利用伊犁两个采样点的雪岭云杉树轮样本,采用X-Ray树轮密度分析方法,提取出7种树轮宽度和密度参数,建立了7种树轮参数的年表,并以其为基础进行气候序列的重建。通过相关分析发现1~8月的帕尔默干旱指数(PDSI)与树轮晚材宽度年表具有良好的相关性,相关系数达到0.66(建模期,1970-2005年)。利用树轮晚材宽度年表重建了过去354年来1~8月平均PDSI指数的变化,方差解释量高达48.6%(全时段,1940-2005年),且方程稳定。重建的1~8月PDSI指数序列与中亚广大地区PDSI指数的变化趋势比较一致,具有很强的空间代表性,而且西风环流对这一地区的干湿变化有重要影响。重建序列经历了6个偏湿阶段和5个偏干阶段。利用多窗谱分析,发现重建的伊犁地区PDSI指数序列具有64年(99%)、10年(95%)、8.3年(99%)、6.2年(95%)、4.3年(95%)、3.3年(95%)和2.1年(95%)的准周期变化。
Seven different tree-ring parameters were obtained from Picea schrenkianas using X-ray densitometric techniques at two chronology sites in Yili.Climate correlation analysis indicates that there is significantly positive correlation between PDSI(January~August) and latewood width(r=0.66,1970-2005).The latewood-width chronology was used to reconstruct January~August PDSI for the period of 1652-2005,and it explained the 48.6% of the total PDSI variance during their common period(1940-2005).Six wet periods and five dry periods were identified using the reconstructed PDSI series.Spatial analysis shows that the PDSI in Yili has strong common signals for central Asia.The results reveal that the six dry and five wet period changes of Yili was affected by the westerly circulation.Using the multi-taper method(MTM) spectrum analysis,it is found that the reconstructed PDSI is of 64 a(99%),10 a(95%),8.3 a(99%),6.2 a(95%),4.3 a(95%),3.3 a(95%) and 2.1 a(95%)cycles,which may potentially be the fingerprints of some proposed climate change forcings.