Two types of whistler waves in the hall reconnection region

Abstract

Whistler waves are believed to play an important role during magnetic reconnection. Here we report the near‐simultaneous occurrence of two types of the whistler‐mode waves in the magnetotail Hall reconnection region. The first type is observed in the magnetic pileup region of downstream and propagates away to downstream along the field lines and is possibly generated by the electron temperature anisotropy at the magnetic equator. The second type, propagating toward the X line, is found around the separatrix region and probably is generated by the electron beam‐driven whistler instability or Čerenkov emission from electron phase‐space holes. These observations of two different types of whistler waves are consistent with recent kinetic simulations and suggest that the observed whistler waves are a consequence of magnetic reconnection.

MMS observations of whistler waves in electron diffusion region

“…In Figure 4f, only the PSDs at θ = 0°(black), θ = 90°(red), and θ = 180°(blue) are shown, while in Figure 4g, the PSDs at all pitch angles are presented. In this event, we notice that the whistlers were propagating outward from the EDR, inconsistent with those suggested in streaming-instability scenario [Huang et al, 2016]. In previous studies, streaming instabilities [Divin et al, 2012] and the associated electron holes [Goldman et al, 2014] at separatrices and the perpendicular anisotropy of suprathermal electrons [e.g., Khotyaintsev et al, 2011;Fu et al, 2014] have been suggested as two possible mechanisms responsible for the generation of whistlers.…”

“…For instance, Deng and Matsumoto [2001] reported a good mediation of reconnection rate by whistlers at the Earth's magnetopause, using the Geotail data; Wei et al [2007] observed whistlers prior to reconnection and enhancement of whistlers during reconnection in the Earth's magnetotail, using the Cluster data; Huang et al [2016] presented two types of whistlers during Hall magnetic reconnection, using the Cluster data; Graham et al [2016], Le Contel et al [2016a], and Wilder et al [2016] observed strong whistler emissions in the separatrix region, using the Magnetospheric Multiscale (MMS) data; Khotyaintsev et al [2016] reported whistlers in the outflow region, using MMS data. For instance, Deng and Matsumoto [2001] reported a good mediation of reconnection rate by whistlers at the Earth's magnetopause, using the Geotail data; Wei et al [2007] observed whistlers prior to reconnection and enhancement of whistlers during reconnection in the Earth's magnetotail, using the Cluster data; Huang et al [2016] presented two types of whistlers during Hall magnetic reconnection, using the Cluster data; Graham et al [2016], Le Contel et al [2016a], and Wilder et al [2016] observed strong whistler emissions in the separatrix region, using the Magnetospheric Multiscale (MMS) data; Khotyaintsev et al [2016] reported whistlers in the outflow region, using MMS data.…”

Bursty emission of whistler waves in association with plasmoid collision

“…The present model can explain the bursty nature of whistler emissions as observed in the Earth's magnetosphere (e.g., Deng and Matsumoto, 2001;Wei et al, 2007;Tang et al, 2013;Graham et al, 2016;Huang et al, 2016;Zhao et al, 2016). The key processes to generate the whistlers are intense perpendicular heating of the electrons in association with plasmoid collision and the subsequent compression of the ambient magnetic field.…”

“…Whistler waves are fundamental plasma waves frequently observed in space in association with transient phenomena, such as collisionless shocks (e.g., Olson et al, 1969;Rodriguez and Gurnett, 1975;Lengyel-Frey et al, 1996;Zhang et al, 1999;Hull et al, 2012) and magnetic reconnection (e.g., Deng and Matsumoto, 2001;Wei et al, 2007;Tang et al, 2013;Graham et al, 2016;Huang et al, 2016;Zhao et al, 2016;Uchino et al, 2017). The waves have a righthand polarization with respect to the ambient magnetic field, so they can couple with the electrons through the cyclotron resonance and give rise to pitch-angle scattering and parallel acceleration (e.g., Kennel and Petschek, 1966;Gary and Wang, 1996;Schreiner et al, 2017).…”

Electrostatic and whistler instabilities excited by an electron beam

“…For example, a finite amplitude single electrostatic wave can be excited by a small cold beam 10,11 . Whistler waves can also be excited by an electron beam in a number of space plasma settings 1,[12][13][14] . Some electrostatic structures, such as double layers and electron holes, seems to be generated by current-carrying electron beams in the presence of density inhomogeneities 15 .…”