Three‐dimensional nonlinear simulations of the gradient drift instability in the high‐latitude ionosphere

Abstract

Nonlinear three‐dimensional (3‐D) simulations of the gradient drift instability (GDI) are presented for a two‐dimensional equilibrium density gradient representing a polar cap plasma patch. The overall evolution of structuring of the plasma patch is influenced markedly by the effects caused by dynamics parallel to the geomagnetic field. The long wavelengths ( kL n ≤ 1) are strongly stabilized in the 3‐D case, and the nonlinear state is dominated by smaller mesoscales ( kL n » 1) (where k and L n are the mode number and density gradient scale length, respectively). The results provide an interpretation to the observations at the high‐latitude ionosphere indicating a generation of mesoscale irregularities associated with the polar cap patches when the interplanetary magnetic field (IMF) B Z is southward and antisunward convection prevails over the polar cap. The polar cap patches are observed to convect to large distances (∼3000 km) undergoing structuring while maintaining their distinct identity. Thus we suggest here that the inclusion of three‐dimensional effects is key to a successful interpretation of high‐latitude irregularities, as well as a prerequisite for a credible simulation of these processes.