Influence of Tropical Cyclone Activities on the Meridional Movement of Western Pacific Subtropical High and Its Possible Mechanisms: A Case Study

The characteristics of the meridional movement of western Pacific subtropical high (WPSH) ridge lines at different pressure levels under the influence of a single tropical cyclone (TC), i.e., Megi, and its possible mechanisms are analyzed by conducting sensitivity experiments with WRF. The results show that the WPSH ridge lines shift southward under the influence of TC Megi. Moreover, the higher the ridge lines are, the more southward they move. The possible mechanisms are that the shift of WPSH ridge lines is directly affected by the zonal wind anomalies in its vicinity, and the zonal wind and temperature gradient anomalies near the ridge lines caused by TC Megi generally satisfy the thermal wind relationship. Therefore, under the influence of the temperature gradient anomalies near the ridge line caused by TC Megi, the zonal wind anomalies will change with altitude, which will affect the vertical distribution of WPSH ridge lines. In addition, the diagnostic analysis results of the temperature tendency equation show that the different physical processes near the ridge, which are stimulated by TC activities, exhibit quite different temporal and spatial distributions. Moreover, the horizontal advection and nonadiabatic heating anomalies caused by TC Megi mainly lead to the abnormal increase of atmospheric temperature. Meanwhile, the vertical transport anomalies mainly lead to the abnormal decrease of atmospheric temperature. Therefore, the thermal effect of TC activities plays an important role in the process of changing the vertical distribution of WPSH ridge lines.