Abstract
Abstract. Chorus-type whistler waves are known to be generated in the vicinity of the magnetic equator, in the low-density plasma trough region. These wave packets propagate towards the magnetic poles, deviating from the magnetic field lines, before being eventually reflected at higher latitudes. Magnetospheric reflection of whistler waves results in bounce oscillations of these waves through the equator. Our study is devoted to the problem of geometrical spreading of these whistler-mode waves after their first magnetospheric reflection, which is crucial to determine where wave–particle interactions occur. Recently, experimental studies stated that the relative intensity of the reflected signal was generally between 0.005 and 0.05 of the source signal. We model such wave packets by means of ray tracing technique, using a warm plasma dispersion function along their trajectory and a realistic model of the inner magnetosphere. We reproduce the topology of the reflected energy distribution in the equatorial plane by modeling discrete chorus elements generated at the equator. Our calculations show that the spatial spreading is large and strongly dependent upon initial wave parameters, especially the chorus wave frequency. Thus, the divergence of each element ray trajectories can result in the filling of a large region (about 4 Earth radii around the source) of the magnetosphere and a reflected intensity of 0.005–0.06 of the source signal in the equatorial plane. These results are in good agreement with previous Cluster and THEMIS observations.
Highlights
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We study the geometrical spreading as a function of the wave initial parameters (R0, ω, θ0, φ0), which allows us to determine the wave power distribution of reflected chorus waves after their first reflection at high latitude
We notably show that the spatial dispersion of reflected chorus waves is large, especially for the lower frequency waves with low θ0, for which it can reach several RE in both radial and azimuthal distances, towards larger L shells
Summary
In Agapitov et al (2011b), a set of observed chorus waves generated at the magnetic equator was propagated in the inner magnetosphere by means of three-dimensional ray tracing technique. The distribution of these rays intersecting the equatorial plane after their first magnetospheric reflection was notably presented. The trajectory of a whistler wave propagating in the inner magnetosphere strongly depends on its initial parameters, in particular its frequency ω (normalized to e,eq) and starting point R0 in the equatorial plane. The deviation in L shell and longitude from their initial magnetic field line is much larger for lower frequencies (ω ≤ 0.3 e,eq), and results in a spread wave power distribution in the equatorial plane. It is necessary first to model discrete chorus elements properly
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