Influence of the finite ionospheric conductivity on dispersive, nonradiative field line resonances

Abstract

Abstract. The in¯uence of the ®nite ionospheric conductivity on the structure of dispersive, nonradiative ®eld line resonances (FLRs) is investigated for the ®rst four odd harmonics. The results are based on a linear, magnetically incompressible, reduced, two-¯uid MHD model. The model includes e ects of ®nite electron inertia (at low altitude) and ®nite electron pressure (at high altitude). The ionosphere is treated as a highintegrated conducting substrate. The results show that even very low ionospheric conductivity (R 2 mho) is not su cient to prevent the formation of a largeamplitude, small-scale, nonradiative FLR for the third and higher harmonics when the background transverse plasma inhomogeneity is strong enough. At the same time, the fundamental FLR is strongly a ected by a state of low conductivity, and when R 2 mho, this resonance forms only small-amplitude, relatively broad electromagnetic disturbance. The di erence in conductivities of northern and southern ionospheres does not produce signi®cant asymmetry in the distribution of electric and magnetic ®elds along the resonant ®eld line. The transverse gradient of the background Alfve n speed plays an important role in structure of the FLR when the ionospheric conductivity is ®nite. In cases where the transverse inhomogeneity of the plasma is not strong enough, the low ionospheric conductivity can prevent even higher-harmonic FLRs from contracting to small scales where dispersive e ects are important. The application of these results to the formation and temporal evolution of small-scale, active auroral arc forms is discussed.

Multi-instrument observations of a large scale Pc4 pulsation

“…Hence the ionospheric conductivities are expected to be lower at the northern than at the southern foot point. However, Streltsov and Lotko (1997) investigated the influence of finite ionospheric conductivity on the structure of dispersive, nonradiative FLRs for the first four odd harmonics. Their results are based on a linear, magnetically incompressible, reduced, two-fluid MHD model which includes effects of finite electron inertia (at low altitude) and finite electron pressure (at high altitude).…”

Ultra Low Frequency Waves in the Magnetosphere

“…However, Streltsov and Lotko (1997) investigated the influence of finite ionospheric conductivity on the structure of dispersive, non-radiative FLRs for the first four odd harmonics. Their results are based on a linear, magnetically incompressible, reduced, two-fluid MHD model which includes effects of finite electron inertia (at low altitude) and finite electron pressure (at high altitude).…”