Abstract
Abstract. We present here the results of multi-instrument observations of auroral torch and Ps6 magnetic pulsations, which are assumed to be the magnetic signature of the spatially periodic optical auroras known as omega bands. Data from TV and ASC cameras in Barentsburg and Ny Ålesund, EISCAT radars in Longyearbyen and Tromsø, as well as IMAGE network were used in this study. The auroral phenomenon which was considered differed from that previously discussed, as it occurred both in an unusual place (high latitudes) and at an unusual time (late morning hours). We show that this might occur due to specific conditions in the interplanetary medium, causing the appropriate deformation of the magnetosphere. In such a case, the IMF turned out to be an additional factor in driving the regime of Ps6/omega bands, namely, only by acting together could a substorm onset in the night sector and Bz variations result in their generation. Since the presumable source of Ps6/omega bands does not co-locate with convection reversal boundaries, we suggest the interpretation of the phenomena in the frame of the interchange instability instead of the Kelvin-Helmholtz instability that is widely discussed in the literature in connection with omega auroras. Some numerical characteristics of the auroral torch were obtained. We also emphasize to the dark hole in the background luminosity and the short-lived azimuthally-restricted auroral arc, since their appearance could initiate the auroral torch development. Keywords. Magnetospheric physics (Auroral phenomena; Plasma convection; Solar wind-magnetosphere interaction)
Highlights
Among others, one remarkable auroral form allowing the investigation of magnetospheric phenomena via the visible features is the large-scale luminosity undulations of the poleward boundary of diffuse auroras first described by Akasofu and Kimball (1964) and named “omega bands” due to their similarity with an inverted Greek letter
In this study we focus on an event that occurred on 22 January 2004 in the late morning hours (∼09:00 MLT) at high latitudes (L ∼16) during the pass of the Earth over the magnetic cloud
We have presented here the results of multi-instrument observations of an auroral torch and Ps6 magnetic pulsations
Summary
One remarkable auroral form allowing the investigation of magnetospheric phenomena via the visible features is the large-scale (up to 1000 km in azimuthal direction) luminosity undulations of the poleward boundary of diffuse auroras first described by Akasofu and Kimball (1964) and named “omega bands” due to their similarity with an inverted (open to the pole) Greek letter. In contrast to auroral arcs, which are the predominant form of auroras, the omega bands are rather rare observational phenomena, probably due to the small extension in the NS direction that creates a difficulty for a ground observer to distinguish them on the all-sky images from a dished auroral arc. For this reason relatively little attention has been paid to omega bands and only a limited number of publications devoted to this kind of auroral activity can be found. Several cases of similar optical phenomena have been reported in the evening sector (Solovyev et al, 1999)
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