Abstract
Abstract. We report observations of pulsations due to Field Line Resonance (FLR) in the morning sector of the high-latitude dayside ionosphere on 1 February 1998. The Geotail spacecraft, ideally skimming the dayside magnetopause, monitored the magnetopause motion, which is seen to induce a modulated response of the ionosphere by means of ULF waves. Pulsations in the Pc5 frequency range were observed in the ground magnetic field measured by the IMAGE array, as well as in the electron and ion temperatures measured by the EISCAT Svalbard Radar. The ion temperature oscillations are an indicator of a modulated convection electric field while field-aligned currents (FAC) associated with the FLR control the electron temperature. We have performed a simulation of the ionosphere experiencing sinusoidal FAC and electric field in order to confirm our hypothesis. In addition to the ionospheric response, the possible cause of the FLR and processes involved are also discussed.Key words. Magnetospheric physics (MHD waves and instabilities; magnetosphere-ionosphere interactions) – Ionosphere (polar ionosphere)
Highlights
IntroductionThe magnetohydrodynamic theory of resonance (Southwood, 1974; Chen and Hasegawa, 1974a, b) explains basically that magnetopause motion of any kind (global motion, surface waves, Kelvin-Helmoltz instabilities) leads to the generation of compressional fast-mode waves that propagate in the magnetosphere across the magnetic field
The magnetohydrodynamic theory of resonance (Southwood, 1974; Chen and Hasegawa, 1974a, b) explains basically that magnetopause motion of any kind leads to the generation of compressional fast-mode waves that propagate in the magnetosphere across the magnetic field
It is believed that Field Line Resonance (FLR) in the dawn side are most of the time due to the over reflection process (Mann et al, 1999), whereas on the dusk side FLRs tend to be driven by solar wind buffeting or running pulse propagating along the magnetopause
Summary
The magnetohydrodynamic theory of resonance (Southwood, 1974; Chen and Hasegawa, 1974a, b) explains basically that magnetopause motion of any kind (global motion, surface waves, Kelvin-Helmoltz instabilities) leads to the generation of compressional fast-mode waves that propagate in the magnetosphere across the magnetic field. The energy from the KHI is able to penetrate and propagate into the magnetosphere as compressional and shear-Alfven waves, as explained above It seems that the trigger processes are slightly different depending on which flank of the magnetosphere is considered. It is believed that FLRs in the dawn side are most of the time due to the over reflection process (Mann et al, 1999), whereas on the dusk side FLRs tend to be driven by solar wind buffeting or running pulse propagating along the magnetopause This may be explained by the fact that interplanetary magnetic field lines hit the magnetopause tangentially on the dusk (garden hose effect). Field line resonances in the morning and afternoon sector seem to have different properties (Ziesolleck et al, 1994)
Published Version
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