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Electrodynamic structure of the morning high‐latitude trough region
Author(s) -
Vanhamäki H.,
Aikio A.,
Voiculescu M.,
Juusola L.,
Nygrén T.,
Kuula R.
Publication year - 2016
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2015ja022021
Subject(s) - ionosphere , equatorial electrojet , trough (economics) , electrojet , longitude , f region , latitude , daytime , morning , geophysics , atmospheric sciences , incoherent scatter , electric field , convection , geology , geodesy , radar , physics , meteorology , earth's magnetic field , magnetic field , astronomy , telecommunications , quantum mechanics , computer science , economics , macroeconomics
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.