低频天气图方法在四川盆地夏季延伸期强降水预报中的应用

Extended-Range Forecast of Summer Strong Precipitation by the Method of the Low-Frequency Synoptic Map in Sichuan Basin

利用四川盆地2008~2013年夏季降水量资料以及500h Pa风场资料,基于低频天气图方法,通过分析影响四川盆地强降水过程的500h Pa低频天气系统的活动规律,对强降水时段对应的低频风序列做经验正交分解,分析低频系统的主要空间分布型及其流场配置。统计降水时段对应的低频系统空间位置、分布及持续出现频数,划分出与预测区域降水过程密切关联的8个低频关键区,主要包括中低纬的西太平洋副热带高压及台风的主要活动区（1）、南海附近地区（2）、阿拉伯海和孟加拉湾附近地区（3）,中高纬的蒙古至河套附近地区（5）和青藏高原及其以北的低频系统集中区域（6）这五个活跃关键区。计算各关键区低频系统历史周期发现低纬关键区（1、2、3）以及高原关键区（6）低频系统的周期都较短,而中高纬关键区（4、5、7、8）低频系统的周期相对较长。建立预测区域强降水过程的低频图预测模型。用此方法对2013年四川盆地延伸期强降水过程进行预报试验,发现预测6~7月上中旬的强降水过程效果较好,但对盛夏高温连晴伏旱时段（7月下旬~8月）的预报能力有所下降。

Based on the application of the low-frequency synoptic map（ LFSM）,this paper analyzed the active characteristics of low-frequency weather systems on 500 h Pa for the summer strong precipitation process in Sichuan basin,by the data of summer precipitation data between 2008 and 2013,wind data on 500 h Pa. The low-frequency wind series during strong precipitation process were calculated by Empirical Orthogonal Function（ EOF）. The main spatial pattern and the wind allocation of the main low-frequency weather systems were studied. Eight low-frequency key regions,very related with precipitation process in forecast area,were divided by the spatial position,distribution and frequency of low-frequency weather systems.They are the active region of Northwest Pacific high and typhoon at low latitude,South China Sea,Arabian Sea and Bay of Bengal,the area from Mongolia to the middle of Yellow River,Tibetan Plateau,The periods of each key region is calculated. It shows that the periods in low latitude key regions（1,2,3） and Tibetan Plateau key region（6） are short,while long in high latitude key regions（4,5,7,8）. We analyzed the allocation and history period of low-frequency weather systems in each key region during strong precipitation process,gained the relationship between precipitation process and the activity of low-frequency weather systems,established the forecast model by the method of low-Frequency synoptic map for predicting the strong precipitation process. With this method,we forecasted the strong precipitation process in Sichuan Basin in the summer of 2013. We found that we forecasted good during June and middle of July,but not good from late July to August,when it＇s hot and dry.