Abstract:In this study, we propose a new way to obtain motion vectors for extrapolation nowcasting， namely the adaptive-scale tracking radar echoes by correlation （ATREC）, which can automatically adjust the size of tracking area according to the scale of convection systems. ATREC method tracks the large-scale motion of the radar echo which is identified by the automatically determined convection edges, then the different subscale motions are deduced by tracing the self-split small parts of radar echoes. ATREC method can retrieve the motions of different scales of the convection system and get a smooth motion field for extrapolation. Thereafter, this method can resolve the problems caused by the fixed size of tracking area applied in the traditional tracking radar echoes by correlation (TREC) methods, especially the inapplicability of TREC methods in small-scale convective systems. Nowcasting experiments using the ATREC method and MTREC (multi-scale tracking radar echoes by correlation) method are carried out in this study to demonstrate the practical ability of the ATREC method. Comparison based on a series of weather cases shows that the ATREC method has the abilities of automatically analyzing and flexibly adjusting convective systems with different scales and different types. The evaluation scores of case study and the statistic verifications based on 128 cases in April 2016 indicate that ATREC method has better performance than the MTREC method.