西北地区东部强降水过程与大气低频振荡关系分析

Relation between Heavy Precipitation Process and Atmospheric Low-Frequency Oscillation in the Eastern Part of Northwest China

利用Butterworth带通滤波器对降水量、风场、相对涡度、OLR进行了30~50天滤波处理,分析了西北地区东部强降水低频特征及与大气低频振荡的关系。结果表明,2012年5—9月期间该地区降水主要集中于6月中旬至9月中旬,尤其集中于6、7、8月的月末,降水存在30天左右的周期振荡,强降水均发生在低频滤波曲线的正位相时段。西北地区东部强降水过程均发生在低频偏南气流与低频偏北气流汇合后低频偏南气流时段;正好出现在相对涡度30~50天低频振荡的正位相期及附近;大多发生在对流扰动的负位相区,也就是强对流活动区,其中45°N以南的负位相对流振荡向南传播及该地区西面的负位相对流振荡向东传播到此,共同形成了该地区的强降水过程。应用大气低频振荡方法对西北地区东部强降水过程进行预报,近4年预报准确率在67%以上,预报时效在1 0~30天,有效地衔接了天气与气候预报的时间缝隙。

The precipitation,wind,relative vorticity and OLR were filtered of 30 ~ 50 days period with Butterworth band-pass filter.Analyzed the low frequency characters of heavy precipitation and the relationship between heavy precipitation and atmospheric low-frequency in the eastern part of northwest China.The results indicated that the precipitation occurred from middle ten days of June to middle ten days of September,especially at the end of June July and August during May to September 2012.There was occurred about 30 days period oscillation at this precipitation period,and the heavy precipitation occurred at the positive phase of the low-frequency filtered curve.The heavy precipitation occurred at the diffuse period of southern low- frequency wind which followed the convergence of northern and southern low-frequency wind;it also occurred at the positive phase of 30~50 days oscillation relative vorticity;and also occurred at negative phase of convective activity which was the severe convection region.The heavy precipitation was formed from convective oscillation＇s negative phase diffused from southern and eastern to this region.Used atmospheric low-frequency approach to forecast heavy precipitation in the eastern part of northwest China.It showed that the forecast accuracy can reach to 67%,and the forecast effectiveness was 10-30 days in recent 4 years.It joined forecast time gap of weather and climate.