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.

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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.

Quiet time arcs observed from the Greenland all‐sky camera network have been ordered in corrected geomagnetic latitude/time mass plots according to the values of the Y and Z components of the IMF. Two different patterns of discrete quiet arcs occur. In one system the arcs are ordered along the statistical auroral oval; in the other, which we have called the polar cap pattern of discrete arcs, the arcs are ordered partly in the sun‐earth direction over the polar cap, especially on the dawnside of the pole, partly along the 78°–80° corrected geomagnetic latitude curve in the morning to noon and noon to evening hours. The oval arc pattern is most prominent when Bz is negative. It gradually contracts and finally practically vanishes as the steady IMF is shifted toward a northward direction. The contraction takes place differently, depending on the sign of By. The polar cap pattern is dominant when Bz is positive. The sun‐aligned arcs of the polar cap pattern gradually disappear as Bz goes toward negative values. The high‐latitude arcs in the forenoon sector seem to be present for all values of Bz considered. No dependence on By has been found in the pure polar cap pattern. Apart from periods of extremely great numerical values of Bz, the oval and the polar cap discrete arc patterns are found to coexist, at least in our statistical presentation.

Auroral arcs observed from the Greenland all‐sky camera network during quiet intervals (AE<50 nT) have been ordered in corrected geomagnetic latitude/time mass plots for different values of AE. The arcs are distributed in a pattern which is shown to coincide with the precipitation belt of auroral electrons determined by the DMSP satellites. This belt is known to be composed of two parts: an equatorial part (average energy of >500 eV) and a poleward, low‐energy part. Previous studies have shown that the arc pattern is composed of two subpatterns, too, the “polar cap arc pattern” and the “oval arc pattern.” It is demonstrated that the “polar cap arc pattern” is situated in the poleward, low‐energy part of the precipitation belt, connected to the low‐latitude boundary layer, whereas the “oval arc pattern” is in the equatorial higher energy belt, connected to the plasma sheet. The dividing line between the two arc patterns is associated with the boundary of trapped ≥40‐keV electrons. The designation “polar cap arc pattern” is shown to be ambiguous, wherefore it is proposed to replace it by the term “high‐latitude arc pattern.”