贵州省不同强度区域性凝冻过程环流形势对比分析

Comparative Analysis of Regional Freezing Rain Events with Different Intensities in Guizhou Province

利用贵州省84个气象站逐日观测资料以及再分析资料,对4种不同强度区域性凝冻过程进行对比分析。结果表明:500 hPa位势高度场上中高纬度的亚洲东部区域距平场呈现“+-”的分布或有切断低压分布,贝加尔湖至中国华北地区以经向环流为主;850 hPa风场上云南南部以南受偏南风和西南风控制,并且在江南至华南存在西南或西风急流,是4种不同强度凝冻过程中形势场共性特征。500 hPa高度场上中高纬度地区呈两槽一脊或一槽一脊分布;风场上850 hPa东北风回流和700 hPa西南急流形成上暖下冷的形势场,同时850 hPa形成稳定低层切变线;温度场上存在冷暖冷的夹心结构,近地面层0℃线维持在900 hPa以下,均是较强等级以上的区域性凝冻过程中形势场共性特征。而对于一般性区域性凝冻过程,500 hPa位势高度场上呈多槽脊分布,风场上是否存在东北风回流和低层切变线,温度场上是否存在冷暖冷的夹心结构以及近地面层0℃线位置等特征均不统一。温度剖面图上,当近地面层0℃线位置最低时或出现冷暖冷的夹心结构时段与凝冻过程影响范围最广、灾情最重的时间段对应。

Using the percentile method,the regional freezing process intensity is divided into four levels:extremely strong,strong,general strong,and general.Based on the daily observation data from 84 stations in Guizhou Province and reanalysis data,the cooling amplitude,number of affected stations,duration,altitude field,wind field,and temperature field are being analysed in a comparative way on 12 regional freezing Processes which are selected from four different intensities.The conclusions are as follows.The common features of the four freezing events with different intensities are:in the height field at 500 hPa,a distribution of“positive-negative”anomalies or a cut-off low is being exhibited over the East Asia region in the middle and high latitudes,with meridional circulation dominating from Lake Baikal to northern China;in the wind field at 850 hPa,the southern part of Yunnan Province is being controlled by southerly and southwestern winds,and there is a southwestern or westerly jet stream from Jiangnan to southern China.For the regional freezing rain events with strong intensity,a“two trough and one ridge”or“one trough and one ridge”distribution in the height field at 500 hPa is shown over the middle and high latitude regions.In the wind field at 850 hPa,there is a pattern of warm air advection aloft and cold air advection near the surface,with north-easterly winds return at 850 hPa and a southwestern jet stream at 700 hPa,while a stable low-level shear line is formed at 850 hPa.In the temperature field,a sandwich structure of cold-warm-cold is observed,with the 0℃isotherm below 900 hPa in the near-surface layer.However,for the regional freezing rain events with moderate intensity,multiple troughs and ridges are distributed at 500 hPa.There are no common features for the north-easterly winds advection and low-level shear line in the wind field,as well as the cold-warm-cold sandwich structure and the position of the near-surface 0℃isotherm in the temperature field.On the temperature profile,the period with the lowest position of the near-surface 0℃isotherm or the occurrence of the cold-warm-cold sandwich structure corresponds to the time when the freezing rain events have the extensive impact and result in the most severe disaster.In the prediction of the freezing process,predict experiments can be conducted based on the position of the 0℃line near the ground level and the strength of the temperature inversion layer.