Stochastic Heating, Differential Flow, and the Alpha-to-Proton Temperature Ratio in the Solar Wind

Abstract

We extend previous theories of stochastic ion heating to account for the motion of ions along the magnetic field. We derive an analytic expression for the ion-to-proton perpendicular temperature ratio in the solar wind for any ion species, assuming that stochastic heating is the dominant ion heating mechanism. This expression describes how this temperature ratio depends upon the average velocity of the ions along the magnetic field direction and the ratio of the parallel proton pressure to the magnetic pressure. We compare our model with previously published measurements of alpha particles and protons from the WIND spacecraft. We find that stochastic heating offers a promising explanation for these measurements when the fractional cross helicity and Alfven ratio at the proton-gyroradius scale have values that are broadly consistent with solar-wind measurements.

9 pages, 17 figures, submitted to the Astrophysical Journal

References in corpus (3)

• Residual Energy Spectrum of Solar Wind Turbulence
• The Dispersion Relations and Instability Thresholds of Oblique Plasma Modes in the Presence of an Ion Beam
• Observational Test of Stochastic Heating in Low-$\beta$ Fast Solar Wind Streams

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• Identification of Magnetic Flux Ropes from Parker Solar Probe Observations during the First Encounter
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• Three-dimensional magnetic reconnection in particle-in-cell simulations of anisotropic plasma turbulence
• Deceleration of Alpha Particles in the Solar Wind by Instabilities and the Rotational Force: Implications for Heating, Azimuthal Flow, and the Parker Spiral Magnetic Field
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• Dependence of Solar Wind Proton Temperature on the Polarisation Properties of Alfvénic Fluctuations at Ion-kinetic Scales
• The Velocity-Space Signature of Transit-Time Damping
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• Compound Effect of Alfvén Waves and Ion-cyclotron Waves on Heating/Acceleration of Minor Ions via the Pickup Process
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