气象学报
氣象學報
기상학보
ACTA METEOROLOGICA SINICA
2015年
3期
425-441
,共17页
东北龙卷%环境条件%低空急流%干线%低层增湿
東北龍捲%環境條件%低空急流%榦線%低層增濕
동북룡권%배경조건%저공급류%간선%저층증습
Northeast China tornadoes%Environmental conditions%Low level jet%Dryline%Low level moisture increasing
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。
東北地區是中國龍捲相對多髮區之一。為瞭瞭解中國東北龍捲髮生的環境特徵，基于常規觀測資料、衛星觀測資料、地麵加密觀測資料和模式分析資料分析瞭近十年髮生在東北的13箇龍捲箇例的環境特徵及龍捲環境形成的物理過程。結果錶明，東北龍捲髮生的環境具有如下特點：（1）龍捲多髮生在東北冷渦揹景下，直接影響繫統為冷渦南側次天氣呎度短波槽，且常齣現在槽區或前傾槽後；（2）較之夏季江淮流域和華南龍捲，東北龍捲環境溫度直減率較大，700—500 hPa 溫差為20—22℃，850—500 hPa溫差為30—33℃；（3）低層水汽含量及濕層厚度比江淮及華南龍捲顯著偏低，地麵露點溫度可低至13℃，濕層厚度常在1．5 km 以下，850 hPa 露點溫度多在8℃以下；（4）龍捲環境中常齣現彊低空急流（850—925 hPa 風速16—20 m／s）和對流層中層急流（500 hPa 風速20—25 m／s），且對流層中層急流通常與榦下沉氣流相伴。因此，低層（0—1 km）和深層（0—6 km）風垂直切變均彊，低層風垂直切變約12．0×10－3s－1，深層風垂直切變大于4．0×10－3s－1。產生龍捲的對流風暴一般由邊界層輻閤線所觸髮，輻閤線兩側溫差不明顯而露點差異明顯，常錶現為榦線。也就是說，東北地區龍捲風暴主要由榦線及其伴隨的彊邊界層輻閤觸髮。龍捲通常髮生在傍晚前後，而從早晨的環境條件通常看不到龍捲可能髮生的跡象，龍捲髮生前幾小時環境參數變化顯著。有利于龍捲的環境條件形成過程中500 hPa急流和彊低空急流的存在至關重隨著500 hPa西北急流的增彊，在中空西北急流的平流下溫度直減率大值區東移，疊加到低層濕區之上；低空急流對暖濕空氣的輸送使低層顯著增濕且溫度直減率增大。傍晚髮生的龍捲通常處于08時探空顯示的低空濕舌西北側100 km左右的榦區中，傍晚龍捲髮生時則位于噹時的濕舌邊緣。
동북지구시중국룡권상대다발구지일。위료료해중국동북룡권발생적배경특정，기우상규관측자료、위성관측자료、지면가밀관측자료화모식분석자료분석료근십년발생재동북적13개룡권개례적배경특정급룡권배경형성적물리과정。결과표명，동북룡권발생적배경구유여하특점：（1）룡권다발생재동북랭와배경하，직접영향계통위랭와남측차천기척도단파조，차상출현재조구혹전경조후；（2）교지하계강회류역화화남룡권，동북룡권배경온도직감솔교대，700—500 hPa 온차위20—22℃，850—500 hPa온차위30—33℃；（3）저층수기함량급습층후도비강회급화남룡권현저편저，지면로점온도가저지13℃，습층후도상재1．5 km 이하，850 hPa 로점온도다재8℃이하；（4）룡권배경중상출현강저공급류（850—925 hPa 풍속16—20 m／s）화대류층중층급류（500 hPa 풍속20—25 m／s），차대류층중층급류통상여간하침기류상반。인차，저층（0—1 km）화심층（0—6 km）풍수직절변균강，저층풍수직절변약12．0×10－3s－1，심층풍수직절변대우4．0×10－3s－1。산생룡권적대류풍폭일반유변계층복합선소촉발，복합선량측온차불명현이로점차이명현，상표현위간선。야취시설，동북지구룡권풍폭주요유간선급기반수적강변계층복합촉발。룡권통상발생재방만전후，이종조신적배경조건통상간불도룡권가능발생적적상，룡권발생전궤소시배경삼수변화현저。유리우룡권적배경조건형성과정중500 hPa급류화강저공급류적존재지관중수착500 hPa서북급류적증강，재중공서북급류적평류하온도직감솔대치구동이，첩가도저층습구지상；저공급류대난습공기적수송사저층현저증습차온도직감솔증대。방만발생적룡권통상처우08시탐공현시적저공습설서북측100 km좌우적간구중，방만룡권발생시칙위우당시적습설변연。
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 envi-ronmental 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 pro-duce tornadoes are usually triggered by the boundary convergence line,in which the temperature difference near the conver-gence 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 be-fore tornadoes occur.The 500 hPa jet and the low-level strong jet are crucial environmental conditions to Northeast China tor-nadoes.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.
