中国陕西关中及周边地区近500年来初夏干燥指数序列的重建

本文采用华山东峰、西峰和南峰的华山松树轮宽度差值年表重建了1500年以来中国陕西关中及周边地区的初夏干燥指数序列,对重建序列进行了统计特征分析,并同大尺度大气环流场进行了相关分析。结果表明:华山年表的变化与该地区初夏平均干燥指数序列的变化具有很好的一致性,可用来重建该地区的初夏干燥指数序列;该地区在1502～1511年、1570～1580年以及1807～1814年间的初夏季节存在3次较为严重的干旱;该地区初夏干燥指数变化存在着较为明显的周期特征,其中以13a左右和4a左右的周期最为显著,但周期特征在不同的历史阶段存在着明显的差异;重建序列在1784年前后发生了一次较大幅度的方差变化,而1587年前后的均值突变则表现为干燥指数值的急剧降低;该地区初夏季节的干燥程度可能与前期极涡的中心强度及冷空气活动有关。

RECONSTRUCTION OF EARLY-SUMMER DROUGHT INDICES IN MID-NORTH REGION OF CHINA AFTER 1500 USING TREE RING CHRONOLOGIES

The climatic condition of the mid north region of China is semi arid and trees grow in this region are sensitive to the temperature of late spring and the precipitation of early summer. The early summer drought indices are calculated based on the precipitation and temperature in May and June and well represented the climatic condition of the key period for tree′s growth.In this study we used three ring width chronologies of Huashan Pine sampled in west, east and south peaks of Huashan Mts. to reconstruct the early summer drought indices series in mid north region of China from 1500 to 1992.The early summer drought indices have a higher correlation coefficient in a wide region of Guanzhong Plain of Shaanxi Province and the highest value of correlation coefficient is 0.96. The reconstructed series were analyzed with statistical methods and further correlated with the large scale atmospheric circulation. The chronologies of Huashan Pine were well consistent with the early summer drought indices in the last several decades and can be used in the indices reconstruction. The fluctuation of the early summer drought indices was significant during 1500 and 1600 as well as after 1800. The fluctuation of the drought indices was out obvious for the period from 1700 to 1800. Three severe drying periods are found in this region in the past 500 years, which are 1502 to 1511, 1570 to 1580 and 1807 to 1814. Thirteen years and four years period cycles are found significant in the reconstructed series, but the periodic statistical characteristics are different among each time periods. The wavelet analysis was used to analyze the structure of period cycles of the reconstructed summer drought indices series. The abrupt change of average value in 1587 and the abrupt change of standard deviation in 1944 were found in the reconstructed series.The drought indices in May and June have a high correlation coefficient with the strength of polar eddy in North Hemisphere a few months before. A stronger polar eddy indicated a more arid climatic condition of the mid north region of China.