Evolution and Structure of a Heavy-Precipitation-Producing Quasi-Linear Convective System Along a Mesoscale Outflow Boundary

Abstract

This study explored the complex evolution mechanism and fine-scale structures of a quasi-linear convective system (QLCS) in the eastern Taihang Mountain from 1300 BST 12 to 0300 BST 13 August 2018 by using Doppler radar data, high-resolution surface observations and sounding data. The QLCS which produced heavy precipitation was maintained as the southeasterly being lifted when flowed over a mesoscale outflow boundary (MOB) associated with a cold pool. Topographic blocking effect of Taihang Mountain and the cold environmental northeasterly enhanced the uplift of southeasterly at southwest and northeast of the MOB. Northeastward extension of the QLCS was promoted by the prevailing southeasterly airflow and high convective available potential energy. Meanwhile, the dry cold layer between 850 and 500 hPa obviously prevented southeastward movement of the QLCS. A clear increase of the disturbance pressure took place due to water loading increase other than the temperature dropping. Northwestward oriented “echo training” of convective cells facilitated the perfect-structured QLCS to split into several meso-β-scale rain bands with irregular convergence along the MOB. Mesoscale convective vortices associated with slow-moving strong convective echoes played an important role in middle part of the QLCS development which accounts for the heavy precipitation.