Targeted Observations of Tropical Cyclone Movement Based on the Adjoint-Derived Sensitivity Steering Vector

Since 2003, a field program has been conducted under the name of Dropwindsonde Observations for Typhoon Surveillance near the Taiwan Region (DOTSTAR) (Wu et al. 2005a). For DOTSTAR, the targeted observation is one of the most critical objectives. The important basis to design the observing strategy is to identify the sensitive areas, which would have the critical impact on the numerical forecast results or the fast growth of the forecast error. In addition to various sensitivity products already adopted in DOTSTAR, a new way to identify the sensitive area for the targeted observation of tropical cyclones based on the MM5 adjoint model has been proposed. By appropriately defining the response functions to represent the steering flow at the verifying time, a simple vector, Adjoint-Derived Sensitivity Steering Vector (ADSSV) has been designed to clearly demonstrate the sensitivity locations at the observing time. Typhoons Meari and Mindulle of 2004 have been selected to demonstrate the use of ADSSV. In general, unique sensitive areas 36 h after the observing time are obtained. The impact of the vortex initialization and the dry assumption on the ADSSV has also been studied. In order to use the ADSSV in the field program (such as DOTSTAR), the procedure of the model calculation has been to meet the realtime need. It is shown that the realtime use of ADSSV is feasible, and the results are fairly consistent with our previous findings. The ADSSV is implemented and examined in the field project, DOTSTAR in 2005, as well as in the surveillance mission of Atlantic hurricanes conducted by HRD. Further analysis of the results will be very important to validate the use of ADSSV.