This study investigated the structural and track change of cyclone Nepartak occurred over the western North Pacific in July 2021, a cyclone appeared at the surface level, using ERA5 data, focusing on the relationship with an upper-tropospheric cutoff low (COL). The COL was shown to dominate the structural change of Nepartak which developed as a subtropical cyclone with a hybrid structure. As the surface cyclone approached the COL, it was overlapped by the COL and became a cyclone with a two-storied structure, resulting in its abrupt track change. An analysis of the potential vorticity (PV) tendency showed that the movement of Nepartak toward the COL ceased because of the counter-balance of the horizontal/vertical PV advection with the PV anomaly generated by diabatic heating, whereas the surface cyclone northward motion was primarily due to the horizontal PV advection associated with the COL. Nepartak is a case in which changes in the structure and track of a cyclone are controlled by a COL.

中文翻译：

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受对流层上层截止低压控制的副热带气旋尼帕塔克 (2021) 的特征

本研究利用ERA5数据调查了2021年7月发生在北太平洋西部的气旋“尼帕塔克”的结构和路径变化，该气旋出现在地表，重点关注与对流层上层截止低压（COL）的关系。研究表明，COL 主导了尼帕塔克的结构变化，尼帕塔克发展成为具有混合结构的副热带气旋。当地面气旋接近COL时，它与COL重叠，成为一个两层结构的气旋，导致其轨迹发生突变。对位涡（PV）趋势的分析表明，由于水平/垂直PV平流与非绝热加热产生的PV异常的平衡，Nepartak向COL的运动停止了，而表面气旋向北运动主要是由于与 COL 相关的水平 PV 平流。Nepartak 是由 COL 控制气旋结构和轨迹变化的情况。