Birkeland Currents and Energetic Particles Associated with Optical Auroral Signatures of a Westward Traveling Surge

摘要

The surflike auroral shape commonly associated with the westward traveling surge (WTS) is a remarkably repeatable feature of the polar auroral display. This paper examines the details of one such form that is located on the poleward edge of the diffuse aurora. This study used the simultaneous imagery, high-resolution magnetic field, and charged particle measurements from the DMSP F7 spacecraft, acquired in the northern hemisphere. F7 is the latest of the DMSP series and the first to include a magnetic field experiment. A large-scale upward directed Birkeland current dominates across the entire form, colocated with precipitating electrons having spectra peaked from 3 to 12 keV. Appear to diverge to higher and lower latitudes because of an intrusion of aurora from lower latitudes and later local times. In the center of the intrusion, the Birkeland current is directed upward and electrons exhibit accelerated spectra with a monoenergetic peak at 12 keV similar to spectra observed at much lower latitudes. Each of the two narrow arcs poleward and equatorward of the diffuse region is characterized by intense upward directed Birkeland currents, 'inverted V' electrons with spectra peaked from 1 to 3 keV, and enhanced ion fluxes. Electron spectra in both arcs suggest that these particles are streaming earthward from the plasma-sheet boundary layer. Thus, the WTS appears to result from an expansion of the plasma sheet and an intrusion of the plasma-sheet boundary layer into the high-latitude tail lobe, and is related to a Kelvin-Helmholtz instability in the distant magnetotail. Keywords: Ionosphere; Field aligned currents; Aurora; Reprints. (jhd)