Statistics of the Fine Structure of Chorus Wave Packets

Abstract:

Wave-particle interactions in the Earth’s magnetosphere
can lead to an efficient exchange of energy between waves
and different particle populations, including the energetic
electrons in the outer Van Allen radiation belt. Whistler
mode chorus waves have been shown to influence
the radiation belt dynamics via transfer of energy from injected
electron populations. These waves have also been shown to cause
pitch angle diffusion and subsequent precipitation of electrons
leading to pulsating auroral patches. Properties of the
fine structure of sub-packets of whistler mode chorus can
influence all these processes.

Nearly two years of systematic in situ measurements of whistler
mode chorus have been collected by the Van Allen Probes Electric
and Magnetic Field Instrument Suite and Integrated Science’s
Waves instrument. In its continuous burst mode, this instrument
records selected multicomponent waveforms with a duration
of 6 seconds and with a sampling frequency of 35 kHz. We use this
data set to analyze the fine structure of chorus wave packets,
which corresponds to bandwidths of tens to hundreds of hertz and
to peak amplitudes of tens to hundreds of pT, with extreme
values up to a few nT. We investigate properties
of instantaneous wave amplitudes and wave vector directions
within peaks of this sub-packet structure. We use a large number
of events and we analyze statistics of these crucial parameters
of the nonlinear wave-particle interactions.