北方一次强降雪过程的中尺度数值模拟

利用中尺度数值模式MM5对2003年3月14~16日发生在内蒙古中部偏南地区的一次强降雪过程进行了二重嵌套的48 h数值模拟研究。结果表明:模式较好地模拟了本次过程强降雪中心的强度、位置以及强降雪的时间变化。导致本次过程降雪产生的主要影响系统是地面倒槽和700 hPa中α尺度低涡,其影响时间相对持久。强降雪的出现则是由于高空短波槽产生的高层强辐散强迫与低层增强的辐合相互耦合所致。高低层系统这一适宜配置的维持时间相对短暂,却导致了本次过程降雪强度的两个峰值的出现。同时,中α尺度低涡的形成和加强及其与低空暖湿急流的适宜配置也是强降雪产生的一个有利因素。阴山山脉对本次过程强降雪的强度和位置具有重要影响:山脉使降雪在其南麓增强,北麓减弱。山地强迫抬升是导致这一结果的直接原因。另外,山地在其迎风坡使上升运动增强的同时也使正涡度减小和低层辐散增强。

Mesoscale Numerical Simulation of a Heavy Snowfall Process in Northern China

Using the mesoscale modle MM5, a snowstorm process in the middle and southern part of Inner Mongolia from 14 to 16 March, 2003 is simulated. The results shown that the strength, position and time change of heavy snowfall center are successfully simulated. The main effect system of causing snowstorm process is surface inverse trough and 700 hPa meso-a-scale low vortex, and its impact time is relative to the lasting. The couple of divergence in upper troposphere and convergence in lower troposphere prod- ucted the short wave trough in upper level induced the heavy snowfall to occur, but it induced two peak values in the snowfall process. Meanwhile, the forming and strengthening of meso-a-scale low vortex and its fitting collocation with warm and wet jet flows in low level are another factor of heavy snowfall occurring. The Yinshan mountain has a great impact on the strength and position of the snowfall process. It made the snowfall strenthened at the south of mountain and minimized at the north of mountain. The lifting of topographic forcing is direction reason of the heavy snowfall. The impact of the topography on the divergence was complex and in this condition the association between the lower level divergence and the ascending motion became faintness.