Northeast China Cold Vortex: Three-Dimensional Structure, Life Cycle, and Dynamical Understanding

This study examines three-dimensional structure, life cycle, and physical mechanism responsible for growth and decay processes of the Northeast China Cold Vortex (NCCV) by utilizing daily reanalysis data of ERA5, a set of data of NCCV occurrence days, and diagnostic results from a simplified potential vorticity (PV) tendency equations. Composite anomalous circulation fields reveal that NCCV is a deep cyclone with a "warm-above and cold-below" vertical temperature profile. NCCV is also accompanied by an anticyclone to the north and a weaker cyclone downstream, collectively forming a dipolar pattern. This dipolar pattern is associated with a wider and slower midlatitude zonal jet and a wave train-like meridional wind pattern. In the mid troposphere, diabatic heating (cooling) corresponds to ascending (descending) motion on the eastern (western) flank of NCCV. NCCV's life cycle is characterized by an upstream wave train propagation and interactions with a retreating blocking, leading to formation of the dipolar pattern of NCCV. Dynamical diagnoses reveal horizontal advection is the primary mechanism driving NCCV's growth and decay. Diabatic heating and vertical motion also contribute to NCCV's evolution. Nonlinear processes, particularly the interaction between the upstream wave train and the retreating blocking, disrupt the connection between NCCV and high-latitude PV, thus contributing to NCCV's formation as a cut-off low.