Abstract:

Based on hourly precipitation data from 512 automatic meteorological observation stations at the eastern foothills of Helan Mountains in Ningxia province, the ERA5 reanalysis data, and conventional meteorological detection data, the moist potential vortex characteristics of the two extreme rainstorm events occurred on July 22, 2018, and August 11, 2020, in this region were compared and analyzed.The occurrence and development mechanism of the two rainstorm events were explored.The results show that the two extreme rainstorm processes occur under the circulation situation of "high in the east and low in the west".The southerly flow on the west side of the western Pacific Subtropical High, the configuration of high and low air jets, and the typhoon provide favorable water vapor and dynamic conditions for the heavy rainfall processes.In the lower troposphere of 700~850 hPa, 3 ~ 6 h before the rainstorm, there is a dense isocontourt zone with the transition between the negative center of the positive pressure term of the moist potential vortex (MPV1) and the positive and negative center of the moist potential vortex baroclinic term (MPV2), and its movement development and duration correspond well to the occurrence and development of the rainstorm, which can indicate the rainstorm forecast.In the lower troposphere, the position where MPV1 negative region and MPV2 positive region are superposed is an area prone to heavy rainfall, and the stronger and longer the intensity and duration of MPV1 and MPV2 are, the stronger the precipitation will be.When MPV1 and MPV2 approach zero, the atmospheric stratification will be stable and the rainfall process will gradually end.

Key words: Rainstorm forecast, Moist potential vortex, Heavy rainfall