A Series of Advances in Analytic Interplanetary CME Modeling

Abstract

Coronal mass ejections (CMEs) and high speed streams (HSSs) are large‐scale transient structures that routinely propagate away from the Sun. Individually, they can cause space weather effects at the Earth, or elsewhere in space, but many of the largest events occur when these structures interact during their interplanetary propagation. We present the initial coupling of Open Solar Physics Rapid Ensemble Information (OSPREI), a model for CME evolution, with Mostly Empirical Operational Wind with a High Speed Stream, a time‐dependent HSS model that can serve as a background for the OSPREI CME. We present several improvements made to OSPREI in order to take advantage of the new time‐dependent, higher‐dimension background. This includes an update in the drag calculation and the ability to determine the rotation of a yaw‐like angle. We present several theoretical case studies, describing the difference in the CME behavior between a HSS background and a quiescent one. This behavior includes interplanetary CME propagation, expansion, deformation, and rotation, as well as the formation of a CME‐driven sheath. We also determine how the CME behavior changes with the HSS size and initial front distance. Generally, for a fast CME, we see that the drag is greatly reduced within the HSS, leading to faster CMEs and shorter travel times. The drag reappears stronger if the CME reaches the stream interaction region or upstream solar wind, leading to a stronger shock with more compression until the CME sufficiently decelerates. We model a CME–HSS interaction event observed by Parker Solar Probe in January 2022. The model improvements create a better match to the observed in situ profiles.

Updating Measures of CME Arrival Time Errors

“…The model inputs include both the reconstructed CME properties and the background solar wind through which the CME propagates. We know that CME reconstructions can be affected by large uncertainties (e.g., Kay & Palmerio, 2024; Verbeke et al., 2023) and that these can translate into AT errors of the order of 10 hr (e.g., Kay et al., 2020). This alone is sufficient to mask the effects of any background SW effects or inadequacies in the models.…”

“…The DONKI values should be used for the NASA GSFC predictions and should be similar to what was used by others, but each forecaster likely has their own coronal CME reconstruction that then use to drive their model. Coronal reconstructions are notoriously uncertain (e.g., Kay & Palmerio, 2024; Verbeke et al., 2023) so we expect there could be significant variation between the inputs used by different models. We have no means of comparing with the specific values used for each prediction, but suspect we may find more significant correlations if we could.…”

Challenges in Forecasting the Evolution of a Distorted CME Observed During the First Close Solar Orbiter Perihelion

“…The small difference in the two lines indicates a good fit between the GCS and the CME's neutral line tilt suggesting the absence of any significant CME rotation. In addition, Kay et al (2023) showed that any largescale rotations of a CME may only have minimal effects on the CME distortion compared to any solar wind drag effects.…”