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

Abstract

We 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 −3 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.

Spatial Coherence of Interplanetary Coronal Mass Ejection Sheaths at 1 AU

“…There is not, however, an understanding of the extent to which different structures and their generation mechanisms are localized in the sheath. This knowledge of the longitudinal extent of magnetic fluctuations is highly important for understanding the formation and evolution of the sheaths and for the capability to predict and estimate their geoeffectiveness (Kay et al., 2020; Manchester et al., 2005). Recent studies (e.g., Lugaz et al., 2018; Owens et al., 2017) have even questioned the coherence of ICME ejecta, which are more organized structures than sheaths.…”

Spatial coherence of interplanetary coronal mass ejection sheaths at 1 AU

“…There is not, however, an understanding of the extent to which different structures and their generation mechanisms are localized in the sheath. This knowledge of the longitudinal extent of magnetic fluctuations is highly important for understanding the formation and evolution of the sheaths and for the capability to predict and estimate their geoeffectiveness (Manchester et al, 2005;Kay et al, 2020). Recent studies (e.g., Owens et al, 2017;Lugaz et al, 2018) have even questioned the coherence of ICME ejecta, which are more organized structures than sheaths.…”

OSPREI: A Coupled Approach to Modeling CME-Driven Space Weather with Automatically-Generated, User-Friendly Outputs

“…Within FIDO, the CME continues to expand as it passes over the spacecraft according to the speeds provided by ANTEATR. FIDO can also forecast the shock and sheath ahead of a CME using the Rankine-Hugoniot shock conditions with the CME and solar wind properties (Kay et al, 2020). This is a simple analytic shock model for the average sheath and cannot produce the stochastic fluctuations that are commonly observed.…”