Spatial spreading of magnetospherically reflected chorus elemDisecunsstiosnsin the inner magnetosphere
Abstract
Chorus-type whistler waves are known to be generated
in the vicinity of the magnetic equator, in the lowdensity
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.
Origin : Publication funded by an institution
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