Analysis of the three-dimensional circulation changes during the August 2022 extremely heavy rainfall event in Qinghai province, China

The three-dimensional circulation structure including the upper troposphere temperature characteristics is taken as a breakthrough point to analyze the impact of the evolution of the three-dimensional circulation structure on the formation and development of the short-term extremely heavy precipitation that caused flood disasters in Datong county of Xining city, Qinghai province during 17—18 August 2022. Hourly rain gauge records, sounding data and the ERA5 reanalysis dataset are used to analyze fine-scale characteristics of the short-term heavy rainfall that caused flood disasters in Datong county of Xining city, Qinghai province during 17—18 August 2022. The results show that before the heavy precipitation, there was an obvious warm anomaly at 300 hPa over the Northwest of China. As time went by, the warm anomaly slightly moved to the southeast and gradually intensified, reaching the strongest at the peak time of precipitation. Due to hydrostatic adjustment, positive (negative) geopotential height anomaly appeared above (below) the warm anomaly. Corresponding to this configuration, anticyclonic circulation anomalies occurred in the upper troposphere, creating a favorable condition for high-level divergence. Following the intensification of the warm anomaly movement, the westerly jet anomaly in upper levels moved to the southeast and strengthened. On the other hand, a cyclonic shear occurred in the middle and lower troposphere, and the easterly winds in the lower troposphere changed to southerly winds in the front of the cyclone, which created a favorable condition for the enhancement of warm and humid condition in the lower troposphere and the increase in atmospheric instability in the precipitation region. This three-dimensional circulation structure not only provided favorable circulation conditions in upper and lower levels as well as moisture condition for the formation of heavy precipitation, but also laid the foundation for the accumulation of unstable energy. At the same time, under the influence of the trumpet topography, which is high in the northwest and low in the southeast of Datong county, abundant water vapor carried by southerly winds in lower levels accumulated there, which, joined with strong unstable energy, contributed to the formation of the short-term extremely heavy precipitation.