A new approach for modelling chromospheric evaporation in response to enhanced coronal heating: I The method

TL;DR

This paper introduces a novel computational method that models chromospheric evaporation more accurately by treating the lower transition region as a discontinuity, improving density predictions in coronal loop simulations.

Contribution

The paper presents a new jump condition approach that enhances the modeling of the transition region in coronal heating simulations, reducing the need for high spatial resolution.

Findings

Improved coronal density evolution in coarse-resolution models.

Significant accuracy gains over unresolved transition region models.

Applicable to both 1D hydrodynamic and 3D MHD simulations.

Abstract

We present a new computational approach that addresses the difficulty of obtaining the correct interaction between the solar corona and the transition region in response to rapid heating events. In the coupled corona, transition region and chromosphere system, an enhanced downward conductive flux results in an upflow (chromospheric evaporation). However, obtaining the correct upflow generally requires high spatial resolution in order to resolve the transition region. With an unresolved transition region, artificially low coronal densities are obtained because the downward heat flux jumps across the unresolved region to the chromosphere, underestimating the upflows. Here, we treat the lower transition region as a discontinuity that responds to changing coronal conditions through the imposition of a jump condition that is derived from an integrated form of energy conservation. To illustrate and benchmark this approach against a fully resolved one-dimensional model, we present field-aligned simulations of coronal loops in response to a range of impulsive (spatially uniform) heating events. We show that our approach leads to a significant improvement in the coronal density evolution than just when using coarse spatial resolutions insufficient to resolve the lower transition region. Our approach compensates for the jumping of the heat flux by imposing a velocity correction that ensures that the energy from the heat flux goes into driving the transition region dynamics, rather than being lost through radiation. Hence, it is possible to obtain improved coronal densities. The advantages of using this approach in both one-dimensional hydrodynamic and three-dimensional magnetohydrodynamic simulations are discussed.