Statistical Study of Whistler Waves in the Solar Wind at 1 au

Abstract

Whistler waves are intermittently present in the solar wind, while their origin and effects are not entirely understood. We present a statistical analysis of magnetic field fluctuations in the whistler frequency range (above 16 Hz) based on about 801,500 magnetic field spectra measured over three years aboard ARTEMIS spacecraft in the pristine solar wind. About 13,700 spectra (30 hours in total) with intense magnetic field fluctuations satisfy the interpretation in terms of quasi-parallel whistler waves. We provide estimates of the whistler wave occurrence probability, amplitudes, frequencies and bandwidths. The occurrence probability of whistler waves is shown to strongly depend on the electron temperature anisotropy. The whistler waves amplitudes are in the range from about 0.01 to 0.1 nT and typically below 0.02 of the background magnetic field. The frequencies of the whistler waves are shown to be below an upper bound that is dependent on β e . The correlations established between the whistler wave properties and local macroscopic plasma parameters suggest that the observed whistler waves can be generated in local plasmas by the whistler heat flux instability. The whistler wave amplitudes are typically small, which questions the hypothesis that quasi-parallel whistler waves are capable to regulate the electron heat flux in the solar wind. We show that the observed whistler waves have sufficiently wide bandwidths and small amplitudes, so that effects of the whistler waves on electrons can be addressed in the frame of the quasi-linear theory.

Plasma Waves near the Electron Cyclotron Frequency in the Near-Sun Solar Wind

“…The near-f ce wave observations from Parker Solar Probe presented here are distinct from the vast majority of those reported in these prior studies in several regards: (i) the wave frequencies are considerably higher, centered on 0.7 f ce or f ce in Parker Solar Probe data, compared to 0.1 < f /f ce < 0.3 reported in prior studies (Lengyel-Frey et al 1996;Lin et al 1998;Moullard et al 2001;Lacombe et al 2014;Kajdič et al 2016;Stansby et al 2016;Tong et al 2019), (ii) the waves are electrostatic up to the sensitivity of the FIELDS data, whereas most prior studies identified whistler-mode waves using exclusively magnetic field data (Beinroth & Neubauer 1981;Lacombe et al 2014;Kajdič et al 2016;Tong et al 2019), (iii) the waves observed by Parker Solar Probe are both narrow band and frequently observed, observed up to 30% of the time when magnetic field conditions favorable to wave growth exist (prior studies of non-turbulence whistler-mode waves show much lower detection rates (e.g. (Lacombe et al 2014;Tong et al 2019))), and (iv) the near-f ce waves observed by Parker Solar Probe often include electron Bernstein modes, which have previously been reported in the solar wind only near shocks (Wilson et al 2010) or in conjunction with the AMPTE Li ion release (Baumgaertel & Sauer 1989).…”

“…(Wilson et al 2009;Ramírez Vélez et al 2012) and references therein) and stream interaction regions (Beinroth & Neubauer 1981;Lin et al 1998;Lengyel-Frey et al 1996;Breneman et al 2010), (ii) associated with the turbulent cascade of magnetic field fluctuations (e.g. (Lengyel-Frey et al 1996;Bruno & Carbone 2013;Narita et al 2016) and references therein), and (iii) present in the free solar wind (Zhang et al 1998;Lacombe et al 2014;Stansby et al 2016;Tong et al 2019).…”

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

“…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, ). All these properties support the similarity of generation mechanism of the whistler mode waves discussed in this paper to the WHFI.…”

Nonlinear Evolution of the Whistler Heat Flux Instability

“…The monotonous growth of βc is due to a numerical heating of the core electron population. (Tong et al 2019a). Namely, the spacecraft measurements showed that whistler waves amplitudes are generally below 0.02 B 0 , while typical amplitudes are of about 3 · 10 −3 B 0 (Tong et al 2019a).…”

“…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. The amplitude is positively correlated with β e and generally with the electron heat flux.…”