Synthesis Analysis of Summer Storm Circulation Situation in Longquanyi District

Abstract

In order to analyse the storm circulation situation in Longquanyi District over the past 41 years, NCEP reanalysis data from 1980 to 2010, with a grid spacing of 1 ˚ × 1 ˚ and a time interval of 6 h. The 24-hour daily precipitation observations at this station in Longquanyi District were used to synthesize the characteristics of the high and low-level large-scale circulation background and its influence system for a total of 93 typical rainstorm processes that occurred in Longquanyi District during the 41 years from 1980 to 2020. The study shows that. 1) Most of the heavy rainfall weath-er processes in Longquanyi District are caused by the joint interaction of the South Asian high pressure at 100 hPa and the Western Pacific subtropical high pressure at 500 hPa, and the joint action of the weak high pressure and the southwest vortex in the eastern part of the plateau and the split low pressure trough in the northern part of Sichuan. However, the circulation situation varies slightly from month to month, the main difference being that the location of the influencing systems varies and the extent of the rainfall caused by them also varies. 2) A comparative study found that a strong South Asian high pressure was present during all the rainstorms in June the South Asian high pressure was relatively low, with its ridge at around 30 ˚ N, and in July and August the ridge was relatively high at around 35 ˚ N. 3) The position of the ridge is relatively high during heavy rainfall in all months, with the lowest position of the ridge in June at 20 ˚ N and all other months at 25 ˚ N. The highest position of the ridge in July can reach around 30 ˚ N, which provides favourable water vapour conditions for the occurrence of heavy rainfall. 4) The heavy precipitation in July and August was controlled by a southwesterly vortex, accompanied by strong wind shear, while moisture from the Bay of Bengal and the South China Sea converged in the upper part of the Longquanyi area and formed a southwesterly-northeasterly axial rapid convergence zone in the upper layers.