Alfven resonator in the topside ionosphere beneath the auroral acceleration region

Abstract

[1] The possible occurrence of a new resonator in the topside ionosphere at auroral latitudes is proposed. This resonator is formed between the E-layer of the ionosphere and the bottom boundary of the auroral acceleration region (AAR), which has a localized fieldaligned potential drop. The AAR is shown to effectively reflect Alfven waves with transverse scales less than the Alfven transit scale l A . The proposed resonator can trap and accumulate Alfvenic small-scale disturbances with periods from a few seconds to a few tens of seconds, and with transverse scales from a kilometers to a few tens of kilometers. The eigenfrequencies of the AAR-associated resonator are estimated to be lower than that of the ionospheric Alfven resonator. The small-scale Alfvenic structures commonly observed by satellites can be generated by a nonsteady field-aligned current transported by precipitating electrons and trapped in the AAR-associated resonator. Observations by ground-based magnetometers at auroral latitudes often show the occurrence of intensifications in the dynamic spectra of Pi1 pulsations in accordance with the predictions of the model.

Turbulent microstructures and formation of folds in auroral breakup arc

“…Thus the IFI operating in the IAR will evolve much more quickly than the instability based on FLR, and so the former may be called as a fast IFI while the FLR version is a slow IFI. There are theoretical predictions that auroral acceleration region-associated resonator (socalled RAAR) might be more effective than IAR [Pilipenko et al, 2002].…”

CHAMP observation of intense kilometer-scale field-aligned currents, evidence for an ionospheric Alfvén resonator

“…Such a relation has been experimentally identified for small-scale waves (Dubinin et al, 1985;Hirano et al, 2005). A somewhat modified Alfvén resonator has been recently proposed by Pilipenko et al (2002) using results from the reflection and transmission of waves at the auroral acceleration region (AAR) derived by Vogt and Haerendel (1998). Contrary to the common IAR, where the upper reflection boundary is the strong gradient of the Alfvén velocity above the F-layer maximum, the upper reflection boundary of this resonator is assumed to be the AAR.…”

Frequency-dependent polarization characteristics of Pc1 geomagnetic pulsations observed by multipoint ground stations at low latitudes

“…Part of the compressional wave energy, with a frequency above the cutoff frequency, can be trapped in the ionospheric duct in the F layer and propagate horizontally to lower or higher latitudes. The same ionospheric cavity forms the Ionospheric Alfvén Resonator (IAR) [e.g., Polyakov and Rapoport, 1981;Pilipenko et al, 2002], where part of the incident Alfvén wave energy can be trapped. On the ground, the electromagnetic fields of these ionospheric waves are observed as Pc1 geomagnetic pulsations in the frequency range of 0.2-5.0 Hz.…”