850 hPa daily meridional wind field data of East Asia in March to September in 2002 is used to establish principle oscillation prediction model (POP). The model is used to conduct 10-30 d extended-range independent forecast experiment to temporal and spatial variation of main low-frequency meridional wind field () affecting heavy rainfall process in the lower Yangtze region. The experiment results show that among 135 predictions in summer half year, relevant forecasting technique of forecasts 20 d in advance is above 0.50 and they have fully forecasted low-frequency variation process of corresponding meridional wind to 3 heavy rainfalls in the summer. Obvious years of data of forecasting experiments to 20-30 d oscillation shows that these prediction models are effective methods to forecast temporal and spatial evolution of low-frequency circulations and are of great value to improve forecast accuracy of heavy rainfall process in the lower Yangtze region in next 3 to 4 weeks. 　　 

(1) The principle oscillation model has good forecasting effect for about 27 d time-scale East Asia West Pacific zonal wave train’s eastern-spreading process of East Asian subtropical area’s low level low-frequency wind field in March to September 2002, with forecast efficiency up to about 20 d. It can also predict the 850 hPa low-frequency South wind anomaly evolution affecting the heavy rainfalls in lower Yangtze region, which is of important application value. 

(2) The temporal and spatial evolution forecast experiment of summer 20-30 d oscillation signals in East Asia provides important evidence for forecasting 10-30 d extended-range rainfall intensity and time in the lower Yangtze region. As the 20-30 d oscillation signals intensity has obvious yearly variation (which is related to the air-sea interaction in Pacific region), this method has different prediction effect in different years. For years with obvious summer 20-30 d oscillation (in early stage, sea temperature of northwest Pacific Ocean is high), the principle oscillation model’s prediction efficiency can be stably 20d and can provide important information for heavy rainfall in the lower Yangtze region in summer. For years with weak 20-30d oscillation, influence of 10-20d and 30-60d oscillation and other oscillation intensify variation within one season shall be further considered. 

Years of prediction study show that the principle oscillation dynamic statistical model which is based on circulation field’s low-frequency evolution can describe communication process of main low-frequency wave. Besides, it is important to select proper subsequence length and to make independent forecast of dynamic model establishment because it can transmit feedback of complex system’s spatial structure changes and cycle length changes to prediction model to improve prediction accuracy. Therefore, this method is of important application and reference value in real-time extended-range forecast and is one of the main methods to build real-time extended-range forecast business. On this basis, statistic model can be further used to make 10-30d extended-range occurrence probability forecast of continuous rainfall, heavy rainfall, rainstorm and other extreme events in the lower Yangtze region. 

The above research achievement is published in “Acta Meteorologica Sinica” 70 (5): 1045-1054, 2012