Comprehensive MHD modelling of ten successive CMEs driving a historic geomagnetic storm -- The 2024 Mothers Day event

TL;DR

This paper presents a comprehensive MHD simulation of ten interacting CMEs during the 2024 Mothers Day event, successfully modeling the geomagnetic storm's timing and intensity, and discusses challenges in simulating complex heliospheric interactions.

Contribution

It introduces a detailed 3D MHD modelling approach for multiple interacting CMEs and evaluates its effectiveness in predicting a historic geomagnetic storm.

Findings

Simulation predicted storm arrival within 2 hours of actual event.

Estimated storm strength with approximately 70% accuracy.

Highlights the importance of accurate CME input parameters for modelling success.

Abstract

Interacting coronal mass ejections (CMEs) result in complex heliospheric structures that can dramatically enhance their geoeffectiveness compared to isolated events. A striking example of such complex structures is that of the Mothers Day event, which occurred during 10-14 May 2024, leading to the strongest geomagnetic storm in decades. It was driven by at least ten interacting CMEs accompanied by flare and filament eruptions from the solar western hemisphere. We aim to understand its solar and heliospheric origins, variation in plasma and magnetic characteristics, and predict its geoeffectiveness. Furthermore, we focus on bringing to the community the challenges and limitations faced during themodelling of such a complex, yet important environment. We use multi-point remote observations of CMEs and employ different methods to estimate their speeds and geometry. These parameters drive the 3D magnetohydrodynamic simulations of CME evolution and heliospheric propagation in the framework of the EUHFORIA model. The best-performing simulation reproduced the arrival time of the storm and peak intensity with a lead of 2 hours, and estimated the storm strength with about 70% accuracy. This work underscores the requirements and challenges involved in accurately modelling extreme events. The major bottleneck was to constrain the CME input parameters that dictate the accuracy of the data-driven simulations. Predicting the impacts of the complex heliospheric structures during this event required the modelling of the CME-CME interactions accurately. As a community, we need to invest more in observational infrastructure while improving the speed and accuracy of our MHD forecasting models.