王秀明,俞小鼎,周小刚. 2015. 中国东北龙卷研究:环境特征分析[J]. 气象学报, 73(3):425-441, doi:10.11676/qxxb2015.031
中国东北龙卷研究:环境特征分析
Study of Northeast China torandoes:The environmental characteristics
投稿时间:2014-08-19  修订日期:2015-01-06
DOI:10.11676/qxxb2015.031
中文关键词:  东北龙卷  环境条件  低空急流  干线  低层增湿
英文关键词:Northeast China tornadoes  Environmental conditions  Low level jet  Dryline  Low level moisture increasing
基金项目:国家自然科学基金项目(41175043、41475042)、公益性行业(气象)科研专项(GYHY201406002)、国家重点基础研究计划项目(2013CB430103)。
作者单位E-mail
王秀明 中国气象局气象干部培训学院, 北京, 100081  
俞小鼎 中国气象局气象干部培训学院, 北京, 100081 xdyu1962@126.com 
周小刚 中国气象局气象干部培训学院, 北京, 100081  
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中文摘要:
      东北地区是中国龙卷相对多发区之一。为了了解中国东北龙卷发生的环境特征,基于常规观测资料、卫星观测资料、地面加密观测资料和模式分析资料分析了近十年发生在东北的13个龙卷个例的环境特征及龙卷环境形成的物理过程。结果表明,东北龙卷发生的环境具有如下特点:(1)龙卷多发生在东北冷涡背景下,直接影响系统为冷涡南侧次天气尺度短波槽,且常出现在槽区或前倾槽后;(2)较之夏季江淮流域和华南龙卷,东北龙卷环境温度直减率较大,700—500 hPa温差为20—22℃,850—500 hPa温差为30—33℃;(3)低层水汽含量及湿层厚度比江淮及华南龙卷显著偏低,地面露点温度可低至13℃,湿层厚度常在1.5 km以下,850 hPa露点温度多在8℃以下;(4)龙卷环境中常出现强低空急流(850—925 hPa风速16—20 m/s)和对流层中层急流(500 hPa风速20—25 m/s),且对流层中层急流通常与干下沉气流相伴。因此,低层(0—1 km)和深层(0—6 km)风垂直切变均强,低层风垂直切变约12.0×10-3s-1,深层风垂直切变大于4.0×10-3s-1。产生龙卷的对流风暴一般由边界层辐合线所触发,辐合线两侧温差不明显而露点差异明显,常表现为干线。也就是说,东北地区龙卷风暴主要由干线及其伴随的强边界层辐合触发。龙卷通常发生在傍晚前后,而从早晨的环境条件通常看不到龙卷可能发生的迹象,龙卷发生前几小时环境参数变化显著。有利于龙卷的环境条件形成过程中500 hPa急流和强低空急流的存在至关重要:随着500 hPa西北急流的增强,在中空西北急流的平流下温度直减率大值区东移,叠加到低层湿区之上;低空急流对暖湿空气的输送使低层显著增湿且温度直减率增大。傍晚发生的龙卷通常处于08时探空显示的低空湿舌西北侧100 km左右的干区中,傍晚龙卷发生时则位于当时的湿舌边缘。
英文摘要:
      The Northeast region of China is one of the favorable regions for tornadoes. In order to improve the understanding of the environment favorable for tornado within the Northeast region of China, the environmental elements of the 13 tornadoes of this region which occurred in the past decade are investigated, and the physical processes that dominate the change of the environmental condition are investigated. The study is based on the conventional data, Automatic weather station (AWS) data, satellite data and numerical model analysis data. The environmental characteristics of Northeast China tornadoes are as follows. (1) Tornadoes occurred around the northeast cold vortex, directly affected by the sub-scale short-wave trough at the south part of cold vortex, and often occurred in the trough or behind the forward tilt trough. (2) Compared with tornadoes occurred at summer over the Yangtze-Huaihe river basin and South China, the lapse rate is greater for Northeast China tornadoes, with the temperature difference between 700 hPa and 500 hPa being 20-22 ℃, and the difference between 850 hPa and 500 hPa being 30-33 ℃. (3) The low level moisture is often not significant with the moist depth thin, the surface dew point as low as 13 ℃, the moisture layer often less than 1.5 km, and the dew point at 850 hPa often below 8 ℃. And (4) the low-level are and middle troposphere jet are strong, 850-925 hPa wind speed is 16-20 m/s, 500 hPa wind speed is 20-25 m/s, and the middle level jet is usually accompanied by dry downdraft. Therefore, the low and deep vertical wind shear are strong, the low-level wind shear is about 12.0×10-3s-1, and the deep vertical wind shear is greater than 4.0×10-3s-1. Convective storms which produce tornadoes are usually triggered by the boundary convergence line, in which the temperature difference near the convergence line is not obvious, but the dew point difference is distinct. That's to say, northeast China tornadoes are mainly triggered by strong dryline and its associated convergence. Tornadoes usually occur around evening, and the environmental conditions at the morning usually are not favorable for tornadoes, with the environmental parameters changing significantly a few hours before tornadoes occur. The 500 hPa jet and the low-level strong jet are crucial environmental conditions to Northeast China tornadoes. With the strengthening of 500 hPa northwestly air flow, it transports the high lapse rate layer to its east,and overlaps to the low level moisture area. The low level jet transports warm moisture air, which humidifies the atmosphere significantly and enhances the temperature lapse rate. The tornado positions are usually in the dry section at morning as shown by the 08:00 sounding data, which are away from low level moist tongue about 100 km at its northwestern side, whereas tornadoes mostly occur near the moist tongue around evening as a result of the moist-air advection northwest and the middle level high lapse rate air advection eastward from the Da-xing'an-ling Mountain.
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