and AMSR-E radiometers) in rainy atmospheres and satellite derived rain rates (PATER algorithm) has been developed at the Meteorological Service of Canada (MSC). The 1D-Var scheme is very similar to that developed at ECMWF (Moreau et al., 2004). The observation operator includes a radiative transfer model and moist physical parametrization schemes. Moist processes are described by the Kain-Fritsch scheme for deep convective clouds and by the Tompkins-Janiskova scheme for stratiform clouds. The Jacobians of the physical processes are computed via finite differences. Atmospheric profiles are taken from a research version of the GEM global forecast model named "mesoglobal" whose configuration includes a horizontal resolution of 45 km and 58 vertical levels with a model top of 10 hPa. Both 1D-Var techniques allow the retrieval of temperature and humidity profiles in rainy areas. A preliminary evaluation of the two methods has been done for several tropical cyclones. Both methods are successful in improving significantly the model surface rain rate. However, temperature increments (~ 0.4 K) are larger than those obtained at ECMWF. As a consequence, assimilating 1D-Var analyzed Integrated Water Vapour in the MSC 3D-Var or 4D-Var systems does not seem to be an interesting option.