Reconstruction of the starting time series of rainy season in Yunnan and the evolvement of summer monsoon during 1711-1982

According to the textual research into the historical documents dominated by archives yearly, as well as the verification with several other kinds of data, the later or earlier starting time of the rainy seasons in Yunnan during 1711-1982 has been reconstructed. The analysis indicates that there are obvious fluctuations in the starting date of the rainy seasons in Yunnan in a year or years, and long fluctuation on the decadal scale. The rainy season comes earlier in the early 18th century, later in the 19th century and earlier again in the 20th century. This reflects to a certain degree the gradual change of the summer monsoon in Yunnan. There exists an obvious quasi-3 years cycle, which is related to EI-Nino＇s quasi-3 years cycle, and a 11.3-year cycle which is notably related to the 11-year cycle of the solar activity of starting date of the rainy seasons in Yunnan. Meanwhile, the dissertation finds that the EI-Nino is very important to the starting date of the rainy seasons in Yunnan. The starting date of the rainy seasons in Yunnan often comes later or normally in the year of EI-Nino. However, there is an obvious imperfect period in such influence, which in turn may mean that there is a certain fluctuation in the effect of ENSO on Asian summer monsoon.

Variations in the starting date of the pre-summer rainy season in South China, 1736-2010

The starting dates of the pre-summer rainy season during historical times （1736- 1911） in Fuzhou and Guangzhou of South China, were determined and reconstructed on the basis of historical documents in the Yu-Xue-Fen-Cun archive, together with observed features of precipitation during the pre-summer rainy season. In addition, starting dates of the pre-summer rainy season from 1953 in Fuzhou and from 1952 in Guangzhou were reconstructed for the instrumental period. These data allowed for analyses of inter-annual and inter-decadal changes in the starting dates of the pre-summer rainy season in South China over the past 300 years. Results show that the mean starting date of the pre-summer rainy season in South China was the first pentad of May; in addition, periodicities in the starting dates of 2-3 years, 10 years, and 40 years were detected during the period 1736-1911, and of 2-3 years, 10 years, and 22 years during the instrumental period. From 1736 to 1911, the earliest starting dates at Fuzhou and Guangzhou both occurred at the fourth pentad of April, while the latest starting dates were at the sixth pentad of May in Fuzhou and the first pentad of June in Guangzhou. During the instrumental period, the earliest and latest starting dates were at the fourth pentad of April and the first pentad of June, respectively, in both Fuzhou during 1953-2010 and Guangzhou during 1952-2010. The maximum difference between neighboring decades during 1736-1911 was 2.2 and 1.6 pentads in Fuzhou and Guangzhou, respectively, and during the instrumental period it was 2.5 and 2.4 pentads in Fuzhou and Guangzhou, respectively.

近21年东北雨季变化特征

为研究我国东北雨季平均降雨量特征,将我国东北按照地理位置划为4个区域(包括黑龙江、吉林、辽宁、内蒙古东部),并利用1997—2017年我国208个测站观测数据,采用统计方法、相关性和线性趋势等方法,统计东北雨季的平均降雨量、持续天数、综合强度、开始/结束时间变化的基本特征。结果表明,1997—2017年东北雨季平均起止日期分别为6月27日和9月9日。1997—2017年东北雨季平均降雨量和天数变化均存在较大年际差异,平均降雨量1998年最多(461.7 mm),2007年最少(141.4 mm);天数2014年最长(109 d),2000年最短(58 d);且年平均降雨量为313.21 mm,年平均持续天数为84 d。东北雨季平均降雨量受到多个因素的综合影响,其中东北雨季平均降雨量和雨季持续天数呈现显著正相关,相关系数为0.815。

利用雨雪分寸重建福州前汛期雨季起始日期的方法研究

阐述清代福州雨雪分寸记录的特点;并利用福州1961—2010年器测降水记录,分析福州3～7月降水特征,提出辨识福州前汛期雨季开始日期的指标。在此基础上,根据清代福州雨雪分寸记录的内容和形式,分类构建利用雨雪分寸辨识福州前汛期雨季起始日期的方法;依据日降雨分寸、降雨日期和强度、时段的降水日期(或时段起止日期)及降水日(次)数与时段降雨状况描述等各类记录所具有的降雨信息特点,确定量化辨识"降雨强度突增"和"少雨期"指标的具体标准,解决在缺少日降雨分寸记录条件下定量辨识雨季开始日期这一难点问题,为重建过去300年华南地区前汛期雨季长序列提供方法。

过去300年中国西南与东部地区雨季始期变化特征的比较研究

亚洲夏季风强弱、雨季来临早迟与我国夏季旱涝的关系密切,因此深入探究亚洲季风的长期变化规律及其各子区域季风系统的相互联系与稳定性具有重要科学意义。文章在参考中国气象局据气象观测资料制定的西南地区雨季开始期行业标准的基础上,结合历史文献清代雨雪分寸的记载特点,重建了1736~1911年成都地区的雨季开始日期序列,分析了其年际-年代际变化的基本特征,并与昆明、华南、长江中下游和华北等地的雨季开始日期序列进行了对比。发现:历史时期成都雨季的初始日与1951~2015年一致,均为5月6候;1740s~1790s、1840s~1850s、1880s~1890s、1960s~1970s和2000s雨季来临较早,而1800s~1830s、1860s~1870s、1900s、1950s和1980s~1990s雨季则推迟;尽管中国东部季风雨带在历史时期的推进过程与现代基本一致,差异为1~3天,但随着季风强度的变化,表现出明显的年代际波动;成都雨季受到南亚季风和东亚季风的共同影响,其雨季来临早晚的变化与昆明相关性更高,与长江中下游梅雨季开始的早晚关系不明显。此外,研究结果还显示亚洲季风在1980~2000年减弱的现象,也曾经发生在1810~1830年。

1736-2010年华南前汛期始日变化

根据清代华南雨雪分寸记载的内容、特点，参照华南地区前汛期降水特征，提出了利用雨雪分寸记载重建华南前汛期开始时间的方法，重建了1736—1911年福州与广州前汛期开始日期变化序列；并利用福州与广州（分别始于1953和1952年）逐日降水观测记录辨识了器测时期两地前汛期的逐年开始时间；据此分析了过去300年华南前汛期开始日期的年．年代际变化特征。结果表明：1736—2010年间，福州、广州两地前汛期开始时间平均为5月第1候；但存在显著的年际和年代际波动，其中重建时段（1736-1911年）的主周期为2～3年、准10年和准40年，器测时段的主周期为2～3年、准10年和准22年。在年际尺度，重建时段福州和广州前汛期开始时间最早的年份均为4月第4候，最晚的年份则分别为5月第6候和6月第1候；而器测时段两地前汛期开始时间的最早年、最晚年均为4月第4候和6月第1候。在年代际尺度，重建时段福州和广州相邻年代最大变幅分别为2．2候和1．6候；器测时段福州和广州相邻年代最大变幅则分别为2．5候和2．4候。