Large‐Amplitude Electromagnetic Ion Cyclotron Waves and Density Fluctuations in the Earth's Magnetosheath

  The Earth's Magnetosheath is a region slowing down high‐speed particles originating from the solar wind, protecting the Earth from the hazards of high‐energy charged particles. A considerable fraction of the energy of energetic particles is transferred into plasma waves.

  Using measurements by Magnetospheric Multiscale mission,Dr.Jinsong Zhao from the Purple Mountain Observatory and his collaborators found an observational event of large‐amplitude low‐frequency electromagnetic ion cyclotron waves lasting nearly 6 hr, propagating from the outer magnetosheath to the inner magnetosheath. Density fluctuations are found to coexist with these electromagnetic waves. Applying the measurements of charged particles to modeling, they showed the observed waves are likely excited by free energy provided by ions with an anisotropic temperature distribution, consistent with wave theory.

By with ZHAO Jinsong

  Fig. Overview for the plasma and magnetic field measurements from MMS1on 16 April 2018.(a) The ion and electron density; (b) the ion spectrogram of differential energy flux; (c) the electron spectrogram of differential energy flux; (d) the ion bulk velocity; (e) the ion and electron temperature; (f) the magnetic field in GSE coordinates; and (g) the total magnetic field. The MMS1 trajectory in XY and XZ planes in GSE coordinates is shown in panels (h) and (i), where the dotted and dashed lines correspond to the time interval of 00:00:01–23:59:59 and 06:33:00– 12:35:00 on 16 April 2018. The burst mode continually operates in the time interval of 10:23:14–10:58:32 UT, labeled by two dashed lines in panels (a)–(g) and by the red stars in panels (h)–(i).