关键词: 暴雨, 高空槽, 切变线, 中尺度对流, 触发机制

Abstract:

Based on NCEP/NCAR reanalysis data, conventional observation data, cloud top brightness temperature data with 0.1°×0.1° horizontal resolution from Fengyun (FY-2E) satellite, hourly rainfall observations from Automatic Weather Stations (AWS) and the radar data in Dalian, diagnostic analysis was made about the two shear-line rainstorm processes in Liaodong Peninsula during 28-30 July 2013. It was focused on the evolution of synoptic background during the two rainstorm events and triggering mechanism for development of mesoscale convective systems (MCSs). Results show that mesoscale convective complexs (MCCs) or mesoscale convective cloud clusters occurring along shear-line were rainstorm-producing systems under the favorite large-scale circulation background. However, the dynamic and thermal conditions and triggering mechanisms of the two rainstorms were various because of the different relative position between shear-line and the upper trough northward. When the shear line was located in front of upper trough, a plenty of moisture could be transported to Liaodong Peninsula by lower level jets for long time. Meanwhile, there existed strong convergence in lower layer and a deeper moisture layer over the rainfall area. So, the intensification of the lower layer-jet was the key factor to trigger the convection, and the rainstorm area was located in the maximum wind speed zone of the southerly jet, the south side the surface convergence line. In comparison, when the shear line was located behind the upper trough, the supplementary of water moisture over Liaodong Peninsula was less due to the rapid moving eastward of the water transportation band. There was a weaker water convergence in the lower layer and shallow moisture layer. The cold air intrusion from the north wind behind the upper trough served as the key factor to trigger the rainstorm, and the rainstorm position occurred in the north of the surface convergence line.

Key words:
rainstorm, upper-tropospheric westerly trough, shear line, mesoscale convection, trigger mechanism