扫描式t检验的新应用:对美国西部近8000年干湿期的划分

A NEW APPLICATION OF SCANNING t-TEST:PARTITION OF DRY/WET EPISODES IN THE WESTERN USA

文章应用扫描式t检验算法,对美国西部近8000年来树木年轮重建的内华达州(Nevada)第3气候区年度降水量序列,进行了多尺度突变现象的检测。由检测得到22个突变点,将该序列划分为23个相对干、湿的气候时段。经过对取自内华达州Pyramid湖底沉积物中的TIC和δ18O记录,与该降水量重建序列之间作突变相干性的分析,以及引用已发表的相关研究文献进行验证,每个时段都能够得到或多或少的旁证。同时还与全球气候变化及中国的气候变化进行了比较。由此考验了扫描式t检验及其相干性分析算法的实用性,同时也表明该降水量重建序列,对于研究美国西部百年际尺度上的气候变化具有相当好的参考价值。由于TIC和δ18O记录是每隔3年至14年不等时间间隔上取样读数的,相应地开发了针对不等时间间隔取样序列的扫描式t检验及其相干性分析算法。

changes in an 8000-year time series of precipitation reconstruction in the southwestern USA were detected with the algorithm of scanning t test,which detects multi-scale abrupt changes in the level of sub-series. The time series is a raw reconstruction without filtering, and was reconstructed from tree-rings for annual （from prior July to current June） precipitation （ in cm） for Nevada Climate Division 3 for total 7997 years from 6000BC to 1996A. D. 285 tree-ring samples with an average length of 748 years were collected from a number of sites scattered over eight states of the southwestern USA. There are at least 10 tree ring series at each year giving a rough chronological accuracy of a year or two for more than 1000 years. All samples were standardized with either a negative exponential or straight line of zero or negative slope to remove growth trend of the tree, and are nearly in the normal distribution. The scanning t test detected 22 change points in the precipitation reconstruction series, and 23 episodes of relatively wet, dry or normal wetness were partitioned and were classified into 5 grades according to average levels of reconstructed precipitation value. All 23 episodes were collaborated first by the coherency analyses of abrupt changes, which are based on the scanning t test, between the precipitation reconstruction series and the TIC/δ^18O records from cored sediments of Pyramid Lake in Nevada, then by comparisons with published results of related studies. Meanwhile, the episodes were also compared with the global climate changes and with the climate changes in China during the same period. It is found that the warm and dry episodes in the western USA coincide usually with the global warm phases, while the cold and wet spells in the western USA associate often with the global cold epochs. Comparison to the climate changes in China, however, is complicated. The results suggest that this precipitation reconstruction is quite valuable in researches of the climate changes on multi-centurial time-scales in the southwestern USA for the last 8000 years; and that the algorithm of scanning t test and coherency detection has a wide practicality for detection of multi-scale abrupt changes in a long time series and coherency of abrupt changes between two series. TIC and δ^18O records have shown series with in-equable intervals between 3 and 14 years, a special computing program of the scanning t test has been thus developed for the study of the series with in-equable intervals.