Abstract:

Based on the daily precipitation of 21 stations from 1960 to 2013 in Anhui Province and the NCEP/NCAR reanalysis data, the temporal and spatial distribution characteristics of extreme precipitation indices were analyzed by using the trend analysis, moving average, M-K test and EOF methods. And on this basis, the anomalous characteristics of atmospheric circulation of daily extreme precipitation events were studied by using composite analysis. The results are as follows:(1) The continuous dry index (CDD) showed a weak downward trend in the past 54 years, while other extreme precipitation indices were rising, and the decreasing trend of CDD in north of the Huaihe river was significant, the increasing trends of the extreme precipitation (R95p), the five-day maximum precipitation (RX5day) and the daily precipitation intensity (SDII) in south of the Yangtze river were obvious, while the change trends of those indices was slight in Jianghuai. (2) As far as the spatial distribution to be concerned, the R95p gradually increased from north to south in Anhui Province, the RX5day was similar to the R95p except for Mengcheng and Chuzhou stations, while the CDD gradually descreased from northwest to southeast, and the SDII was higher in the north and southwest of Anhui and lower in the middle of Anhui. (3) There were three main distribution types of the R95p in Anhui, which were the spatial consistency, opposite variation in the north and south, and adverse variation trend in Huaibei, Jiangnan and Jianhuai. (4) The thresholds of the daily extreme precipitation events were 25.52 mm/d on the 95th percentile and 39.06 mm/d on the 99th percentile in Anhui, and the annual variation fluctuated greatly with a weak upward trend, additionally, the daily extreme precipitation events tended to occur from May to August，especially from late June to middle July. (5) In spring, the blocking high in Ural Mountains and Okhotsk Sea affected the occurrence of extreme precipitation events in Anhui, and the convergence in low-level circulation field over Anhui was obvious, the subtropical high was weaker. In summer, the circulation situation in low-level was similar to that in spring, but the subtropical high was stronger. As a result, the water vapor from the anomalous anticyclone periphery in the Bay of Bengal and the South China Sea transported northward into Anhui area, and cooperated with the cold air southward, the daily extreme precipitation events happened in Anhui.

Key words: Anhui, extreme precipitation indices, daily extreme precipitation events, circulation anomaly

摘要：

利用1960～2013年安徽21个气象台站逐日降水观测资料及NCEP/NCAR再分析资料，对极端降水指数时空分布规律及区域性极端日降水环流异常特征进行分析，结果表明：（1）时间尺度上，安徽近54 a持续干燥指数（CDD）呈微弱下降趋势，其余指数呈上升趋势，其中淮北持续干燥指数（CDD）下降显著，江南极端降水量（R95p）、5 d最大降水量（RX5day）、日降水强度（SDII）上升显著，而江淮之间各指数变化趋势较弱；（2）空间尺度上，极端降水量（R95p）由北向南逐渐增大，5 d最大降水量（RX5day）除蒙城和滁州外分布情况与R95p相似，持续干燥指数（CDD）则相反，平均日降水强度（SDII）在安徽北部和西南部较大，中部较小；（3）安徽极端降水量主要空间分布类型为整体一致型、南北差异型和淮北、淮南与江淮差异型；（4）安徽省极端日降水量95%和99%分位阈值分别为25.52 mm/d和39.06 mm/d，年际变化呈微弱的上升趋势，5～8月是极端日降水的多发期，尤其是6月下旬至7月中旬；（5）春季，安徽极端日降水事件的发生受乌拉尔山和鄂霍次克海阻塞高压活动影响；夏季，副高较强，低层安徽处于上升运动区，南海、孟加拉湾水汽由西南气流输送至安徽上空，同时，在北方冷空气南下的配合下，形成极端日降水。

关键词: 安徽, 极端降水指数, 极端日降水, 环流异常