Testing the hypothesis of the Earth's magnetosphere behaving like an avalanching system

The global auroral dissipation power as observed by the imager on the Polar spacecraft is used as a proxy for the power dissipation of the Earth's magnetosphere to examine whether or not the magnetosphere is an avalanching system. It is found that the probability density distributions for the area and power of auroral activity sites have a power law component within a finite scale range, suggestive of a scale-free nature in this finite-size system. This property is robust, prevailing with variations in the threshold used to define auroral activity sites and in the strength of the external driver, namely, the solar wind. The statistical characteristics on the temporal evolution of auroral sites are then examined, which leads to a criterion that can be used to predict about 42min in advance the total energy dissipation during the lifetime of an auroral activity site. The scale-free characteristics of auroral activity appears to be an intrinsic feature of the magnetosphere based on a comparison of the probability density distribution in the total auroral brightness power with that of the solar wind power input parameters in the same period as the auroral observations. These results are consistent with the hypothesis of the magnetosphere behaving like an avalanching system