Electrodynamic structure of the morning high‐latitude trough region

• Published in: Journal of geophysical research. Space physics 2016-03, Vol.121 (3), p.2669-2682
• Main Authors: Vanhamäki, H., Aikio, A., Voiculescu, M., Juusola, L., Nygrén, T., Kuula, R.
• Format: Article
• Language: English
• Subjects: Convection; Electric fields; Electrodynamics; Electrons; Equivalence; F region; Geophysics; Ion temperature; Ionosphere; Ionospherics; Latitude; Morning; Radar; trough
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1002/2015JA022021

We describe the electrodynamics of a postmidnight, high‐latitude ionospheric trough, observed with the European Incoherent Scatter radar in northern Scandinavia on 24–25 June 2003 around 22:00–02:30 UT during quiet conditions. The UHF radar made meridian scans with a 30 min cadence resulting in nine cross sections of ionospheric parameters. The F region electric field was also determined with the tristatic system. Ionospheric equivalent currents, calculated from ground magnetometer data, mostly show an electrojet‐like current that is reasonably uniform in the longitudinal direction. Combined analysis of the conductances and equivalent current with a local Kamide‐Richmond‐Matsushita (KRM) method yields the ionospheric electric field and field‐aligned current (FAC) in a 2‐D (latitude‐longitude) area around the radar. We conclude that the most likely scenario is one where the trough is initially created poleward of the auroral oval by downward FAC that evacuates the F region, but as the trough moves to lower latitudes during the early morning hours, it becomes colocated with the westward electrojet. There the electron density further decreases due to increased recombination caused by enhanced ion temperature, which in turn is brought about by a larger convection speed. Later in the morning the convection speed decreases and the trough is filled by increasing photoionization. Key Points Electrodynamics of a summer time, postmidnight, high‐latitude ionospheric trough Ion temperature and electric field are elevated, and FAC is mostly downward in the trough Equatorward edge is associated with particle precipitation, enhanced conductances, and upward FAC