Observations of a detached, discrete arc in association with field line resonances

Abstract

Data from the Canadian Auroral Network for the OPEN Unified Study (CANOPUS) array in Canada are used to analyze the magnetic fields and auroral structures which were associated with a field line resonance which occurred near local midnight and in the early morning sector. The electric fields of this resonance, which have a frequency of about 1.95 mHz, were observed by the Johns Hopkins University, Applied Physics Laboratory HF radar at Goose Bay and had a maximum at about 70.7° invariant latitude. Effects of the field line resonance were seen in the 5577 Å, meridian scanning photometer data and the magnetometer data from the CANOPUS array. The field line resonance was accompanied by precipitating energetic electrons (energies greater than 3 keV) in a narrow auroral arc which was 3°–4° equatorward of the resonance structure seen in the radar data and approximately 1° equatorward of field lines threading the inner boundary of the proton plasma sheet. The electron precipitation in this arc was modulated at the frequency of the field line resonance. The effects of the resonance are also seen as pulsations in the magnetometer data, and the horizontal polarization of the pulsations showed a change in sense of rotation across the arc. The oscillations in the precipitating electrons might have been caused by modulation in the ELF/VLF growth rates due to the presence of the magnetohydrodynamic waves associated with the resonance, by mode conversion to kinetic Alfvén waves, or by the formation of electrostatic ion cyclotron waves due to field‐aligned currents associated with a second field line resonance collocated with the arc. The evidence presented here suggests that the modulation of ELF/VLF by magnetohydrodynamic waves on field lines near the plasmapause was the most likely cause of the auroral oscillations.

Simultaneous satellite and ground‐based observations of a discretely driven field line resonance

“…We take this as an indication that auroral luminosity was being modulated by the resonances, consistent with the work of other authors [Samson et al, 1991bXu et al, 1993]. The resonances in this case were observed after the onset of a substorm.…”

Post-noon two-minute period pulsating aurora and their relationship to the dayside convection pattern

“…Several workers have advocated ULF waves as the driving mechanism for auroral arc formation (e.g. Samson et al, 1991;Xu et al, 1993;Moen et al, 1994). In the present case, the auroral arc in question is the optical manifestation of the region 1 current system, and hence its generating mechanism is of great importance with respect to the excitation of magnetospheric/ionospheric convection.…”

A decade of the Super Dual Auroral Radar Network (SuperDARN): scientific achievements, new techniques and future directions

“…The Goose Bay radar was also successful in providing the first HF radar studies of magnetospheric ULF waves Samson et al 1991;Walker et al 1992) and atmospheric gravity waves Bristow et al 1994). Subsequently, another, almost identical, radar was built at Halley, Antarctica with a geomagnetically conjugate field of view.…”