Features of steady magnetospheric convection

Abstract

The large‐scale patterns of ionospheric convection and particle precipitation are described during two intervals of steady magnetospheric convection (SMC) on November 24, 1981. The unique data set used in the analysis includes recordings from the worldwide network of magnetometers and all‐sky cameras, global auroral images from the DE 1 spacecraft, and particle precipitation data from low‐altitude NOAA 6 and NOAA 7 spacecraft. The data show that intense magnetospheric convection continued during more than 10 hours under the steady southward interplanetary magnetic field without any distinct substorm signatures. All data sets available confirmed the stable character of the large‐scale magnetospheric configuration during this period. In particular, the magnetic flux threading the polar cap was stable (within 10%) during 3.5 hours of continued DE 1 observations. The dayside cusp was located at an unusually low latitude (70° CGL). The nightside auroral pattern consisted of two distinct regions. The diffuse aurora in the equatorward half of the expanded (10° wide) auroral oval was well‐separated from the bright, active auroral forms found in the vicinity of the poleward boundary of the oval. The twin‐vortex convection pattern had no signature of the Harang discontinuity; its nightside “convection throat” was spatially coincident with the poleward active auroras. This region of the auroral oval was identified as the primary site of the short‐lived transient activations during the SMC intervals. The energetic particle observations show that the auroral precipitation up to its high‐latitude limit is on closed field lines and that particle acceleration up to > 30‐keV energy starts close to this limit. The isotropic boundaries of the > 30‐keV protons and electrons were found close to each other, separating regions of discrete and diffuse precipitation. This suggests that these precipitation types originate on the very taillike and very dipolelike field lines, respectively.

Magnetospheric source region of discrete auroras inferred from their relationship with isotropy boundaries of energetic particles

“…We also considered the observations made in the northern hemisphere during the steady magnetospheric convection (SMC) event on 24 November 1981. This event is a good example of thè`d ouble oval'', which is well documented by auroral and other observations [see Yahnin et al (1994a) for more detailed description]. A few all-sky cameras at Greenland and Kola Peninsula operated during that day, and on two occasions we had simultaneous ground and spacecraft observations in the same region.…”

“…A detailed description of the SMC interval of 24 November 1981 is given in Yahnin et al (1994a). A rather stable auroral distribution pattern was observed during that day as shown by both the ground-based observations and the DE-1 imager data.…”

“…This type of situation is quite typical for the recovery phase of a substorm where the so-called``double oval'' is formed (Elphinstone et al, 1995); it is also typical for long-duration events of the steady magnetospheric convection (SMC) (e.g. Yahnin et al, 1994a;Sergeev et al, 1996). The overlapping of poleward bright part of the double oval with the velocity-dispersed ion structures (VDIS) (Kovrazhkin et al, 1987;Zelenyi et al, 1990), as well as the mapping in the specially prepared magnetospheric model for two SMC events (Sergeev et al, 1996), both con®rmed that these high-latitude discrete auroras come from the far tail or PSBL.…”

Balanced reconnection intervals: four case studies

“…Until now, F pc has been used only to support other data, rather than as a way to determine if an event is an SMC (Yahnin et al, 1994). Sergeev et al (1996) studied several SMC events, but were limited to 5 due to lack of satellite data coverage in the magnetotail.…”

“…The global coverage did, however, allow them to do a very detailed analysis of the magnetospheric dynamics during these events. Yahnin et al (1994) also did an in-depth study on features occurring in the 24 November 1981 SMC. While these investigations illuminated many features of steady magnetospheric convection, there has been a lack of statistical analysis of SMCs.…”