2013年滨海新区大雪过程的湿位涡分析

Analysis of Moist Potential Vorticity(MPV)for a Heavy Snow Process in Tianjin Binhai New Area in 2013

应用湿位涡理论及NCEP再分析资料(水平分辨率1°×1°),对2013年12月17日滨海新区出现的大雪过程进行诊断分析。结果表明:500,h Pa高空冷涡和中低空切变线是造成强降雪的主要天气系统。降水时刻滨海新区相对湿度大于90%。偏东气流带来渤海海面的水汽,同时低空流场汇合有利于水汽辐合。暴雪发生在850,h Pa湿位涡正压项MPV1零值区和湿位涡斜压项MPV2负值区中。MPV2绝对值增大,大气湿斜压性增强导致下滑倾斜涡度发展是形成此次暴雪的重要原因,它对暴雪预报有着很好的指示作用。

Based on the theory of moist potential vorticity（MPV） and NCEP reanalysis data（Horizontal resolution 1° ×1°）,a heavy snow took place on Dec. 17,2013,in Tianjin Binhai New Area was analyzed. The results showed that cold vortex at 500,hPa and low-altitude shear line formed the main weather system that caused this large-scale heavy snow. Relative humidity in the area was above 90%on the precipitation moment;easterly winds brought moistures from Bohai Sea,and the convergence of the flow field at low altitude was advantageous to the moisture convergence. The heavy snow occurred in the value of zero area of MPV1 at 850,hPa and negative area of MPV2 at 850,hPa. It pre-sented that the development of down sliding slantwise vorticity caused by both the increasing of absolute value of MPV2 and atmospheric wet baroclinity was the main reason that caused this heavy snow. This may be a good indicator for heavy snow forecast.