Assimilating fractions of precipitation area: an idealized study with an intermediate AGCM
Assimilating precipitation observations into an atmospheric model is a challenging issue due to nonlinear processes and non-Gaussian PDF of precipitation. Previous studies adopted variable transformation techniques such as the logarithmic transformation and the Gaussian transformation. Here we propose an alternative approach: assimilating fractions of precipitation area based on the precipitation map from remote-sensing techniques such as radars and satellites. Within n-by-n grid points centered at the analysis point, the number of grid points exceeding a given threshold of precipitation rate is assumed as the "observation." Applying this observation model to the observed and simulated precipitation fields, we perform data assimilation. In this presentation, idealized experiments with an intermediate atmospheric general circulation model known as the SPEEDY and the local ensemble transform Kalman filter (LETKF) will be presented.
Dr. Shigenori Otsuka RIKEN