Abstract: A two-step variational method is used to retrieve the “0604” typhoon (called Bilis) of 2006. The retrieval results using the single radar data were compared with that using the dual-Doppler radar data. The results indicate that the two-step variational method can not retrieve well the structure of typhoon using the single radar data. However, this method can retrieve the vortex structure of typhoon at the first step with the dual-Doppler radar data. The Rankine model and the Chen 3 model fit well within and outside the radius of the maximum tangential velocity of typhoon Bilis, respectively. The experiential symmetrical model is added in the two-step variational method in order to determine the moving path of typhoon with the single radar data. The result shows it improves the retrieval ability of the two-step variational method. The retrieval result of wind field is better at the first step by using single radar data after adding the symmetrical model and it is similar to that by using the dual-Doppler radar data. The correlation coefficients of u and v between retrieval results with the single radar data adding the symmetrical model and with the dual-Doppler radar data are both above 0.8, and the mean square errors of u and v at the heights of 2-7 km decrease significantly.

Key words: Doppler radar data, Typhoon retrieval, Wind field model, Weak constraint