Impact of Front-Dryline Merger on Convection Initiation near a Mountain Ridge in Beijing

Abstract

case study is presented of Convection Initiation (CI) resulting from the merger of a cold front with a dryline in southwestern Beijing, China, on the afternoon of 11 June 2011. This process is analyzed with S-band Doppler radar data, surface Automatic Weather Station data, and mesoscale numerical simulation results. The formation of this dryline is analogous to that on the Great Plains of the United States, and it is conducive to CI with mesoscale updrafts generated from the baroclinic frontogenesis, and with favorable instability immediately on the moist side. Prior to front?dryline merger, as the cold front approached the observed boundary-layer convergence line, or the simulated meso-?-scale secondary dryline, CI occurred ahead of the cold front with little contribution from frontogenetic baroclinity of the dryline. The cold front then merged with the dryline, the baroclinity of the dryline was enhanced by the associated convergence, to a degree comparable to that caused by frontogenesis of the dryline itself, thus leading to more CI. During the front?dryline merger, meso-?-scale discrete cold pools associated with the cold front led to a diverse distribution of CI.