Comparison of a statistical model for magnetic islands in large current layers with Hall MHD simulations and Cluster FTE observations

Abstract

[1] Magnetic islands have been observed in long current layers for various space plasmas, including the magnetopause and solar corona. In previous work exploring these magnetic islands, a statistical model was developed that described their formation, growth, convection, and coalescence in very large systems, for which simulations prove inadequate. An integro-differential equation was derived for the island distribution function, which characterized islands by the flux they contain ψ and the cross-sectional area they enclose A. The steady-state solution of the evolution equation predicted a distribution of islands. Here, we use a Hall MHD (magnetohydrodynamic) simulation of a very long current sheet with large numbers of magnetic islands to explore their dynamics, specifically their growth via two distinct mechanisms: quasi-steady reconnection and merging. We then use the simulation to validate the statistical model and benchmark its parameters. A database of 1,098 flux transfer events (FTEs) observed by Cluster between 2001 and 2003 is also compared with the model's predictions. In both simulations and observations, island merging plays a significant role. This suggests that the magnetopause is populated by many FTEs too small to be recognized by spacecraft instrumentation.