Toward a Synthesis of Auroral Index Scaling Measurements

One route for study of magnetospheric energy release has been provided by scaling analysis of the Auroral Electrojet indices (AE, AU, AL). The scale invariance of aspects of the AE index family was one-but not the sole-motivation to suggest self-organised critical ``avalanche'' scenarios of the magnetosphere. In that of Chapman et al. [1998] the appearance of a characteristic scale in otherwise scale-free magnetospheric signals was identified with the properties of ``systemwide'' avalanches. It has long been recognised that the indices show a two-component nature, originally hypothesised to reflect solar wind-driven (DP2) and intrinsic (DP1) components in the ionospheric convection currents. Following the first avalanche scenarios, debate was sparked by one of the alternative possibilities, that the scale-invariant nature of the indices was due to Kolmogorov or Kraichnan scaling in solar wind MHD turbulence. We will present an up-to date review of subsequent work on scaling by the Warwick and BAS groups. We will also discuss the inter-relationships of our results with those of other workers.