传统梅雨区西北部梅雨期降水特征研究

本文从气候平均角度及年际时间尺度对传统梅雨区(28°~34°N,110°~123°E)的西北部(NW区)梅雨期降水及其与大气环流和海温的关系进行了研究,重点比较其与典型梅雨区梅雨期降水的异同。结果表明:(1)气候平均而言,850 hPa层次上大于40 g·m·kg^-1·s^-1的水汽输送带无法覆盖NW区,导致该地区在35~37候没有类似于江南地区、长江中下游地区和江淮地区梅汛期集中性降水的特征。(2)1979—2017年共39 a中,NW区有24 a出现了梅雨现象,有15 a为空梅,平均入梅日期为6月27日,比长江流域偏晚13 d,平均出梅日期为7月13日,与长江流域相近,梅雨期平均日降水量与长江流域相当。(3)NW区梅雨期时,雨量偏多的地区在我国黄淮地区,此时江南地区雨量偏少。东亚夏季风系统成员,如南亚高压、西太平洋副热带高压、青藏高原南部梅雨锚槽、低层西北太平洋反气旋等都比长江流域梅雨时偏北。(4)与典型梅雨区不同,NW区的入梅时间与赤道印度洋、赤道中东太平洋等关键区海温没有显著关联。

The precipitation characteristics during Meiyu period in the northwestern part of traditional Meiyu area

The northwestern part (NW) of the traditional Meiyu area (28°-34°N, 110°-123°E) is close to the typical Meiyu area of the Yangtze and Huaihe River Basin. The precipitation in the NW area during the Meiyu period and its relationship with atmospheric circulation and sea surface temperature from the perspective of climatological mean and interannual time scales were studied, focusing on comparing its similarities and differences with the precipitation during the Meiyu period in typical Meiyu regions. Results show that (1) in terms of climatology, the water vapor conveyor belt larger than 40 g·m·kg^-1·s^-1 at the 850 hPa cannot cover the NW area. Therefore, the concentrated precipitation that is observed in the middle and lower reaches of the Yangtze River, the south of the Yangtze River, and Jianghuai Region disappears in the NW area during pentad 35-37. (2) During the 39 years from 1979 to 2017, there are 24 years with Meiyu in the NW area, and 15 years without Meiyu. The average meiyu onset date is June 27, which is 13 days later than that in Yangtze River Basin; and the average meiyu ending date is July 13, which is similar to that in the Yangtze River Basin. The average daily precipitation rate during the Meiyu period is equivalent to that in the Yangtze River Basin, although the Meiyu amount is less than that in the Yangtze River Basin. (3) During the NW meiyu period, the area with more rainfall is in the Huanghuai region in China, and the rainfall in the south of the Yangtze River is less than normal. Members of the East Asian summer monsoon system, such as the South Asian high, the western Pacific Subtropical high, the Meiyu anchor trough in the southern Tibetan Plateau, and the low-level Northwest Pacific anticyclone, are all located more northward than those during the Meiyu period of the middle and lower reaches of the Yangtze River. (4) Unlike the typical Meiyu area, the time series of Meiyu onset date in the NW area is not significantly related to the sea surface temperature in key areas such as the equatorial Indian Ocean and the equatorial central and eastern Pacific.