南京地区夏季暴雨年际变化的主要模态及其与大气环流的联系

EEMD(集合经验模态分解)方法在处理非线性及非平稳时间序列时表现出了很大的优势和应用潜力。利用EEMD方法研究南京地区夏季暴雨年际变化周期，对55年(1946-2000)的南京地区夏季暴雨频数进行分解，分别得到一系列模式，其中包含有2-3年周期分量和7年周期分量,而且2-3年周期分量幅度较大，变化特征与暴雨频数原始数据变化具有很高的相似性。不同于传统方法，EEMD方法给出了暴雨频数在不同时间尺度上各自分离的变化特征.这两种时间变化模态对应于不同的200hPa环流型,前者主要作用区域在南亚和欧亚大陆到西太平洋的副热带地区,而后者相关区域在西太平洋热带和亚洲中纬度地区。

Principal modes of the heavy rainfall over Nanjing in Summer and Its Relationship to Atmospheric Circulation

EEMD (Ensemble Empirical Mode Decomposition) technique has indicated the advantages and potentials in applications related to processing the nonlinear and non-stationary time series. In this paper, EEMD method was adopted to study the interannual variation of the heavy rainfall in Nanjing summer. Using the EEMD method, the numbers of the heavy rainfall in Nanjing for 55 years (1946-2000) can be decomposed into a series of modes, including 2-3 years periodic (quasi-Biennial Oscillation) component, and 7-year component. Among those, the 2-3 year periodic with the larger amplitude has the high correlations with original numbers of the heavy rainfall. In a nutshell, the EEMD method other than the traditional and conventional methods can bring us the isolated characteristics of the variations of the heavy rainfall on various time scales. These two modes correspond to the different regions of influence for the zonal wind at 200 hPa. The former is over the South Asia and subtropical western Pacific and Eurasia continent, while the latter is over the tropical western Pacific and the mid-latitude of Eurasia.