FIDO‐SIT: The First Forward Model for the In Situ Magnetic Field of CME‐Driven Sheaths

Abstract

AbstractWe have shown previously that the in situ magnetic field of coronal mass ejections (CMEs) can be well reproduced by simple, physics‐driven flux rope models using the ForeCAT In situ Data Observer (FIDO, Kay et al., 2017). Here, we show that a similar approach can be taken to forward model the shock and sheath of a CME (Sheath Induced by Transient [SIT]). We develop a relation between the downstream density and magnetic field strength that only depends on the upstream properties and downstream speed. Next, we establish a set of well‐observed CME‐driven shocks combining results from several online catalogs. We establish a baseline using the observed downstream speed and show that the mean absolute errors only increase slightly to 3.4 cm and 3.8 nT when using a predicted downstream velocity. We also develop a model for the sheath duration or the standoff distance of the CME‐driven shock. While there is certainly room for improvement, our model does perform better than those currently available, reducing the error from 7.0 to 4.6 hr. We couple our flux rope and sheath models as FIDO‐SIT and present results for four observed cases. For three of the four cases, FIDO‐SIT reproduces the sheath magnetic field with an error of one third the total magnitude for each individual vector component.