Research progress in the unusual variations of typhoons before and after landfalling

Much work has been conducted, and some significant results have been achieved in the National (Key) Basic Research and Development (973) Program of China entitled "Unusual Variations of Landfalling Tropical Cyclones and Associated Physical Mechanisms" during 2009-2013. Systematic observations of 16 typhoons have been made, and new observational results about the drag coefficient over shallow water areas and the changes in boundary-layer height were obtained. Notable progress in the multi-source data synthesis and assimilation techniques has been made, particularly in the retrieval of radar wind fields and the associated assimilation. Physical mechanisms for the roles of the systems on different scales in the sudden change of typhoon tracks, the rainfall reinforcement associated with landfalling tropical cyclones, and the formation of concentric eyewalls have also been revealed. Through improving the vortex initialization and cumulus convective parameterization schemes, developing new cloud-radiation parameterization scheme, and establishing an air-land-sea coupled model, the performance of typhoon forecasting by regional numerical models in China has been significantly improved. The progress of the Program is summarized, and associated scientific issues are discussed.