Effect of Ionospheric Electron Density on the Amplitude of Field Line Resonances
Abstract
Ultra-low frequency (ULF) field line resonances are recorded on the ground because shear Alfvén mode waves are reflected at the ionosphere, allowing the formation of standing field line eigenoscillations. For detection at the ground, ULF wave energy must also pass through the ionosphere and atmosphere. We may expect that the ionospheric conductance affects the propagation of ULF waves and hence the amplitude of field line resonances at the ground. However, few studies of this effect have been reported. Here we describe a combined theoretical and observational study of the effect of ionospheric electron density on FLR amplitude at the ground. We use the one-dimensional model of ULF wave propagation through the ionosphere by Sciffer et al. (2005) to determine wave amplitude and phase and conductance profiles for a range of conditions (time, season, latitude, solar F10.7 flux) incorporating input data from the empirical IRI, MSIS and IGRF ionospheric, atmospheric and magnetic field models. We also examine ground magnetometer and ionospheric electron density data from a range of locations, and compare the observed variation in electron density in the ionospheric F and E regions with the FLR amplitude for specific days and on a statistical basis. We find that high electron densities in the F region, and in particular in the E region, for example associated with sporadic E, reduce the amplitude of the FLR amplitude on the ground as a result of the enhanced ionospheric conductance.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMSA33A2268M
- Keywords:
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- 2471 IONOSPHERE / Plasma waves and instabilities;
- 2772 MAGNETOSPHERIC PHYSICS / Plasma waves and instabilities;
- 7836 SPACE PLASMA PHYSICS / MHD waves and instabilities