Variational retrieval of cloud profile from ATOVS observations

Radiation observations such as those from the Advanced Tiros Operational Vertical Sounder (ATOVS) on board the National Oceanic and Atmospheric Administration satellites provide information about cloud systems. However, like the other cloud observations they are not used in global data assimilation systems. As an essential step towards the assimilation of such data, a fast infrared and microwave radiation model and its linearized version (tangent linear and adjoint operators) have been developed for the computation of model-equivalent cloud-affected satellite radiances. They are used in a global one-dimensional variational (1D-Var) analysis of ATOVS radiances over open oceans. In non-precipitating areas, it is shown that the 1D-Var can remove, create and modify the cloud variables in each model layer to fit the observed radiances. The retrieved profiles have a degree of realism that will improve with better background constraint. This study is a first step towards the assimilation of clouds by variational analysis of clouds and dynamics at once, and will be further continued.