Current-driven flare and CME models

TL;DR

This paper reviews the role of electric currents in solar flares and CMEs, emphasizing the importance of current configurations, EMF, and magnetic helicity in energy release and eruption dynamics.

Contribution

It introduces a semi-quantitative multi-current model and highlights the lack of a comprehensive self-consistent model for flare energy transport.

Findings

Currents are central to energy release in flares and CMEs.

Magnetic helicity influences CME acceleration and structure.

Current configurations change during eruptions, affecting energy dynamics.

Abstract

Roles played by the currents in the impulsive phase of a solar flare and in a coronal mass ejection (CME) are reviewed. Solar flares are magnetic explosions: magnetic energy stored in unneutralized currents in coronal loops is released into energetic electrons in the impulsive phase and into mass motion in a CME. The energy release is due to a change in current configuration effectively reducing the net current path. A flare is driven by the electromotive force (EMF) due to the changing magnetic flux. The EMF drives a flare-associated current whose cross-field closure is achieved by redirection along field lines to the chromosphere and back. The essential roles that currents play are obscured in the "standard" model and are described incorrectly in circuit models. A semi-quantitative treatment of the energy and the EMF is provided by a multi-current model, in which the currents are constant and the change in the current paths is described by time-dependent inductances. There is no self-consistent model that includes the intrinsic time dependence, the EMF, the flare-associated current and the internal energy transport during a flare. The current, through magnetic helicity, plays an important role in a CME, with twist converted into writhe allowing the kink instability plus reconnection to lead to a new closed loop, and with the current-current force accelerating the CME through the torus instability.