A study of omega bands and Ps6 pulsations on the ground, at low altitude and at geostationary orbit

Abstract

Abstract. We investigate the electrodynamic coupling between auroral omega bands and the inner magnetosphere. The goal of this study is to determine the features to which omega bands map in the magnetosphere. To establish the auroralmagnetosphere connection, we appeal to the case study analysis of the data rich

Combined optical, EISCAT and magnetic observations of the omega bands/Ps6 pulsations and an auroral torch in the late morning hours: a case study

“…Using one of the Tsyganenko magnetic field models, Tagirov (1993) has shown that the auroral torches are magnetically linked to the equatorial plane of the magnetosphere to a distance of 5-6 R E , which is consistent with the result derived by Steen et al (1988). Jorgensen et al (1999) also concluded that omega bands are the electrodynamic signature of a corrugated inner edge of a current sheet in the near-Earth (geostationary) magnetosphere. A different location of the -band and source in the magnetosphere was reported by Pulkkinen et al (1991).…”

“…Later, on the basis of results obtained with simultaneous multi-instrument observations, André and Baumjohann (1982), Opgenoorth et al (1983), and Steen et al (1988) showed that the -bands and the positive spikes in the D-or Y-component (Ps6 pulsations) may be regarded as the same phenomenon seen by different instruments. This led some investigators to identify -bands by means of groundbased magnetometer data, even when optical images were not available (Lühr and Schlegel, 1994;Jorgensen et al, 1999;Wild et al, 2000) or have too a low spatial resolution as a result of being taken from high altitudes (Connors and Rostoker, 1993). In accordance with early results, one of the morphological features of the Ps6 is their association with magnetospheric substorms (Saito, 1978).…”

“…Later, to explain torch development, Tagirov (1993) applied the mechanism suggested by Lyatsky and Maltsev (1978) for bulge formation. Recently, Jorgensen et al (1999) mentioned that "the presumed location of the magnetospheric source of -bands has undergone a similar earthward motion as the presumed location of substorm onsets". We can extend the analogy of the torch with substorm activity by noting the following: 1) both are preceded by a short-lived brightening of discrete auroras: azimuthally-extended auroral arcs in the case of substorm onset (the so-called pseudo-breakup event) and azimuthallyrestricted arc-like forms in the case of torch formation; 2) we connected the torch formation with the interchange instability arising due to the magnetosphere-ionosphere decoupling.…”

“…Safargaleev and Maltsev (1986) noted that interchange-like disturbances can arise even if there is no sharp boundary between areas with different plasma content. Taking into account that the considered optical phenomena were observed inside the auroral oval and that two other mentioned mechanisms Maltsev, 1984 andJorgensen et al, 1999) imply the presence of a plasma boundary in the magnetosphere, we think that the interchange instability is more likely the reason for generation of omega auroras. In accordance with Lui and Hamilton (1992), the radial profile of the quiet-time plasma pressure in the magnetotail exhibits a peak at L=3-4 and then decreases monotonically from L=4 and L=9.…”

“…The instability of the magnetosphereionosphere system, which also resulted in the omega-like structures, was discussed theoretically by Lyatsky and Maltsev (1984) (see also Tagirov, 1993), while numerical modeling was performed by Janhunen and Huuskonen (1993). Also worth mentioning is a mechanism described by Jorgensen et al (1999), who assumed that the waves excited on the inner edge of the current sheet are responsible for optical omegaband generation via the production of the field-aligned electric fields causing spatially-periodic electron precipitations.…”