Dynamics of auroral precipitation in the morning sector observed with the imaging riometer at South Pole station: evidence of co-rotating precipitation regions

Abstract

The movement of auroral radio absorption events over distances up to 300 km has been studied for several intense substorms using the imaging riometer at South Pole station. In the morning sector, two kinds of motion have been identified. Individual events move through the field-of-view at speeds generally in the range 400–900 m/s, and there is a tendency for successive absorption peaks to maximize at an almost constant longitude for several hours. The gradient-curvature drift of electrons with energies of order 25 keV may contribute to the rapid motions observed, though their tendency not to follow the path of constant invariant latitude suggests that other factors may be involved. Several mechanisms that might account for co-rotating precipitation regions have been examined, but none has been found to be entirely satisfactory. The most plausible hypothesis is that they are a consequence of irregularities in the cold plasma in the magnetosphere.