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Significant changes in subseries means and variances in an 8000-year precipitation reconstruction from tree rings in the southwestern USA

Abstract. Both algorithms were applied to an 8000-year long time series of annual precipitation that was reconstructed from tree rings in the southwestern USA. One of the algorithms is the scanning t-test, which detects significant changes in subseries means (the first center moments) on various time scales. Another is the scanning F-test, which detects significant changes in subseries variances (the second center moments) on multi-time scales. Firstly, the scanning t-test identified 22 change points in subseries means and partitioned the series into 23 relatively wet, normal or dry episodes. Secondly, the scanning F-test detected 15 change points in subseries variances and divided 16 phases in comparatively steady (with smaller variance) or unsteady (with larger variance) features. Thirdly, the 23 wetness-episodes were characterized as the steady or unsteady situations by jointing the results from the scanning F-test into those from the t-test. Fourthly, the 23 episodes were compared to those in the TIC and δ18O records from cored sediments in the deep basin of the Pyramid Lake in Nevada by using a coherency analysis of the t-test between the precipitation reconstruction and the TIC or δ18O series. Fifthly, the 23 episodes were collaborated with some published papers in related studies. In addition, the 23 episodes were also compared with studies of the global climate change and with documents of climate changes in China during the same periods. As the TIC and δ18O record series are high resolution with unequal sampling intervals between 3 and 14 years, an algorithm in the scanning t-test for dealing with the unequal time intervals was developed in this study.