Terrestrial magnetosphere as a nonlinear resonator

Time domain techniques are used to identify a dynamical model for the evolu tion of the D-st index under the influence of the solar wind. Frequency dom ain analysis of this model is used to study spectral properties of the D-st index dynamics. These properties indicate that the dynamics of the D-st in dex is similar to that of a linear oscillator under the action of an extern al force. This dynamical system should possess two main properties. Firstly the external driving force should be a nonlinear function of the solar win d parameter VBs and secondly the eigen frequency of the oscillator should b e very low in comparison to the temporal characteristics of external force variations. The main process of energy loading in such systems involves non linear coupling between different spectral components of the external force with a transfer of their energy to the main resonant frequency.