Highlights

– an overview of the SWR1, SWR2, CD5, CD7 session –

Evangelia Samara(1); Tinatin Baratashvili(2)
(1)NASA/GSFC;
(2)Leuven University

Empirically drivel global model of the heliosphere (Riley et al. 2001)

CMEs, SEPs and the fast solar wind are the major drivers of space weather in the heliosphere. Understanding these phenomena and being able to timely and reliably predict them is of utmost importance not only to mitigate their possible consequences to our planet, but also to protect our technologies and systems in space. Even though during the last decades significant progress has been made towards their physical understanding by employing multi-space observations and state-of-the-art models, many more steps should be undertaken to fully comprehend their complexity. To discuss the latest advances in that   direction, sessions SWR1, SWR2, CD5 and CD7 will host a number of engaging talks which address this matter. More specifically, during SWR1, a number of contributions on the magnetic topology, dynamics, and coupling throughout the different layers of the solar atmosphere that help understanding the formation mechanisms of solar wind structures and the drivers of solar energetic phenomena, will be presented. In SWR2, recent advances in both observations and modelling of CMEs and SEP events and their impacts will be discussed aiming to initiate collaborations between researchers and industry. CD5 will provide a forum for new and ongoing efforts bridging the gap between lower and high particle energies, facilitating space weather research and extending future predictive capabilities. Last but not least, CD7 session aims to explore current topics pertaining to the origin, evolution, and space weather-related effects of slow and fast solar wind.

You can get more insights of the talks in the SWR1 session on Thursday afternoon (17:30 – 18:30) and Friday morning (9.00 – 10.15). SWR2 will be held on Monday (14:00 – 16:00), Tuesday & Wednesday (9:00-10:15) and Thursday during both morning and afternoon intervals (9:00 – 10:15 and 14:15 – 15:15). The talks of the CD5 will take place Monday morning (12:00 – 13:00) and Thursday afternoon (17:30 – 18:30). The talks of CD7 will take place Tuesday afternoon during two time intervals (14:15 – 15:15 and 17:30 – 18:30) as well as Thursday afternoon (17:30 – 18:30). 

The Figure shows the variation with height of the temperature, LOS velocity, field strength and inclination across different optical depths in the solar atmosphere,

Fabiana Ferrente et al., (talk on Thursday, 07.11 at 18:15; contributed highlight text, here), the SWR1 highlight provides new insights into the vertical structure of solar flares but also highlights the complex interplay between thermal and magnetic processes during and after such events. More specifically, the authors take a closer look at an X1.6-class solar flare that occurred in active region AR 12192 on October 22, 2014, during solar cycle 24. Using data from the IRIS instrument and advanced spectropolarimetric techniques, they aimed to uncover the thermal and magnetic properties of this significant flare event. The analysis focused on both the chromosphere and photosphere of the Sun during this flare. By using the DeSIRe inversion code, they were able to explore the spatial distribution of the flare ribbon and the vertical stratification of key atmospheric parameters. “One of the most notable findings […]” of this work is that “[…] the lower layers of the atmosphere, particularly the photosphere, remained relatively undisturbed, while the chromosphere experienced a striking temperature increase, reaching up to 15,000 K. This intense heating was paired with strong upward plasma flows moving at speeds up to 20 km/s, suggesting that the flare was producing hot material moving outwards from the Sun.“

As a highlight of the SWR1 session, David Afonso Delgado et al., (talk on Friday, 08.11 at 09:00; contributed highlight text, here) will underline in his presentation the importance of the upcoming Chromospheric Magnetism Explorer (CMEx) mission.  CMEx is being developed with the purpose of exploiting the full potential of the ultraviolet region of the solar spectrum to quantify the magnetic field vector throughout the solar atmosphere. MHD simulations predict that certain types of solar eruptions require the prior formation of a magnetic flux rope (MFR). The MFR develops from a simpler sheared magnetic arcade (SMA) before the eruption. The stratification of the magnetic field from the photosphere to the chromosphere is very different between these two plasma structures. While in the MFR the magnetic field is approximately constant, the SMA presents a significant magnetic field gradient. In this work, the authors “ […] performed complex radiative transfer calculations in two MHD simulations representative of both MFR and SMA scenarios to model synthetic observations of the Mg II and Fe II polarization profiles in the 255 – 281 nm spectral window. “ Their results confirm that CMEx will be able to measure the difference in the magnetic field stratification of the MFR and SMA structures.

The SWR2 conveners proposed two highlights for the session they organize, namely Erika Palmerio and Marco Pinto.  Erika Palmerio, (talk on Monday, 04.11 at 14:05; contributed highlight text, here), underlines the importance of multipoint observations in the heliosphere not only for advancing our understanding of the physical phenomena coming from the Sun but also for improving validation opportunities of modelling  efforts. The talk will “[…] showcase four example events, each featuring  multi-point observational insights as well as an associated modelling effort: (1) the first widespread SEP  event of the current cycle, which took place on 29 November 2020, and related simulations with the physics based STAT model; (2) the multi-spacecraft SEP event of 9 October 2021, which featured several probes  clustered over relatively narrow longitudes, and related model development with the test particle code  SEPMOD; (3) the weak CME of 23 September 2021, observed by four spacecraft close to radial alignment  between 0.4 and 1.0 au and simulated with the CME analytical model OSPREI; and (4) the “Labour Day”  CME of 5 September 2022, characterized by exceptional remote-sensing and in-situ observations from the  solar corona through interplanetary space and simulated with the magnetohydrodynamic (MHD) CORHEL model. Each of these events highlights the importance of complementing spacecraft data with modelling  results, where observations can be used to constrain and drive simulations, and simulations to inform and contextualize observations.”

Pinto et al., (talk on Tuesday, 05.11 at 9:00; contributed highlight text, here), examines the “BepiColombo and JUICE capabilities to characterize SEP events. One highlighted such event occurred on 2024 May 13, in which JUICE was the best well-connected spacecraft (Figure 2, left). Its angular and radial proximity to STEREO-A and the Earth were ideal for cross-calibration between instruments, and to study small angular changes of the SEP at ~1 au. Another highlighted SEP event happened on 2024 May 20, in which BepiColombo head-on was hit (Figure 2, right), which caused a significant increase in memory errors on the OnBoard Computer. The SEP event also led to a ground-level enhancement on Mars which was downstream of BepiColombo, further showcasing the potential contribution of planetary missions and their instruments to other planetary missions, heliophysics, space weather in general.” 

BepiColombo (orange) and JUICE (pink) location in the Solar System with respect to the Earth and other interplanetary missions during the 2024 13th May (left) and the 2024 May (right) SEP events.

The highlight of the adverse space weather (CD5) session is Karl-Ludwig Klein et al., (talk on Tuesday, 05.11 at 17:30; contributed highlight text, here), who focuses on the time profile of relativistic solar particle events and its relationship with solar activity.  […] In their upcoming talk, the authors explore “[…] the physical reason for the astonishingly similar behavior of energetic particle signatures in very different solar events. Two directions of investigation are envisaged. One assumes that the time profile is predominantly shaped by the propagation of the particles between the Sun and Earth, where they are subject to interactions with the turbulent solar and heliospheric magnetic field. A second approach searches for systematic relationships between the rise time of the particle event and the parameters of the solar eruption.” One of the author’s findings is, for example, that “[…] the fastest rising particle events tend to be those with the fastest coronal mass ejections”.

Steph Yardley, (talk on Tuesday, 05.11 at 14:15; contributed highlight text, here), the current highlight will be presented during CD7. The authors analyze “[…] remote-sensing observations along with plasma and magnetic field in situ measurements that were taken as part of a coordinated observation campaign on solar wind connection science operated by Solar Orbiter during its perihelion in March 2022. The solar wind observation campaign took place between 3-6 March 2022, during which a large equatorial coronal hole and active region complex were present on the Sun. In order to observe the source region of the solar wind that would arrive at Solar Orbiter a few days later, the authors model the magnetic connectivity of Solar Orbiter using the connectivity tool (Rouillard et al. 2020).” According to this tool, Solar Orbiter was magnetically connected to these source regions . Through this analysis, the authors have shown that “[…] the variability of the solar wind is driven by the change in connectivity across multiple sources (the coronal hole and active region complex) and the evolution of the sources themselves.”

Solar wind density from the time-evolving model used in the Predictive Science Inc. 2024 eclipse prediction.

Jon Linker, (talk on Tuesday, 05.11 at 17:30; contributed highlight text, here), is the highlight and invited speaker of the CD7 session. This contribution gives an overview of the ambient solar corona and solar wind modelling from the first attempts to the state-of-the-art. The solar wind can be reconstructed by the empirical relations based on the magnetic field expansion factor from potential field source-surface (PFSS) models of the corona (Wang & Sheeley, 1990). The accelerated solar wind can also be obtained by using the mapped Distance from Coronal Hole Boundaries (DCHB) in the coronal model to specify solar wind speeds at the inner boundary of the heliospheric model (Riley et al. (2001)). Arge et al. (2003) combined the WS and DCHB approaches in the WSA model. This led to the empirically driven WSA-Enlil model (Odstrcil et al., 2005) which is computationally the least demanding, and so it has received considerable attention and has been replicated with several model frameworks. But on the other hand, MHD models starting in the corona  incorporate more realistic energy transport mechanisms to model solar wind. A major limitation for the models is that the data in the standard observatory maps, which is used as model inputs, is old. Assimilative Surface Flux Transport (SFT) models attempt to mitigate this issue by predicting the evolution of the field on the unobserved portions of the Sun. “From a space-weather perspective, the time-dependent approach is more efficient, because it avoids the artificial relaxation of the solution, and this makes it an attractive future direction for operational models. However, limitations of the data can drive artificial dynamics that may be non-physical. Time-dependently driving both a coronal and heliospheric solar wind model can mitigate some of the issues. PSI demonstrated this approach for a month of evolution around the time of the April 8, 2024 total solar eclipse with an assimilative, time evolving model.”