Modeling properties of chromospheric evaporation driven by thermal conduction fronts from reconnection shocks

TL;DR

This paper develops a 1-D hydrodynamical model to study how thermal conduction fronts from reconnection shocks influence chromospheric evaporation, revealing scaling laws that can diagnose flare energy release parameters.

Contribution

It introduces a simplified atmospheric model to connect flare loop parameters with observable properties at the flow reversal point, providing new diagnostic tools.

Findings

Scaling-law relationships between flare parameters and FRP properties.

Identification of how post-shock and transition region temperatures affect evaporation.

Provision of quantitative diagnostics for coronal energy release based on chromospheric observations.

Abstract

Magnetic reconnection in the corona results in contracting flare loops, releasing energy into plasma heating and shocks. The hydrodynamic shocks so produced drive thermal conduction fronts (TCFs) which transport energy into the chromosphere and drive upflows (evaporation) and downflows (condensation) in the cooler, denser footpoint plasma. Observations have revealed that certain properties of the transition point between evaporation and condensation (the "flow reversal point" or FRP), such as temperature and velocity-temperature derivative at the FRP, vary between different flares. These properties may provide a diagnostic tool to determine parameters of the coronal energy release mechanism and the loop atmosphere. In this study, we develop a 1-D hydrodynamical flare loop model with a simplified three-region atmosphere (chromosphere/transition region/corona), with TCFs initiated by shocks introduced in the corona. We investigate the effect of two different flare loop parameters (post-shock temperature and transition region temperature ratio) on the FRP properties. We find that both of the evaporation characteristics have scaling-law relationships to the varied flare parameters, and we report the scaling exponents for our model. This provides a means of using spectroscopic observations of the chromosphere as quantitative diagnostics of flare energy release in the corona.