Abstract
Based on the fifth-generation atmospheric reanalysis of the global climate released by the European Centre for Medium-Range Weather Forecasts (ECMWF), this study firstly objectively identifies the Northeast cold vortex (NECV) processes during the winters from 1951 to 2021. Subsequently, using the observational data from 245 meteorological stations in Northeast China, cold vortex snowstorm (CVS) events in Northeast China are defined and further classified into three types based on the NECV intensity, which are named as northwestern-path, southern-path and northern-path types according to the movement paths of the associated NECVs. The results show that for CVSs of the southern-path type, the NECVs feature the southernmost position, with the whole Northeast China dominated by abnormal cyclone at 850 hPa. For CVSs of the northern-path type, there are two abnormal cyclones in a stepped distribution. However, at the sea level, the surface systems of the southern-path and northern-path types develop into cyclones, leading to distinct moisture transport paths among the three types. The high moisture flux regions correspond well with the snowfall area across all three types, as do the high moisture divergence regions with the extreme snowfall regions. The upper-level jet core is located near 30°N. As the Northeast China region is situated north of the upper-level jet exit, the upward motions in the southern-path and northern-path types are stronger than that in the northwestern-path type. For CVSs of the northern type, significant positive vorticity is located away from the snowstorm center. Warm advection dominates the region from the lower to middle troposphere, and strong upward motion lifts warm and humid air, thereby resulting in the snowstorm. CVSs of the northwestern-path type intermediate in upper-lower level configurations between the other two types. For CVSs of the southern-path type, there is a deep vertical system. Cold advection prevails the mid-to-low levels over the snowfall area, which provides a cold cushion near the ground that forces warm and humid air to ascend, thereby producing heavy snow. Furthermore, the downward extension of the high-level potential vorticity to the mid-to-low levels, along with the intrusion of dry-cold air from the upper levels into the mid-to-low levels facilitate the persistence of the cold vortex and the intensification of snowfall.