摘要:
用长江下游降水低频分量和全球850 hPa低频经向风主成分,建立扩展复数自回归模型(ECAR),对2013年1-12月长江下游降水低频分量进行延伸期逐日变化预报试验。结果表明,20-30 d 时间尺度的长江下游低频降水预测时效可达43 d左右,能较好地预测与暴雨过程对应的低频分量的非线性增长过程,预报能力明显优于自回归模型(AR)。这种通过构造主要低频序列组成的扩展复数矩阵(ECM)进行复数自回归(CAR)建模的ECAR方法,也为展现气候系统内部分量之间相互作用的动力学过程提供了崭新的描述。基于全球环流主要20-30 d振荡型的发展和演变，对于提前27 d预报长江下游地区2013年10月上旬后期大暴雨过程很有帮助,其中南半球热带外环流20-30 d振荡是影响2013年夏秋季长江下游地区延伸期强降水变化的一个主要因子。
Abstract:
Low-frequency rainfall over the lower reaches of Yangtze river valley (LYRV) and the principal component of the global 850 hPa meridional wind anomalies are adopted to construct an extended complex autoregressive (ECAR) model, which can be applied to the daily forecasting of the low-frequency rainfall component over LYRV in 2013 for the extended range forecast. Results show that this model for the forecasting of the 20-30-day rainfalls over LYRV has a good predictive skill up to 43 days, which is able to well predict the nonlinear enhancement processes of low-frequency rainfall component associated with heavy rainstorm process. And the correlation skill of the extended range forecast produced form the ECAR model is superior to the autoregressive model (AR) forecast. This method, in which the complex autoregressive (CAR) models are set up via constructing the extended complex matrix (ECM) for the principal low-frequency time series, provides a new description for the emerging dynamic processes of the interactions between components in climate systems. Based on the development and evolution of the principal 20-30-day oscillations of the global circulation, it is help for better forecast the process of heavy rainfall in the early October of 2013 over LYRV for times ahead of about 27 days. In these low-frequency variabilities, the 20-30-day oscillation in extratropics over the Southern Hemisphere is one of the main factors causing the changes of the heavy rainfall over LYRV for the extended range during the summer and fall in 2013.
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