Analysis and Discussion of a Strong Cold Air Process in Spring

Based on NCEP 1°×1°daily reanalysis data and conventional surface observation data, using the vortex theory to analyze a strong cold air activity process of Karamay occurred on 15-16 May 2019, the results show that: 1) The weather had obviously baroclinic characteristic. A strong cold tongue extended straight to Central Asia from the high latitude area, and the cold air was strong and deep. The driving effect of cold trough could accelerate it to move southward. The Aral Sea vortex obstructed the warm air in the north high latitude area, and the southwest air flow in the front of the vortex conducted to the transportation of water vapor to Central Asia. 2) Compared with the climate average field of 1981-2010, the northwest flow at 500 hPa in May 2019 was aggressive, which had frequently influenced Xinjiang by cold air from the north high latitude regions. The east flow of the bottom layer not only input cold air to Karamay, but also formed the windward slope effect with the terrain. Moreover, it increased the vertical wind shear and induced the upward movement. 3) The center of high potential vorticity with high latitude fell southward, and the center of low potential vorticity in Central Asia moved eastward rapidly, they combined and then moved toward Xinjiang, which made the strong cold air erupt rapidly. When the moved axis of the center of the high potential vorticity and the strong west flow superposed over the area of Karamay, the center of the rainfall area appeared 6 hours later.