一次东风波大暴雨过程诊断分析
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摘要
利用美国环境预报中心0.5°气候预报系统再分析资料,研究了1988年"7.30"浙东大暴雨过程,发现低空南、北两支东风扰动的合并及其与高空急流的相互作用是暴雨产生的主要原因。高空冷涡与华北高压共同强迫,形成了东南向的高空急流;急流具有明显的动量下传特征,加大了对流层中层的东风分量,构成深厚的东风波系统。"7.30"过程的对流有效位能主要是海上气团的平流输送。低压倒槽的切变辐合积聚了大气的水汽含量,形成深厚的高相当位温层。对流层高层存在冷平流,使得东风波西移过程中对流有效位能能够持续稳定。风暴相对螺旋度与东风波系统匹配较好,能够清楚反映南、北两支东风扰动的合并过程。风暴相对螺旋度移动速度略快于东风波系统和垂直涡度,能够提前预报东风波降水的落区。
The heavy rainfall process occurred on 30 July 1988 around the southeastern coast of Zhejiang Province is investigated by 0.5° NCEP Climate Forecast System Reanalysis data.It is found that the heavy rainfall was mainly caused by the merging of two low-level east-wind perturbations from south and north,respectively,and its interaction with upper-level jets.The south and north branches of the easterly wave originated from the abrupt westerly,southerly evolution of the subtropical anticyclone,and the development of convective perturbations triggered by the typhoon inverted trough,respectively.The eastwest oriented upper-level jet was formed under the combined forcing of the upper-level cold vortex and the Huabei anticyclone system.The upper-level jet possessed an obvious downward transmission feature in momentum,which would enhance the easterly wind component at middle troposphere and form a deep easterly wave system.The convective available potential energy(CAPE)in the heavy rainfall event of 30 July 1988was mainly caused by the advection of air mass on the sea.The convergence in low pressure converted trough could accumulate water content in air and form a deep level with high equivalent potential temperature.This high equivalent potential temperature level may moved westward along with the easterly wave system and concentrate CAPE to convection development.There existed cold advection at the upper troposphere which could make the value of CAPE maintain steady during the westerly moving of easterly wave.The potential possibility of heavy rainfall caused by moving easterly wave could not be predicted by the single point sounding on the ground.The storm relative helicity matched with the easterly wave system very well and from it the emerging process of the south and north branches of east-wind perturbations could be reflected clearly.The moving speed of the storm relative helicity was a little faster than that of the easterly wave system and vertical vorticity,and therefore the storm relative helicity can be used to predict the falling area of the easterly wave heavy rainfall in advance.
The heavy rainfall process occurred on 30 July 1988 around the southeastern coast of Zhejiang Province is investigated by 0.5° NCEP Climate Forecast System Reanalysis data.It is found that the heavy rainfall was mainly caused by the merging of two low-level east-wind perturbations from south and north,respectively,and its interaction with upper-level jets.The south and north branches of the easterly wave originated from the abrupt westerly,southerly evolution of the subtropical anticyclone,and the development of convective perturbations triggered by the typhoon inverted trough,respectively.The eastwest oriented upper-level jet was formed under the combined forcing of the upper-level cold vortex and the Huabei anticyclone system.The upper-level jet possessed an obvious downward transmission feature in momentum,which would enhance the easterly wind component at middle troposphere and form a deep easterly wave system.The convective available potential energy(CAPE)in the heavy rainfall event of 30 July 1988was mainly caused by the advection of air mass on the sea.The convergence in low pressure converted trough could accumulate water content in air and form a deep level with high equivalent potential temperature.This high equivalent potential temperature level may moved westward along with the easterly wave system and concentrate CAPE to convection development.There existed cold advection at the upper troposphere which could make the value of CAPE maintain steady during the westerly moving of easterly wave.The potential possibility of heavy rainfall caused by moving easterly wave could not be predicted by the single point sounding on the ground.The storm relative helicity matched with the easterly wave system very well and from it the emerging process of the south and north branches of east-wind perturbations could be reflected clearly.The moving speed of the storm relative helicity was a little faster than that of the easterly wave system and vertical vorticity,and therefore the storm relative helicity can be used to predict the falling area of the easterly wave heavy rainfall in advance.
引文
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[16]Suranjana S,Shrinvas M,Pan Hualu,et al.The NCEP Cli-mate Forecast System Reanalysis.Bull Amer Meteor Soc,2010,91:1015-1057.
[17]包澄澜.影响长江中下游的东风波个例分析[J].南京大学学报:自然科学版,1974,2:75-88.
[18]Lilly D K.The structure,energetics and propagation of rota-ting convective storms Part I:Helicity and storm stabilization[J].J Atmos Sci,1986,43:126-140.
[19]Woodall G R.Qualitative forecasting of tornadic activity usingstorm-relative environmental helicity[C]∥16th Conf on Se-vere Local Storms,1990,22-25.
[20]Davies-Jones R P,Burgess D W,Foster M.Test of helicity asa tornado forecast parameter[C]∥16th Conf on Severe LocalStorms,1990,588-592.
[21]Davies J M,Johns R H.Some wind and instability parametersassociated with strong and violent tornadoes Part I:Wind shearand helicity[M].Tornado:Its Structure,Dynamics,Predic-tion,Hazards[R].Geophys Monogr No 79Amer Geophys U-nion,1993:573-582.
[22]Maddox R A.An evaluation of tornado proximity wind andstability data.Mon Wea Rev,1976,104:133-142.
[23]Levich E,Tzverkov E.Helical cyclogenesis[J].Phys Lett,1984,100(A):53-56.
[2]卢家麟,滕卫平,斯公望.一次热带云团引起的浙东特大暴雨过程分析[J].应用气象学报,1991,2(2):147-155.
[3]郑峰.一次东风波及其诱生低涡发生发展的诊断和数值试验[J].气象科学,2006,26(3):323-327.
[4]Riel H.Tropical meteorology[M].New York:McGraw-Hill,1954,392.
[5]肖文俊.东风波天气区域分布与基本气流垂直切变的关系[J].北京大学学报:自然科学版,1990,26(3):333-339.
[6]梁必骐,杨运强,梁经萍等.热带环流和系统学术会议论文集[M].北京:海洋出版社,1982,155-167.
[7]梁必骐.近年来我国对热带天气系统的研究[J].气象科技,1983,(4):1-8.
[8]吴阳,周毅.影响我国的东风波特征分析[J].海洋通报,2005,24(3):88-91.
[9]Merritt Earl S.Easterly waves and perturbation,a reappraisal[J].J Apple Meteor,1964,3:367-382.
[10]郑峰.东风波诱生低涡发生发展的螺旋度演变特征分析[J].气象科技,2006,34(3):275-279.
[11]曹楚,王忠东.一次东风波暴雨过程诊断分析[J].气象科技,2011,39(3):308-314.
[12]夏秋萍,张滨.一次东风波引起的特大暴雨天气过程分析[J].海洋预报,2011,28(3):68-73.
[13]杜立群.7.29暴雨的天气、能量特征及地形作用[J].浙江气象科技,1989,10(3):12-15.
[14]夏秋萍,王鹤祥.由低层东风波引起的宁海特大暴雨初探[J].航空气象科技,1989,(4):11-16.
[15]卢家麟,滕卫平.一次热带对流云团暴雨过程初析[J].浙江气象科技,1989,10(2):8-11.
[16]Suranjana S,Shrinvas M,Pan Hualu,et al.The NCEP Cli-mate Forecast System Reanalysis.Bull Amer Meteor Soc,2010,91:1015-1057.
[17]包澄澜.影响长江中下游的东风波个例分析[J].南京大学学报:自然科学版,1974,2:75-88.
[18]Lilly D K.The structure,energetics and propagation of rota-ting convective storms Part I:Helicity and storm stabilization[J].J Atmos Sci,1986,43:126-140.
[19]Woodall G R.Qualitative forecasting of tornadic activity usingstorm-relative environmental helicity[C]∥16th Conf on Se-vere Local Storms,1990,22-25.
[20]Davies-Jones R P,Burgess D W,Foster M.Test of helicity asa tornado forecast parameter[C]∥16th Conf on Severe LocalStorms,1990,588-592.
[21]Davies J M,Johns R H.Some wind and instability parametersassociated with strong and violent tornadoes Part I:Wind shearand helicity[M].Tornado:Its Structure,Dynamics,Predic-tion,Hazards[R].Geophys Monogr No 79Amer Geophys U-nion,1993:573-582.
[22]Maddox R A.An evaluation of tornado proximity wind andstability data.Mon Wea Rev,1976,104:133-142.
[23]Levich E,Tzverkov E.Helical cyclogenesis[J].Phys Lett,1984,100(A):53-56.