Characteristic Analysis of Northwest Vortex Causing Torrential Rains in Northern Shaanxi

Abstract

The composite characteristics of northwest vortex that causes torrential rain in northern Shaanxi were analyzed statistically based on the in-situ observations from the automatic meteorological stations， ground-based sounding observations and reanalysis data from NECP.The main conclusions are as follows： one third of the torrential rains in northern Shaanxi can be attributed to the northwest vortex， which mainly occurred in July or August； the northwest vortex， mainly originated in the western Qinghai province， will probably trigger torrential rains in northern Shannxi 36 to 48 hours later； the torrential rains in the northern Shaanxi were closely related to the upper-level jet， the upper trough， the western Pacific subtropical high and 700 hPa northwest vortex.In-depth analysis of northwest vortex showed that the torrential rain area was just corresponding to the southeast of 700 hPa positive vorticity center， which was featured by the significant upward movement induced by high-level divergence and low-level convergence； the torrential rain in northern Shannxi was also beneficial from the favorably unstable and high humidity conditions， which were closely linked with the southern and eastern water vapor transportation.

Keywords

• northwest vortex
• torrential rainfall
• high-level divergence
• low-level convergence
• moisture transport