东北地区两次历史罕见暴风雪天气过程的分析

Analysis of Two Cases of Extremely Severe Snowstorms in Northeast China

使用地面和高空观测资料、NCEP/NCAR再分析的格点资料和WRF中尺度数值模拟结果,对1983年4月29日黑龙江省暴风雪天气和2007年3月3—5日辽宁省暴风雪天气过程进行了分析,阐明了暴风雪天气发生的环境条件及其出现的时间和位置特点,对天气预报和防灾减灾有重要意义。研究结果表明,两次有史以来最猛烈的、大范围的、持续性的暴风雪天气的影响系统为爆发性气旋,气旋在300 h Pa南支急流出口区北侧和北支急流入口区南侧之间的区域爆发性加深,气旋中心的海平面气压24 h平均加深率分别为1.2 h Pa·h^(-1)(观测)和0.71 h Pa·h^(-1)(模式)。单站上空风随高度顺转,风速随高度增长,4.5~8 km出现等风速层,对流层存在显著的垂直风切变。对流层高层辐散低层辐合,上升运动由于暖平流和高空辐散抽吸而发展,贯穿整个对流层。暴风雪天气主要出现在地面气旋中心区域的西部和北部,其中气旋中心西偏北方向110 km附近气压梯度最大的地方,出现7~9级的偏北风,12 h降水量达到20~35 mm,是暴风雪天气最猛烈的地方。在地面气压下降最快的时期,地面风速急剧增长,降水强度达到最大。9~10级东南风出现在气旋中心的东南方向约300 km,近地面有暖湿空气的入流急流。在气旋中心正北方3~5个纬度的范围内,仍有较强的暴雪和大风天气,出现暴风雪时的风力为6~7级,大部分测站的最大风出现在降水结束后。使用VAPOR对两次过程的风速进行三维显示,结果表明,风速大于25 m·s-1的区域在两支急流之间从对流层高层伸展至近地面,说明暴风雪天气过程中的地面强风能量来源于对流层高层大气。

Based on data from observations, NCEP/NCAR reanalysis and the WRF simulations, two cases of in- tense snowstorms with blizzard conditions on 29 April 1983 and on 4 March 2007 in northeast China are investigated, in order to discuss the features of the environment conditions of these violent and persistent snowstorms which occurred over wild areas, and try to make accurate where and when it would occur. Results show, these snowstorms produced by the extensively deepened cyclones, which developed under the left side of the exit region of the southern jet and the right side of the entrance region of the northern jet at 300 hPa level, with the central cyclone sea level pressure drop rates of 1.2 hPa · h^-1（observation） and 0. 71 hPa · h^-1（ model grids） respectively. Wind shears in the troposphere are very remarkable, wind direction changed in clockwise with height, wind velocity increased with height, there exist an equally velocity layer from 4. 5 to 8 km. Airflow divergent in the upper troposphere and convergent in the lower layer, updrafts developed due to the wanner air inflow and pumping caused by the divergence in the upper layer. Heavy snowfall and severe winds occurred at the northern and western parts of the cyclone, 10 rain mean northerly surface winds greater than 20. 8 m · s^-1 occurred about 110 km away northwest of the central cyclone, with a snowfall rate of 20-35 mm · （12h）^-1（liquid water）. The surface winds velocity and the snowfall accumulation increased to their highest values rapidly during the period of the sea level pressure dropped most quickly. A mesoscale warm and moist jet closed to the surface was formed at about 300 km away southeast of the central cyclone. Heavy snowfall accompanied by less severe winds of about 10. 8 - 17. 2 m· s^-1 also presented within areas of 3- 5 latitudes away from the cyclone in the northern part, surface winds velocity of most stations derived their maximize values just after the snowfall terminated. The 3D VAPOR visualization of the velocity from the GRIB grids and the WRF simulations show, severe surface winds are connected to the airflow a- mong the two upper-level jets, suggesting that the surface winds energy originated from the upper troposphere aloft.