1961—2005年黄土高原地区积温演变

Evolvement of the Cumulative Temperatures in China Loess Plateau

为揭示黄土高原积温区域变化特征,采用EOFS、小波分析和分形分维分析等方法,研究了该区域在近45 a的年正负积温变化.结果表明:黄土高原正负积温变化的区域一致性程度较高;负积温存在以3-4 a为主的年际振荡,正积温存在以2-4 a为主的年际振荡;负积温在1982年左右发生突变,年总量呈明显减少,3 a周期加强;正积温在1985/1986年突变后呈明显增加趋势,2 a周期消逝,4 a周期衰减,3 a周期突出.积温大振幅区集中在黄土高原腹地,变化信息由高原中部向周边传播;负积温分维数大于正积温,负积温变化全程复杂于正积温,这可能与冬夏季大气环流活跃程度和冷暖空气在近地面运动受大地形影响有关.

The China Loess Plateau, about 517 000 km^2 in area, is a climatic transition zone from hemi --wetness to hemi-dryness, which is a very sensitive and vulnerable region. By applying empirical orthogonal function （EOF）, expanded empirical orthogonal function （EEOF）, complex empirical orthogonal function （CEOF）, Fractal Dimension and wavelet analysis, the weather data of the plateau from 1961 to 2005 are analyzed in detail, in order to make clear the climatic characteristics of the region, especially, the spatial and temporal variations of cumulative temperatures on the plateau. It is revealed that the cumulative temperatures have good response to climate changes. The cumulative negative temperature had two remarkable phases divided by 1982 and also the cumulative positive temperature had two remarkable phase divided by 1985/1986. By wavelet analysis, 3-4 a, 7 a and 10-14 a periods are identified in the cumulative negative temperature, and the 3-4 a period was principal. 2-4 a, 6 a and 10 a periods are identified in the cumulative positive temperature and the 2 - 4 a period was principal. In the cumulative positive one, after 1985/1986, the 2 a period disappeared, the 4 a period became indistinct, and the 3 a period became distinct. The variation is pronounced in the center plateau. The variation amplitude and the variation signal of the cumulative temperatures decline from the center to the margin of the plateau. The Fractal Dimension of cumulative negative temperature was 0. 436 and that of the cumulative positive one was 0. 353. The Maximum Fractal Dimension was in the cumulative negative temperature of the China Loess Plateau, of which the reason is that the cumulative negative temperature is more complicated than the cumulative positive temperature in the plateau. It might have something to do with atmosphere circumfluence in summer/winter and the activity of cold or warm air mass.