Electromagnetic fluctuations of the whistler‐cyclotron and firehose instabilities in a Maxwellian and Tsallis‐kappa‐like plasma

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Abstract
Observed electron velocity distributions in the Earth's magnetosphere and the solar wind exhibit a variety of nonthermal features which deviate from thermal equilibrium, for example, in the form of temperature anisotropies, suprathermal tail extensions, and field‐aligned beams. The state close to thermal equilibrium and its departure from it provides a source for spontaneous emissions of electromagnetic fluctuations, such as the whistler. Here we present a comparative analysis of the electron whistler‐cyclotron and firehose fluctuations based upon anisotropic plasma modeled with Maxwellian and Tsallis‐kappa‐like particle distributions, to explain the correspondence relationship of the magnetic fluctuations as a function of the electron temperature and thermal anisotropy in the solar wind and magnetosphere plasmas. The analysis presented here considers correlation theory of the fluctuation‐dissipation theorem and the dispersion relation of transverse fluctuations, with wave vectors parallel to the uniform background magnetic field, in a finite temperature anisotropic thermal bi‐Maxwellian and nonthermal Tsallis‐kappa‐like magnetized electron‐proton plasma. Dispersion analysis and stability thresholds are derived for these thermal and nonthermal distributions using plasma and field parameters relevant to the solar wind and magnetosphere environments. Our results indicate that there is an enhancement of the fluctuations level in the case of nonthermal distributions due to the effective higher temperature and the excess of suprathermal particles. These results suggest that a comparison of the electromagnetic fluctuations due to thermal and nonthermal distributions provides a diagnostic signature by which inferences about the nature of the particle velocity distribution function can be ascertained without in situ particle measurements.

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