2002年夏季东亚地区环流20-30d主振荡型延伸期预报研究

Study of the extended range forecast of the principal 20-30 day oscillation pattern of the circulation over East Asia in the summer of 2002

用2002年3—9月逐日东亚地区850hPa经向风场资料建立主振荡预测模型(POP),对影响长江下游地区强降水过程的主要低频经向风场(20—30d时间尺度)的时空变化进行10—30d延伸期独立预报试验。试验结果表明,在夏半年135次预测中提前20d预报的相关预报技巧在0.50以上,很好地预报了夏季3次强降水过程对应的经向风的低频变化过程。对20—30d振荡显著的多年资料预报试验表明,这些预测模型是预报低频环流时空演变的有效工具,对于提高未来3—4周长江下游强降水过程的预报准确率有重要意义。

A series of the principal oscillation pattern （POP） models are set up based on the low-frequency meridional wind of 850 hPa over East Asia for March September in 2002 on the time scale of the 20 - 30 day, and the independent forecast experi- ments of POP models are performed for investigating the propagation of the low-frequency oscillation associated with theheavy precipitation process over the lower reaches of the Yangtze River valley in terms of the extended range of the 10 - 30 days. The results show that the skill score of the correlation prediction up to 20 days ahead of time could reach more than 0.50 in the 135 forecast runs, with the corresponding low frequency variations of the positive meridional wind to three severe precipitation e- vents in summer well forecasted. Based on the forecast experiments against the years of distinct 20 - 30 day oscillation, it is shown that this POP model is a useful tool to predict the spatial and temporal evolutions of the low frequency oscillation. Hence, it is important for improving accuracy of forecasting the severe precipitation process over the lower reaches of the Yan- gtze River valley for future 3 - 4 weeks.