中国黄土高原地区春寒时空演变

利用1961～2000年春季日均气温资料,采用EOFs、小波分析和分维分析等方法,研究了该区域春季春寒变化.结果表明,黄土高原地区春寒强度大致由北向南递减,又存在东西梯度.春寒强度线性递减率高原中部大于周边,3月、4月变化的线性趋势显著,分别以0.3 ℃/10 a、1.7 ℃/10 a速度减少.春寒强度变化呈现较高的全区一致,高原大部分春寒强度明显减弱,高原腹地易出现强春寒.春寒强度变化存在周期振荡,3月以2～4 a周期为主,4月以3～4 a为主,5月存在2～4 a和6 a左右周期;1990s春寒强度最弱,最强时段在3、4、5各月分布不同;4月春寒强度演变在1980年附近发生了转折,下降明显.分数维D由3月到5月逐渐增大,春寒强度变化复杂程度提高.春寒空间演变中大振幅区在高原腹地,振幅向四周衰减;变化信息,在西部存在东流的趋势,在高原东部存在回流趋势.

The Evolvement of Spring Cold Weather Intensity in Chinese Loess Plateau

Based on the mean daily temperature data in spring from 1961 to 2000,using empirical orthogonal function(EOF) and complex empirical orthogonal function(CEOF),fractal dimension,and wavelet analysis methods,the spatial and temporal evolvement of spring cold weather intensity in Chinese loess plateau was analyzed in this paper.Results show that the spring cold weather intensity decreased approximately from north to south,and also there was a gradient from east to west;the linear decreasing rate of the spring cold weather intensity in the middle of the plateau was bigger than that in the peripheral,and the changing tendency was remarkable in March and April;there was periodic oscillation of the spring cold weather intensity change,which were about 2~4 a in March,3~4 a in April,2~4 a and 6 a in May,respectively.The spring cold weather intensity was weakest in 1990s.The strongest period of spring cold weather in March,April and May,and the distribution was different in each month.The spring cold weather intensity change in April had a transition in 1980,and then it decreased obviously.The fractal dimension increased gradually from March to May,the changing complex degree of the spring cold weather intensity increased at the same time.The big amplitude area of spring cold weather was in the center of the plateau.The change information flew to east in the west and southwest in the east of the plateau.