Whistler Waves Driven by Field‐Aligned Streaming Electrons in the Near‐Earth Magnetotail Reconnection

Abstract

We analyze Magnetospheric Multiscale Mission observations of whistler waves and associated electron field‐aligned crescent distribution in the vicinity of the magnetotail near‐Earth X‐line. The whistler waves propagate outward from the X‐line in the neutral sheet. The associated field‐aligned streaming electrons exhibit a crescent‐like shape, with an inverse slope (df/d|v|||>0) at 1–5 keV. The parallel phase velocity of the waves is in the range (1–5 keV) of the inverse slope of the field‐aligned crescents in the velocity space. We demonstrate that the observed whistler waves are driven by the electron field‐aligned crescents through Landau resonance. The cyclotron resonance is at the high‐energy tail with negligible free energy of pitch angle anisotropy in these events.

Statistical Characteristics in the Spectrum of Whistler Waves Near the Diffusion Region of Dayside Magnetopause Reconnection

“…Such electron distributions may correspond to a parallel temperature anisotropy ( T e ⊥ / T e ‖ < 1) in the observations. The electron field‐aligned beams/crescent are a natural product of magnetic reconnection (Burch et al., 2016b; Ren et al., 2019). MMS studies show that field‐aligned electron beams are a common energy source for whistler waves (S. Huang et al., 2020; Ren et al., 2019; Zhao et al., 2020).…”

“…Near the separatrix region of magnetotail reconnection, whistler waves are expected to be driven by field‐aligned electron beams (Fujimoto, 2014; S. Y. Huang et al., 2016; Zhou et al., 2011). Analysis of Magnetospheric Multiscale (MMS) observations in magnetotail reconnection demonstrates that electron field‐aligned crescent beams drive whistler waves through Landau resonance (Ren et al., 2019).…”

Modulation of Whistler Mode Waves by Ion‐Scale Waves Observed in the Distant Magnetotail

“…In the Earth's magnetosphere, whistler mode waves can be generated by electron temperature anisotropy ( T ⊥ > T ∥ ) (Kennel & Petschek , ; Li et al, ) or electron beams (Ren et al, ; Sauer & Sydora, ). In this study, the whistler mode waves are generated by electron populations streaming on one side along the magnetic field and such a mechanism resembles the whistler heat flux instability (WHFI) (Kuzichev et al, ; Tong, Vasko, Marc, et al, ) observed in the solar wind.…”

Collisionless Magnetic Reconnection and Waves: Progress Review

“…Such waves have oblique wave normal angles of ∼45 • , have large amplitude electric fields with polarization close to linear, i.e., E ⊥ and E || of similar amplitude (Wilder et al, 2017;Khotyaintsev et al, 2019). Solving a kinetic dispersion solver using the observed electron distributions suggests whistler generation by electron beams is viable for both magnetotail and magnetopause conditions (Khotyaintsev et al, 2019;Ren et al, 2019).…”