华北旱涝变化的混沌性质分析

SOME CHAOTIC FEATURES OF THE WET/DRY FLUCTUATIONS IN NORTH CHINA

利用华北海河流域近７００多年的旱涝等级序列，从功率谱特点、吸引子分数维和可预报时间等方面分析了历史旱涝变化的混沌性质。由专门设计的误差控制计算方案得到的旱涝变化分数维大于４。只有经过大平滑处理，旱涝序列的分数维才能显著地降至３．５。通过分析系统的局部Ｋｏｌｍｏｇｏｒｏｖ熵，发现偏早态和偏涝态的可预报时间基本相同，即约４ａ。但经平滑处理后偏涝态的可预报性改善较多，说明从较长时间尺度看，干旱期的旱涝预报比之湿润期要更困难些。

ased on the historical wet/dry grade series of North China, back to 1261 AD, some nonlinear features of the regional wet/dry fluctuations are analyzed. The spectral structure of the wet/dry system is quite similar to that of the chaotic model such as the Lorenz' s. A special error-controlled method is designed to calculate the attractor' s dimension, which is then estimated as a fractal one larger than 4. The smoothed series that mainly represents the 102-year-scale fluctuations tends to have a smaller dimension about 3. 5. The local Kolmogorov entropy is analyzed and a 4-year-predictable time is estimated for the wet/dry fluctuations. The K-entropy of the smoothed series is small, but that for those 'drier' phasepoints seems much smaller. This implies that at the long time-scale, the climate prediction in the drier period is more difficult than that in the wetter one.