Analysis of the water vapour transport and accumulation mechanism during the “7.31” extreme rainstorm event in the southeastern Hami area, China

Abstract

A combination of reanalysis, merged-product, satellite, observation station and Global Positioning System (GPS)-based precipitable water vapour data is used to analyse the characteristics of water vapour transmission and aggregation during an extreme rainstorm event that occurred in the southeastern Hami area of Xinjiang, China, in July 2018. The strengthening of the low-level easterly jet stream in the Hexi Corridor and terrain convergence were the main drivers for the rapid accumulation of water vapour. Results suggest there was continuous water vapour transport toward the rainstorm area which occurred in three different stages. During the first stage, the rainstorm area humidified slowly under the influence of the mid-latitude trough. In the second stage, the location of the western Pacific subtropical high (WPSH) was anomalously shifted to the north, and a southerly air flow carrying water vapour from the South China Sea merged with the easterly jet stream south of the WPSH, near the Hexi Corridor. The wet water vapour from the ocean was transported to the southeastern Hami area by an easterly water vapour relay transmission. In the last stage, as the low-level jet stream in the Hexi Corridor strengthened, the abundant water vapour was accumulated and gathered in the heavy rainstorm area. The extreme precipitation was caused by the transport of water vapour from the lower to the upper level, which made it rapidly converge, rise and condense.