EMIC wave properties according to their distance to the magnetopause

Abstract:

Wave particle interactions play an important role in the magnetosphere dynamics. ElectroMagnetic ion cyclotron (EMIC) waves are one of the kind of plasma waves involved in these interactions. After the first in situ observations of EMIC waves close to the plasmapause, many statistical studies pointed out that the dayside magnetosphere region close to the magnetopause is the place where the EMIC occurrence rate is the highest. In this region the EMIC wave occurrence is related to magnetosphere compression events, in relation with solar wind kinetic pressure increases.

Mapping of EMIC waves in the dayside magnetosphere are usually performed according to the L-shell value of the observations (the L-shell value of a location in the magnetosphere being the distance to the Earth). It is more difficult to investigate the wave occurrence rates according to their distance to the magnetopause because the magnetopause position is not precisely known at a given time. Considering a magnetopause model allows to get around this difficulty.

The considered EMIC wave events are the ones gathered by Usanova et al. (2012) based on Flux Gate Magnetometers measurements onboard THEMIS spacecraft and the magnetopause position is given by the Shue et al. model (1998). EMIC waves are found to maximize in the vicinity of the magnetopause (within 2 Earth radii), in the morning and noon magnetic local time (MLT) sectors. Dependence of EMIC wave parameters (wave normal angle, ellipticity, and degree of polarization) on the distance to the magnetopause and on the magnetic latitude of the observations are compared to the EMIC wave occurrence rates in order to estimate the location of wave amplification region.