E-region echo characteristics governed by auroral arc electrodynamics

• Published in: Annales Geophysicae
• Main Authors: Milan, S. E., Sato, N., Lester, M., Murata, Y., Shinkai, Y., Doi, H., Frey, H. U., Saemundsson, T.
• Format: Article in Journal/Newspaper
• Language: English
• Published: European Geosciences Union (EGU), Copernicus Publications, Springer Verlag (Germany) 2017
• Subjects: Science & Technology; Physical Sciences; Astronomy & Astrophysics; Geosciences; Multidisciplinary; Meteorology & Atmospheric Sciences; Geology; ionosphere; ionospheric irregularities; electric fields and currents; HF RADAR BACKSCATTER; SPECTRAL CHARACTERISTICS; IMAGE SPACECRAFT; FORMS; Iceland
• Online Access: http://www.ann-geophys.net/21/1567/2003/; http://hdl.handle.net/2381/39333; https://doi.org/10.5194/angeo-21-1567-2003

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. CUTLASS is supported by the Particle Physics and Astronomy Research Council (PPARC grant no. PPA/R/R/1997/00256), UK, the Swedish Institute for Space Physics, Uppsala, and the Finnish Meteorological Institute, Helsinki. The optical auroral observation project in Iceland was facilitated by the Science Institute, University of Iceland, and supported by Grant in Aid for Overseas Science Survey (grant no. A: 11304029) from the Japanese Society for the Promotion of Science (JSPS). Peer-reviewed Publisher Version