A coupled map as a model of the dynamics of the magnetotail current sheet

Abstract

A magnetic field model of the magnetotail current sheet in the form of a coupled-map lattice (CML) is presented. It is continuously driven (“running”) and based on the MHD diffusion equation. Solar wind vB S data (solar wind speed multiplied by the southward component of IMF) are used for driving the model, and it is shown to exhibit perturbations (avalanches) with power-law scalings in their distributions of duration and size. Such distributions may indicate self-organized critical (SOC) behavior. Furthermore, it is shown that the power spectra of the model outputs are of bicolor power-law form with different slopes for high and low frequencies. Although the “running” model gives power-law distributions independent of the strength of the driver, it is argued that the model is in SOC state only when driven slowly. When the driver is strong the model acts more like an input–output system, and the power laws are possibly due to the statistics of the driver. This is supported by the fact that durations of southward turnings of IMF have also a power-law distribution. It is also shown that by driving the model very strongly we can reproduce AE data with correlation 0.74 by using large resistivity, and Dst with correlation 0.79 by using small resistivity.