冷季不同锢囚类型温带气旋强降水过程统计分析

Statistical Analysis of Heavy Precipitation Events Caused by Extra-tropical Cyclones of Different Occlusion Types during the Cold Season

利用2006-2021年常规观测和风云卫星云顶黑体亮温(TBB)资料,结合欧洲中期天气预报中心(European Center for Medium-Range Weather Forecasts,ECMWF)0.25°×0.25°的ERA5再分析资料,对冷季影响华北和东北地区北上类温带气旋强降水过程进行了统计分析。结果表明:(1)温带气旋爆发性发展过程中大多数有锢囚锋形成,但发展过程有所不同,Shapiro-Keyser(以下简称SK型)和经典的挪威(以下简称NW型)气旋发展过程各占一半,SK型气旋500hPa上为一深槽,斜压性强,引导气流为东北偏北气流,导致气旋路径偏西,造成的降水更偏北、范围更广;NW型气旋500hPa上为一浅槽,槽后冷平流弱,引导气流为东北偏东气流,导致气旋路径偏东,降水偏南,强度更强。(2)NW型气旋的大气河强于SK型气旋,相应的强降水范围更大、强度更强;随着气旋发展,SK型气旋大气河北侧有明显的后弯特征,导致SK型气旋的暖锋降水中心位于气旋西北象限,而NW型气旋暖锋降水中心位于气旋中心附近。(3)SK型气旋西北侧的暖锋锋生明显强于NW型,气旋锋生强迫产生的强上升运动,有利于强降雪。(4)SK型气旋300 hPa上存在高音符形状的强位涡块,NW型气旋高层块状位涡较弱。SK型气旋上空平流层位涡下传与低层高位涡连通形成位涡塔,其附近有深厚暖式锢囚结构;而NW型气旋高层位涡下伸不明显,没有位涡塔生成,SK型气旋首先在对流层中低层发展,然后发展到地面,而NW型气旋是从对流层低层发展起来。

Based on the conventional observation,the cloud top blackbody brightness temperature data of Fengyun satellite,and the European Centre for Medium-Range Weather Forecasts 0.25°×0.25°ERA5 reanalysis data from 2006 to 2021,we have conducted a statistical analysis on the heavy precipitation events caused by extratropical cyclones over northern and northeastern China during the cold season.The results show that:(1)Most of the extratropical cyclones occluded during the explosive development phase,but the development process is different,with the Shapiro-Keyser(SK-type)and the classical Norwegian(NW-type)cyclones each accounting for half.The SK-type cyclone has a deep trough at 500 hPa,strong baroclinicity,and steering airflow in the north-northeast-orientation,resulting in westerly cyclone path,and northward,widespread precipitation;the NW-type cyclone has a shallow trough at 500 hPa,with weak cold advection behind the trough,and the steering airflow in the east-northeast orientation,resulting in an easterly cyclone path,more to the south and more intense precipitation.(2)The atmospheric rivers of the NW-type cyclone are more intensethan those of the SK-type cyclone,and the corresponding heavy precipitation is extensive and more intense.With the development of the cyclones,the atmospheric rivers of the SK-type cyclone gradually turn to a north-south orientation,and there is a clear backward-turning feature on the north side of the atmospheric river,resulting in a warm front precipitation center of the SK-type cyclone located in the northwest quadrant of the cyclone,and the warm front precipitation center of the NW-type cyclone is close to the center of the cyclones.(3)The warm front frontogenesis in the northwest quadrant of the SK-type cyclone is significantly more intense than that of the NW-type cyclone,and the intense lifting forced by the front is conducive to heavy snowfall.(4)The SK-type cyclone has an intense potential vorticity structure in the shape of treble-clef at 300 hPa,while the NW-type cyclone has weaker potential vorticity in the upper levels.The stratospheric potential vorticity over the SK-type cyclone extends downwards,connecting with the low-level potential vorticity to form a potential vorticity tower,with a deep warm occluded structure nearby;while,the upper-level potential vorticity of the NW-type cyclone does not extend downward significantly,and there is no potential vorticity tower generated.The SK-type cyclone first develops in the middle troposphere,and then reachesthe surface,while the NW-type cyclone develops from the lower troposphere.