基于REOF和ESMD的降水场时空耦合分析:以山东省冬季降水为例

Spatiotemporal coupling analysis of precipitation field based on REOF and ESMD:A case study on winter precipitation in Shandong province

冬季降水对于土壤墒情及作物过冬和春耕备播具有重要影响。以山东省冬季降水为例,采用REOF和ESMD相结合的方法分析了近68年来山东省冬季降水场的时空耦合特征。结果表明:从整个区域的空间变率来看,山东冬季降水呈现为整体一致、西北东南反相位及东北西南反相位3种主要分布型场结构,并以降水整体一致为主。从地域性特征来看,山东冬季降水场可以划分为3个空间模态,即东南型、北部型和西部型。3个空间模态的周期分析显示,东南型表现出较显著的准2.9年和准11.6年的周期特征;北部型表现出较显著的准2.52年和准8.29年周期变化;西部型则具有准3.63年、准6.44年和准14.50年的周期变化。从各模态的趋势项来看,以年代际波动为主导特征,并未表现出明显的线性变化趋势。该研究表明,REOF和ESMD是分析大尺度区域性气象数据时空耦合关系的有效工具,山东省冬季降水场时空耦合研究结果对于合理规划和指导山东省农业生产具有一定的科学实践意义。

[Background]The precipitation in winter has an important influence on soil moisture,winter crops,spring plowing and sowing.Shandong is a major agricultural province in China.However the characteristics of spatio-temporal distribution of winter precipitation in Shandong province is still unclear.The purpose of this study is to reveal the spatio-temporal distribution of winter precipitation and its relationship in Shandong province.[Methods]The data required for the paper comes from China National Meteorological Information Center,and the minimum time scale for data monitoring is 12 h.Based on the methods of both Rotated Empirical Orthogonal Function(REOF),Extreme-Point Symmetric Mode Decomposition(ESMD)and precipitation data from China National Meteorological Information Center,the spatial mode and cycle characteristics of winter precipitation field in Shandong province in recent 68 years were analyzed.[Results]1)According to analysis of EOF reflecting the spatial variability of the whole region,the winter precipitation in Shandong province presents three main distribution modes:overall consistent,northwest-southeast antiphase and northeast-southwest antiphase.And variance contributions of three modes from EOF were 68.7%,10.39%and 6.38%respectively.Obviously the first mode,overall consistent one of winter precipitation,was the most important distribution pattern.2)Based on regional characteristics from REOF analyses,winter precipitation in Shandong province has formed a spatial distribution structure with the high-load areas of southeastern Shandong,northern Shandong and western Shandong respectively.The variances of the three modes were 34.17%,30.20%and 21.10%respectively,indicating that the winter precipitation anomalies in these three regions had relatively obvious regional characteristics.The results of the period analysis based on FFT(fast Fourier transform)indicated that time coefficients(TCs)of southeast mode had the significant periodic characteristics with quasi-2.9-year and quasi-11.6-year,TCs of the north mode with quasi-2.52-year and quasi-8.29-year,TCs of the west mode with quasi-3.63-year,quasi-6.44-year and quasi-14.50-year.Meanwhile,the trend components of each mode decomposed by ESMD showed that the inter-decadal fluctuation was dominant,and there was no obvious trend of linear change,which indicated that the winter precipitation of the three modes in Shandong didn’t show a single trend characteristic during the monitoring period.Further analysis shows that the southeastern type shows a weak fluctuation and non-significant increase trend,while the northern type showed a weak fluctuation and insignificant decrease trend,while the western type shows little overall change.[Conclusions]REOF and ESMD are effective methods to analyze the spatiotemporal coupling relationship of large scale regional meteorological data.Taking winter precipitation of Shandong province as an example with the above two methods,the research results may provide reference for scientific practice for the rational planning and guidance of agricultural production in Shandong province.