The Coupled Evolution of Electrons and Ions in Coronal Mass Ejection-Driven Shocks

Abstract

We present simulations of coronal mass ejections (CMEs) performed with a new two-temperature coronal model developed at the University of Michigan, which is able to address the coupled thermodynamics of the electron and proton populations in the context of a single fluid. This model employs heat conduction for electrons, constant adiabatic index (γ = 5/3), and includes Alfvén wave pressure to accelerate the solar wind. The Wang-Sheeley-Arge empirical model is used to determine the Alfvén wave pressure necessary to produce the observed bimodal solar wind speed. The Alfvén waves are dissipated as they propagate from the Sun and heat protons on open magnetic field lines to temperatures above 2 MK. The model is driven by empirical boundary conditions that includes GONG magnetogram data to calculate the coronal field, and STEREO/EUVI observations to specify the density and temperature at the coronal boundary by the Differential Emission Measure Tomography method. With this model, we simulate the propagation of fast CMEs and study the thermodynamics of CME-driven shocks. Since the thermal speed of the electrons greatly exceeds the speed of the CME, only protons are directly heated by the shock. Coulomb collisions low in the corona couple the protons and electrons allowing heat exchange between the two species. However, the coupling is so brief that the electrons never achieve more than 10% of the maximum temperature of the protons. We find that heat is able to conduct on open magnetic field lines and rapidly propagates ahead of the CME to form a shock precursor of hot electrons.

Plasma Physical Parameters Along Cme-Driven Shocks. Ii. Observation–simulation Comparison

“…As for the simple solar wind model, it is capable of distributing the energy of the shock transit between electrons and protons as expected from theory. Only the protons are heated by the kinetic energy dissipated at the shock front, while electrons undergo a pure adiabatic compression (which causes a much lower temperature increase, see, e.g., Manchester et al 2012). This model, however, does not take into account any additional phenomena occurring during the shock transit.…”

“…5. As stated in Manchester et al (2012), the electrons are expected not to receive energy dissipated at the shock front, because of their high thermal speed. Thus, a possible approach is to impose a pressure evolution equation for the electrons which does not introduce any dissipation mechanisms, leading to an electron heating only due to the shock compressivity.…”

“…As stated in Manchester et al (2012), the electrons and protons are expected to behave differently when subjected to a shock transit, because of their different thermal velocities. In particular, the electrons should not receive the heating due to kinetic energy dissipation at the shock front, since not even the fastest CME-driven shocks travel faster than the electron thermal speed.…”

“…Liu et al (2011) used the Space Weather Modeling Framework (SWMF; Tóth et al 2005), a 3D magnetohydrodynamic (MHD) simulation code, to simulate the propagation of CMEs and the associated shocks and found that near the Sun the magnetic field lines drape around the flux rope (the CME ejecta) and align themselves with the magnetic field in the flux rope. More recently, Manchester et al (2012) and Jin et al (2012Jin et al ( , 2013 implemented the two-temperature (2T) model of van der Holst et al (2010) in the MHD BATS-R-US code (Powell et al 1999) within the SWMF. They demonstrated that most of the 2T model outputs can fit WL observations of CMEdriven shocks by LASCO C2 and STEREO very well.…”

Global Numerical Modeling of Energetic Proton Acceleration in a Coronal Mass Ejection Traveling Through the Solar Corona

“…A flat spectrum of Alfvén waves is specified at the inner boundary along open field lines, and the wave energy density evolves according to a frequency-averaged wave transport equation in the WKB approximation (Sokolov et al 2009). The simulation used in this paper is one of the first self-consistent studies of global CME evolution in a physics-based solar wind model (Manchester et al 2012). A detailed description of all of the model's features is beyond the scope of this paper.…”