夏季副热带大气系统的多尺度振荡分析

Analysis on Vacillation Mode in the Subtropical Atmosphere System

应用经验模态分析方法(经验模态分解(EMD)和Hilbert谱),对夏季副热带大气系统在周期态和振荡态下的流函数数值解序列进行本征模态函数(IMF)及其Hilbert谱的分析。结果表明:(1)周期态下的流函数分量时间序列一般由1个IMF构成,而且其周期就是该流函数的周期。对周期性的IMF分量使用Hilbert变换得到的瞬时频率和振幅都不随时间变化。(2)振荡态下的流函数分量时间序列一般由2个以上的IMF构成,其中有的IMF分量具有显著的周期性,相应的瞬时频率和振幅都不随时间变化;有的IMF分量则没有显著的周期性,相应的瞬时频率和振幅有变化,而且随着振荡态复杂程度的增大,瞬时频率和振幅的变化也趋于复杂。(3)瞬时振幅有明确的物理意义,表示IMF振荡的能量;振幅的局部相对大值对应着原序列(IMF)的强振荡,小值则对应着弱的变化。瞬时频率的显著增大,表示原序列有大的变化。

Empirical mode decomposition and Hilbert spectrum method are applied to the summer subtropical atmospheric system. It is analyzed the intrinsic mode functions (IMF) and Hilbert spectrum for the solution series of periodicity and vacillation states. The results show that the periodicity state stream function is usually made up of one main IMF component,and periodicity of this IMF component is as same as original serials. When the periodicity IMF component applied by Hilbert transform,instantaneous frequency and amplitude are not change with time. The vacillation state stream function is usually made up of two or more IMF components,and some of them are significant periodicity,correspondingly instantaneous frequency and amplitude are not change with time,others are not significant periodicity,correspondingly instantaneous frequency and amplitude are change with time,and vacillation complexity are more increasing,instantaneous frequency and amplitude are more complicated. Instantaneous frequency has certain physical meaning,and it express IMF vacillation energy. Local relatively great values of amplitude are corresponding to strong vacillation of origin series (IMF),small values to weak vacillation. Instantaneous frequency increasing significantly express that origin series change greatly.