摘要
本文通过用树木年轮资料重建的祁连山地区５～７月份１３１０年以来的湿润指数序列，建立了一个反映该地区湿润指数年际变幅序列，对这两个序列分别进行了等级分类和干湿、强弱的时段分析，并用最大熵谱分析法对这两个序列的不同时段分别进行了周期分析。采用ＨＫ突变检验方法对这两个序列分别进行了突变分析，发现祁连山地区的湿润指数及其年际变幅存在明显的突变年份。
The moisture index(May to July) time series M(i), since 1310 A.D., were obtained from tree-ring chronologies in Qilianshan Mountains (38°51′N, 100°08′E, 3 500m).In order to study the annual moisture indexs variability, of the another time series MV(i) was obtained from the following equation MV(i) = |M(i) -M(i-1)|where M(i) is the i year moisture index. Time series M(i) and MV(i) were classified into five grades, according to the departure of the period average from the mean. The mean of the time series M(i) is 20.75. The period of normal dryness and wetness is defined when the departure of the index is between ±10.5, the medium wet period; when the departure is between 0.5 and 1, the wet period, when the departure is over 1, the medium drought period; when the departure is between -0.5 and -1 and the drought period; when the departure is below-1. As a result, the drought periods extend from 1331 to 1344, from 1404 to 1423, from 1672 to 1681, from 1710 to 1727 and from 1923 to 1941. The medium drought periods extend from 1533 to 1570,from 1588 to 1605, from 1634 to 1653, from 1763 to 1776 and from 1816 to 1831. The wet periods extend from 1345 to 1361, from 1513 to 1532, from 1571 to 1587 and from 1942 to 1959. The medium wet periods extend from 1310 to 1330, from 1391 to 1403, from 1424 to 1461, from 1654 to 1671, from 1728 to 1762, from 1777 to 1783, from 1832 to 1851 and from 1896 to 1922. The periods of normal dryness and wetness extend from 1362 to 1390, from 1462 to 1512, from 1606 to 1633, from 1682 to 1709, from 1784 to 1815, from 1852 to 1895 and from 1960 to 1991. The mean of the time series MV(i) is 2.35. The period of normal annual moistUre index variability is defined when the departure of the index is between ±0.6, the period of medium high annual moisture index variability; when the departure is between 0.6 and 1.2, the period of high annual moisture index variability; when the departure is over 1.2, the period of medium low annual moisture index variability; when the departure is between-0.6 and -1.2, the period of low annual moisture index variability; when the departure is below -1.2. As a result, the periods of high annual moisture index variability extend from 1311 to 1331, from 1395 to 1414, from 1431 to 1510, from 1539 to 1552, from 1722 to 1731 and from 1923 to 1938. The period of medium high annual moisture index variability extends from 1954 to 1982. The periods of low annual moisture index variability extend from 1903 to 1922 and from 1983 to 1991. The period of medium low annual moisture index variability extend from 1363 to 1394, from 1553 to 1576, from 1592 to 1610, from 1640 to 1671, from 1690 to 1699, from 1732 to 1764, from 1778 to 1822 and from 1841 to 1860. The periods of normal annual moisture index variability extend from 1332 to 1362, from 1415 to 1430, from 1511 to 1538, from 1577 to 1591, from 1611 to 1639, from 1672 to 1689, from 1700 to 1721, from 1765 to 1777, from 1823 to 1840, from 1861 to 1889, from 1890 to 1902 and from 1939 to 1953. The periodicity of different time periods for those two time series M(i) and MV (i) was analyzed using maximum entropy spectrum. The results indicate that there are significant periodic climatic variations in the Qilianshan area, but the periodic variation changes during different time periods. Discontinuous changes of the time series M(i) and MV(i) are detected by the lepage test. The result show that there are notable moisture index shifts over the past 680 years(see table 5). The results also show that there are notable annualy moisture index variability shifts during the last 680 years (see table 6).
出处
《第四纪研究》
CAS
CSCD
1996年第4期368-378,共11页
Quaternary Sciences
基金
国家科委基金
关键词
湿润指数
年际变化
气候变化
祁连山地区
moisture index
annual moisture index variability
rapid climate shifts
