Application of high-level environmental field factor in TC's sudden recurvature process

Using the 6-hourly reanalysis data of European Center ERA-Interim with horizontal resolution of 0.25° × 0.25° and hourly typhoon operational data provided by the CMA (China Meteorological Administration), a new high-level environmental field factor is derived, and its application during the recurvature period of No. 14 Typhoon Yagi and No. 18 Typhoon Rumbia in 2018 is compared and analyzed. According to the comparison study, there is always a clear positive abnormal value area of high-level environmental field factor on the northeast of Rumbia during its northward movement, implying an obvious alteration of $\nabla •\overrightarrow{u}$ and a big negative gradient of $\nabla \overrightarrow{u}$ on the northeast of Rumbia. With the eastward movement of the westerly trough and the strengthening of the subtropical westerly jet, Rumbia is expected to veer northeast. However, the change of high-level environmental field factor on the northeast of Yagi is not noticeable, and Yagi is far away from the upper-level jet stream, which is not conducive to Yagi's northeast recurvature.