关键词: 西安, 汉中, 降雪日数, 年冬季平均气温序列

Abstract:

Based on the relationship between annual winter mean temperature and snowfall days which was established according to the meteorological observation data in the Xi'an and Hanzhong areas, the snowfall days for Xi'an and Hanzhong areas derived from historical archives in the Qing Dynasty, the annual winter mean temperature in Xi'an and Hanzhong areas from 1736 to 1910 A D. was calculated, and the annual winter mean temperature series since 1736 A D was reconstructed The analysis of series shows that there existed a general consistency change trend for the two areas The climate is relatively warm in the 18th and 20th centuries and cold in the 19th century Warming trend in the 20th century is obvious During the warm period of the 18th century, the mean temperature appeared a short term valley of cold around 1775 In the 19th century, it entered a cold stage that finished in the early 20th century There were 3 valleys during this period, which centered in 1830, 1860 and 1890 respectively Since the early 20th century, the climate entered a warm period again There are 2 obvious warm peaks in the 1930's～1940's and after the 1980's, the latter is not completed yet until now Both of the 20th warming peaks exceed the warm level of the 18th century, and the warming degree of Hanzhong is more obvious Seen overall, the winter mean temperature of Xi'an in the 20th century tends to rise with fluctuation This ascending trend is more obvious since the late 1970's particularly Besides, the period with minimum variance of the series is the 18th century As for the adjacent periods, variance of cold period is obviously higher than that of warm period, which generally consists with the early conclusion that climate has great instability in cold periods and the stages from cold to warm At the same time, the comparison between the annual winter mean temperature series in Xi'an, Hanzhong and the annual early spring (from March to April) temperature series in Zhen'an reconstructed by tree ring data was analyzed The result shows that low frequency change trend of annual winter mean temperature in Xi'an, Hanzhong and early spring temperature in Zhen'an are generally consistent, but the turning points in Zhen'an are earlier than that of Xi'an and Hanzhong

Key words: Xi’an, Hanzhong, snowfall days, annual winter mean temperature series