| Meiyu over the Changjiang-Huaihe valley is a typical stages in the process of the East Asian summer monsoon from the south to the north of the seasonal advance, the prediction of the beginning date of Meiyu over the Changjiang-Huaihe valley is an important task for the seasonal climate prediction in China. In this paper, by using the daily reanalysis data provided by NCEP/NCAR and the data of Meiyu reeords from Jiangsu Provincial Meteorological Station during the period of 1954-2013, the parameters of Meiyu include Meiyu duration, Meiyu beginning date, Meiyu ending date, Meiyu rainfall and Meiyu cumulative intensity are discussed and the differences of atmospheric circulation characteristics of anormal years of the beginning date of Meiyu. The atmospheric circulation and SST anomaly in pre winter which have impacts on the beginning date of Meiyu are analyzed. Based on the analysis, it can be found that the predictive signals in pre winter impact on Meiyu through two related interactions. One is the tropical ocean-atmosphere interaction, SST anomaly over equatorial region makes the Walker circulation change. The other one is the tropical-extratropical interaction, the Walker circulation anomaly can affect the Hadley cell over the Indonesia region, and then make the location and intensity of western pacific subtropical high change. As the memory effect of SST, this effection can be from winter to early summer. The early or late Meiyu is the result from the comprehensive functions of those two interactions. In terms of above analysis, by using multivariable linear regression technique,a statistical forecast model is established. The hindcast of during 20 years from 1994-2013 is performed to evaluate the performance of this forecast model. The results show that this forecast model can predict the beginning date of Meiyu well. Finally, in order to improve the accuracy of the forecast, the important characteristic parameters and related indexes of Meiyu Nowcasting are discussed. |
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