贺兰山过去196年降水的树轮宽度重建及降水变率

贺兰山属于中国北方的半干旱地区,位于东亚夏季风的西北缘。应用贺兰山南段、中段和北段的3组树轮宽度差值年表合成贺兰山树轮宽度年表,应用邻近采样点的贺兰山东坡、山顶和西坡的气象站资料合成贺兰山气象数据。通过贺兰山树轮宽度年表和贺兰山气象数据的线性回归分析,重建了1802—1997年2—7月降水标准化序列,重建方程的方差解释量是46%。计算重建序列的11年滑动平均标准差后,发现存在着3次标准差的突然变化:1908年标准差由前年的0.38增加到当年的0.56,1942年标准差由两年前的0.57增加到当年的0.70,1956年标准差由前年的0.74降低到当年的0.63。小波分析表明,1908年到1949年之间存在显著的11年准周期,1942年出现2年准周期,该2年准周期到1959年彻底消失。1965—1997年,存在由8年向3年过渡的准周期。11年周期对应着太阳活动周期,2年周期对应“准两年脉动”,8年到3年周期与ENSO周期比较一致。故此认为,当太阳活动、“准两年脉动”或ENSO活动增强时,贺兰山地区降水变率一般比较大,年际间降水变得不稳定。

A 196-YEAR PRECIPITATION RECONSTRUCTION BASED ON TREE-RING WIDTH IN THE HELAN MOUNTAINS OF NORTH CHINA AND THE PRECIPITATION VARIABILITY

The investigated site in the Helan Mountains,is located on northwest margin of East Asian Summer Monsoon circulation,a semiarid region in North China.Three sets of tree-ring width residual chronology are used in this study,which were built using samples collected in south,middle and north of the mountains respectively.These three chronologic data were combined to form Helan chronology.In addition,meteorological data of three stations close to sampling sites were used,respectively in the east slope,on the top,and in the west slope of the mountains.The normalized data from these three meteorological stations were averaged to represent climatic situation of the Helan Mountains.Through linear regression analysis between the Helan chronology and the Helan meteorological data,the normalized precipitation of February-July from 1802 to 1997 was reconstructed and the explained variance was 46%.After 11-a moving standard deviation was calculated on the reconstructed precipitation series,three abrupt changes of standard deviation were found:one took place in 1908,increasing from 0.38 of the previous year to 0.56;the second was in 1942,increasing from 0.57 two years before to 0.70;and the third was in 1956,decreasing from 0.74 of the previous year to 0.63.Wavelet analysis showed that a dominant 11-a quasi-period occurred during 1908-1949,and that a 2-a quasi-period began to predominate in 1942,and then the 2-a quasi-period disappeared completely in 1959.There were significant 8-a transiting to 3-a periods from 1965 to 1997.The 11-a period probably corresponds to the sunspot activity and the 2-a period may correspond to "Quasi-biennial Oscillation".8-to 3-a periods are similar to El Nio/Southern Oscillation periods.Thus,the precipitation variability might be high and the yearly precipitation became unstable in the Helan Mountains when the sunspot activity,Quasi-biennial Oscillation,or El Nio/La Nia activity were strengthened.