The Characteristics of Northeast China Cold Vortex With Different Active Paths in June and Their Relationship With Precipitation and Pre-SST

In this study, a K-means clustering (KMC) method was used to identify the paths of the Northeast China (NEC) Cold Vortex (NCCV). The NCCV was divided into four types according to the identified active paths: (1) Eastward movement type (EM); (2) Southeastward long-distance movement type (SLM); (3) Eastward short-distance movement type (ESM); and (4) Southward short-distance movement type (SSM). The characteristics of the four types of the NCCV, along with their impacts on the precipitation during early summer in NEC, were studied. The results showed that the KMC method can effectively divide the NCCV events into four different types. The maintaining days of these four types of the NCCV were found to have obvious interannual and interdecadal variation features. For example, the maintaining days of the EM and ESM types were mainly characterized by interannual variability, while the SLM and SSM types have the obvious 10–13a interdecadal variation along with interannual variability. In terms of the spatial distributions and impacts on precipitation, the EM type was found to appear in the majority of the areas located in NEC, the SLM type mainly occurred in the northwestern region of NEC and the highest rain center was located in the south-central portion, while the ESM type and SSM type were observed precipitation only appear in a small portion of the northeastern region. In addition, it is also observed the distribution of the sea-surface temperature (SST) anomalies had close relationship with the formation of these four types of the NCCV. The tripole distributions of the SST anomalies in the Atlantic Ocean corresponded to the EM type of the NCCV, the positive anomalies of SST in the eastern equatorial Pacific Ocean and negative anomalies in the western equatorial Pacific corresponded to the SLM type, the positive SSTs in the Northwest Pacific correspond to the ESM type, while negative anomalies SST in the western equatorial Pacific Ocean corresponded to the SSM type of the NCCV.

Microphysical Processes of a Cold Vortex during Its Movement to the East: A Case Study

A cold vortex is an important weather system that can cause low temperatures and large amounts of rainfall. Many scientific studies have focused on the climatological features of the cold vortex along with its formation, maintenance, structure, circulation features and precipitation distribution from a synoptic perspective. However, not many studies have been conducted related to the microphysical processes in a cold vortex. In this paper, a model study is presented on the microphysical features in a cloud system associated with a cold vortex system which lasted for four days. The system formed, strengthened, split into two and dissipated while it moved towards the east and brought extensive precipitation to the influenced area. The type and amount of precipitation were not evenly distributed: liquid precipitation covered the whole area influenced by the cloud system, while solid precipitation mainly covered high latitudes north of 48° N. In this case, the cloud system was very cold and the 0 °C; level was very low, with the result that the microphysical features were dominated by cold cloud processes. The mixing ratio of liquid particles was very small, and liquid particles only covered limited areas in the clouds. Due to the low temperature, there were insufficient cloud droplets throughout the whole system for the efficient production of rain droplets by coalescence. The snow mixing ratio was largest, and ice and snow covered the whole cloud area, with very little graupel, which occurred in only a small area. The distribution of the solid particles was influenced by their growth through aggregation, the Bergeron process or accretion, resulting in many snow particles. There were insufficient liquid particles to support the formation of very large particles such as graupel. Liquid precipitation was primarily caused by the melting of snow particles precipitating out of the clouds; solid precipitation was also primarily caused by snow particles that did not melt, along with some graupel.