Comparative Analysis of Regional Freezing Rain Events with Different Intensities in Guizhou Province
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.
NETL
NSTL
万方数据
维普
