Extended complex autoregressive model of low-frequency rainfalls over the lower reaches of Yangtze river valley for extended range forecast in 2013

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 2030-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 2030-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 2030-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.