中国主雨季极端小时降水时空分布和日变化特征

基于国家级气象站逐小时降水资料，采用百分位阈值的极端降水定义方法，统计研究了中国1951—2021年4—10月小时降水时空分布和日变化特征。结果表明，中国主雨季极端降水阈值东南大、西北小，存在四个分别位于华南、环渤海、长江中下游和四川盆地的大值区，随着极端性增强，北方小时降水阈值的增大较南方更显著，大值中心北移。月尺度上，小时降水的最高频次月份由南向北从5月推迟至8月，华西地区最晚（9—10月），随着极端性增强，最高频次月份由6月、7月推迟到7月、8月，且地区差异减小。日变化特征上，全国范围内小时降水频次占比，呈现午后到夜间的谷峰主循环和后半夜到上午的次循环，且随着极端性增强，主循环振幅增大，次循环峰值减小。不同地理位置看，四川盆地的极端小时降水峰值时刻出现在凌晨，其他三个大值区则与全国平均较为一致，日变化振幅从南到北逐渐减小，西部最大。小时降水峰值时刻具有空间聚集的特征，夜间峰值主要集中在南方沿海和华北、东北，早晨—上午峰值集中在中部、东部、西南和西北部分地区，空间分布中出现的逐渐推迟和突变特征与海陆分布和大地形密切相关。小时降水峰值时刻空间占比与频次占比的日变化特征类似，均有上午峰值平缓、夜间峰值陡峭的特征，这是因为不同站点到达夜间峰值的时刻接近，而到达上午峰值的时刻不同；两者主要区别在随着极端性增强，频次占比夜间主峰值显著增大，而峰值时刻空间占比主峰值几乎不变，这是因为频次的变化主要是由同一些站点上的次数变化导致，而非不同站点之间的差异。

Spatio-Temperal Distribution and Diurnal Variation of Extreme Hourly Precipitation in China During the Main Rainy Season

Based on the hourly precipitation data from national meteorological stations of China and the definition method of extreme precipitation with percentile threshold, this paper makes a statistical study of the spatio-temperal distribution and diurnal variation of hourly precipitation in China from April to October in 1951-2021. The results show that the hourly precipitation thresholds of the main rainy season in China are large in the southeast but small in the northwest, and there are four large threshold value centers lo-cated in South China, the Circum-Bohai Region, the middle and lower reaches of the Yangtze River and the Sichuan Basin. With the increasing extremeness, the hourly precipitation threshold in northern China increases more significantly than that in southern China, and the large threshold center moves northward. On the monthly time scale, from the south to north of China, the month with the highest frequency of hourly precipitation is postponed from May to August and the latest month is in West China (September-October). As the extremeness increases, the month with the highest frequency of precipitation is postponed from June-July to July-August, and the regional differences are reduced. In terms of diurnal variation characteristics, the frequency proportion of hourly precipitation of China presents a main valley-peak cycle from afternoon to night and a sub-cycle from midnight to morning. With the increasing extremeness, the amplitude of the main cycle increases and the peak value of the sub-cycle decreases. From the perspective of different geographical locations, the peak time of extreme hourly precipitation in Sichuan Basin is in the early morning, while the peak time in other three areas is consistent with the mean of whole China. The diurnal variation amplitude declines gradually from south to north of China, with the largest amplitude in weastern China. The peak time of hourly precipitation has the characteristics of spatial concentration. The night peak is mainly concentrated in North China, Northeast China and southern coastal areas of China, while the morning-to-forenoon peak is concentrated in the central, east, southwest and the parts of northwest of China. And the gradual delay and abrupt change in spatial distribution of precipitation peak time are closely related to land-sea distribution and large topography. The diurnal variation characteristics of the spatial proportion and frequency proportion of hourly precipitation peak time are similar, both featured with gentle peak in the morning and steep peak at night. This is because the time of the night peak is close to the time at different stations, but the time of the morning peak is not so. Furthermore, with the increasing extremeness, the main peak of frequency proportion at night increases significantly, but the main peak of spatial proportion at night is almost unchanged. This difference is because the change of frequency is mainly caused by the change of frequency at the same stations, rather than the difference between different stations.