Direct observations of cross-scale energy transfer in space plasmas
arxiv(2024)
摘要
The collisionless plasmas in space and astrophysical environments are
intrinsically multiscale in nature, behaving as conducting fluids at
macroscales and kinetically at microscales comparable to ion- and/or
electron-gyroradii. A fundamental question in understanding the plasma dynamics
is how energy is transported and dissipated across different scales. Here, we
present spacecraft measurements in the solar wind upstream of the terrestrial
bow shock, in which the macroscale ultra-low-frequency waves and microscale
whistler waves simultaneously resonate with the ions. The ion acceleration from
ultra-low-frequency waves leads to velocity distributions unstable to the
growth of whistler waves, which in turn resonate with the electrons to complete
cross-scale energy transfer. These observations, consistent with numerical
simulations in the occurrence of phase-bunched ion and electron distributions,
also highlight the importance of anomalous resonance, a nonlinear modification
of the classical cyclotron resonance, in the cross-scale wave coupling and
energy transfer processes.
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