On the field-aligned currents pattern formation in the magnetosphere

Abstract

Assuming an assembly of field-aligned current (FAC) elements, the interaction of FAC elements irrespective from their wave/static nature is examined. Considering that the FAC assembly elements are governed by the Gibbs distribution module Θ we arrive to a macroscopic/fluid description of the FAC systems. Solutions of the derived nonlinear differential equation yield periodic spatial structures of the FAC systems in the magnetosphere. The FAC structures are a consequence of the pattern formation process that appears owing to the FAC intensity increase down the magnetic field lines. It is shown that critical values (threshold values) for an initiation of FAC structure formation exist. A coexistence of large-scale and intermediate-scale FAC structures is possible above threshold values. The threshold values depend on the ambient plasma temperature and the spatial scales of the newly formed FAC structures. Generally, the critical values are easily attainable for low β plasma conditions realizable for the magnetosphere regions just above the ionosphere.