Modeling Interplanetary Expansion and Deformation of CMEs with ANTEATR‐PARADE I: Relative Contribution of Different Forces

Coronal Mass Ejections (CMEs) are key drivers of space weather activity but most predictions have been limited to the expected arrival time of a CME, rather than the internal properties that affect the severity of an impact. Many properties, such as the magnetic field density and mass density, follow conservation laws and vary systematically with changes in the size of a CME. We present ANTEATR-PARADE, the newest version of the ANTEATR arrival time model, which now includes physics-driven changes in the size and shape of both the CME's central axis and its cross section. Internal magnetic and external drag forces affect the acceleration of the CME in different directions, inducing asymmetries between the radial and perpendicular directions. These improvements should lead to more realistic CME velocities, both bulk and expansion, sizes and shapes, and internal properties. ANTEATR-PARADE is the first model of its kind that provides this level of detail on the time scales needed for future space weather predictions. We present the model details, an initial illustration of the general behavior, and a study of the relative importance of the different forces. The model shows a pancaking of both the cross section and central axis of the CME so that their radial extent becomes smaller than their extent in the perpendicular direction. For a single parameterization of our magnetic field model we find that the drag forces tend to exceed the magnetic forces and the results are very sensitive to the initial velocities of the CME.