Coupling between density structures, electromagnetic waves and ionospheric feedback in the auroral zone

Abstract

[1] This paper presents results from a numerical study of nonlinear interactions between ultra-low-frequency (ULF) electromagnetic waves and the magnetospheric-ionospheric plasma at high latitudes. The study is motivated by observations of density cavities in the ionosphere in regions of downward field-aligned current adjacent to auroral arcs. The role of active ionospheric feedback in the development of intense, small-scale electromagnetic waves with frequencies of 0.1-1 Hz is considered, together with the effects of the waves on the ion dynamics. The numerical results are based on a reduced two-fluid MHD model that self-consistently describes shear Alfvén waves, ion parallel dynamics, and effects of ionospheric E-region activity and magnetosphere-ionosphere feedback instability. Numerical simulations performed in dipole magnetic field geometry with realistic parameters of the ambient plasma show that, under some conditions, ionospheric feedback gives rise to intense ULF electromagnetic waves, which, via the ponderomotive force, produce density cavities in the bottomside ionosphere (between the E-and F-region peaks) and an associated upwelling of the topside ionosphere. The simulated magnitude and spatial and temporal scales of the cavities match the corresponding parameters of cavities observed with ground-based radars.Citation: Streltsov, A. V., and W. Lotko (2008), Coupling between density structures, electromagnetic waves and ionospheric feedback in the auroral zone,

Development of parallel electric fields at the plasma sheet boundary layer

“…Such nonlinear motions can be excited by the Kelvin-Helmholtz instability giving rise to auroral curls [Hallinan and Davis, 1970]. Furthermore, ionospheric feedback instability [Atkinson, 1970;Holzer and Sato, 1973;Sato, 1978;Lysak, 1991;Streltsov and Lotko, 2008] can generate small-scale Alfvén waves due to the interaction with the ionosphere. While these processes are likely to operate and contribute to the structure in the aurora, the phase mixing process has the advantage that it is linear, so that it will operate even if the perturbations are not large, and it is also not affected by a low ionospheric conductivity, which is favored for ionospheric feedback.…”

Simulation of O+ upflows created by electron precipitation and Alfvén waves in the ionosphere

“…In a simulation where the ionosphere is driven by an Alfvén wave with a period of 1 s, an eigenmode of the resonator is excited and ion upflow is driven by the ponderomotive (time-averaged nonlinear Lorentz) force similar to Streltsov and Lotko [2008] as well as by the centrifugal acceleration similar to Cladis [1986]. Note that unlike Streltsov and Lotko [2008], the present model does not use height-integrated conductivity and resolves the full dynamics of the E-layer plasma.…”

“…[39] The ponderomotive effect in IAR was considered previously by Streltsov and Lotko [2008] and Sydorenko et al [2008]. Figure 5 of Streltsov and Lotko [2008] shows modification of ion density by the ponderomotive force.…”

“…Figure 5 of Streltsov and Lotko [2008] shows modification of ion density by the ponderomotive force. Although there is no vertical ion flow velocity data, the increase of the density near the low-altitude boundary suggests that the ion flow is directed downward near this boundary.…”

Use of the International Reference Ionosphere 2012 model to calculate emission frequency scale of the ionospheric Alfvén resonator

“…To formulate the boundary conditions at the lower boundary of the cavity, at first only Pedersen conductivity was involved, and then the Hall conductivity (Lysak & Yoshikawa 2006). Streltsov & Lotko (2008) included coupling to the slow mode in the basic model; Lysak et al (2013) and Waters et al (2013) included the coupling to the fast mode. Pokhotelov et al (2000) found frequency dispersion of the IAR eigenmode due to the Hall conductivity.…”