Whistler Wave Generation by Halo Electrons in the Solar Wind

Abstract

We present an analysis of simultaneous particle and field measurements from the ARTEMIS spacecraft which demonstrate that quasi-parallel whistler waves in the solar wind can be generated locally by a bulk flow of halo electrons (whistler heat flux instability). ARTEMIS observes quasi-parallel whistler waves in the frequency range ∼ 0.05 − 0.2f ce simultaneously with electron velocity distribution functions that are a combination of counter-streaming core and halo populations. A linear stability analysis shows that the plasma is stable when there are no whistler waves, and unstable in the presence of whistler waves. In the latter case, the stability analysis shows that the whistler wave growth time is from a few to ten seconds at frequencies and wavenumbers that match the observations. The observations clearly demonstrate that the temperature anisotropy of halo electrons crucially affects the heat flux instability onset: a slight anisotropy T /T ⊥ > 1 may quench the instability, while a slight anisotropy T /T ⊥ < 1 may significantly increase the growth rate. These results demonstrate that heat flux inhibition is strongly dependent on the microscopic plasma properties.

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

“…Journal of Geophysical Research: Space Physics solar wind WHFI (Tong, Vasko, Marc, et al, 2019). All these properties support the similarity of generation mechanism of the whistler mode waves discussed in this paper to the WHFI.…”

“…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. The electron beta β e (electron thermal pressure vs. the magnetic pressure) in this event varied from 1 to 6 (Figure h), within the statistical range of the instability observed in the solar wind (Tong, Vasko, Artemyev, et al, ), and the properties of these whistler waves that include the frequency range, right‐hand circular polarization, and quasiparallel propagation are all similar to that generated by the solar wind WHFI (Tong, Vasko, Marc , et al, ).…”

Nonlinear Evolution of the Whistler Heat Flux Instability

“…The simultaneous wave and particle measurements have recently shown that, though intermittently, whistler waves are indeed present in the solar wind and they are predominantly quasi-parallel that is consistent with the WHFI scenario (Lacombe et al 2014;Stansby et al 2016;Kajdič et al 2016;Tong et al 2019b,a). Tong et al (2019b) have demonstrated for several events that the whistler waves were indeed generated locally by the WHFI. The extensive statistical analysis by Tong et al (2019a) has shown that in the solar wind whistler waves have amplitudes typically less than a few hundredths of the background magnetic field.…”

Particle-in-cell Simulations of the Parallel Proton Firehose Instability Influenced by the Electron Temperature Anisotropy in Solar Wind Conditions

“…The initial values of the electron number density (n = 25 cm −3 ), magnetic field magnitude and ω e /Ω e are typical for the solar wind around 0.3 -0.5 AU, (e.g. Venzmer & Bothmer 2018;Tong et al 2019). A simulation box with the length of 60 d i has been employed, where d i = c/ω p is the ion inertial length.…”