Abstract
Abstract. We investigate the ray trajectories of nonductedly propagating lower-band chorus waves with respect to their initial angle θ0, between the wave vector and ambient magnetic field. Although we consider a wide range of initial angles θ0, in order to be consistent with recent satellite observations, we pay special attention to the intervals of initial angles θ0, for which the waves propagate along the field lines in the source region, i.e. we mainly focus on waves generated with &theta0 within an interval close to 0° and on waves generated within an interval close to the Gendrin angle. We demonstrate that the ray trajectories of waves generated within an interval close to the Gendrin angle with a wave vector directed towards the lower L-shells (to the Earth) significantly diverge at the frequencies typical for the lower-band chorus. Some of these diverging trajectories reach the topside ionosphere having θ close to 0°; thus, a part of the energy may leak to the ground at higher altitudes where the field lines have a nearly vertical direction. The waves generated with different initial angles are reflected. A small variation of the initial wave normal angle thus very dramatically changes the behaviour of the resulting ray. Although our approach is rather theoretical, based on the ray tracing simulation, we show that the initial angle θ0 of the waves reaching the ionosphere (possibly ground) is surprisingly close - differs just by several degrees from the initial angles which fits the observation of magnetospherically reflected chorus revealed by CLUSTER satellites. We also mention observations of diverging trajectories on low altitude satellites.
Highlights
Together with the lightning induced whistlers, chorus emissions belong to the most distinct electromagnetic waves propagating in the inner magnetosphere
We consider a wide range of initial angles θ 0, in order to be consistent with recent satellite observations, we pay special attention to the intervals of initial angles θ 0, for which the waves propagate along the field lines in the source region, i.e. we mainly focus on waves generated with θ 0 within an interval close to 0◦ and on waves generated within an interval close to the Gendrin angle
Other observations, which are consistent with the existence of diverging trajectories, are the measurements of ELF waves by Santolık and Parrot (1999, 2000) on the lowsible source region near the geomagnetic equator at a radial distance between 5 and 7 RE, and a generation mechanism acting on highly oblique wave vectors near the local Gendrin angle
Summary
Together with the lightning induced whistlers, chorus emissions belong to the most distinct electromagnetic waves propagating in the inner magnetosphere. It has generally been accepted that the lower band chorus is generated with wave vectors directed close to the magnetic field lines The latter assumption is based on the satellite measurements carried out close to the source region, which show that the mean value of wave normal angle θ 0 is usually small, close to zero (Nagano et al, 1996). The detailed ray tracing analysis of the MR chorus shows that the emission has to be generated with relatively large wave normal angles θ 0 to the magnetic field line (Parrot et al, 2004), with the wave vector directed towards the Earth. Chum et al (2003) showed, under the assumption of nonducted propagation, that a span of wave normal angles should exist in the generation region, so that it would be possible to observe a chorus element at higher latitudes. In a related experimental paper (Santolık et al, 20051), we present an interpretation of spacecraft observations of the divergent propagation pattern at high latitudes
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
