Observation and numerical modeling of chromospheric evaporation during the impulsive phase of a solar flare

TL;DR

This study combines observations and numerical simulations to analyze chromospheric evaporation during a solar flare's impulsive phase, highlighting the role of enthalpy flux and ionization effects in producing observed downflows.

Contribution

It demonstrates that enthalpy flux dominates thermal conduction in certain flare conditions and emphasizes the importance of time-dependent ionization in modeling downflows.

Findings

Strong redshift observed only during impulsive phase

Enthalpy flux regime reproduces observed downflows

Time-dependent ionization is crucial for accurate modeling

Abstract

We have studied the chromospheric evaporation flow during the impulsive phase of the flare by using the Hinode/EIS observation and 1D hydrodynamic numerical simulation coupled to the time-dependent ionization. The observation clearly shows that the strong redshift can be observed at the base of the flaring loop only during the impulsive phase. We performed two different numerical simulations to reproduce the strong downflows in FeXII and FeXV during the impulsive phase. By changing the thermal conduction coefficient, we carried out the numerical calculation of chromospheric evaporation in the thermal conduction dominant regime (conductivity coefficient kappa0 = classical value) and the enthalpy flux dominant regime (kappa0 = 0.1 x classical value). The chromospheric evaporation calculation in the enthalpy flux dominant regime could reproduce the strong redshift at the base of the flare during the impulsive phase. This result might indicate that the thermal conduction can be strongly suppressed in some cases of flare. We also find that time-dependent ionization effect is importance to reproduce the strong downflows in Fe XII and Fe XV.