Apparent temperature anisotropies due to wave activity in the solar wind

Abstract

The fast solar wind is a collisionless plasma permeated by plasma waves on many different scales. A plasma wave represents the natural interplay between the periodic changes of the electromagnetic field and the associated coherent motions of the plasma particles. In this paper, a model velocity distribution function is derived for a plasma in a single, coherent, large-amplitude wave. This model allows one to study the kinetic effects of wave motions on particle distributions. They are by in-situ spacecraft measured by counting, over a certain sampling time, the particles coming from various directions and having different energies. We compare our results with the measurements by the Helios spacecraft, and thus find that by assuming high wave activity we are able to explain key observed features of the measured distributions within the framework of our model. We also address the recent discussions on nonresonant wave--particle interactions and apparent heating. The applied time-averaging procedure leads to an apparent ion temperature anisotropy which is connected but not identical to the intrinsic temperature of the underlying distribution function.

9 pages, 4 figures, publisher version under http://www.ann-geophys.net/29/909/2011/angeo-29-909-2011.html

References in corpus (6)

• Magnetic fluctuation power near proton temperature anisotropy instability thresholds in the solar wind
• Spectra and anisotropy of magnetic fluctuations in the Earth's magnetosheath: Cluster observations
• Gyrokinetic turbulence: a nonlinear route to dissipation through phase space
• Inertial range turbulence in kinetic plasmas
• Correlations between the proton temperature anisotropy and transverse high-frequency waves in the solar wind
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Cited by in corpus (12)

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• Enhanced proton parallel temperature inside patches of switchbacks in the inner heliosphere
• A new inner heliosphere proton parameter data set from the Helios mission
• The Impact of Turbulent Solar Wind Fluctuations on Solar Orbiter Plasma Proton Measurements
• Dependence of Solar Wind Proton Temperature on the Polarisation Properties of Alfvénic Fluctuations at Ion-kinetic Scales
• Conditions for proton temperature anisotropy to drive instabilities in the solar wind
• Ion pseudoheating by low-frequency Alfvén waves revisited
• Resonant whistler-electron interactions: MMS observations vs. test-particle simulation
• Turbulent transport in 2D collisionless guide field reconnection
• Minor ion heating in spectra of linearly and circularly polarized Alfvén waves: Thermal and non-thermal motions associated with perpendicular heating
• Wave emission of non-thermal electron beams generated by magnetic reconnection
• Compound Effect of Alfvén Waves and Ion-cyclotron Waves on Heating/Acceleration of Minor Ions via the Pickup Process