A class of high‐m pulsations and its auroral radar signature

Abstract

Bistatic Auroral Radar System radar events showing a repetitive equatorward (or radarward) traveling band signature in the range‐time‐intensity plots have been analyzed. The associated pulsations have many features in common with previously reported high‐m storm time Pc 5 pulsations. The periods, azimuthal wave numbers (m), Dst dependence, and polarization ellipses are similar. One difference is also seen. The pulsation phase velocity of our events often has a significant equatorward component in the ionosphere. However, of the three cases for which the phase velocity direction in the magnetospheric equatorial plane was determined, one had phase velocities close to azimuthal at both locations, one had an azimuthal phase velocity in the magnetosphere but an equatorward component of the phase velocity in the ionosphere, and the final event had equatorward or inward components of phase velocity at both locations. These events are very similar to the equatorward traveling bands events observed by the Sweden and Britain Auroral Radar Experiment system (Tian et al., 1991; Yeoman et al., 1992) except that our m values are distinctly larger. If coupling to energetic protons is involved in exciting these pulsations, this difference implies that the energy of the protons involved decreases with increasing L of the interaction location. Finally, our data do not lend themselves to the plasmapause field line resonance interpretation of Tian et al. (1991).

Intermediate-<I>m</I> ULF waves generated by substorm injection: a case study

“…Similar observations were seen in the BARS (Bistatic Auroral Radar System;McNamara et al, 1983) coherent radar by Grant et al (1992). Later, Yeoman and Wright (2001) presented ULF wave observations close to local noon using the HF radar artificial backscatter technique at Tromsø which demonstrated both wave activity characteristic of drift-bounce resonance and wave activity characteristic of drift resonance activity, with the latter waves showing equatorward phase propagation.…”

“…Taking large pitch angles and the central L-shell of the wave observations, then particle energies of 33 keV are predicted. The characteristics of the ULF wave events with equatorward phase propagation observed by Grant et al (1992), Yeoman et al (1992), Yeoman and Wright (2001), Yeoman et al (2008) and those presented here are summarised in Table 1, along with the energetic particle populations implicated in their generation by the authors concerned. Table 1 shows that whilst wave events are seen with a variety of m-numbers and periods, a clear trend exists in previous observations in that the energy of the proposed particle population inversion decreases as the L-shell of the observation increases.…”

High‐latitude observations of ULF waves with large azimuthal wavenumbers

“…They are observed in the dusk sector during magnetically disturbed intervals. Similar waves, but with an equatorward phase motion, have been seen in the Sweden and Britain Radar Experiment (SABRE) and Bistatic Auroral Radar System (BARS) coherent radar systems in the dusk sector by Yeoman et al [1992] and Grant et al [1992], respectively. The second class of particle-driven ULF waves of interest are giant "Pg" pulsations which have been observed on the ground as well as by orbiting satellites at times when geomagnetic conditions are quiet.…”

The influence of IMF By on the nature of the nightside high-latitude ionospheric flow during intervals of positive IMF Bz

“…Data have been inspected from magnetograms of these two arrays which move through the midnight sector during the study interval. These are the Canadian CANOPUS array (Grant et al, 1992) and the Greenland magnetometer chain (Friis-Christensen et al, 1985). Data from selected stations (denoted by the red-filled circles) will be presented in H , D, and Z coordinates, where H is local magnetic north, D is local magnetic east, and Z is vertically down.…”