Authors: Samriddhi Sankar Maity (Georgia State University, NASA/Goddard Space Flight Center), Talwinder Singh (Georgia State University), Nat Gopalswamy (NASA/Goddard Space Flight Center)

Coronal mass ejections (CMEs) are among the major drivers of extreme space weather phenomena at Earth, producing geomagnetic storms, disrupting satellite operations, and posing risks to both astronauts and terrestrial infrastructure. Statistical studies have shown that CME expansion characteristics vary across solar cycles, creating challenges for space weather forecasting and limiting our understanding of CME propagation dynamics. This study investigates the anomalous expansion behavior of CMEs observed during different solar cycles, with the aim of identifying the physical mechanisms responsible for such variability.

Magnetohydrodynamic (MHD) simulations employing flux-rope-based configurations provide an effective framework for reproducing and analyzing CME evolution. In this work, we present an MHD model of CME expansion based on a spheromak magnetic field configuration implemented within the MS-FLUKSS framework. The spheromak configuration offers a self-consistent representation of CME magnetic structure, enabling a systematic investigation of the influence of varying background solar wind conditions on CME propagation and expansion.

The model successfully reproduces CME propagation and expansion under realistic background solar wind pressure conditions, generating bulk propagation velocities of approximately 750 km s⁻¹. We find that CME attain larger angular widths in lower pressure backgrounds, consistent with observational studies. Simulation results further demonstrate the presence of southward (negative Bz) magnetic field components. We have successfully integrated the coronal model with a heliospheric domain, enabling us to calculate CME properties and characteristics at 1 AU. Future development of this study will involve systematic variations in dipole configurations and background solar wind conditions to understand the CME propagation and expansion.