Beyond Basic Drag - Effects of Solar Wind Pile-Up and High Speed Streams on CME Evolution

Connecting remote and in situ observations of CMEs requires understanding how a CME evolves during its interplanetary propagation. Many interplanetary CME models are limited to a basic drag interaction with the background solar wind, but actual interplanetary CME evolution is a much more complicated process. As a fast CME propagates through interplanetary space it accumulates solar wind material at its front. This pile-up of material, or CME-driven sheath, can be important in determining the geoeffectiveness of a CME. CMEs can also interact with other structures, such as a high speed stream (HSS), during their interplanetary journey. These interactions can lead to significant changes in their propagation and internal properties, potentially leading to large differences between what was originally predicted from remote observations and what was actually seen in situ. We take an existing arrival time model that uses drag, magnetic, and thermal forces for a more realistic evolution of the expansion and deformation of a CME flux rope (ANTEATR, Kay et al. 2018, 2021) and add a pile-up procedure (PUP) as a physics-based approach to modeling the CME-driven sheath. Additionally, we have modified ANTEATR so that it can use any 1D profile for the background solar wind, as opposed to the simple empirical models it previously relied upon. This allows us to explore the interaction between a CME and its sheath and a HSS embedded in the background solar wind. We quantify the significance of the interaction between a CME and its sheath with a HSS stream and identify how the forces acting upon the CME and sheath change throughout the interaction.