Chorus and hiss scales in the inner magnetosphere: statistics from
high-resolution filter bank (FBK) Van Allen Proves multi-point
measurements
Abstract
The spatial scales of whistler-mode waves, determined by their
generation process, propagation, and damping, are important for
assessing the scaling and efficiency of wave-particle interactions
affecting the dynamics of the radiation belts. We use multi-point wave
measurements by two Van Allen Probes in 2013-2019 covering all MLTs at
L=2-6 to investigate the spatial extent of active regions of
chorus and hiss waves, their wave amplitude distribution in the
source/generation region, and the scales of chorus wave packets,
employing a time-domain correlation technique to the spacecraft
approaches closer than 1000 km, which happened every 70 days in
2012-2018 and every 35 days in 2018-2019. The correlation of chorus wave
power dynamics using is found to remain significant up to
inter-spacecraft separations of 400 km to 750 km transverse to the
background magnetic field direction, consistent with previous estimates
of the chorus wave packet extent. Our results further suggest that the
chorus source region can be slightly asymmetrical, more elongated in
either the azimuthal or radial direction, which could also explain the
aforementioned two different scales. An analysis of average chorus and
hiss wave amplitudes at separate locations similarly shows the reveals
different radial and azimuthal extents of the corresponding wave active
regions, complementing previous results based on THEMIS spacecraft
statistics mainly at larger L>6. Both the chorus source
region scale and the chorus active region size appear smaller inside the
outer radiation belt (at L< 6) than at higher L-shells.