Correlations between the proton temperature anisotropy and transverse high-frequency waves in the solar wind

Abstract

Correlations are studied between the power density of transverse waves having frequencies between $0.01$ and $1$ normalized to the proton gyrofrequency in the plasma frame and the ratio of the perpendicular and parallel temperature of the protons. The wave power spectrum is evaluated from high-resolution 3D magnetic field vector components, and the ion temperatures are derived from the velocity distribution functions as measured in fast solar wind during the Helios-2 primary mission at radial distances from the Sun between 0.3~AU and 0.9~AU. From our statistical analysis, we obtain a striking correlation between the increases in the proton temperature ratio and enhancements in the wave power spectrum. Near the Sun the transverse part of the wave power is often found to be by more than an order of magnitude higher than its longitudinal counterpart. Also the measured ion temperature anisotropy appears to be limited by the theoretical threshold value for the ion-cyclotron instability. This suggests that high-frequency Alfvén-cyclotron waves regulate the proton temperature anisotropy.

Some references have been added

References in corpus (2)

• Magnetic fluctuation power near proton temperature anisotropy instability thresholds in the solar wind
• Kinetic Simulations of Magnetized Turbulence in Astrophysical Plasmas

Cited by in corpus (15)

• Solar Wind Turbulence and the Role of Ion Instabilities
• Incorporating Kinetic Physics into a Two-Fluid Solar-Wind Model with Temperature Anisotropy and Low-Frequency Alfven-Wave Turbulence
• The Role of Proton-Cyclotron Resonance as a Dissipation Mechanism in Solar Wind Turbulence: A Statistical Study at Ion-Kinetic Scales
• Vlasov simulations of multi-ion plasma turbulence in the solar wind
• Proton, Electron, and Ion Heating in the Fast Solar Wind from Nonlinear Coupling Between Alfvenic and Fast-Mode Turbulence
• Kinetic cascade beyond magnetohydrodynamics of solar wind turbulence in two-dimensional hybrid simulations
• Radial evolution of the solar wind in pure high-speed streams: HELIOS revised observations
• Observational Test of Stochastic Heating in Low-$\beta$ Fast Solar Wind Streams
• Apparent temperature anisotropies due to wave activity in the solar wind
• Density Fluctuations Associated with Turbulence and Waves: First Observations by Solar Orbiter
• Coherent events at ion scales in the inner Heliosphere: \textit{Parker Solar Probe} observations during the first Encounter
• Relative drifts and temperature anisotropies of protons and $\alpha$ particles in the expanding solar wind -- 2.5D hybrid simulations
• Proton Kinetic Effects and Turbulent Energy Cascade Rate in the Solar Wind
• Temperature anisotropy and differential streaming of solar wind ions -- Correlations with transverse fluctuations
• Dependence of Solar Wind Proton Temperature on the Polarisation Properties of Alfvénic Fluctuations at Ion-kinetic Scales