CMEs and SEPs During November–December 2020: A Challenge for Real‐Time Space Weather Forecasting

Abstract

Predictions of coronal mass ejections (CMEs) and solar energetic particles (SEPs) are a central issue in space weather forecasting. In recent years, interest in space weather predictions has expanded to include impacts at other planets beyond Earth as well as spacecraft scattered throughout the heliosphere. In this sense, the scope of space weather science now encompasses the whole heliospheric system, and multipoint measurements of solar transients can provide useful insights and validations for prediction models. In this work, we aim to analyze the whole inner heliospheric context between two eruptive flares that took place in late 2020, that is, the M4.4 flare of 29 November and the C7.4 flare of 7 December. This period is especially interesting because the STEREO-A spacecraft was located ∼60° east of the Sun-Earth line, giving us the opportunity to test the capabilities of "predictions at 360°" using remote-sensing observations from the Lagrange L1 and L5 points as input. We simulate the CMEs that were ejected during our period of interest and the SEPs accelerated by their shocks using the WSA-Enlil-SEPMOD modeling chain and four sets of input parameters, forming a "mini-ensemble." We validate our results using in situ observations at six locations, including Earth and Mars. We find that, despite some limitations arising from the models' architecture and assumptions, CMEs and shockaccelerated SEPs can be reasonably studied and forecast in real time at least out to several tens of degrees away from the eruption site using the prediction tools employed here.Plain Language Summary Coronal mass ejections (CMEs) and solar energetic particles (SEPs) are phenomena from the Sun that are able to cause significant disturbances at Earth and other planets. Reliable predictions of these events and their effects are among the major goals of space weather forecasts, which aim to tackle all processes related to solar activity that can endanger human technology and society. In recent years, the breadth of space weather science has started to encompass other locations than Earth, ranging from all solar system planets to spacecraft scattered throughout space. In this work, we test our current capabilities in predicting space weather events in the inner solar system (i.e., within the orbit of Mars) for a period in late 2020. We use a chain of models that are able to simulate the background solar wind as well as transient phenomena such as CMEs and SEPs, and compare our results with spacecraft measurements from six well-separated locations, including Earth and Mars. We find that our current forecasting tools, despite their limitations, can successfully provide reasonable predictions of both CMEs and SEPs, especially out to several tens of degrees around the corresponding eruption source region on the Sun.

The Effect of the Ambient Solar Wind Medium on a CME-driven Shock and the Associated Gradual Solar Energetic Particle Event

“…Although such a transport process might have contributed to shaping the SEP event detected at Bepi and Earth, our modeling suggests that variations of the energetic particle emission at the CME-driven shock due to the shock interacting with the varying background solar wind, and in particular the SIR, may have played a dominant role. A similar explanation for another event was proposed by Ding et al (2022), where the authors used the improved Particle Acceleration and Transport in the Heliosphere model (iPATH; see Hu et al 2017, and references therein) to study the SEP event on 2020 November 29, observed by Solar Orbiter, Parker Solar Probe, STEREO-A, and spacecraft near Earth and Mars (Kollhoff et al 2021;Palmerio et al 2022). The CME generating that event also interacted with a high-speed stream, and the authors likewise concluded that this interaction and the resulting deformation of the shock wave played an important role in the variation of time-intensity profiles measured at different spacecraft.…”

Upstream Solar Wind Prediction up to Mars by an Operational Solar Wind Prediction System

“…Although there is data gap from MAVEN, comparing with the plasma data observed by Mars Express (see in Figure A3 from Palmerio et al. (2022)), the predicted CME peak time at Mars is around 22 hr later than the observed peak time. Palmerio et al.…”

Modeling a Coronal Mass Ejection from an Extended Filament Channel. II. Interplanetary Propagation to 1 au

“…By projecting the GCS wireframe onto the plane of sky of the coronagraph imagery, a user can adjust the six free parameters until the obtained shell visually matches the CME's appearance. Forward modeling with the GCS technique is often performed to derive CME input parameters for analytical (e.g., Kay & Gopalswamy 2017;Čalogović et al 2021) and MHD (e.g., Scolini et al 2020;Palmerio et al 2022a) simulations, but in the case of the 2015 July 9 event, there are two factors that make the analysis more complex than usual. First, the Solar Terrestrial Relations Observatory Ahead (STEREO-A) spacecraft was in superior conjunction with Earth, meaning that most of its instruments were not operational and only the SOHO (Earth) vantage point is available.…”

“…This is likely due to the specific geometry and magnetic description of each of the CME ejecta, which may in turn yield different interaction outcomes. For example, in the EUHFORIA +Spheroid run (Figure 4(b)), the lack of a magnetized ejecta is not expected to result in a realistic interaction process (see also Palmerio et al 2022a), but rather in a CME-like disturbance propagating more or less straightforwardly through a background wind. In the EUHFORIA+Spheromak run (Figure 4(c)), the lack of CME legs may represent less of an "obstacle" to the ambient solar wind, which in turn may be able to flow about the ejecta with minimal interaction of the two flux systems.…”