Decay processes and statistical characteristics of continental Northeast China Cold Vortex from April to September

The Northeast China Cold Vortex (NCCV) is a major precipitation-producing weather system in northern China. Based on the ERA-Interim reanalysis data, the NCCV cases from April to September during 2009—2018 are identified and objectively clustered into 5 categories according to the location of the NCCV center. Among them, the northwest type, northeast type and southeast type continental NCCVs, named based on their locations, have significant impacts on northern China. The NCCV decay mainly involves two processes: The erosion of upper level PV (potential vorticity) by diabatic heating and reabsorption of the vortex PV back into the stratospheric reservoir. Statistical characteristics of the three types of continental NCCV that decay in the above two ways respectively are compared and analyzed. It is found that: (1) The decay of the northwest and southeast vortexes is mostly caused by diabatic processes, while the decay of the NCCVs is mostly attributed to reabsorption; (2) the intensity of the reabsorption decay type is generally stronger than that of diabatic decay type, as the north stratospheric reservoir is closer to the former. Besides, the latter is continuously weakened by latent heat release associated with precipitation; (3) the lifetime as well as the fraction of the decay phase for the diabatic decay type are longer than those of reabsorption decay type; (4) the location of the high-level trough relative to the NCCV and precipitation within the NCCV are two main factors that impact the NCCV decay. Strong precipitation near the NCCV center can directly erode the core of the vortex, resulting in diabatic decay. When the NCCV is ahead of or at the bottom of the high-level trough, the NCCV can be easily advected northward, leading to its absorption by the stratospheric reservoir.