Sensitivity of Model Estimates of CME Propagation and Arrival Time to Inner Boundary Conditions. Issue 4 (24th April 2023)

• Record Type: Journal Article
• Authors: James, Lauren A.; Scott, Christopher J.; Barnard, Luke A.; Owens, Mathew J.; Lang, Matthew S.; Jones, Shannon R.
• Is Part Of: Space weather. Volume 21:Issue 4(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-04-24
• Subjects: Space environment -- Periodicals; 551.509992
• DOI: 10.1029/2022SW003289
• Languages: English
• ISSNs: 1542-7390

Abstract

Abstract: Accurately forecasting the arrival of coronal mass ejections (CMEs) at Earth is important to enabling mitigation of the associated space weather risks to society. This is only possible with accurate modeling of the event. To do so, we must understand the propagation of a CME through the heliosphere and quantify the performance of models through comparison with spacecraft observations. For the 12 December 2008 Earth‐directed CME event, we compute ensembles using the HUXt solar wind model to analyze CME distortion with a structured solar wind and explore hindcast arrival time error (ATE). By highlighting the impact CME shape has on Root‐Mean‐Square‐Error (RMSE) values, we show that time‐elongation profiles of fronts captured by the Heliospheric Imager (HI) instruments onboard NASA's STEREO mission match those of the modeled CME nose and flank and can therefore be used to infer details of the longitudinal extent of the CME. We then show that accounting for CME distortion is important to enable accurate estimates of the CME arrival at Earth. This can be achieved by either using observations of multiple features in HI data to infer CME evolution or mapping the solar wind back to a lower inner boundary to allow CMEs to be distorted close to the Sun. For the event studied we show that these approaches resulted in reduced RMSEs of 0.73° and 0.64° with an ATE of 1 hour and 3 hours respectively. Plain Language Summary: Coronal Mass Ejections (CMEs) are giant erupting magnetic flux ropes from the Sun into space. Upon engulfing Earth, they interact with the near‐Earth space environment and result in disruptions to modern electrical infrastructure. Therefore, accurately forecasting CME arrival time at Earth is vital in order to mitigate the risk of space weather. Here, for the 12 December 2008 Earth‐directed event, we use a simple‐physics solar wind model (HUXt) to explore the distortion that occurs to a CME throughout the journey from the Sun to Earth. Features of the leading edge are tracked from the viewpoint of two spacecraft (STEREO) that are positioned away from the Sun‐Earth line and compared to position profiles of bright‐light regions pictured by the mission's Heliospheric Imager cameras. By running the HUXt model many times, we explore the relationship between the error of the tracked features and the arrival time error of the hindcast. We find that using multiple features to quantify model performance can improve the arrival time prediction, compared to tracking a single feature. Alternatively, we can account for changes to the CME geometry that occur close to the Sun by ejecting a CME into the model earlier. Key Points: Best agreement between model and HI1 data is found for ensemble members that also lead to CME arrival times within 3 hr of observation Using data assimilated solar wind speed at the inner boundary showed a 4 hr improvement on CME arrival in this study By back‐mapping the inner boundary conditions to 8 R⊙, we demonstrate a more realistic longitudinal distortion of the CME