By employing NCEP-NCAR 1°×1° reanalysis datasets, the mechanism of the easterlies vortex (EV) affecting the short-term movement of the subtropical anticyclone over the western Pacific (WPSA) in the mei-yu period is examined using potential vorticity(PV) theory. The results show that when the EV and the westerlies vortex (WV) travel west/east to the same longitude of 120°E, the WPSA suddenly retreats. The EV and WV manifest as the downward transport of PV in the upper troposphere, and the variation of the corresponding high-value regions of PV significantly reflects the intensity changes of the EV and WV. The meridional propagation of PV causes the intensity change of the EV. The vertical movement on both sides of the EV is related to the position of the EV relative to the WPSA and the South Asian high (SAH). When the high PV in the easterlies and westerlies arrive at the same longitude in the meridional direction, the special circulation pattern will lower the position of PV isolines at the ridge line of the WPSA. Thus, the cyclonic circulation at the lower level will be strengthened, causing the abnormally eastward retreat of the WPSA. Analysis of the PV equation at the isentropic surface indicates that when the positive PV variation west of the EV intensifies, it connects with the positive PV variation east of the WV, forming a positive PV band and making the WPSA retreat abnormally. The horizontal advection of the PV has the greatest effect. The contribution of the vertical advection of PV and the vertical differential of heating is also positive, but the values are relatively small. The contribution of the residual was negative and it becomes smaller before and after the WPSA retreats.

中文翻译：

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梅雨期东风涡对西太平洋副热带反气旋短期运动影响的位涡诊断分析

利用NCEP-NCAR 1°×1°再分析数据集，利用位涡研究了东风涡（EV）对梅雨期西太平洋副热带反气旋（WPSA）短期运动的影响机制(PV) 理论。结果表明，当 EV 和西风涡旋 (WV) 向西/东行进到同一经度 120°E 时，WPSA 突然后退。EV和WV表现为对流层高层PV的向下输送，对应的PV高值区的变化显着反映了EV和WV的强度变化。PV 的经向传播导致 EV 的强度变化。EV 两侧的垂直运动与 EV 相对于 WPSA 和南亚高压 (SAH) 的位置有关。当东风和西风的高PV在子午方向到达同一经度时，特殊的环流模式会降低西太平洋脊线上的PV等值线的位置。因此，下层气旋环流将加强，导致西太平洋异常东退。等熵面的PV方程分析表明，当EV以西的正PV变化加剧时，它与WV以东的正PV变化连接，形成一个正PV带，使WPSA异常后退。PV 的水平平流影响最大。PV垂直平流和加热垂直差的贡献也是正的，但数值相对较小。