Causality analysis of a disaster-causing squall line event on 24 September in southeastern Inner Mongolia

Abstract

Based on the conventional observation data, automatic weather station data, Doppler radar data and NCEP(0.25°×0.25°) reanalysis data, a strong convective weather event occurred in the southeastern Inner Mongolia on 24 September 2016 caused by the disaster squall line was analyzed. The main conclusions are as follows. In the high and middle levels, cold and dry air masses spread to the southeast with the convergence of the low southwestern jet drastically strengthened, which provides this strong squall line process a very good large-scale circulation background. The CAPE has a significant increase before the strong convective weather occurred. The middle and low level distribution of θse presents like inverted funnel, and decreases with the increase of the height. This kind of dry and wet structure is favorable for the occurrence of strong convective weather such as thunderstorms and hails. The direct trigger and maintenance mechanism of this strong convective weather are due to the longtime maintaining, coupling and increasing between ground scale dew point front(dry line) and mesoscale convergence line. The thunderstorm high pressure stayed after the squall line indicating that there is a surface strong wind. The characteristic of radar echo appears like bow echo. The reflectivity profile of the bow echo front shows that there is a boundary weak echo region(BWER) in the lower layer. In the high-level, it has obvious echo drape. Strong echo zone achieve 50-55 dBz extends to 7.5 km, indicating that a strong upward flow is in the convective storm which is conducive to the formation of short-term heavy rainfall and the large hail. The arcuate velocity profile of the bow echo represents a strong sinking airflow and the middle ground radial convergence (MARC) of the ground wind warning index.

Keywords

• squall line
• bow echo
• dry line
• middle-scale convergence line
• boundary weak echo region
• mid-altitude radial convergence