Finite-Size Scaling of Spatiotemporal Auroral Emissions as a Signature of Reconnection Dynamics in the Plasma Sheet

Through analyses of bright night-side auroral emissions as observed by the UVI experiment on the Polar spacecraft, we have earlier presented evidence for critical dynamics in Earth's magnetotail: (1) Distributions of emission region size, strength, and duration are scale-free over broad ranges of scales. (2) Emission region dynamic growth and survival statistics exhibit power-law evolution in superposed epoch time. (3) Expected scaling relationships between the power-law exponents of items 1 and 2 are satisfied. Given the variability of the solar wind driver, we have further suggested that criticality in the magnetotail dynamics is self organized. To this list of evidence for possibly self-organized critical dynamics in Earth's magnetotail, we add another item that is considered essential in studies of self-organized criticality in numerical avalanching models. We present the results of a finite-size scaling analysis of the auroral emission regions. This analysis will be shown to further support the hypothesis of self-organized criticality while, simultaneously, verifying our earlier estimates of the power-law exponents of item 1 above. Avalanching models of self-organized criticality govern the intermittent spatial transport of a quantity from a region of loading to one of unloading. In our search for a region in the magnetosphere that may influence the auroral emissions while it may also be characterized as a region of scale-free avalanching, we have focused on the plasma sheet. We interpret the results of the auroral emissions analyses in terms of the dynamics of reconnection in the turbulent plasma sheet. We suggest that the transport of magnetic flux/energy through the magnetotail is carried by scale-free avalanches of localized reconnection. We further suggest that this is the true nature of the largest of these avalanches, substorms.