时空投影模型在东北夏季降水延伸期预报中的应用和检验

Application and verification of the spatiotemporal projection model in the extended-range forecast of summer precipitation in Northeast China

基于1979—2021年东北地区逐日降水数据和NCEP/NCAR大气再分析资料,采用旋转经验正交函数分解、集合经验模态分解,分析了东北夏季低频降水的历史规律,结合低频降水及其相关的大气季节内振荡,利用时空投影模型(STPM)对低频降水进行延伸期预报。结果表明:东北地区低频降水有明显的地域性差异,不同区域低频降水的周期有明显的年际变化,周期以10~40 d为主,40~80 d为辅。10~40 d低频降水的预报关键信号为热带大气季节内振荡、欧亚遥相关、丝绸之路遥相关低频波列和西太平洋附近的纬向风场;40~80 d低频降水的预报信号则主要来自东北地区周边的要素场。对东北地区不同频段降水的低频分量进行延伸期逐候回报试验表明,预报能力随提前预报时间的增加而降低。10~40 d低频降水分量的预测时效为10 d;40~80 d低频降水显示出了较高的预报技巧,预报时效可达30 d左右。

Based on the daily precipitation data and the NCEP/NCAR((National Center for Environmental Prediction/National Center for Atmospheric Research))atmospheric reanalysis data in Northeast China from 1979 to 2021,the historical rule of low-frequency precipitation in summer in Northeast China was analyzed using rotating empirical orthogonal function decomposition and ensemble empirical mode decomposition,combined with low-frequency precipitation and its related atmospheric intra-seasonal oscillation.A spatiotemporal projection model(STPM)was used to forecast the extended period of low frequency precipitation.The results show that there are obvious regional differences of low frequency precipitation in Northeast China,and the period of low frequency precipitation in different regions has obvious inter-annual variation,with the period of 10~40 days as the main and 40~80 days as the secondary.The key signals of low-frequency precipitation forecast from 10 to 40 days are tropical atmospheric intra-seasonal oscillation,Eurasian teleconnection,low-frequency wave train of Silk Road teleconnection and zonal wind field near the western Pacific Ocean.The low-frequency precipitation forecast signals from 40 to 80 days mainly come from the factor fields around Northeast China.The experiment on the extension period of the low-frequency precipitation of different frequency bands in Northeast China shows that the forecast ability decreases with the increase of advance forecast time.The predicted validity of low-frequency precipitation for 10~40 days is 10 days.The low frequency precipitation of 40~80 days shows a high forecasting skill,and the forecasting validity can reach about 30 days.