Analysis of fine ELF wave structures observed poleward from the ionospheric trough by the low-altitude satellite DEMETER
Abstract
DEMETER was a three-axis stabilized Earth-pointing spacecraft launched on 29 June 2004 into a low-altitude (710 km) polar and circular orbit that was subsequently lowered to 650 km until the end of the mission in December 2010. DEMETER measured electromagnetic waves all around the Earth except at magnetic invariant latitudes >65 degrees.
The frequency range for the electric field was from DC up to 3.5 MHz and for the magnetic field from a few hertz up to 20 kHz. Electromagnetic ion cyclotron (EMIC) waves have been previously observed by DEMETER close to the ionospheric trough during high magnetic activity, and this paper describes another type of EMIC waves.
These waves are also observed close to the trough, but they extend poleward, with the trough acting as a boundary. They are observed exclusively during the night and preferentially during geomagnetic substorms.
The analysis of wave propagation shows that they propagate nearly along the ambient magnetic field and that they come from larger radial distances.