E-region echo characteristics governed by auroral arc electrodynamics
1Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK
2National Institute of Polar Research, Tokyo 173-8515, Japan
3Graduate University for Advanced Studies, Tokyo 173-8515, Japan
4Tokai University, Kanagawa 259-1292, Japan
5Space Sciences Laboratory, University of California at Berkeley, California, USA
6Science Institute, University of Iceland, Reykjavik IS-107, Iceland
Abstract. Observations of a pair of auroral arc features by two imagers, one ground- and one space-based, allows the associated field-aligned current (FAC) and electric field structure to be inferred. Simultaneous observations of HF radar echoes provide an insight into the irregularity-generating mechanisms. This is especially interesting for the E-region echoes observed, which form the focus of our analysis, and from which several conclusions can be drawn, summarized as follows. Latitudinal variations in echo characteristics are governed by the FAC and electric field background. Particularly sharp boundaries are found at the edges of auroral arcs. Within regions of auroral luminosity, echoes have Doppler shifts below the ion-acoustic speed and are proportional to the electric field, suggesting scatter from gradient drift waves. Regions of downward FAC are associated with mixed high and low Doppler shift echoes. The high Doppler shift component is greatly in excess of the ion-acoustic speed, but seems to be commensurate with the driving electric field. The low Doppler shift component appears to be much depressed below expectations.
Key words. Ionosphere (ionospheric irregularities; electric fields and currents)
Milan, S. E., Sato, N., Lester, M., Murata, Y., Shinkai, Y., Doi, H., Frey, H. U., and Saemundsson, T.: E-region echo characteristics governed by auroral arc electrodynamics, Ann. Geophys., 21, 1567-1575, doi:10.5194/angeo-21-1567-2003, 2003.