MHD Simulations of CMEs with Energy Conservation: Reconnection Thermodynamics as a Critical Aspect of CME Dynamics

A long-standing challenge to both basic space science and space weather capabilities is understanding what determines the amount of energy that goes into the CME (mass motions) versus the flare (plasma heating) in a solar eruptive event. It is also unclear what role thermodynamics plays in shaping CME dynamics. Although there have been many detailed observational studies of this issue using particular events, there have been very few quantitative theoretical studies due to the difficulty in keeping an accurate track of the energy released by the explosive reconnection during the flare impulsive phase.

 

In this work, we conduct MHD simulations of the CME using an energy-conservative numerical scheme, which ensures energy conservation and accurate tracking of the energy release channels. The simulations are based on the Alfvén Wave Solar Model-Realtime (AWSoM-R). We used a simple photospheric magnetic field map composed of two dipoles. We then used the statistical injection of the condensed helicity model to generate CME eruptions.

 

First, we analyzed the evolution of the magnetic, thermal, and kinetic energies during the CME eruption and found that the fraction of the released magnetic energy converted to thermal energy can be \approx 40 \%. We noticed that using the energy conservation scheme results in significantly more energy being converted to kinetic energy.

 

The thermal energy leads to extremely high temperatures in the flare current sheet. We analyzed the evolution of density, electron temperature, and ion temperature in the flare current sheet. We found that extremely high temperatures hinder reconnection, resulting in a long-lasting current sheet. A second CME eruption is triggered due to this current sheet.

 

Our results show that energy conservation and full thermodynamics play a key role in affecting the CME eruption process. We discuss the implications of our results for understanding energy release in a solar eruption and for interpreting observations of CMEs/eruptive flares.