Turbulent Heating between 0.2 and 1 au: A Numerical Study

Abstract

The heating of the solar wind is a key to understand its dynamics and acceleration process. The observed radial decrease of proton temperature in the solar wind is slow compared to the adiabatic prediction and it is thought to be caused by turbulent dissipation. To generate the observed 1/R decrease, the dissipation rate has to reach a specific level which varies in turn with temperature, wind speed, and heliocentric distance. We want to prove that MHD turbulent simulations can lead to the 1/R profile. We consider here the slow solar wind, characterized by a quasi-2D spectral anisotropy. We use the EBM (expanding box model) equations, which incorporate into 3D MHD equations the expansion due to the mean radial wind, allowing to follow the plasma evolution between 0.2 and 1 AU. We vary the initial parameters which are: Mach number, expansion parameter, plasma beta, and properties of the energy spectrum as the spectral range and slope. Assuming turbulence starts at 0.2 AU with a Mach number equal to unity, with a 3D spectrum mainly perpendicular to the mean field, we find radial temperature profiles close to 1/R in average. This is done at the price of limiting the initial spectral extent, corresponding to the small number of modes in the inertial range available, due to the modest Reynolds number reachable with high Mach numbers.

References in corpus (5)

• Electron and proton heating by solar wind turbulence
• Scaling Laws of Turbulence and Heating of Fast SolarWind: The Role of Density Fluctuations
• Anisotropy of third-order structure functions in MHD turbulence
• Evolution of turbulence in the expanding solar wind, a numerical study
• Beyond the Maltese cross: geometry of turbulence between 0.2 and 1 AU

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• Helios 2 observations of solar wind turbulence decay in the inner heliosphere
• On the Conservation of Turbulence Energy in Turbulence Transport Models
• Three-dimensional local anisotropy of velocity fluctuations in the solar wind
• Comparing turbulent cascades and heating vs spectral anisotropy in solar wind via direct simulations
• The effects of expansion and turbulence on the interplanetary evolution of a magnetic cloud