MMS Observations of Lion Roars With Higher Order Harmonic Whistler Waves Inside Earth's Magnetosheath
Journal Article
Overview
abstract
Abstract; During a special MMS Turbulence campaign, almost 80 min of continuous high resolution burst measurements were downlinked from a traversal across Earth's magnetosheath behind mixed quasi‐parallel/perpendicular bow shock conditions. Throughout the magnetosheath, we observed magnetic holes containing intense whistler waves known as “Lion Roars” (LRs). We compared the observed properties of LRs to determine why the whistler waves included higher order harmonics in some magnetic holes but not in others. We refer to the LR events with and without harmonics as “Higher Order Harmonic LRs (HOHLRs)” and “nonharmonic LRs”, respectively. From our observations of the LR events, we found that each wave train featured an electron beam moving at the electron Alfvén speed and parallel to the background magnetic field. We also observed that this electron beam had a stronger phase space density for the LRs near the bow shock. For the HOHLR events, we observed that they exhibited a strong antiparallel Poynting flux and high counts of solitary waves surrounding their corresponding magnetic holes, with some detected solitary waves at the edges of the magnetic hole. Additionally, the fundamental frequencies for the HOHLRs were observed around 0.18–0.23 of the electron cyclotron frequency, . For the nonharmonic LR events, we observed a strong presence of solitary waves within the confines of their magnetic hole, leading to a population of trapped electrons with a parallel/antiparallel temperature anisotropy, strong fluctuations, and Poynting flux flowing in an oblique direction with respect to the background magnetic field. Additionally, the fundamental frequencies of nonharmonic LRs were lower, ranging from 0.11 to 0.18 .
