Formation and disruption of current filaments in a flow-driven turbulent magnetosphere

Abstract

Recent observations have established that the magnetosphere is a system of natural complexity. The co-existence of multi-scale structures such as auroral arcs, turbulent convective flows, and scale-free distributions of energy perturbations has lacked a unified explanation, although there is strong reason to believe that they all stem from a common base of physics. In this paper we show that a slow but turbulent convection leads to the formation of multi-scale current filaments reminiscent of auroral arcs. The process involves an interplay between random shuffling of field lines and dissipation of magnetic energy on sub-MHD scales. As the filament system reaches a critical level of complexity, local current disruption can trigger avalanches of energy release of varying sizes, leading to scale-free distributions over energy perturbation, power, and event duration. A long-term memory effect is observed whereby the filament system replicates itself after each avalanche. The results support the view that that the classical and inverse cascades operate simultaneously in the magnetosphere. In the former, the high Reynolds-number plasma flow disintegrate into turbulence through successive breakdowns; in the latter, the interactions of small-scale flow eddies with the magnetic field can self-organize into elongated current filaments and large-scale energy avalanches mimicking the substorm.