Predicting the Time of Arrival of Coronal Mass Ejections at Earth From Heliospheric Imaging Observations

Abstract

The time of arrival (ToA) of coronal mass ejections (CMEs) at Earth is a key parameter due to the space weather phenomena associated with the CME arrival, such as intense geomagnetic storms. Despite the incremental use of new instrumentation and the development of novel methodologies, ToA estimated errors remain above 10 h on average. Here, we investigate the prediction of the ToA of CMEs using observations from heliospheric imagers, i.e., from heliocentric distances higher than those covered by the existent coronagraphs. In order to perform this work, we analyze 14 CMEs observed by the heliospheric imagers HI-1 onboard the twin STEREO spacecraft to determine their front location and speed. The kinematic parameters are derived with a new technique based on the Elliptical Conversion (ElCon) method, which uses simultaneous observations from the two viewpoints from STEREO. Outside the field of view of the instruments, we assume that the dynamics of the CME evolution is controlled by aerodynamic drag, i.e., a force resulting from the interaction with particles from the background solar wind. To model the drag force, we use a physical model that allows us to derive its parameters without the need to rely on drag coefficients derived empirically. We found a CME ToA mean error of 1.6 ± 8.0 h ToA and a mean absolute error of 6.9 ± 3.9 h for a set of 14 events. The results suggest that observations from HI-1 lead to estimates with similar errors to observations from coronagraphs.

Why are ELEvoHI CME Arrival Predictions Different if Based on STEREO‐A or STEREO‐B Heliospheric Imager Observations?

“…For the five events, that are also included in our study, we obtain similar results as Braga et al. (2020). Please note that we run ELEvoHI in ensemble mode in this study.…”

“…Braga et al (2020) studied 14 CMEs using the drag model and a modified version of the ELCon model, to get the CME parameters (e.g., ϕ, λ, f) based on HI observations from both STEREO spacecraft simultaneously. For the five events, that are also included in our study, we obtain similar results as Braga et al (2020). Please note that we run ELEvoHI in ensemble mode in this study.…”

Why are ELEvoHI CME arrival predictions different if based on STEREO-A or STEREO-B heliospheric imager observations?

“…φ, λ, f ) based on HI observations from both STEREO spacecraft simultaneously. For the five events, that are also included in our study, we obtain similar results as Braga et al (2020). Please note that we run ELEvoHI in ensemble mode in this study.…”

“…by changing the values for f (from 0.4 to 0.7). Braga et al (2020) found a value of f ∼ 0.6 for most of the CMEs in their study.…”

“…Liu et al, 2010;Lugaz, 2010;Volpes & Bothmer, 2015). Braga et al (2020) studied 14 CMEs using the drag model and a modified version of the ELCon model, to get the CME parameters (e.g. φ, λ, f ) based on HI observations from both STEREO spacecraft simultaneously.…”