【摘要】 对青藏高原东部牧区1967～1996年30年中春季发生的成灾性降雪天气过程进行了较为详细的分析,发现有45％的成灾性降雪过程与该地区的低涡天气系统有关。在归纳总结高原春季降雪天气形成的3种环流模型的基础上,重点分析了通常情况下高原切变线对高原低涡发生发展所起的主要作用:(1)高原切变线西南段区域内为上升运动区且气流的气旋性涡旋处于发展阶段,切变线东北段区域内为下沉运动区且气流的反气旋性涡旋处于发展阶段,是低涡形成的前期条件;(2)高原切变线附近的流场有利于将周围水汽聚拢,使低涡系统得到持续不断的水汽供给,其中负的水汽通量散度扰动中心位于切变线中段南侧,形成水汽汇,正的水汽通量散度扰动最大值部分位于切变线西南段南侧,是低涡水汽的主要来源。文中还给出了高原部分测站降雪量、最低气温的预报方程,可供有关预报人员参考。更多还原

【Abstract】 The forming process of disastrous snowing weather in spring over 30 years (1967～1996) in the eastenpasture-area of Qinghai-Xizang Plateau has been analyzed in detail. It has been found that 45% of disastrous sno-wing processes were related to the vortex system of the area. On the basis of summed up three kinds of spring circu-lation patterns of forming snowing weathers, the role of plateau shear line acting on occurrence and development ofvortex system has heen stressed: (1) the earlier stage condition forming vortex system is that southwest section ofthe plateau shear line is rising area and the cyclonic circulation is in developing stage, and its northeast section issubsiding area and anticyclonic circulation is in developing stage; (2) the main water vapor source of the vortex sys-tem is that the stream field nearby the shear line is advantageous to gathering water vapor up, making the vortexsystem to get supply of water vapor continuously and in this field, the negative perturbative center of divergence ofvapor flux is located at south side of central section of the shear line, forming water vapor concentration and thepositive perturbative maximum section of divergence of vapor flux is located at south side of southwest section of theshear line. In the end of the paper, the forecasting equations for snowing, minimum temperature, snow-covereddepth and snow coverage days at some stations of the p1ateau have been showed for forecasting reference.更多还原