2011年初北疆强寒潮过程诊断分析

Diagnosis of a Strong Cold Wave Process in the Beginning of 2011 in Northern Xinjiang

2010年12月31日至2011年1月2日,新疆出现了一次强寒潮天气,北疆41个站的极端最低温度突破或接近历史同期极值,气温由偏高转为异常偏低,给当地群众生产生活造成了严重危害。本文利用NCEP 1°×1°的6 h分析资料和常规观测等资料,对本次强寒潮天气过程的环流背景、冷空气源地、向南爆发的机制及强降温的原因进行了分析。结果表明,本次强寒潮天气的成因是:(1)前期乌拉尔山脊异常增强,脊顶东扩,使西西伯利亚低涡西退南压形成横槽,横槽北侧的东北气流引导的超极地冷空气、槽后北风带引导的极地冷空气及西路冷空气在西西伯利亚合并加强,形成异常强的冷高压、高空强锋区和强冷平流。乌拉尔山高压脊向南衰退,导致强冷空气大规模向南爆发。(2)强冷平流是造成本次寒潮剧烈降温的主要原因。(3)随着冷空气进入新疆,北疆上空涡散场和垂直速度场上出现了较明显的辐合上升运动,为降雪提供了动力条件。(4)850 hPa和700 hPa偏西急流将里咸海上空湿空气部分携带到新疆上空,为降雪提供了基本水汽条件。由于没有副热带锋区配合,西南暖湿气流无法补充到北疆地区,因此本次寒潮过程的降水不明显。

From December 31,2010 to Jane 2,2011,a strong cold wave process broke out in northern Xinjiang.The lowest temperature at 41 weather stations made a breakthrough in extreme temperature on record,and the average temperature changed from higher to lower than historical average.Using NCEP 1 ° ×1 ° reanalysis data and conventional observation data the circulation background,source region of cold air,formation mechanism and the reason of steep descent of temperature during the strong cold wave process were analyzed.The results show that the causes of the strong cold wave weather are as follow：（1）the Ural mountain ridge abnormal increase and the ridge top eastward expansion made the west Siberian vortex formed a transverse trough and the northeast super cold air from the north of it,the polar cold air from the back of it and the westerly cold air merged over the West Siberian and formed the strong cold high,strong frontal zone in the upper layer and strong cold advection,then the Ural ridge declined and lead to strong cold air mass outbroke to the south;（2） the strong cold advection was the main reason for the steep descent of temperature;（3） with the cold air into Xinjiang,obvious convergence ascending motion was the dynamic conditions of snowfall;（4） the westerly jet at 850hPa and 700hPa transported the vapor from the Aral Sea to Xinjiang and provided water vapor to snow.Without cooperating of the subtropical frontal zone,the southwest warm-moist air flow could not supply to form obvious snowfall in the northern Xinjiang.