SIR-HUXt—A Particle Filter Data Assimilation Scheme for CME Time-Elongation Profiles

Abstract

We present SIR-HUXt, the integration of a sequential importance resampling data assimilation scheme with the HUXt solar wind model. SIR-HUXt assimilates the time-elongation profiles of Coronal Mass Ejection (CME) fronts in the low heliosphere, like those extracted from heliospheric imager (HI) data. Observing System Simulation Experiments are used to explore SIR-HUXt's performance for a simple synthetic CME scenario of an Earth directed CME in a uniform solar wind, where the CME is initialized with the average CME speed and width. These experiments are performed for a range of observer locations, from 20° to 90° behind Earth, spanning the L5 point where ESA's Vigil mission will return HI data for operational space weather forecasting. For this idealized scenario, SIR-HUXt performs well at constraining the CME speed, and has some success at constraining the CME longitude while the CME width is largely unconstrained by SIR-HUXt. Rank-histograms suggest the SIR-HUXt ensembles are well calibrated, with no indications of bias or under/over dispersion. Improved constraints on the initial CME speed lead to improvements in the CME transit time and arrival speed. For an L5 observer, SIR-HUXt reduced the transit time and arrival speed uncertainties by 69% and 63%. Therefore, SIR-HUXt could improve the real-world representivity of HUXt simulations and reduce the uncertainty of CME arrival time forecasts. The idealized scenario studied here likely enhances SIR-HUXt's performance relative to the challenge of simulating real-world CMEs and solar wind conditions. Future work should validate SIR-HUXt with case studies of real CMEs in structured solar wind.