Synoptic-Scale Circulation Precursors of Extreme Precipitation Events Over Southwest China During the Rainy Season

This study analyzes the synoptic-scale circulation patterns favorable for regional extreme precipitation events over southwest China (SWC) from 1979 to 2018 occurring during the rainy seasons. The whole SWC is regionalized into two subregions, western SWC and eastern SWC, according to the spatial distribution of two extreme precipitation indices. Furthermore, the atmospheric patterns associated with the independent regional extreme precipitation events (REPEs) that occurred over the two subregions are categorized into two types using k-means clustering. For type 1, a Rossby wave train originating from the Northeast Atlantic almost a week before REPEs leads to an anomalous low over the eastern Tibetan Plateau (TP), inducing upper-troposphere divergence and ascending motion over SWC. Moreover, anomalous convective activities over India and the Bay of Bengal (the enhanced and westward-extended western Pacific subtropical high) are critical precursors of REPEs over western (eastern) SWC. For type 2, an anomalous high is developed over the Ural Mountains at least a week prior to REPEs. The subsequent anomalous low over Lake Baikal and eastward-shifted South Asian high are conducive to forming updrafts over SWC. An anomalous anticyclone at the middle-to-lower troposphere south of the TP is the main moisture contributor. Discrepancies in the zonal location of the Lake Baikal low and the strength of the Ural Mountain high, as well as the intensity of atmospheric circulation anomalies at low latitudes, are the major differences between the type 2 events occurring in western and eastern SWC. Key Points Two types of atmospheric circulation anomalies are favorable for extreme precipitation events over southwest China during rainy seasons Rossby wave trains from the Northeast Atlantic and the Ural Mountains are critical precursors of the extreme precipitation events The low-latitude atmospheric circulation anomalies mainly determine the spatial differences and the extremeness of the events

Automated summary

The study identified two types of atmospheric circulation anomalies that are favorable for extreme precipitation events over southwest China during the rainy seasons. Rossby wave trains from the Northeast Atlantic and the Ural Mountains are critical precursors of the extreme precipitation events. The low-latitude atmospheric circulation anomalies mainly determine the spatial differences and the extremeness of the events.