Suprathermal Electrons in the Solar Corona: Can Nonlocal Transport Explain Heliospheric Charge States?

Abstract

There have been several ideas proposed to explain how the Sun's corona is heated and how the solar wind is accelerated. Some models assume that open magnetic field lines are heated by Alfven waves driven by photospheric motions and dissipated after undergoing a turbulent cascade. Other models posit that much of the solar wind's mass and energy is injected via magnetic reconnection from closed coronal loops. The latter idea is motivated by observations of reconnecting jets and also by similarities of ion composition between closed loops and the slow wind. Wave/turbulence models have also succeeded in reproducing observed trends in ion composition signatures versus wind speed. However, the absolute values of the charge-state ratios predicted by those models tended to be too low in comparison with observations. This letter refines these predictions by taking better account of weak Coulomb collisions for coronal electrons, whose thermodynamic properties determine the ion charge states in the low corona. A perturbative description of nonlocal electron transport is applied to an existing set of wave/turbulence models. The resulting electron velocity distributions in the low corona exhibit mild suprathermal tails characterized by "kappa" exponents between 10 and 25. These suprathermal electrons are found to be sufficiently energetic to enhance the charge states of oxygen ions, while maintaining the same relative trend with wind speed that was found when the distribution was assumed to be Maxwellian. The updated wave/turbulence models are in excellent agreement with solar wind ion composition measurements.

Accepted for publication in Astrophysical Journal Letters. 5 pages (emulateapj style), 3 figures

References in corpus (2)

• Self-consistent Coronal Heating and Solar Wind Acceleration from Anisotropic Magnetohydrodynamic Turbulence
• A Contemporary View of Coronal Heating

Cited by in corpus (13)

• Origins of the Ambient Solar Wind: Implications for Space Weather
• Non-Equilibrium Processes in the Solar Corona, Transition Region, Flares, and Solar Wind \textit{(Invited Review)}
• A Steady-State Picture of Solar Wind Acceleration and Charge State Composition Derived from a Global Wave-Driven MHD Model
• Physical correlations lead to kappa distributions
• Suprathermal electron distributions in the solar transition region
• Ion Charge States in a Time-Dependent Wave-Turbulence-Driven Model of the Solar Wind
• The electron acoustic waves in plasmas with two kappa-distributed electrons at the same temperatures and immobile ions
• The collision frequencies in the plasmas with the power-law q-distributions in nonextensive statistics
• The Theory of Thermodynamic Relativity
• Effect of magnetic field on viscosity in the weakly ionized and magnetized plasma with power-law q-distributions in nonextensive statiostics
• Stationary states of polytropic plasmas
• A parametric study of solar wind properties and composition using fluid and kinetic solar wind models
• Multi-diagnostic convergence: a single measurement in weakly collisional plasmas