豫西山区一次回流暴雪天气成因分析
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摘要
利用NCEP再分析资料对2017年2月21日豫西山区一次回流暴雪天气过程进行分析。结果表明:较强的西南暖湿气流使槽前的上升运动增强,不仅为暴雪区上空输送了水汽,而且有利于不稳定能量的集聚,槽后冷平流对能量的释放起触发作用。低涡前切变线与低空西南风急流左侧较强辐合区相配合为暴雪的产生提供动力抬升条件。回流冷空气长时间影响,使暴雪区辐合上升运动增强。"天南地北"形势场,使风的垂直切变加大,对称不稳定增强,降雪强度增大。低层回流冷空气使低层大气长时间维持大湿度区,并与上层东移的大湿度区相叠加,增加了湿层厚度,有利于降雪持续而形成强降雪。低层回流的偏东风遇到地形后引起上升运动,与上游700~850 h Pa的低值系统前部的上升运动汇合形成深厚的、大范围的强烈上升运动是产生强降雪的关键性条件。锢囚锋产生的锋面次级环流与回流冷空气遇地形阻挡产生的正、逆环流圈,伴随着较强的垂直上升运动,对强降雪有重大贡献。由锋面造成的温度梯度、风的垂直切变及地形作用在暴雪区形成的对称不稳定和中低层西南暖湿急流产生的对流性不稳定,有利于暴雪形成。
NCEP reanalysis data set was used to analyze a circumfluence snowstorm in western Henan mountain areas on Feb.21, 2017. The results showed that the stronger southwest warm and wet air strengthened the ascending motion in front of trough. It not only transported the water vapor, but also contributed to the accumulation of unstable energy. The cold advection behind trough triggered the energy release. The vortex with front shear line and the convergence area on the left of the southwesterly low-level jet provided dynamic lifting conditions for the snowstorm. The long-term effects of backflow cold air increased the convergence ascending motion in the snowstorm area. The position field increased the vertical wind shear.The symmetric instability was enhanced and the snowfall intensity increased. The return cold air at the low level made the lower atmosphere in a high humidity area for a long time and stacked with the high humidity area moving eastward at the high level, which increased the thickness of the wet layer and snow continued to fall and formed heavy snow. The ascending motion occurred when the return east wind at the lower level encountered the topography. It converged with the ascending motion in front of the low-pressure system of upstream 700~850 h Pa and the deep and extensive ascending motion was formed. This was critical to the occurrence of heavy snowfalls. Accompanied by strong vertical ascending motion, the positive and negative circulation occurred when the frontal secondary circulation due to the occluded front and the return cold air was obstructed by the topographic barrier. This was favorable for the heavy snow. The symmetric instability affected by the front-caused temperature gradient, vertical wind shear and topographic effects and the convective instability due to west-south warm and wet jet stream, which facilitated the formation of heavy snow.
NCEP reanalysis data set was used to analyze a circumfluence snowstorm in western Henan mountain areas on Feb.21, 2017. The results showed that the stronger southwest warm and wet air strengthened the ascending motion in front of trough. It not only transported the water vapor, but also contributed to the accumulation of unstable energy. The cold advection behind trough triggered the energy release. The vortex with front shear line and the convergence area on the left of the southwesterly low-level jet provided dynamic lifting conditions for the snowstorm. The long-term effects of backflow cold air increased the convergence ascending motion in the snowstorm area. The position field increased the vertical wind shear.The symmetric instability was enhanced and the snowfall intensity increased. The return cold air at the low level made the lower atmosphere in a high humidity area for a long time and stacked with the high humidity area moving eastward at the high level, which increased the thickness of the wet layer and snow continued to fall and formed heavy snow. The ascending motion occurred when the return east wind at the lower level encountered the topography. It converged with the ascending motion in front of the low-pressure system of upstream 700~850 h Pa and the deep and extensive ascending motion was formed. This was critical to the occurrence of heavy snowfalls. Accompanied by strong vertical ascending motion, the positive and negative circulation occurred when the frontal secondary circulation due to the occluded front and the return cold air was obstructed by the topographic barrier. This was favorable for the heavy snow. The symmetric instability affected by the front-caused temperature gradient, vertical wind shear and topographic effects and the convective instability due to west-south warm and wet jet stream, which facilitated the formation of heavy snow.
引文
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[2]郭进修.华北地区1978的初雪[J].气象,1980,1(1):14-15.
[3]王建中,丁一汇.一次华北强降雪过程的湿对称不稳定性研究[J].气象学报,1995,53(4):451-460.
[4]靳冰凌,孙仲毅,王辛方,等.2009年11月10~12日河南北部暴雪天气诊断分析[J].气象与环境科学,2010,33(2):63-67.
[5]吴蓁,赵培娟,苏爱芳,等.2008年河南持续低温、冻雨和暴雪成因[J].气象与环境科学,2009,32(1):9-15.
[6]张迎新,张守保.华北平原回流天气的结构特征[J].南京气象学院学报,2006,29(1):107-113.
[7]张迎新,候瑞钦,张守保.回流暴雪过程的诊断分析和数值试验[J].气象,2007,33(9):25-32.
[8]赵桂香.一次回流与倒槽共同作用产生的暴雪天气分析[J].气象,2007,33(11):41-48.
[9]周雪松,谈哲敏.华北回流暴雪发展机理个例研究[J].气象,2008,34(1):18-26.
[10]李青春,程丛兰,高华,等.北京一次冬季回流暴雪天气过程的数值分析[J].气象,2011,37(11):1380-1388.
[11]王珏,梁琪瑶,易伟霞,等.2008年1月18~22日南阳市强降雪过程诊断分析[J].气象与环境科学,2009,32(2):54-58.
[12]朱乾根,林锦瑞,寿绍文,等.天气学原理和方法[M].北京:气象出版社,2007:313-319.
[13]候瑞钦,张迎新,范俊红,等.2009年深秋河北省特大暴雪天气成因分析[J].气象,2011,37(11):1352-1359.
[14]朱乾根,林锦瑞,寿绍文,等.天气学原理和方法[M].北京:气象出版社,2007:99-100.