X-CME: From In Situ Flux-Rope Reconstruction to CME Propagation Forecasting

TL;DR

The paper tackles the challenge of accurate CME arrival-time forecasting by bridging late-stage in situ magnetic structure measurements with early to intermediate-distance reconstructions. It introduces X-CME, which combines a local elliptical-cylindrical flux-rope fit embedded in a global tapered-torus geometry with a drag-based propagation model in a Parker-wind background, incorporating gravity, self-similar expansion, and a geometry-aware swept-area calculation. Validation on two events observed by PSP and Solar Orbiter shows arrival-time forecasts at Earth with typical errors of a few hours (about 2–4 hours) and the ability to distinguish central encounters from glancing blows, while also enabling Mars-proximity forecasts. The approach demonstrates that integrating intermediate-distance magnetic reconstructions with a physically consistent propagation framework can substantially improve inner-heliospheric CME forecasts and impact assessment for planetary and space infrastructure.

Abstract

Accurate forecasts of Coronal Mass Ejection (CME) arrival times and impact geometry remain a major challenge for space-weather operations. Coronagraph-based techniques typically achieve mean absolute errors of order ten hours, while in situ measurements at L1 provide excellent magnetic-field information but only tens of minutes of warning. In this work we introduce X-CME, a framework that links in situ flux-rope reconstructions at intermediate heliocentric distances with a physics-based CME propagation model. The internal magnetic structure is obtained with an elliptical cylindrical, radial poloidal flux-rope model and embedded into a tapered torus CME geometry. The subsequent propagation is computed by solving a drag-based equation of motion in a Parker solar-wind background, including gravitational deceleration, self-similar expansion of the cross section, and an explicit calculation of the CME wetted area and swept area in the ecliptic plane. We apply X-CME to two events observed by the Parker Solar Probe and Solar Orbiter spacecraft, respectively, and propagate the reconstructed structures to Earth and Mars. For both cases, the model reproduces the observed in situ signatures at L1 and predicts the CME arrival time at Earth with errors of a few hours (typically about 2-4 hours), while correctly distinguishing between central encounters and glancing blows. These results demonstrate that combining intermediate-distance magnetic reconstructions with a geometrically consistent propagation scheme can substantially improve CME arrival-time forecasts and impact assessment in the inner heliosphere.

Figures (12)

• Figure 2: Propagation velocity of the CME and solar wind velocity.
• Figure 3: a) Wetted area of the Tapered Torus, showing the intersection with the $z=0$ plane and the spacecraft located along the $x$-axis. b) Swept area of the CME in the ecliptic plane.
• Figure 4: CME angular extent projected onto the Solar System ecliptic plane.
• Figure : Event 1: PSP (18 August 2022).
• Figure : Event 1: propagation forecast from PSP to Earth and Mars.