Chromosphere of the quiet sun: II. Atmospheric response to small-scale magnetic flux emergence

TL;DR

This study uses 3D radiative-MHD simulations to explore how small-scale magnetic flux emergence influences the chromosphere and corona in the quiet Sun, revealing complex heating and temperature responses.

Contribution

It provides new insights into the thermodynamic coupling between the chromosphere and corona driven by small-scale magnetic flux emergence.

Findings

Chromospheric temperatures and heating increase with magnetic field strength.

Coronal base temperature peaks at intermediate magnetic amplitudes and decreases at higher strengths.

Stronger magnetic fields enhance chromospheric heating and mass loading, affecting coronal thermodynamics.

Abstract

Coupling between the photosphere, chromosphere and corona in the quiet Sun (QS) is governed by a complex interplay between magnetic structuring, heating, mass loading, and radiative cooling. Constraining how this balance responds to variations in small-scale magnetic flux remains limited. We investigate how chromospheric heating and its thermodynamic coupling to higher atmospheric layers vary as a function of small-scale magnetic flux emergence. We performed a parametric set of 3D radiative-MHD simulations with the Bifrost code, starting from a weakly magnetised QS reference model and injecting horizontal magnetic flux of increasing amplitude into the sub-surface convection zone. The resulting chromospheric dynamics, heating, mass loading, and coronal response were analysed. Chromospheric temperatures and mechanical heating rise monotonically with increasing magnetic-field strength. Although the fractional contribution of shocks decreases, reconnecting current sheets keeps maintaining about 50%. In contrast, the temperature at the base of the corona exhibits a non-monotonic response, reaching a maximum at intermediate magnetic amplitudes and decreasing for the strongest-field case. We show that stronger magnetic-field strength increases chromospheric heating, which increases the coronal-base density through efficient mass loading, and amplifies radiative losses. These density-driven radiative losses dominate the coronal energy balance and thus lead to reduced coronal-base temperatures despite increased heating. Our results demonstrate the sensitivity of chromospheric structure and dynamics to small-scale flux emergence, and its key role in regulating coronal thermodynamics. This result illustrates the chromosphere-s role as a thermodynamic gatekeeper, and further warrants future investigations of atmospheric models relevant to global solar-wind models and space-weather forecasts.