2007年3月3-5日强雨雪过程中的干冷空气活动及其作用

Activities of Cold-Dry Air and Its Impact on Heavy Rain-Snow Processes in North China during March 3—5,2007

利用FY-2卫星资料、多普勒雷达资料、地面观测站常规资料及1°×1°NCEP/NCAR再分析资料,运用红外云图云顶亮温TBB、等熵位涡IPV、水汽通量、位温θ、相对湿度及风场等物理参量对北方晚冬一次强雨雪过程的水汽来源和干冷空气活动及其作用进行了分析。结果表明：江淮气旋为强雨雪的产生提供充沛的水汽,而干冷空气则在不同高度、不同路径活动,扮演着多种角色。对流层低层干冷空气作为“冷垫”锲入暖湿气流中,促进锋生和暖湿空气的抬升、凝结;对流层上层具有高位涡的干冷空气沿320 K等熵面（等位温面）自高纬冲下,给江淮气旋的加强、维持提供了动力和热力条件,同时等熵正位涡高值区（IPV≥10-6m2.s-1.K.kg-1）和相对湿度小于等于45%的干区与红外云图暗区（TBB≥-32℃）对应得非常吻合,这说明利用卫星资料来追踪高位涡轨迹的可行性。云头部次冷输送带干冷空气在2-3 km高度卷入、叠加在暖湿层上,有利于不稳定层结的形成和不稳定能量的释放,是造成渤海西岸局部大到暴雪天气的重要因素。

The activity of cold-dry air and its impact on a heavy rain-snow storm in late winter in North China is studied by using FY-2 meteorological satellite data,Doppler radar data,normal observations and 1°×1° NCEP/NCAR reanalysis data,and the water vapor source is analyzed with black body temperature（TBB）,isentropic potential vorticity（IPV）,water vapor flux,relativity humidity and wind fields.Results show that the east and south airflow of the Jianghuai cyclone provided abundant water vapor for the heavy rain-snow storm,meanwhile,cold-dry air played different roles at different heights and paths：1）in the lower troposphere,cold-dry air acted as a cold cushion that wedged into the bottom of warm wet air flow,resulting in frontogenesis,elevation of warm-wet air and condensation.2）in the upper troposphere,cold-dry air with high potential vorticity moved downward from high latitude along 320 K isentropic surface which offered the dynamical and thermal conditions for Jianghuai cyclone＇s triggering,strengthening and maintaining.The area with high positive potential vorticity（IPV≥10-6m2·s-1·K·kg-1） and the dry zone with a relative humidity≤45% on the isentropic surface correspond well to the dark zone of TBB≥-32 ℃ on the infrared cloud image,suggesting means that it is feasible to trace the high positive potential vorticity track by satellite data.3）The intrusion into the storm and overlay on the warm/wet air flow of the cold-dry air from the sub-cold transfer belt at the head of spiral cloud at the height 2—3 km was beneficial to the formation of unstable straification and the release of unstable energy,therefor,it is one the important factor for the local heavy and violent snow in the western coastal of Bohai Bay.