Improved precipitation forecasting of landfalling tropical cyclones by data assimilation of microphysical structures retrieved from TRMM

Work is in progress to develop a system to assimilate retrieved precipitation fields from TRMM (Tropical Rainfall Measuring Mission) satellite radar observations into a cloud resolving forecast model of a tropical cyclone. The goal is to improve quantitative precipitation forecast of rainfall of tropical cyclones at landfall. Our technique is to employ retrieval techniques developed by Panegrossi et al, 1998 and Pannegrossi et al, 1999 to retrieve three-dimensional rain and ice fields. We are modifying the NCEP EDAS (National Center for Environmental Prediction Eta Data Assimilation System) to assimilate these retrievals into the University of Wisconsin Nonhydrostatic Modeling System (UW-NMS) where cloud resolving forecasts of the tropical cyclone are made.

We are co-developing both the UW-NMS microphysical scheme and the the retrieval technique to optimally facilitate the assimilation. Inconsistencies between the model simulated microphysical fields and the TRMM microwave radiances are analyzed to find biases that may suggest needs to alter the bulk microphysical formulations of the model. On the other hand, the model will provide the data set from which structure functions comparing microwave radiances to microphysical structure are developed. Our initial testing is on simulations of Bonnie and Georges both of which were observed by aircraft during CAMEX.

We have already completed a large cloud resolving forecast simulation of hurricane Bonnie during the time of a TRMM pass and have made comparisons of our retrieval fields (using TRMM) against the simulated microphysics. We are currently making modifications to EDAS and expect preliminary results of data assimilation tests by the time for the conference