Return currents and energy transport in the solar flaring atmosphere

TL;DR

This paper investigates how background drift velocities influence energy loss rates of electrons in solar flares, proposing a new model that better fits observational data than traditional ohmic return current models.

Contribution

It introduces a novel formula for electron energy loss rate considering background drift velocities and validates it with RHESSI data, improving upon standard ohmic models.

Findings

New energy loss rate formula fits observational data better.

Background drift velocities significantly affect electron energy loss.

Traditional ohmic models are less accurate in describing energy transport.

Abstract

According to a standard ohmic perspective, the injection of accelerated electrons into the flaring region violates local charge equilibrium and therefore, in response, return currents are driven by an electric field to equilibrate such charge violation. In this framework, the energy loss rate associated to these local currents has an ohmic nature and significantly shortens the acceleration electron path. In the present paper we adopt a different viewpoint and, specifically, we study the impact of the background drift velocity on the energy loss rate of accelerated electrons in solar flares. We first utilize the Rutherford cross-section to derive the formula of the energy loss rate when the collisional target has a finite temperature and the background instantaneously and coherently moves up to equilibrate the electron injection. We then use the continuity equation for electrons and imaging spectroscopy data provided by RHESSI to validate this model. Specifically, we show that this new formula for the energy loss rate provides a better fit of the experimental data with respect to the model based on the effects of standard ohmic return currents.