Spatial And Temporal Characteristics Of The Hourly Extreme Precipitation Over Yangtze-River Valley In Warm Season

Based on the hourly merged gauge-satellite precipitation product with the horizontal resolution of 0.1° during 2008-2014, the spatial and temporal characteristics of the hourly extreme precipitation over the Yangtze River Basin in warm season has been analyzed. The diurnal and seasonal variation of the hourly extreme precipitation and the background of atmospheric circulation related to the regional extreme precipitation have been revealed as well.Results show that the hourly extreme precipitation amount (PA) exhibits two strong extreme precipitation centers over Sichuan Basin and the lower reach of the Yangtze River. The extreme PA account for over 30% of the total PA in warm season over most part of the studying area. Meanwhile, over 60% of the total extreme PA in most area is contributed by the short-duration extreme PA. In addition, it is noted that a relatively larger center of the proportion of the long-duration extreme PA to the total extreme PA is located over Sichuan Basin and surrounding areas.The hourly extreme PA displays remarkable diurnal cycle:extreme precipitation events mostly happened in early evening before 00:00 o’clock over the eastern Tibetan Plateau and Sichuan Basin, the peak time of extreme precipitation with different duration time is before dawn, while over the lower reach of Yangtze River, the extreme precipitation has two diurnal peaks, one occurs in early morning and the other happens in late afternoon, furtherly, the extreme precipitation with short (long) duration time over the lower reach of Yangtze River mainly peaks in afternoon (early morning). We also find that the diurnal cycle of extreme precipitation has different characteristics over the lower reach of Yangtze River in seasonal scale:extreme precipitation shows an obvious early morning peak in pre-meiyu period and late afternoon peak in post-meiyu period, while in meiyu-period, extreme precipitation exhibits comparable early morning and late afternoon peaks. The diurnal peak of extreme precipitation displays an eastward phase transition along the Yangtze River and extreme events with long duration time have more obvious propagation, meanwhile, the eastward extent has seasonal difference that the propagation can reach to 115° E in pre-meiyu season but 110° E in post-meiyu season.Further analysis show that the regional extreme precipitation is mainly associated with the farther west and north location of the sub-tropical high as well as the active southern branch trough, the dipole circulation anomaly at 850hPa can accelerate the southwesterly (southeasterly) and bring about abundant water vapor to lower reach of Yangtze River (Sichuan Basin). Moreover, the abnormal deep vertical ascending motion over the precipitation area also favors to generate regional extreme precipitation. The frequency of regional extreme events over Sichuan Basin (the lower reach of Yangtze River) shows diurnal peak at around 03:00 (09:00) A.M. The occurrence frequency of regional extreme precipitation events over the lower reach of Yangtze River displays remarkable seasonal variations:the regional extreme precipitation events occur more in pre-meiyu season than in meiyu season and post-meiyu season, however, the regional extreme precipitation events are fewest in post-meiyu seaon among the 3 sub-seasons. The occurrence frequency of the regional extreme precipitation events over Sichuan Basin in warm season shows very small seasonal variations. The northward push of the southerly wind makes the regional extreme events northward and westward move into the interior of Sichuan Basin.