Total solar eclipse 2024 modelling with COCONUT

TL;DR

This work validates the full 3D MHD coronal model COCONUT by forecasting the 2024 total solar eclipse from $1\,R_\odot$ to $30\,R_\odot$ and comparing against eclipse images and white-light/polarized-brightness observations. It contrasts quasi-steady and time-dependent inner-boundary driving using GONG magnetograms, showing that dynamic driving improves streamer reproduction, with daily versus hourly cadence having limited impact due to processed magnetic maps. The study highlights west-limb accuracy and east-limb sensitivity to backside magnetic data, and demonstrates the feasibility of using data-driven MHD models for eclipse-based validation and space-weather forecasting, while outlining the need for higher-resolution, less-processed magnetograms and broader validation. Overall, COCONUT provides a practical framework for time-dependent coronal modelling and forward WL/pB synthesis, contributing to more reliable coronal reconstructions during highly magnetically active periods.

Abstract

Coronal modelling is crucial for a better understanding of solar and helio-physics. Due to the strong brightness of the Sun and the lack of white light observations of the solar atmosphere and low corona (1-1.5R$_\odot$), total solar eclipses have become a standard approach for validating the coronal models. In this study, we validate the COCONUT coronal model by predicting the coronal configuration during the total solar eclipse on April 8, 2024. We aim to predict the accurate configuration of the solar corona during the total solar eclipse on April 8, 2024. We utilise the full 3D MHD model to reconstruct the solar corona from the solar surface to $30\;R_\odot$. The upcoming total solar eclipse predictions were conducted in three different regimes: quasi-steady driving of the inner boundary conditions (BCs) with a daily cadence and dynamic driving of the inner BCs with both daily and hourly cadences. The results from all the simulations are compared to the total solar eclipse images. Additionally, the synthetic white-light (WL) images are generated from the STEREO-A field of view and compared to COR2 observed images. Normalised polarised brightness is compared in the COR2 and synthetic WL images. The predicted solar corona does not vary significantly in the first half of the prediction window. The dynamic simulations yielded better results than the quasi-steady predictions. The west limb was reconstructed better in the simulations than the east limb. We have predicted the total solar eclipse coronal configuration 18 days before the total solar eclipse. We can conclude that the dynamic simulations produced more accurate predictions. The availability of comprehensive observations is crucial, as the emergence of the active region on the east limb made it difficult to accurately predict the east limb coronal configuration due to incorrect input of magnetic field data.

Figures (10)

• Figure 1: The original GONG (upper panels) and pre-processed input magnetograms (lower panels) for March 21, March 28, April 3 and April 8. The colour maps are saturated to [-20, 20] G range. All maps are rotated to align with the Earth's view angle as of April 8, 2024. Squares 1, 2 and 3 represent the areas of interest.
• Figure 2: Total solar eclipse predictions by the COCONUT model in the quasi-steady regime. Each figure corresponds to the corona prediction for different magnetogram files from Figure \ref{['fig:input_magnetograms']}. The solar surface is coloured with the radial magnetic field values saturated to [-4,4] G. The magnetic field lines are overplotted on the eclipse image. The blue lines indicate the directions of the selected streamers based on the eclipse image. Red lines correspond to the direction of the same streamers as modelled by COCONUT simulations. Eclipse image credits: Eclipse team of Nanjing University - Wu, Sizhe (photographer); Li, Yihua; Huang, Yuhao; Lao, Qinghui; Cheng, Xin; Qu, Zhongquan.
• Figure 3: Total solar eclipse predictions by the COCONUT model in the dynamic regime with daily updated magnetograms. Each figure corresponds to the corona prediction for different magnetogram files from Figure \ref{['fig:input_magnetograms']}. The solar surface is colored with the radial magnetic field values saturated to [-4,4] G. The magnetic field lines are overplotted on the eclipse image. The blue lines indicate the directions of the selected streamers based on the eclipse image. Red lines correspond to the direction of the same streamers as modelled by COCONUT simulations. Eclipse image credits: Eclipse team of Nanjing University - Wu, Sizhe (photographer); Li, Yihua; Huang, Yuhao; Lao, Qinghui; Cheng, Xin; Qu, Zhongquan.
• Figure 4: Total solar eclipse predictions by the COCONUT model in the dynamic regime with hourly updated magnetograms. Each figure corresponds to the corona prediction for different magnetogram files from Figure \ref{['fig:input_magnetograms']}. The solar surface is colored with the radial magnetic field values saturated to [-4,4] G. The magnetic field lines are overplotted on the eclipse image. The blue lines indicate the directions of the selected streamers based on the eclipse image. Red lines correspond to the direction of the same streamers as modelled by COCONUT simulations. Eclipse image credits: Eclipse team of Nanjing University - Wu, Sizhe (photographer); Li, Yihua; Huang, Yuhao; Lao, Qinghui; Cheng, Xin; Qu, Zhongquan.
• Figure 5: Total solar eclipse predictions by the COCONUT model with the magnetogram observed on April 10 in the quasi-steady, dynamic daily cadence and dynamic hourly regimes. The solar surface is colored with the radial magnetic field values saturated to [-4,4] G. The magnetic field lines are overplotted on the eclipse image. The blue lines indicate the directions of the selected streamers based on the eclipse image. Red lines correspond to the direction of the same streamers as modelled by COCONUT simulations. Eclipse image credits: Eclipse team of Nanjing University - Wu, Sizhe (photographer); Li, Yihua; Huang, Yuhao; Lao, Qinghui, Cheng, Xin; Qu, Zhongquan.