Role of stochastic fluctuations in the magnetosphere-ionosphere system: A stochastic model for the AE index variations

摘要

A new stochastic model for the AE index variations is developed to investigate the role of stochastic fluctuations in the magnetosphere-ionosphere system. In contrast to pioneering stochastic models by Hnat et al. (2003, 2005), here the model is set up for the actual integrated quantity, i.e., AE index itself, instead of differenced variables, i.e., AE(t + Δt) ? AE(t) and because of the different approach used in the derivation of the model, we do not restrict our model parameters to the power law behavior only. Also, we integrate the model to obtain a time series to which the observed AE is then compared to. The model suggests that the fluctuations are of internal magnetospheric origin, though the bursts can be triggered by an external perturbation, and are an interplay of deterministic and stochastic components of a stationary out-of-equilibrium system. The fundamental result of the study is that stochastic fluctuations play a central role in the evolution of the AE index and cannot be grossly neglected. Also, in the model, the basic mechanism for all burst sizes is the same and thus no specific “substorm”-related bursts can be extracted from the AE index fluctuations. This suggests that from the global perspective, a specific well-defined “class of substorms” may not exist. On the basis of their assumed spatiotemporal locality, impulsive dissipation events (IDE) (Sergeev et al., 1996) were proposed to be the fundamental physical building block of the AE index fluctuations. The average temporal size of IDEs may explain the 3 mHz break in the power spectra of the time derivative of the AE index reported here.