Authors: C. Kay (NASA GSFC/CUA), T. Nieves-Chinchilla (NASA GSFC), S. J. Hofmeister (Leibniz Institute for Astrophysics), E. Palmerio (Predictive Science)

Coronal mass ejections (CMEs) cause severe space weather effects throughout our solar system. 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. We take an existing arrival time model that includes expansion and deformation of the CME flux rope (ANTEATR, Kay et al. 2018, 2021) and add in a pile-up procedure (PUP) as a physics-based approach to modeling the CME-driven sheath. ANTEATR-PUP solves the Rankine-Hugoniot equations for an oblique shock to determine the shock speed and sheath density, magnetic field, temperature. The extra sheath mass affects the background drag calculation. Additionally, we introduce the ability for ANTEATR to use any 1D profile for the background solar wind, as opposed to the simple empirical models it previously relied upon. We present initial results from ANTEATR-PUP and compare with previous ANTEATR findings. Using results from an MHD simulation, we explore the effects of interactions with a static high speed stream (HSS) on the CME’s and sheath’s interplanetary evolution. We find that the drag forces essentially disappear while a CME remains within the HSS, but reappear stronger once the CME exits. The HSS-CME interaction produces the largest changes in the CME and sheath properties at 1~au when it occurs either close to the Sun or right before the CME reaches 1~au. We estimate that these changes could significantly affect the geoeffectiveness.