A study of high-latitude auroral arcs using radar, optical, and in situ techniques
Weiss, Loretta A.
Reiff, Patricia H.
Doctor of Philosophy
Two experimental campaigns designed to study high-latitude auroral arcs have been conducted in Sonde Stromfjord, Greenland. The Polar Acceleration Regions and Convection Study (Polar ARCS) on February 26, 1987, consisted of a coordinated set of ground-based and sounding rocket measurements of a weak, sun-aligned arc within the duskside polar cap, while the Rodeo I and II experiments, conducted during December, 1988 and October, 1989, involved uniquely coordinated optical and radar measurements of high-latitude arcs occurring at the poleward boundary of the auroral oval. Analysis of the large-scale Polar ARCS data indicate anti-sunward convection in the region between the duskside auroral oval and the sun-aligned arc. This convection signature is consistent with either a model in which the sun-aligned arcs formed on open field lines over the polar cap or on closed field lines threading an expanded low-latitude boundary layer, but not a model in which the polar cap arc field lines map to an expanded plasma sheet. Electron measurements indicate that the rocket passed through three narrow ($\le$20 km) regions of low-energy ($\le$100 eV) electron precipitation. An electrodynamic analysis has shown the electric and magnetic field perturbations in these regions to be well correlated and associated with small-scale upward and downward field-aligned currents of 1-2 $\mu$A/m$\sp2.$ The Rodeo measurements have been used to examine the aeronomic and electrodynamic characteristics of two optically stable arcs occurring at different magnetic local times and exhibiting different relationships to the polar cap/convection reversal boundary. The first case study is associated with a reversal from antisunward to sunward flow and also the boundary between open and closed field lines. In contrast, the second case study involved an arc with a much greater average precipitation energy and a significant cross-arc flow, evidenced by the radar measurements as well as the convective motion of a polar cap patch directly across the arc. Owing to the relative motion between the F-layer plasma and the arc precipitation, this arc is interpreted as forming across the nightside merging gap on field lines which map to a region of stable reconnection in the tail.
Astronomy; Astrophysics; Atmospheric sciences