Direct Assimilation of Satellite Cloudy Radiances with a 3D-VAR System

Direct assimilation of satellite radiances into numerical weather prediction models has become practical in operational centers. However, with current data assimilation system, only cloud-cleared (clear-sky) radiances can be assimilated. Radiances in the cloud and precipitating areas still can not be directly assimilated into the models due to lack of cloud/rainwater scattering and absorbing process in the fast radiative transfer model (forward model). In order to fully utilize the available satellite radiances information, it is necessary to incorporate more advanced radiative transfer model into the data assimilation system.

In this study, the progress has been making to incorporate an advanced radiative transfer model with mesoscale community model (i.e., weather research and forecasting (WRF) model) and its 3-dimensional variational data assimilation system. The advanced radiative transfer model is capable to calculate the radiances in cloud and precipitation conditions because the model reads atmospheric soundings and cloud hydrometeor profiles and take cloud absorption and scattering processes into account. It is anticipated that the incorporation of this type of forward models into the analysis system will certainly allow the radiances in the cloudy/precipitating regions to be directly assimilated into the numerical model. The tangent linear and adjoint model of the advanced radiative transfer model is under development and the preliminary numerical experiment will be conducted. The progresses and preliminary results will be presented in the conference.