Comparisons Of Different Approaches In Separating TC Circulation From Its Environment Over The Western North Pacific

The tropical cyclone (TC) activity is affected by multi-time scale flows in the western North Pacific. The separation of the TC circulation from observation is an important step for understanding the interaction between multi-time scale flows and TC circulation. In this study, three methods including TCs spatial removal technique, Lanczos filter in time and multi-scale window transform (MWT) filter in time, and their different approaches combinations are compared based upon the FNL and the TCs best-track datasets from NCEP and JTWC, respectively.Through using them to idealized and observational wind fields and the analysis of the influence of TCs on the monthly wind fields, it is found that the primary TC circulation can be separated by the TCs spatial removal technique, which will lead to exaggerate impact of TCs on other circulations to some extent, but considerable cyclonic circulation remains in the environment near the TC centers. The results also suggested that Lanczos filtering and MWT filtering, compared to spatial remove method, can effectively separate the TC circulation from the environment although some small residual cyclonic circulation can be seen along TC tracks. Further, the combined TCs spatial removal technique and Lanczos filter or MWT filter are more useful for separating TC circulation. Moreover, the combinations of Lanczos filter and spatial removal approaches, has less advantages over the combinations of MWT filter and spatial removal approaches.The comparisons of the different approaches in separating TC circulation from its environment is conducted and further pointed out that their combinations have more advantages than a single approach. The study will show great potential ability for investigating the interaction between TC and multi-time scale flows over the Western North Pacific.