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受西西伯利亚低槽和中亚低槽结合东移的影响,2009年2月10日午后～12日夜间,北疆、东疆出现了强降温和明显的降雪天气,北疆大部地区、东疆地区达寒潮,阿勒泰为强寒潮。此次寒潮天气后,北疆地区从前期的温高少雪转为多雪低温时段。分析此次寒潮天气,发现2月份100 hPa极涡的活动存在异常。100 hPa的极区环流经历了一波(极涡绕极型)转二波(极涡偶极型)和二波偏东转正二波的演变过程,为此次转折性寒湖天气的产生提供了高层大气环流背景。同时100 hPa极涡活动的异常也导致了半球范围内500 hPa环流发生调整。大西洋沿岸低槽加深,欧洲高压脊发展东移,导致西西伯利亚低压槽在南下过程中与中亚低槽结合,“突变”加强西西伯利亚低槽东移,造成了此次寒潮天气过程。同时高低空流场分析表明:北风带的偏北气流起到了向该区输送冷空气的动力作用,而南支上的西南气流起到了向该流场区输送暖湿热能作用,2个作用的结合,使位势不稳定且能量增加,有利于上升运动的发展,这是新疆产生冬季大降水天气的动力条件。同时,2月10～11日,700 hPa层上,温度露点差场在中亚到北疆地区有大片的高湿区,500 hPa上,该区域有多个站T-Td<4℃,中亚槽为该区西部至天山中部地区的明显降雪起到重要作用。对此次天气过程的相关物理量进行诊断分析发现,强烈的冷平流输送及冷暖平流梯度和较充沛的水汽也在此次强降温、降雪天气过程中起到了重要作用。
Affected by the combination of the low trough of West Siberia and the low trough of Central Asia, on the afternoon of February 10, 2009 to the night of the 12th, heavy snowfall and obvious snowfall occurred in the northern and eastern Xinjiangs. In most northern areas, Xinjiang reached the cold wave, Aletai strong cold wave. After the cold weather, the northern region from the previous high temperature snow to snowy low temperature period. Analysis of the cold weather, found in February 100 hPa polar vortex activity anomalies. The polar circulation of 100 hPa experienced the evolution from one wave (polar vortex pole) to the second wave (polar vortex dipole) and from the second wave eastward to the second wave, providing the production of the turning cold lake weather High-level atmospheric circulation background. At the same time, the anomaly of 100 hPa polar vortex also resulted in the adjustment of the 500 hPa circulation in the hemisphere. The deepening of the low trough on the Atlantic coast and the development of the European ridge of high pressure moved eastward, resulting in the combination of the low pressure trough in the West Siberian Basin and the low trough in the Central Asia during the southward move. The “sudden change” intensified the eastward movement of the low trough in West Siberian Ocean, resulting in the cold weather. At the same time, the analysis of high and low flow field shows that the northerly airflow in the north wind belt plays a dynamic role in transporting cold air to this area, and the southwest airflow on the south branch plays a role of conveying warm and humid energy to the flow field area. Of the combination of instability and increase the potential energy is conducive to the development of upward movement, which is Xinjiang’s winter heavy precipitation weather conditions. Meanwhile, at 700 hPa from February 10 to February, the temperature dew point difference field has a large area of high humidity in Central Asia and northern Xinjiang. At 500 hPa, there are several stations in this area with T-Td <4 ° C, medium The sub-trough plays an important role in the significant snowfall in the western part of this area to the central part of Tianshan Mountains. Based on the analysis of the related physical quantities of the weather process, it is found that strong cold advection, cold-warm advection gradient and abundant water vapor also play an important role in the strong cooling and snowing weather.