一种月尺度单站预报方法研究

利用实况资料,分析了2004年12月20日-22日出现在华北地区的大到暴雪天气的干侵入特征,得出：a）此次降雪主要受中层切变线影响,降雪带与切变线相对应,强降雪中心就出现在切变线交汇的东南到东侧.b）此次降雪过程中,干冷空气主要来自对流层高层,分3路持续入侵,与3条切变线密切对应,而中低层西南和南2支暖湿气流在对流层中层耦合加强,与于冷空气交汇,产生强降雪;强降雪落区位于相对湿度梯度最大处的湿区一侧且有强风辐合的区域.c）随着中层切变线的东移发展,湿不稳定增强并向下延伸,高位涡区向东输送并向下传播,从而触发不稳定能量释放,导致强降雪.d）对流层高层持续的干侵入,使得中低层切变线稳定维持,有利于其前方西南急流的稳定加强和对流性不稳定的持续发展,是导致强降雪持续、增幅的重要原因.

Characteristics of Snowing Caused by Shearline Dry Invasion

The dry intrusion characteristics of snow-storm which occurred on December20-22,2004 in Northern of China was analyzed using recording data. The results showed ： a） The middle layer shearline caused this snow-storm. The zone of snowfall corresponded to the shearline. The center of snow-storm was southeast and east of the shearline intersection, b） The dry old air was from the upper troposphere. The dry cold air invasion in three ways and corresponded closely to three shearlines. The two warm and moist stream was coupling and strengthen in southwest and south and met with the dry cold air. It resulted in the heavy snow. Area of heavy snow located at the relative humidity gradient of the largest side of the wet area and there was strong wind convergence zone. c） Mid-layer shearline moved eastward and the wet instability strengthened and extended downward. High vortex area spread eastward and transmitted downward. It resulted in the instability in the energy release and leaded to heavy snowfall. d） The upper troposphere persisted dry intrusion and made the low-level shear line to remain stable. It was beneficial to the front of the southwest jet to enhance the stability and sustainable evelopment of convective instability. It leaded to continued and increase heavy snowfall.