摘要
The features of the decadal evolution of different durations of continuous Meiyu precipitation and their possible cause from the viewpoint of the low-level intraseasonal oscillation(ISO) are examined in this study. It is found that the total frequency of Meiyu precipitation events of certain duration gradually decreases as the duration of the events increases,and the main center of the events moves from the northern Yangtze-Huaihe River Valley(YHRV) to the southern YHRV. The linear trends of different durations of continuous Meiyu precipitation indicate that longer-duration precipitation has become significantly less frequent since 2000,while 2-day and 3-4-day continuous precipitation processes have become more frequent. At the same time,a close relationship between the variation in the low-level ISO and the decadal evolution of frequency of longer-duration Meiyu precipitation is detected. Clearly,since 2000,the low-level ISO has significantly decreased,and a single peak of longer-duration events has been replaced by several peaks of shorter-duration events,which has resulted in a significant decrease in the frequency of longer-duration precipitation. Meanwhile,low-level baroclinicity increased(decreased) during each period,which is in accordance with the increasing(decreasing) frequency of longer-duration precipitation. It is confirmed that longer-duration precipitation has significantly decreased in recent years.
The features of the decadal evolution of different durations of continuous Meiyu precipitation and their possible cause from the viewpoint of the low-level intraseasonal oscillation （ISO） are examined in this study. It is found that the total frequency of Meiyu precipitation events of certain duration gradually decreases as the duration of the events increases, and the main center of the events moves from the northern Yangtze-Hualhe River Valley （YHRV） to the southern YHRV. The linear trends of different du- rations of continuous Meiyu precipitation indicate that longer-duration precipitation has become significantly less frequent since 2000, while 2-day and 3^-day continuous precipitation processes have become more frequent. At the same time, a close rela- tionship between the variation in the low-level ISO and the decadal evolution of frequency of longer-duration Meiyu precipitation is detected. Clearly, since 2000, the low-level ISO has significantly decreased, and a single peak of longer-duration events has been replaced by several peaks of shorter-duration events, which has resulted in a significant decrease in the frequency of longer-duration precipitation. Meanwhile, low-level baroclinicity increased （decreased） during each period, which is in accor- dance with the increasing （decreasing） frequency of longer-duration precipitation. It is confirmed that longer-duration precipita- tion has significantly decreased in recent years.
基金
supported by the National Department Public Benefic Research Foundation (GYHY200906015)
the National Key Technology R&D Program (2009BAC51B03)
the National Natural Science Foundation of China (40901016 and 40805041)
