The T-TREC technique for retrieving the winds of landfalling typhoon in China. Key Laboratory of Mesoscale Severe Weather/MOE

In this study, an extension of TREC (Tracking Radar Echo by Correlations) technique, named Typhoon Circulation TREC (T-TREC), is developed. The TREC analysis is performed on a polar coordinate centered on the tropical cyclone (TC) eye using arc shaped correlation cells and arc shaped search area with a shorter dimension in the radial direction and a longer dimension in the azimuthal direction in order to reflect the fact that the tangential component of typhoon circulation is usually much larger than its radial component. The search for the best correlation match is limited to the cyclonic direction for TCs in the Northern Hemisphere on the basis of the cyclonic circulation characteristics of TCs. And the typhoon center is determined objectively by the weak echo finding technique. In addition to reflectivity data, the Doppler radar radial velocity is incorporated to estimate the search range and create a velocity correlation matrix in order to alleviate the uncertainty of tracking reflectivity only.By applying the T-TREC algorithm to the data of Landfalling Typhoon Saomai (0608) collected by China new generation radar the Weather Surveillance Radar-1998 Doppler (CINRAD WSR-98D) on the southeast coast of China, it can be seen that this new method can estimate the typhoon circulation more accurate than TREC method, and the mean radial velocity errors in landfalling typhoon are less than 4 m/s. The incorporation of radial velocity information could distinctively improve wind retrievals of intense typhoon, especially reducing the underestimation caused by fairly uniform reflectivity patterns in the vicinity of the eyewall and rainband outside. It is noted that the error rates of retrieved wind at low levels increased partly due to the interference of ground clutter and the new convection forced by the interaction of the typhoon circulation with the terrain, as the typhoon approached the land. The quantitative evaluation of the influence of typhoon center and cell size on the wind estimation demonstrates that the quality of TTRECretrieved circulation depends on the estimation of the typhoon cent er, and a 4 km deviation of the TC center may result in 10% increase of retrieved wind error. The effect of cell size depends on typhoon scale: a smaller cell can obtain better results for a smaller scale typhoon.