1.College of Meteorology and Oceanography, National University of Defense Technology;2.Jiangsu Collaborative Innovation Center for Climate Change, Nanjing University
本文利用WRF模式，通过开展敏感性试验讨论了单个热带气旋（tropical cyclone, TC）—— Megi影响下西太平洋副热带高压不同高度脊线的偏移特征，并分析了TC Megi活动影响副高脊线垂直分布的可能机理。结果表明，副高脊线在TC Megi的影响下总体发生了向南偏移，且高层脊线的偏移程度更大。其可能机理为，副高脊线位置受其附近纬向风异常的直接影响，而TC Megi活动所导致的脊线附近纬向风异常与温度异常总体满足热成风关系，当TC Megi活动造成副高脊线附近出现温度经向梯度正异常时，西风异常会随高度增加而增强，因此会导致副高脊线向南的偏移程度也随高度增加而增大。另外，利用温度倾向方程的诊断分析结果表明，TC Megi活动所引起的温度水平输送异常和非绝热加热异常主要导致了大气温度的异常升高，而垂直输送异常则有利于大气温度的异常降低。总之，TC的热力效应在导致副高脊线垂直分布状况发生变化的过程中起到了重要作用。
Characteristics of meridional movement of western Pacific subtropical high (WPSH) ridge lines at different heights under the influence of a single tropical cyclone (TC) ——Megi and its possible mechanism are analyzed by conducting sensitivity experiment with WRF. The results show that the WPSH ridge lines shift southward under the influence of TC Megi. Furthermore, the higher the ridge lines are, the more southward they move. The possible mechanisms are that the shift of WPSH ridge is directly affected by the zonal wind anomalies in its vicinity regions, and the zonal wind anomalies and temperature anomalies near the ridge line caused by TC Megi activities generally satisfy the thermal wind relationship. Therefore, when the temperature gradient anomalies near the ridge line are positive under the influence of TC Megi, the westerly anomalies will strengthen with altitude, which will lead to the southward movement of ridge increasing with altitude, too. In addition, the diagnostic analysis results of temperature tendency equation show that the horizontal advection anomalies and non-adiabatic heating anomalies caused by TC Megi mainly lead to the abnormal increase of atmospheric temperature, while the vertical transport anomalies are always beneficial to the abnormal decrease of atmospheric temperature. It is concluded that thermal effect of TC plays an important role in the process of changing the vertical distribution of WPSH ridge lines.