Quiet‐time intensifications along the poleward auroral boundary near midnight

Abstract

Radar and optical measurements from Sondrestrom are combined with satellite and Goose Bay data in a study of the poleward edge of the nightside auroral oval during a quiet period. The By and Bz components of the interplanetary magnetic field were close to zero, and the Bx component was ∼8 nT for more than 24 hours. On a large scale, the convection and precipitation patterns remained almost constant during this period; on a small scale, however, the conditions were quite dynamic. At 10‐ to 20‐min intervals the arc that marked the poleward auroral boundary intensified, and a new arc appeared poleward of it. About once per hour, stronger intensifications were observed. One such event is examined in detail. The auroral arcs first appeared to dim, and then they brightened, with a factor of 10 increase in E region electron density. At the time of the brightening a new arc formed poleward of all the arcs. The arcs then drifted southward at velocities of ∼270 m/s. A plasma drift disturbance, characterized by a doubling of the southward velocity and a reversal in the east‐west component, propagated westward at 900 m/s through the fields of view of the Sondrestrom and Goose Bay radars. A simultaneous satellite overpass close to the radars revealed the presence of an energetic ion event similar to the “velocity dispersed ion structures” observed on the Aureol satellite and presumed to be the signature of fast ion beams within the plasma sheet boundary layer. The stronger arc intensification events observed by the Sondrestrom radar are associated with an increase in plasma flow across the boundary between open and closed magnetic field lines. We interpret this increased flow as the ionospheric signature of abrupt, localized increases in the reconnection rate in the midnight sector.

Strong sunward propagating flow bursts in the night sector during quiet solar wind conditions: SuperDARN and satellite observations

“…Thus, the observations are not consistent with the predictions of the Kelvin-Helmholtz instability. b) De la Beaujardière et al (1994) have observed, in the midnight sector and during very quiet conditions, southward flow bursts drifting westward, associated with southward moving auroral arcs. These observations are very similar to the ones presented here in the night sector (see Fig.…”

“…7). De la Beaujardière et al (1994) have associated these events with plasma injections from the tail resulting from enhanced reconnection, essentially on the basis of their analogy with daytime flux transfer events and their association with velocity dispersed ion structures (VDIS). On the other hand, nightside, northsouth elongated auroral structures moving southward have long been observed (Sergeev et al, 1990).…”

“…Using incoherent scatter radar and DMSP satellite data, De la Beaujardière et al (1994) have reported strong southward flow bursts in the night sector associated with velocity dispersed ion precipitation that are believed to be the manifestation of reconnection in the tail. More recently, strong flow bursts with velocities larger than 2000 m/s have also been observed by a SuperDARN HF radar (Walker et al, 1998).…”

Six auroral generators: A review

“…Unfortunately no low-altitude satellite measurements of the electrodynamic parameters of such streamers have been reported. Equatorward propagation speeds deduced from auroral imaging range from 270 m/s [de la Beaujardière et al, 1994] and 2 km/s [Nishimura et al, 2010]. A more complete set of low-altitude data would be highly desirable in order to check their consistency with the currents predicted by the braking of BBFs.…”

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

“…Flows in the nightside ionosphere, however, are more directly controlled by magnetospheric dynamics than by the instantaneous nature of the IMF (e.g. de la Beaujardière et al, 1994;Yeoman and Lühr, 1997;Opgenoorth and Pellinen, 1998;Grocott et al, 2002Grocott et al, , 2003Grocott et al, , 2004. Although the dynamics of the magnetosphere itself are largely influenced by the IMF (e.g.…”