低频扰动增量法在华南冬季低温延伸期预报中的应用研究

通过扰动物理量分解方法和增量预报方法,提出低频扰动增量的定义,分析冬季大气低频扰动信号与华南低温事件的可能联系,构建基于低频扰动增量的华南冬季低温延伸期预报模型,为低温延伸期预报提供科学参考依据。分析表明:(1)东半球500 hPa高度场低频扰动变化显著区域主要位于中高纬度45°×80°N地区,尤其在乌拉尔山脉附近及其以西的东欧地区和贝加尔湖以北的中西伯利亚地区;(2)500 hPa中高纬高度场和风场低频扰动增量的前两个EOF模态反映了周期为20 d左右低频振荡的传播型模态,EOF1反映的是导致中高纬度两槽一脊型的环流形势得以维持的低频扰动特征,EOF2反映的是中高纬度高空槽东移后出现的低频扰动特征,研究揭示了华南最低气温低频扰动增量与该低频传播模态的关系十分密切;(3)基于低频扰动增量的延伸期预报准确率明显优于直接应用原始场的延伸期预报,重点抓住大尺度环流的低频扰动增量及由其引起的预报量的扰动增量,可以提高延伸期预报的准确率。

Study of the Extended Range Forecast of Low Temperature over Southern China in Winter Based on Low-frequency Anomaly Increment

This study proposes the definition of low-frequency anomaly increment based on the methods of physical decomposition and increment prediction,and the connection between atmospheric low-frequency disturbances and low temperature events over South China in Winter has also been analyzed.Furthermore,a forecast model based on low-frequency anomaly increment has been developed which could be a scientific reference for the extended range forecast of low temperature.The results are as follows:(1)the most significant low-frequency disturbances of geopotential height(HGT)on 500 hPa in Eastern Hemisphere is located in mid-high latitudes ranging from 45°N to 80°N,particularly in the vinicity of Ural Mountains,the Eastern Europe to the west of Ural Mountains and central Siberia to the north of Lake Baikal;(2)The first two EOF modes of low-frequency anomaly increment of HGT and wind fields on 500 hPa in mid-high latitudes represent the propagation modes of low-frequency oscillation with a period of 20 d.EOF1 indicates the feature of low-frequency disturbances that maintains the two-trough and one-ridge circulation pattern.EOF2 indicates feature of low-frequency disturbances that prevails after the trough of mid-high latitudes moving eastward.And a strong connection between the low-frequency propagation mode and low-frequency low temperature anomaly increment in South China has been captured.(3)The accuracy of the extended range forecast based on the low-frequency anomaly low-frequency increment is significantly better than that of the extended range forecast directly applying the original physical fields.The forecast accuracy of the extended range could hopefully be improved by focusing on the low-frequency anomaly increment of large-scale circulation and the accompanying anomaly increment of forecast variables.