Temporal-Spatial Distribution Characteristics and Synoptic Conceptual Models of Short-Time Heavy Rainfall over the Qinghai Plateau

Abstract

Based on the hourly rainfall data and other conventional data from 52 surface weather stations， and the National Centers for Environmental Prediction （NCEP） Final Analysis （FNL） data， the synoptic circulation patterns for the short-time heavy rainfall over the Qinghai Plateau are classified into three categories， namely the westerly airflow pattern， the subtropical high pattern， and the plateau low vortex-shear line pattern.Results show that the short-time heavy rainfall over the Qinghai Plateau occurs in the area east of 95°E， with the center in the southeast of the plateau.It mainly occurs from May to September， with the maximum in August， followed by July.For the diurnal variation， the short-time heavy rainfall occurs most from 17:00 to 22:00 （Beijing Time）， i.e.， the nightfall to midnight.The influence systems of the westerly airflow pattern are the high-level trough and the straight westerly short-wave trough.The dynamical instability caused by the vertical wind shear induces the short-time heavy rainfall.For the subtropical high pattern， the thermal instability caused by the low-level southerly or easterly warm-humid airflows results in the short-time heavy rainfall.For the plateau low vortex-shear line pattern， the plateau heating， and the weak cold airflow strenthen the low-level frontal area and trigger the short-time heavy rainfall.The composite analysis shows that the South Asian high， the subtropical westerly jet in the upper troposphere， the short-wave trough in the middle-lower troposphere， the shear line， the southerly warm-humid airflow， and the plateau heating field are the main influence systems for the short-time heavy rainfall.The convergence of water vapor from the Indian monsoon， the southeast of the western Pacific subtropical high and the northwest of the westerly trough is conducive to the short-time heavy rainfall in eastern Qinghai.

Keywords

• short-time heavy rainfall
• unstable conditions
• water vapor convergence
• composite analysis