New Theory of Whistler Waves Observed during Magnetotail Reconnection*
Abstract:Themis measurements1 in the vicinity of dipolarization fronts in Earth's magnetotail have detected a spectrum of quasi-parallel whistler waves in a band of frequencies roughly between 0.3 and 0.7 times the electron cyclotron frequency. The whistler waveforms are frequently punctuated by bipolar field structures interpretable as electron phase space holes. It has been suggested1 that the whistlers are driven by (measured) electron temperature anisotropy and that the holes may arise from nonlinear electrostatic trapping associated with the whistlers.
Kinetic theory and simulations are used to study this interpretation in more detail and to explore an alternate explanation in which electron hole quasiparticles drive whistlers by Čerenkov emission, as recently found in reconnection simulations and explained by theory.2 Many features of the observations are consistent with the new explanation, including whistler phase velocities and frequencies.
*Work supported by NASA MMS-IDS Grant
1Deng, et al., J. Geophys. Res. 115, A09225 (2010)
2Goldman, et al., Phys. Rev. Lett, 112, 145002 (2014)