Pre-noon high-latitude auroral arcs as a manifestation of the interchange instability

Abstract

Abstract.On 7 December 2000, TV ASC camera in Barentsburg (Svalbard) observed pre-noon (at 09:00-10:00 MLT) rayed auroral arcs, which occurred at the poleward edge of the auroral oval after an IMF transition from B y -dominated (B y = +8.8, B z = +4.3) to strongly northward dominated (B y = +2.7, B z = +8.6). The arcs appeared from the area of enhanced luminosity seen in the western (nightside) horizon, and developed to the east, progressing at a velocity of about 1.5 km/s. Simultaneously, the arcs were drifting poleward at a velocity of 300-500 m/s, whose value was equal to the F-region ionospheric plasma drift velocity observed by the Incoherent Scatter Radar (ESR). The arc appearance and motion corresponded well to the poleward expansion of the auroral oval following the IMF shift, which was observed by the UVI on board the Polar satellite. The observed auroras were associated with closed LLBL indicated by the particle precipitation data from DMSP satellites showing also several-keV electrons of PS origin. The observations allow us to suggest that the arcs arise due to the interchange instability that starts to develop at the boundary between the magnetospheric plasma and the magnetosheath flux tubes entering the closed magnetosphere due to the reconnection beyond the cusp after the IMF changes. The interchange instability can be suggested as a possible mechanism for the formation of the LLBL.

Optical, radar, and magnetic observations of magnetosheath plasma capture during a positive IMF <I>B<sub>z</sub></I> impulse

“…The solar wind can also be considered as a source of new plasma, which forms the low latitude boundary layer (llbl) in the dayside (Song and Russel, 1992). Instabilities in the llbl may lead to the formation of auroral arcs (Kozlovsky et al, 2003).…”

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

“…These possibilities were previously discussed by Lyatsky and Sibeck (1997) and Kozlovsky et al (2003) in connection with the problem of the generation of different kinds of dayside auroras. Our data presented in Fig.…”

“…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.…”

“…This boundary was assumed to appear during the substorm recovery phase. 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.…”

Changes of dayside auroral distribution caused by a solar wind pressure pulse and associated interplanetary magnetic field disturbances

“…On the other hand, solar wind pressure changes are, as a rule, associated with simultaneous IMF changes, which can also affect the dayside aurora, especially in the most poleward part of the oval. For instance, the auroral oval motion following IMF B z changes was observed by Polar UVI in both prenoon (Kozlovsky et al, 2003a) and post-noon (Kozlovsky and Kangas, 2001) MLT sectors. The IMF B y control of dayside high-latitude auroras was demonstrated by Trondsen et al (1999).…”