Chromosphere of the quiet Sun: II. Atmospheric response to small-scale magnetic flux emergence
Abstract
Context. The couplings between the photosphere, chromosphere, and corona in the quiet Sun (QS) are governed by a complex interplay between magnetic structuring, heating, mass-loading, and radiative cooling. The current constraints on how this balance responds to variations in small-scale magnetic flux are limited. Aims. We investigate how chromospheric heating and the thermodynamic response of higher atmospheric layers vary as a function of small-scale magnetic flux emergence under QS conditions. Methods. We performed a parametric set of 3D radiative-MHD simulations with the Bifrost code, starting from a weakly magnetised quiet-Sun reference model and injecting horizontal magnetic flux of increasing amplitude into the sub-surface convection zone. We analysed the resulting chromospheric dynamics, heating, mass-loading, and coronal response in quasi-static regimes. Results. Chromospheric temperatures and mechanical heating rise monotonically with increasing magnetic-field strength. Although the fractional contribution of shocks decreases from 23 to 5%, reconnecting current sheets (CSs) continue to remain steady at 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, thereby increasing 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. Conclusions. Our results demonstrate the sensitivity of chromospheric structure and dynamics to small-scale flux emergence and its key role in regulating coronal thermodynamics. In particular, this study has revealed a non-monotonic thermodynamic response in the upper atmosphere: stronger heating in the chromosphere can paradoxically lead to lower coronal temperatures as increased mass-loading enhances radiative losses. This result illustrates the chromosphere’s role as a thermodynamic gatekeeper, warranting further investigations of realistic flux-emergence models, as well as surface-to-corona parametrisation across various magnetic configurations, relevant to global solar wind models and space weather forecasts.
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BibTeX
@article{noraz2026chromosphere,
title = {{Chromosphere of the quiet Sun: II. Atmospheric response to small-scale magnetic flux emergence}},
author = {Q. Noraz and M. Carlsson and Guillaume Aulanier},
journal = {Astronomy \& Astrophysics - A\&A},
year = {2026},
month = jun,
doi = {10.1051/0004-6361/202660067},
eprint = {2605.03019},
archivePrefix = {arXiv},
url = {https://hal.science/hal-05742292v1},
note = {CC BY},
}
RIS
TY - JOUR
TI - Chromosphere of the quiet Sun: II. Atmospheric response to small-scale magnetic flux emergence
AU - Q. Noraz
AU - M. Carlsson
AU - Guillaume Aulanier
PY - 2026
DA - 2026/06/16
JO - Astronomy & Astrophysics - A&A
DO - 10.1051/0004-6361/202660067
UR - https://hal.science/hal-05742292v1
AB - Context. The couplings between the photosphere, chromosphere, and corona in the quiet Sun (QS) are governed by a complex interplay between magnetic structuring, heating, mass-loading, and radiative cooling. The current constraints on how this balance responds to variations in small-scale magnetic flux are limited. Aims. We investigate how chromospheric heating and the thermodynamic response of higher atmospheric layers vary as a function of small-scale magnetic flux emergence under QS conditions. Methods. We performed a parametric set of 3D radiative-MHD simulations with the Bifrost code, starting from a weakly magnetised quiet-Sun reference model and injecting horizontal magnetic flux of increasing amplitude into the sub-surface convection zone. We analysed the resulting chromospheric dynamics, heating, mass-loading, and coronal response in quasi-static regimes. Results. Chromospheric temperatures and mechanical heating rise monotonically with increasing magnetic-field strength. Although the fractional contribution of shocks decreases from 23 to 5%, reconnecting current sheets (CSs) continue to remain steady at 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, thereby increasing 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. Conclusions. Our results demonstrate the sensitivity of chromospheric structure and dynamics to small-scale flux emergence and its key role in regulating coronal thermodynamics. In particular, this study has revealed a non-monotonic thermodynamic response in the upper atmosphere: stronger heating in the chromosphere can paradoxically lead to lower coronal temperatures as increased mass-loading enhances radiative losses. This result illustrates the chromosphere’s role as a thermodynamic gatekeeper, warranting further investigations of realistic flux-emergence models, as well as surface-to-corona parametrisation across various magnetic configurations, relevant to global solar wind models and space weather forecasts.
SN - 0004-6361
SN - 1432-0746
ER -