样条函数步长变化对树轮宽度年表与气候相关性的影响初探

利用天山中部北坡头屯河及三屯河流域4个天山云杉采点的树轮样本,研制样条函数不同步长的树轮宽度标准化年表,分析样条函数不同步长对树轮宽度标准化年表与气候的相关性的影响发现:①随着样条函数步长的增加,位于森林中下部林缘的庙尔沟煤矿和三屯河的树轮宽度标准化年表与小渠子气象站上年7月至当年6月的降水量的相关系数曲线均呈现出先增后减小的变化形式,但在局部有差异,最佳步长分别为40 a和30 a。②随着样条函数步长的增加,处于森林上限的东南沟和小渠子的树轮宽度标准化年表与大西沟气象站当年2-3月的月平均气温的相关系数的曲线都呈现光滑的先升后平的对数曲线型,最终确定220 a、185 a分别作为东南沟和小渠子树轮宽度标准化年表的样条函数步长。③通过分析发现最佳的样条函数步长比传统方法给定的样条函数步长和按树轮宽度序列公共区间长度的1/2的样条函数步长所含的气候信息多。

Effect of Spline Function Step Size on Relationship between Tree-ring Width Chronology and Climate

Tree-ring samples collected from four sites in Toutun River and Santun River basins on the north slope of middle Tianshan Mountains were used to develop tree-ring width chronologies at different spline function step size.Analysis on the effect of different spline function step size on correlation between tree-ring width chronology and climate showed:(1)With increase of spline function step size,the curves of correlation coefficient between two tree-ring width chronologies at low forest limit and precipitation during prior July to current June of a related meteorological station all showed changes of increase in former part and decline in posterior part,but with local differences.The best step sizes were 40 years and 30 years,respectively.(2)With increase of spline function step size,the curves of correlation coefficient between two tree-ring width chronologies at up forest limit and temperature during current February to March of a related meteorological station all showed a smooth logarithmic form with increase in former part and no change in latter part.The best step sizes were 220 years and 185 years,respectively.(3)It was found that the best step size of spline function conserved more information than the ones which were given on base of traditional method or half of length of public tree-ring chronology series.