Draft version September 9, 2022 Typeset using L A T E X modern style in AASTeX62 Modeling FETCH Observations of a Coronal Mass Ejection E. A. Jensen, 1 W. B. Manchester IV, 2 D. B. Wexler, 3 J. E. Kooi, 4 T. Nieves-Chinchilla, 5 L. K. Jian, 5 A. Pevtsov, 6 and S. Fung 7 1 Planetary Science Institute, 1700 E Fort Lowell Rd STE 106, Tucson, AZ 85719, USA 2 Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI 48109, USA 3 Space Science Laboratory, University of Massachusetts Lowell, 600 Suffolk St., Lowell, MA 01854, USA 4 Remote Sensing Division, U.S. Naval Research Laboratory, 4555 Overlook Ave. SW, Washington, DC 20375, USA 5 Heliophysics Science Division, NASA Goddard Space Flight Center, 8800 Greenbelt Rd., Greenbelt, MD 20771, USA 6 National Solar Observatory 7 Goddard Space Flight Center ABSTRACT This paper evaluates the quality of CME analysis that has been undertaken with the rare Faraday rotation observation of an eruption. Exploring the capability of the FETCH instrument hosted on the MOST mission, a four-satellite Faraday rotation radio sounding instrument deployed between the Earth and the Sun, we discuss the opportunities and challenges to improving the current analysis approaches. Keywords: solar coronal mass ejections, solar magnetic fields, polarimetry, magneto- hydrodynamics 1. INTRODUCTION 1.1. History Coronal mass ejections produce the largest-scale disturbances in the heliosphere. As they approach Earth, CME magnetic ejecta may extend over 0.25 AU and the CME-driven shock may extend twice as far. For example, the intensity of the 2005 May CME disturbance is impressive at 1 AU with velocities approaching 2000 km/s, magnetic fields observed at over 100 nT and plasma densities at 50 protons cm -3 , magnitudes which range from 5 to 10 times ambient solar wind values. As such, these disturbances possess both the scale and intensity that strongly affect radio wave propagation through the heliosphere, which in turn allows for remote sens- ing of these extraordinary events. CMEs have been imaged with Thomson-scattered Corresponding author: E. A. Jensen ejensen@psi.edu arXiv:2209.03350v1 [astro-ph.IM] 7 Sep 2022