Electromagnetic waves generated by ionospheric feedback instability

Abstract

[1] A new interactive M-I coupling model that describes the dynamic interaction between magnetospheric dispersive waves, compressional modes, and auroral electron precipitations is applied to investigate the geomagnetic electromagnetic pulsations observed in Earth's magnetosphere in terms of magnetospheric waves triggered by ionospheric feedback instability. Two new aspects of this work are that (1) we treat the full nonlinear MHD equations, i.e., include the full compressional modes and their coupling with shear Alfvén waves in the magnetosphere; and (2) the height-integrated Pedersen conductivity is treated as a dynamic parameter by electrodynamically coupling the 2D finite element wave model ''TOPO'' to the ionospheric ionization model ''GLOW''. It is shown that the feedback instability can be triggered by a very small-scale, small amplitude density perturbation; and the small-scale electromagnetic oscillations and their associated density fluctuations observed in magnetosphere can be attributed to the feedback instability. We demonstrate that, unlike in a field line resonance where the ponderomotive force causes the plasma to move mainly along the field line, the plasma in the feedback instability is distributed either as a bump or a cavity along a field line and leads to a multibanded structure in the radial direction. The nonlinear feedback instability model can successfully explain the formation of plasma density and electromagnetic perturbations with the same frequency, which disagree with current FLR scenario.

Alfvén wave‐driven ionospheric mass outflow and electron precipitation during storms

“…As these waves propagate inward they are subject to the action of phase mixing [Heyvaerts and Priest, 1983;Allan and Wright, 2000;Lysak and Song, 2008;Mottez and Génot, 2011] and a variety of instabilities [Wu and Seyler, 2003], which drive a cascade toward smaller scales. Upon reaching the ionosphere further structuring may occur through the action of ionospheric feedback associated with wave reflection [Lysak, 1991;Streltsov and Lotko, 2005;Lu et al, 2008;Russell et al, 2013] and nonlinear interactions between counterpropagating Alfvén wave packets [Song and Lysak, 1994]. If kinetic scales are reached these waves will drive particle acceleration and be dissipated [Chen, 1999].…”

A unified model of auroral arc growth and electron acceleration in the magnetosphere‐ionosphere coupling

“…A feedback instability in the M‐I coupling has been proposed as a mechanism of quiet auroral arc growth [ Atkinson , ; Sato , ]. Since then, a variety of extensions to the original works have been made by including global profiles of the ionospheric density and currents [ Miura and Sato , ], a three‐dimensional magnetohydrodynamic (MHD) model for the magnetosphere [ Watanabe and Sato , ; Watanabe et al , ], the ionospheric density cavity [ Lysak , ; Pokhotelov et al , , ], two‐fluid effects of the magnetospheric plasma [ Streltsov and Lotko , , , ], the E × B drift nonlinearity [ Watanabe , ], a realistic Alfvén velocity profile along a field line [ Hiraki and Watanabe , , ], and the dipole geometry [ Lu et al , , ]. All these models are, however, based on fluid descriptions of the magnetospheric plasma and insufficient to deal with auroral particle acceleration.…”

Cross-scale coupling in the auroral acceleration region

“…The structuring of auroral arcs is generally attributed to either ionospheric feedback, phase mixing, plasma instabilities or a combination of these. Recently significant effort has been devoted to advancing understanding of the role of ionospheric feedback in the structuring of auroral currents [ Lysak and Song , 2002; Streltsov and Lotko , 2004, 2008; Lu et al , 2008; Russell et al , 2010]. In this process electron precipitation and current closure through the ionosphere drive enhanced ionization and depletion of current carriers in regions of upward and downward current respectively.…”