SHINE 2024 Sessions and Summary Reports

Organizers: Farrish, Notsu, Samara, Dissauer

Main sequence cool stars like the Sun have magnetized stellar winds which carry particles, angular momentum, and magnetic flux out into their surroundings, establishing their own space weather environments. While the solar wind can be studied in situ, our understanding of stellar winds relies solely on modeling and limited remote sensing observations. Cool star populations provide a wide range of magnetic activity levels not seen in the present-day Sun, which can give insights to it’s more active past. Therefore it is important to discuss the ways that solar and stellar wind observations and modeling can inform each other, as well as understand the present challenges and constraints in employing solar wind models for stellar simulations. In addition, solar and stellar winds are shaped by the magnetic field of the host star, and constitute the foundation of (extra)-solar space weather research, concurrently serving as the medium through which transient events, such as eruptions, propagate. Therefore, we also seek to explore how solar observations and modeling can enhance our understanding of stellar space weather and activity, including transient phenomena and magnetic field dynamics.

1) What are the present constraints and challenges in employing solar models for stellar investigations, particularly in the context of wind modeling?

2) What are the gaps in our current understanding of the Sun-as-a-star analogue, and what kinds of solar and stellar modeling and observations are needed to fill these gaps?

3) How can current investigations on solar and stellar magnetic fields contribute to the physical understanding of stellar wind environments?

Progress and Prospects Session Summary

Convenors: Alison O. Farrish, Evangelia Samara, Yuta Notsu, Karin Dissauer

This session was divided into two parts. The scene setter for Part I “Solar wind modeling” was Meng Jin (Lockheed Martin Solar and Astrophysics Laboratory) and for Part II “The Observational Side of Stellar Winds” R.O. Parke Loyd (Eureka Scientific, Inc.).

Summary for Part I:

Solar wind modelling is currently performed in the form of kinetic, MHD, and hybrid wind modeling. Key parameters that serve as input for this modeling are still hard to constrain. For example, the addition of Bipolar Magnetic Regions (BMR) in Zeeman-Doppler Imaging (ZDI) maps is difficult to constrain by observations due to degeneracies especially concerning hemisphere effects and resolution limitations. Significant part of the discussion was focused on stellar CMEs, their potential detection methods as well as their limitations (e.g., detections via coronal dimmings, Doppler shifts, type-II radio bursts) and how solar statistics can aid in understanding stellar CME dynamics, providing e.g., context for the rarity of dimming without CMEs. It was commented that we do not have a good coverage of EUV observations for stars, which might contribute to the low number of detections. Magnetic confinement was identified as one reason why detection of stellar CMEs is so rare compared to stellar flares.

Summary for Part II:

The study of stellar winds, particularly in stars similar to the Sun, offers important insights into stellar evolution and magnetism. Stars of types K and M, are ideal analogs for understanding the Sun’s wind dynamics. Younger stars tend to rotate faster, and magnetized winds are crucial for comprehending their long-term evolution. Compared to the Sun, these stars offer a broader range of parameters for studying stellar winds. However, uncertainties in measuring stellar magnetic fields are large.

High-mass stars are not suitable analogs for the Sun due to differences in their dynamo mechanisms, which makes them less relevant for understanding solar wind dynamics. Pulsations in massive stars may affect stellar winds, but this remains an unresolved issue. Exoplanets, though difficult to use directly to study winds, could provide indirect information through interactions with stellar winds.

Other observations, such as Lyman-alpha emissions interacting with the interstellar medium (ISM), offer potential for studying stellar wind properties. Past efforts, like those by Bourrier et al. (2016), have aimed to observe ion-neutral interactions, shedding light on stellar wind dynamics. Coronal mass ejections (CMEs) and coronal dimming are also key to understanding stellar winds.

The early solar wind is still not well understood, with ongoing research needed to determine its characteristics. Patterns of stellar spin-down, observed in various stars, show complex behaviors, including rapid transitions and stalling, which remain poorly understood. Kepler data and asteroseismology provide valuable information on stellar rotation, aiding our understanding of stellar evolution. Models of angular momentum and stellar rotation focus on global dynamics, but they must address the differential rotation of stars, especially during the stall phase. The role of neutrinos in momentum transfer from the Sun remains minimal, as they do not interact significantly with magnetic fields.

Overall, the study of stellar winds is an evolving field, with many questions still to be answered through improved modeling and observation techniques.

Organizers: Mahajan, Hess-Webber

In order to understand the origin and evolution of magnetic field inside the Sun and its manifestation on the photosphere, it is imperative to understand the nature of plasma flows inside the Sun. The modulation of these flows on different spatial and temporal scales has direct consequences on the solar cycle, build up of the polar field and may even be related to the triggering of eruptive events like solar flares and CMEs.

1. What drives changes in solar differential rotation and meridional flow over the course of a solar cycle?

2. How do transient flows like inflows around active regions affect the build up of the polar field?

3. What is the structure of meridional flow inside the Sun?

Organizers: Tilipman, Kazachenko

Recent developments in modeling and observations (e.g. DKIST, Sunrise, SO) have allowed us to probe small-scale dynamics and magnetism on the solar surface and in the lower atmosphere. These small scale processes may be responsible for energy build-up and transfer in the lower solar atmosphere, particularly in the absence of active regions. Examples of such processes include rotational motions (vortices), nanoflares, small-scale reconnections, flux cancellations, sunquakes, etc. The goal of this session is to discuss the importance of such events (how much of the limited observing time should be devoted to them?) and strategies on how to study them.

How important are small-scale events to our understanding of the energy transfer in the solar atmosphere?

Which observational and numerical approaches are best suited to study these events?

Presentations

Milan Gosic’s presentation

Raphael Attie’s presentation

Organizers: Dahlin, Kazachenko, Uritsky

The CSHKP model has been highly successful in qualitatively explaining the morphology and evolution of solar flares. However, in recent years a plethora of new observations have revealed key details not addressed in this “standard model”, particularly through enhanced spatiotemporal resolution of fine-scale features. Meanwhile, advances in numerical modeling and computational power have enabled coupling of disparate scales and physical regimes, making striking advances in forward modeling of these previously unobserved details and linking them to the flare energetics. In this session, we aim to bring together modelers and observers to critically examine these advances to look beyond the CSHKP model. Relevant flare topics include, but are not limited to, the onset problem, plasmoids, flare ribbon fine structure, magnetic shear evolution, termination shocks, turbulence, supra-arcade downflows (SADs), nonthermal emission at flux rope footpoints, as well as reconnection-driven density depletion manifested in EUV dimmings. We welcome observational contributions from (but not limited to) SDO, IRIS, SolO, EOVSA, BBSO, DKIST, ASO, as well as contributions from the theoretical and numerical simulation communities providing new insights into the flare physics and setting the stage for the next-generation standard model.

What features of flare configuration & dynamics beyond the standard model have been revealed by recent observations?

How can advances in flare modeling triage and explain new features identified in the observations?

How do the latest advances in observations and numerical models uncover or identify physical mechanisms converting magnetic energy into plasma and particle energies?

Progress and Prospects Summary Report

Joel Dahlin (UMD/GSFC), Maria Kazachenko (CU Boulder), Vadim Uritsky (CUA)

Part I: Jiong Qiu

Jiong Qiu set the scene for the first half of the discussion by laying out a series of questions relating to the properties of the magnetic field structure & reconnection during a flare, including some features that go beyond the typical standard model pictures, e.g., fine/bursty structure, evolution of magnetic shear, confined flares, etc.

A major topic of debate surrounded the meaning and scope of what is encompassed in the ‘Standard Model’. For some participants, a narrow view focused on the primary large-scale morphological observables (e.g., flare loops, pairs of ribbons) that inspired the development of the CSHKP model. However, in another view it was argued that the advances to the standard model result from inclusion of more details of what occurs in the reconnection process (e.g., plasmoids, turbulence, shocks).  It was argued for example that many details that might be presented as ‘beyond the standard model’ are natural implications of reconnection, bolstered by advances in the study of reconnection in the intervening years since the CSHKP picture emerged.

An overall theme was that it was important to discern which of the new features have an impact on the energy conversion in a flare. It was also clear that types of flares beyond the standard model (N-ribbon flares, with N>2; circular ribbon flares, confined flares) are relatively unsettled in terms of a ‘standard’ model.

Part II: Bin Chen

The scene for the second part of the session was led by Bin Chen, who laid out some questions regarding where energy conversion takes place in a flare, drawing on an analogy to an internal combustion engine and arguing for analogies to the ‘generator’ (above-the-looptop), ‘connector’ (X-point), and ‘load’ (region exhaust/sepatrix region). This analogy drew spirited debate, with particular discussion as to in what sense the above-the-looptop would serve as a ‘generator’. The key point raised in the discussion was that it was important to take a thoughtful look at where energy is converted vs. transferred in a flare. This was underscored by recent radio results showing energetic electron concentrations above-the-looptop.

Organizers: Welsch, Gilchrist, Wheatland, Liu

The widely believed “storage and release” paradigm of solar flares and coronal mass ejections (CMEs) posits that these dynamic phenomena are powered by energy stored in coronal electric currents. Do these coronal currents evolve in systematic ways before, during, and after flares and CMEs? How can the sudden photospheric magnetic changes that are often caused by large flares be understood in terms of evolution in coronal currents? Because the coronal vector magnetic field cannot be directly measured, properties of coronal currents are typically inferred using modeling and indirect methods, such as radio observations and extrapolations from photospheric observations. New data sources (EOVSA, SO/PHI, DKIST, etc.), large existing data catalogs (from SDO/HMI & AIA, IRIS, BBSO’s GST, etc.), and modeling approaches (such as improved methods for NLFFF extrapolation & data-driven dynamic modeling and Gauss’s separation method) are promising tools for better understanding how currents evolve around the times of flares and CMEs.

1. PRE-EVENT EVOLUTION: In what systematic ways, if any, do active-region coronal currents evolve prior to the onset of flares and CMEs?

2. EVENT-ASSOCIATED EVOLUTION: In what systematic ways, if any, do active-region coronal currents evolve during and immediately after flares & CMEs?

3. POST-EVENT EVOLUTION: In what ways, if any, does post-event evolution differ systematically from pre-event evolution?

Presentations

Flare & CME-Associated Evoluation of Active-Region Coronal Currents – Brian Welsch

Review of recent works on coronal/photospheric currents before/during flares – Maria Kazachenko

Session Questionnaire

Questionnaire Responses

Organizers: Andreas Weiss GSFC, Erika Palmerio (PSI), Jaye Verniero ( GSFC), Adam Szabo (GSFC)

Large-scale structures, such as ICMEs, have been studied for decades using single point observations using a large variety of different models and approaches. Certain events appear as text-book observations that are fully reconstructable using simple models while others show perplexing complexity. There still exists a large amount of ambiguity of how these structures actually look like in reality, with even the simplest cartoon-like figures not being verifiable using single point observations and currently available methods. This calls for new, and larger, constellation missions to probe the full three dimensional structure to enhance our understanding. This may also require accompanying methods to analyze the expected observations in a proper way.

Are single-case event studies and catalogs of large-scale structures sufficient to advance our understanding and knowledge beyond the current state?

How can we properly make use of multi-point measurements, including magnetic fields or non-thermal and energetic particles, from planned or envisioned large mission constellations?

Could we make use of smaller scale phenomena, such wave-particle interactions, to help us infer the global magnetic field topology and evolution?

Progress and Prospects Summary Report

Organizers: Andreas Weiss, Jaye Verniero, Erika Palmerio, Adam Szabo

Scene-setters: Fernando Carcaboso, Yeimy Rivera

The first half of the session primarily was focused on a discussion regarding data or event catalogs and dissipation of knowledge. Participants commented on the fact that there currently are numerous, partially duplicative, efforts for collecting and cataloging observations and CME/SEP events and large-scale structures in general, but that it can be very hard for either early career scientists or scientists to find them because there is no central authority or location that keeps track of all resources. This led to the discussion on whether such a central “catalog of catalogs” is desirable in the first place. Potential issues that were raised concerned the funding of such an effort, as it may create additional competition with current efforts for existing catalogs that assemble data instead of meta-data, and objectiveness. No consensus appeared to have been reached regarding this discussion. Another catalog-related discussion point that was raised was the fact that papers that analyze events that exist in single or multiple catalogs often do not reference the catalog at all or only reference the entire catalog itself without having the ability to reference a specific event. This results in two problems, that first, catalog creators have a hard time gauging the usefulness of their work, and second, that other researchers are not easily able to find papers regarding specific events that they may be interested in.

The scene setters brought up the question whether the scientific community is currently strongly biased towards the most “sensational” large or strong events, such as the Bastille day CME that has been extensively studied for the past 20 years. It was pointed out that many CME propagation models only aim to predict arrivals and space weather effects at 1 au, and only a couple of efforts are currently working on self-consistent modeling of CMEs and other structures from the Sun out into the heliosphere. It was proposed whether “campaign events” efforts, where multiple groups simulate and validate their models against the same event, are necessary.

Organizers: Samuel Badman (CfA), Yeimy Rivera (CfA), Samantha Wallace (ERAU), Cooper Downs (PSI)

The biggest open questions around coronal and solar wind physics (and heliophysics more broadly) are interdisciplinary and system-level. For example, a complete understanding of the solar wind evolution requires combining remote diagnostics across the corona with a complementary set of in situ signatures out in the solar wind. This session seeks to provoke discussion around how to leverage collaboration between multiple missions with complementary science objectives to close such science questions. This will be discussed from the perspective of successes and lessons learned from current community coordinating and modeling efforts, as well as identifying specific examples of instrumentation gaps. We will close by summarizing a set of recommendations aimed at capitalizing on and improving future multi-mission observations backed by specific examples raised in the discussion.

What are examples of success stories where hypotheses were conclusively tested with multi-mission coordination?

What are examples of and lessons learned from recent scientific investigations where coordinated observations with existing missions or new instrumentation could have made the conclusions much more impactful?

What avenues exist at the community, NASA, and interagency levels to coordinate future science objectives and observing strategies of upcoming missions?

Progress and Prospects Summary Report

1. Session goals and questions: To discuss how we can move towards concrete conclusions on the big science questions in our community using different missions working together. Questions : Examples of success, Examples of gaps (what do we need), Routes for improvement/action
2. First half : Ben Chandran : “Big” open questions

1. Scene Setting Context of coronal and solar wind heating/acceleration – introduced some established results and some open questions and a wishlist of measurements
2. Discussion

– Lots of state of the art results come from Parker, but routes to push things forward:

→ Conjunctions and statistics with what we have, more powerful together!
→ Extrapolate results within inner radius of Parker with remote (UVCS, radio, coronal

magnetometry) (need better communication of existing capabilities, see e.g. radio session) → Go new places (e.g. improve 3d knowledge of sun (e.g. 4pi))
→ Integrate model development and expertise into our push for new missions

– Ended with touching on big vs small mission and science return

3. Second half : Nicki Viall : High level strategy

1. Scene setting: The case for a top down science strategy funded program balanced by grass roots community input (Ex.: ISTP) to understand the time dependent 3d formation and dynamics of the corona and solar wind. Nicki laid out how an ISTPNext program could cover the different solar and solar wind regimes necessary to answer the science questions from the first half.
2. Discussion
   – Funded program level endeavors can be successful because they combine funding with scientific focus.
   – How do we implement something this big within and between agencies
   – Broad agency funding discussion and impact of decadal
   – How do we influence budget top lines (grass roots advocacy?)
   – Elements that shouldn’t be forgotten : → Open data sharing is key (important part of istp)
   → Integration of modeling development, missions at different scales
   → Lab plasmas/ongoing benchmarking of atomic physics parameters
   → Collaboration with ground based observatories (particularly radio) at a community level and inter-agency level e.g. NASA/NSF collaboration
   → Small/science soft money research support inside paradigm of big pieces, → International partners beyond ESA and JAXA

4. Takeaways

1. We take big strides with individual new missions in new locations but many open questions remain
2. In constrained funding environment we need to think carefully about strategy going forward and how to get the most accomplished while keeping the community equitably supported
3. The session had great participation from students/early career scientists which we attributed to having a first half on detailed science, and a second half on a high level view; as well as having early career conveners and explicitly inviting student voices at the start of the session.

Organizers: Phillip Hess (NRL), Christina Kay (GSFC), Erika Palmerio (PSI)

Thanks to new data from Parker Solar Probe and Solar Orbiter, it is now possible to directly compare remote sensing imaging of CMEs to in-situ data. In the past, when comparing the observations closer to the Sun to the in-situ measurements at 1 AU, it was easy to dismiss any discrepancies in the observed structures as the product of complex evolution in the heliosphere. Now with more in-situ measurements closer to the Sun allowing for direct comparison between imaging and in-situ data, the various physical interpretations of the different data should align. In practice, there are still wide gaps between these two observing communities that must be addressed to form a comprehensive understanding of CME structure(s) from the Sun throughout the heliosphere.

1. Can our current understanding of CME internal structures explain what is observed in imaging and with in-situ probes when these observations are taken nearly simultaneously?

2. Are we observing features in any of these data sets that can be confidently extrapolated to global properties, or are local effects playing too large a role?

3. Do we need to rethink/reformulate our understanding of CME evolution from a fundamental physics standpoint in light of the most novel observations?

Progress and Prospects Summary Report

Erika Palmerio (PSI), Christina Kay (APL), Phillip Hess (NRL)

Part I: Remote-sensing Discussion Led by Alessandro Liberatore

Lots of discussion on how to interpret CME structure in new images. A significant amount of discussion was on whether simple models/ideas (i.e. 3-part structure, GCS fittings etc.) that were able to accurately describe many events seen in lower resolution are still useful tools for conceptualizing CME structures. Now that there are additional complexities seen in the data, more detailed physical models may better describe the images but would also be harder to constrain with no guarantee of improved physical accuracy. There are still a number of open questions on how to best extract physical information from images, especially given the significant different noise contributions. An issue that is largely not emphasized enough is how different image processing techniques highlight and obscure different features and identifying what is real and what is an artifact is challenging.

Part II: In-situ Discussion Led by Nada Al-Haddad

There was some carry over discussion, as the question of whether current in-situ reconstruction codes are too oversimplified to be useful mirrored what was said about remote-sensing data. Furthermore, a big question was on the extent to which local CME measurements can describe global CME properties. This has always been an unanswered question for CMEs, and an increasing number of events that hit multiple spacecraft have shown that sometimes, even with small longitudinal separations, CME structures can appear extremely different. Simultaneous imaging and in-situ flythrough data for common events have also been difficult to reconcile with one another. Overall, the discussion was very successful at identifying important issues related to CME physics, but there is not much consensus on the best path forward. For example, the community seems to have mixed opinions on whether simple/simplifying models are “good enough” or whether we need more complex structures and physics to properly gain deeper insight into the structure and evolution of CMEs.

Organizers: Sam Schonfeld (AFRL), Sherry Chhabra (NRL), Shaheda Begum Shaik (NRL), Surajit Mondal (NJIT)

Radio observations combined with other wavelengths and physical models provide powerful diagnostics of the fundamental physics and characterization of space-weather-relevant events. Building on the success of our session from SHINE 2023, “What radio data can do for you!”, this session will use recent studies that utilize radio data from various instruments as catalysts to spark discussion and brainstorm new collaborative SHINE research. This session will be geared towards bringing together radio experts with other members of the SHINE community to develop ideas for new research made possible by combining the strengths of the broader community. The session will cover the entire range of SHINE environments, from the low solar atmosphere out to CMEs and the solar wind and from magnetic fields to high-energy particles.

What are the most promising synergies between novel radio probes and other data and models for addressing SHINE focus areas?

Progress and Prospects Summary Report

In the session “Addressing your SHINE Science Questions with Radio Data,” we facilitated collaboration between experts using radio data and interested members of the SHINE community through the question “What are the most promising synergies between novel radio probes and other data and models for addressing SHINE focus areas?” This led to a wide-ranging discussion about the strengths and limitations of radio observations guided by our two scene-setting speakers, Bin Chen and Mario Bisi.

During the first half of the session, Bin introduced recent research where radio observations were used to probe the physical parameters in solar flares and CMEs and the properties of accelerated particles and their propagation environments. This led to excellent discussions about the ability of GHz radio observations to directly probe the coronal magnetic field. There was some concern about the discrepancy between radio and optical measurements of the coronal magnetic field. But, whether during flares or in active regions, the physical mechanisms that encode the magnitude of the magnetic field into radio observations are fundamental to those emission mechanisms and leave no questions about the strength of the field. However, because these radio emission mechanisms are tied directly to high-energy electron dynamics, their sources may be much more localized than thermal emission measured in the optical and EUV, potentially explaining discrepant observations. At the same time, it was also pointed out that the relatively low-resolution radio observations cannot resolve the flare X-point, so strong fields measured there are not necessarily inconsistent with weak fields in the reconnection current sheet. Instead, the radio observations measure the stronger fields as the magnetic field is advected and compressed towards the reconnection region. Higher resolution observations with DKIST and a potential future FASR radio observatory may help resolve this conflict.

There was also a discussion about using radio measurements to study CMEs in the low corona. When available, these observations can help constrain CME cone fitting models by providing direct measurements of nonthermal electron density and magnetic field strength integrated along the LOS. However, it can be hard to track CME evolution because different radio emission mechanisms at vastly different frequencies activate in different regimes. Disentangling these effects in an inherently dynamic source can be difficult.

However, the opposite is true when observing plasma emission in Type III radio bursts where the emission frequency is a direct measure of the local plasma density through which the high-energy electrons propagate. Therefore, by tracking frequency drift, it is possible to remotely sample the local plasma density around particle beams. It can be difficult to isolate the exact source of this emission along the line of sight, and this was discussed as an area of potential collaboration with coronal and inner heliosphere modelers to provide insights about the expected magnetic field connectivity, or multi-instrument studies that can triangulate source regions. With PSP and SolO exploring the inner heliosphere, there are even opportunities to compare in-situ and radio measurements of particle beams and solar wind plasma densities.

In the second half of the session, Mario discussed the possibilities and challenges of using interplanetary scintillation and rotation measure studies to measure solar wind plasma density and magnetic field strength. This involves measuring the variation in the twinkling (for density) and linear polarization angle (for magnetic field) of background radio sources (e.g. pulsars or AGN) as solar wind structures and CMEs propagate in front of these sources. Combining many of these measurements over the sky and using them to drive time-dependent tomographic inversions can enable low-resolution monitoring of the plasma density and its evolution throughout the inner heliosphere. There was much discussion about how these measurement-driven models work in practice, including limitations on their accuracy due to integrating the relevant signals through the entire heliosphere, practical inner boundaries to these models (~15 R_Sun, similar to MHD models), and the difficulties of performing similar inversions for the magnetic field because the polarization measurements are more demanding and signals are much weaker. It was also pointed out that these measurements indicate more outflows along the legs of CMEs than is seen in ENLIL modeling.

Overall, there was great discussion in the session and the prospects of some new collaborations as we had hoped. If we were to hold a similar session in the future, we would include a non-radio expert who has successfully utilized radio data in their work to give one of the scene-setting talks and reserve 3-5 minutes per interested session attendee to discuss the details of their needs and how radio observations could address them.

Organizers: Anshu Kumari, Peijin Zhang, Atul Mohan

How do radio observations across various wavelengths deepen our knowledge of solar and heliospheric phenomena, particularly solar flares, coronal mass ejections (CMEs), and the solar wind? These phenomena are critical to the study of space weather and its impact on Earth, yet they remain incompletely understood due to their complex nature. Radio astronomy offers a unique vantage point, providing insights into the plasma processes and magnetic field dynamics within the Sun’s atmosphere and the heliosphere. By exploring data from decameter to millimeter wavelengths, this session seeks to uncover the underlying mechanisms driving these solar activities and assess their implications for space weather forecasting.

(1) What are the final steps has to be done to bring radio imaging and solar atmosphere model together?

(2) How can we benefit from the rich information of the higher solar atmosphere (1.5-2.5 Rs) that we obtain from low-frequency radio observation?

Organizers: Jim Ryan, UNH; Joe Giacalone, U Arizona; Pierre-Simon Mangeard, U Delaware; Ashraf Moradi, U Arizona

Ground Level Enhancements are rare events and signatures of the most energetic particles that the Sun produces. They result from a conspiracy of several agents and processes that together produce these extreme events. We examine the various factors, their importance and impact, that make these events happen, working backwards from the ground to the low corona.

How can neutron monitors do a better job of detecting and measuring GLEs?

Are GLEs peculiar or do they constitute the tail of an existing distribution?

What aspects of the progenitor CME and shock are most important in producing a GLE?

Organizers: Wei Liu (LMSAL/BAERI), Radoslav Bucik (SwRI), Christina Cohen (Caltech), Gang Li (UAH)

The production of high-energy particles and their far-reaching consequences are at the heart of space weather and involve a multitude of physical processes coupled from the Sun to the heliosphere. Exactly where, when, and how particles are accelerated remains a fundamental open question. Flares on the Sun and CME-driven shocks in the heliosphere are the two primary processes of particle acceleration. Observational and modeling advances in recent decades have revealed that these two processes are more closely related than previously thought. For example, there are puzzling correlations between the spectral indexes of electrons at 1 AU and of hard X-ray producing electrons on the Sun (Krucker et al. 2007; Dresing et al. 2021). Enrichments by orders of magnitudes in 3He and heavy ions, a characteristic of impulsive SEP events (e.g., Mason 2007; Hart et al. 2022), are also commonly found in gradual SEP events (e.g., Desai et al. 2016; Bucik et al. 2023). Both problems point to the need of a second-stage re-acceleration of flare-accelerated particles by a CME-driven shock (Petrosian 2012, 2016). In fact, the origin of seed populations required by shock acceleration for SEPs is an outstanding problem by itself, with particles from flares as a potential candidate (Tylka and Lee 2006). It has also been recognized that the coupling between the flare and CME-shock acceleration processes is not one-way. For example, the Fermi Gamma-ray Space Telescope has detected gamma-rays associated with flares occurring up to ~50 degrees behind the solar limb (Pesce-Rollins et al. 2015, 2022; Ajello et al. 2021) and long-duration gamma-ray emission for up to ~20 hours (Ackermann et al. 2014), long after the flare X-ray and EUV emissions have died down. Both puzzles point to the possibility of CME-shock accelerated particles traveling back to the Sun to produce gamma-rays, a pioneering idea proposed three decades ago (Cliver, Kahler, and Vestrand 1993), with growing observational and modeling support (e.g., Gopalswamy et al. 2018; Jin et al. 2018).

This session will bring together timely discussions on this important subject, aiming to answer the three-fold science questions:

1. What are the relative roles of flares on the Sun and CME-driven shocks in the heliosphere in producing SEPs and (long-duration) gamma-ray emission?

2. What is the physical relationship between particle acceleration processes in flares and at CME-driven shocks?

3. To what extent and how do solar flares contribute to the seed particles of SEPs?

Organizers: Riddhi Bandyopadhyay (Princeton University), Manuel E. Cuesta (Princeton University), J. Grant Mitchell (NASA Goddard Space Flight Center)

In this SHINE session, we ask what we have learned about SEP acceleration mechanisms near the Sun. With the launch of inner heliosphere missions such as Parker Solar Probe and Solar Orbiter, many interesting SEP events have been observed, such as the September 5, 2023 Labor day event. Utilizing simulations along with these observations has reveal new insights into the nature of SEP acceleration in the near-Sun environment. Our goal in this session is to understand the role of different mechanisms such as turbulence, shock, and reconnection in accelerating SEPs near the Sun.

1. What are the roles of turbulence, shock, and reconnection in SEP acceleration close to the Sun.

2. How can in-situ SEP signatures be identified to understand and determine the mechanism responsible for their acceleration?

Organizers: Claudio Corti (CCMC/Univ. of Hawaii), Junxiang Hu (UAH/NASA GSFC), Rohit Chhiber (Univ. of Delaware/NASA GSFC), William Matthaeus (Univ. of Delaware)

The diffusive transport of Solar Energetic Particles (SEPs) in the inner heliosphere is primarily governed by the turbulent solar wind magnetic field. Remote-sensing and in-situ observations have greatly improved our understanding of the properties and evolutions of solar wind turbulence in recent years. Different global heliospheric turbulence transport models have been further developed lately with the help of PSP and SolO observations. Multiple diffusion theories (e.g., quasi-linear theory, non-linear guiding center theory, weakly non-linear theory, unified non-linear transport theory, field line random walk theory) have been proposed to describe the diffusive transport of SEP in the turbulent magnetic field, each being valid in different regimes. However, there are still many uncertainties and unknowns in the spatial extent of the turbulence parameters, and how we interpret the role of turbulence in energetic particles’ diffusive behaviors. In this session, we intend to bring together the turbulence and SEP communities and discuss the following important science questions:

1) How does the interplay between cross-field diffusion and field line meanderings affect the perpendicular transport of SEPs?

2) How do global heliospheric turbulence transport models compare with recent PSP and SolO observations?

3) How can the SEP modeling community benefit from the recent advances in turbulence transport theory and observations to improve space weather forecast capabilities?

Progress and Prospects Summary Report

Organized by Claudio Corti (CCMC/U. Hawaii), Junxiang Hu (UAH/NASA GSFC), Rohit Chhiber (U. Delaware/NASA GSFC), and William Matthaeus (U. Delaware).

The first scene-setting speaker was Andreas Shalchi (U. Manitoba, Canada), who introduced the concepts of turbulence and diffusion from a theoretical perspective. The second scene-setting speaker was Du Toit Strauss (NWU, South Africa), who talked about his experience as a SEP transport modeler. The discussion touched various aspects of the relationship between parallel and perpendicular diffusion and turbulence in the solar wind.

For parallel diffusion, an open problem is that quasi-linear theory (QLT) predicts zero scattering at 90 degrees, which is inconsistent with the isotropization assumption used in the derivation of the parallel diffusion coefficient and with numerical simulations. This issue can be solved by broadening the resonance between the turbulence scale and the particle gyroradius in a couple of ways: either by using a second-order QLT, or by changing the turbulence dynamics. While both approaches might produce similar results, the underlying physics is different and it’s still unclear/unresolved how to disentangle their relative contributions. PSP observations of pitch-angle distributions require understanding of the full pitch-angle scattering coefficient, not just of the pitch-angle averaged parallel diffusion coefficient.

For perpendicular diffusion, the big question is whether it is more correct to use a perpendicular diffusion coefficient on top of a pure Parker field or to assume all perpendicular transport is due to particle motion tied to field line random walk (FLRW). Multiple theories of increasing sophistication exist that describe the perpendicular diffusion coefficient, but they have validity limitations which might render them not fully applicable in all cases of solar wind turbulence, especially close to the Sun. From a modeling point of view, both approaches seem to work equally well, but some technicalities are needed to avoid problems. For example, when modeling FLRW, care needs to be taken to avoid infinite path lengths. It was suggested that the step size should be set by the gyroradius of the lowest particle energy, since particles won’t feel smaller field line kinks anyway. However, it looks like the FLRW diffusion coefficient needs to be rescaled a lot with respect to the theoretical value in order to match observations.

When trying to model SEP transport from first principles, we’re faced with many unknowns, especially about the radial evolution of turbulence close to the Sun (2D vs slab contribution, spectral break positions and slopes) and about the pitch-angle dependence of the perpendicular diffusion, which seems to be a theoretical problem not yet addressed. PSP observations will help in reducing some uncertainties, but we’re still missing a coherent theoretical picture providing a comprehensive turbulence description close to the Sun.

Other points of discussions were:

 – the desire to have a theoretical description of the dissipation range, needed to model SEP electrons below 100 keV.

 – how dropouts can be interpreted in terms of meandering field lines and perpendicular diffusion, and whether they should occur more often closer to the Sun with respect to 1 AU.

 – how to model the effect of meso-scale structures (>0.1 AU) moving in solar wind on particle transport.

 – the relation between turbulent drift processes and perpendicular diffusion, and the yet unknown role of a turbulent current sheet on particle transport.

Organizers: Soukaina Filali Boubrahimi and Shah Muhammad Hamdi

In this session, we delve into the critical pursuit of understanding and predicting rare solar events, pivotal phenomena with substantial implications for space weather and technological infrastructure. Our focus centers on three key scientific questions: firstly, identifying pivotal photospheric magnetic field parameters that reliably predict solar flares; secondly, assessing the availability of ground-truth data for rare yet impactful solar events; and thirdly, exploring the capabilities of current simulation models in generating high-quality synthetic samples of these rare occurrences. This talk aims to contribute to advancing our predictive capabilities and fortifying our comprehension of the dynamic solar atmosphere, ultimately aiding in the anticipation and mitigation of solar flare effects on Earth and space technologies.

1. What are the most important photospheric magnetic field parameters that can predict solar flares?

2. Do we have enough ground-truth data for predicting the most impactful but rare-occurring events?

3. How can present simulation models provide high-quality synthetic samples of rare solar events?

Progress and Prospects Summary Report

Organizers: S. M. Hamdi (Utah State University), M. EskandariNasab (Utah StateUniversity), S. F. Boubrahimi (Utah State University), P. Hosseinzadeh (Utah State University)

This session highlighted significant advancements in the use of machine learning (ML) for predicting solar flares and Solar Energetic Particle (SEP) events, focusing on data preprocessing, feature selection, and model development. The session opened with Shah Muhammad Hamdi discussing the use of multivariate time series (MVTS) data from photospheric magnetic field parameters for predicting solar flares. He showcased how Long Short-Term Memory (LSTM) networks and attention-transformer models can leverage temporal patterns and key feature selection within solar magnetic field parameters to enhance flare prediction performance. He also presented a list of key photospheric magnetic field parameters identified through an LSTM-based feature selection framework, which can assist various ML classifiers in enhancing flare prediction performance. Mohammad Reza Eskandari Nasab followed with a deeper exploration of data preprocessing techniques, focusing on challenges like missing data, normalization, and class imbalance, and emphasizing the importance of methods such as imputation and class balancing when working with large, incomplete datasets like the SWAN-SF dataset. His presentation showcased methods such as FPCKNN imputation for filling gaps and LSBZM normalization to handle skewness in data. Eskandari Nasab highlighted how these preprocessing steps significantly improve model performance by addressing class overlap and using advanced sampling techniques like SMOTE and NDBSR to enhance classifier accuracy.

The second half of the session shifted towards SEP event prediction, beginning with Pouya Hosseinzadeh, who presented data augmentation and multimodal representation learning to predict SEP events. His approach combined proton flux data with solar coronagraph imagery and used models like TSF (Time Series Forest) and ROCKET to capture the complex temporal patterns linked to SEP events. Hosseinzadeh emphasized the need for data augmentation techniques such as SMOTE and Gaussian noise injection to balance the data and improve prediction accuracy, especially for high-energy SEP events. Soukaina Filali Boubrahimi concluded the session with a focus on explainable ML models, using shapelets and Matrix Profile (MP) to mine representative patterns from time series data. This approach not only improved SEP prediction but also made the models more interpretable, providing insights into the physical processes driving SEP events. Filali Boubrahimi stressed the importance of creating models that are both accurate and understandable, enabling operational space weather forecasters to make more informed decisions. Overall, the session underscored the importance of combining robust preprocessing techniques, advanced machine learning models, and interpretability to advance space weather forecasting.

Organizers: Vincent David, Evan Yerger, Ben Chandran

The helicity barrier is a recent discovery which may have significant implications for heating in the solar wind. The barrier has been shown to allow only the balanced portion of the turbulent Alfvenic energy flux to cascade past the ion gyroscale to electron scales. Understanding the effects of the helicity barrier in detail are therefore critical for estimating the ion-to-electron heating ratio. Recent observations and simulations of imbalanced turbulence are consistent with analytical predictions of the barrier; however, the community remains divided over its existence. This session aims to discuss the analytical and empirical evidence for the helicity barrier as well as its implications for the solar wind.

1. Does the helicity barrier exist?

2. Is there a helicity barrier in solar wind turbulence and what is the numerical and observational evidence for it?

3. What are the implications for the helicity barrier on coronal heating and the structure of the solar wind?

Progress and Prospects Summary Report

Part 1:

Physics summary: The helicity barrier is the consequence of a transition from cross helicity to magnetic helicity across the proton gyro-scale. Both types of helicity are separately conserved; cross helicity exhibits a direct forward cascade and magnetic helicity exhibits an inverse cascade. The result is that only the balanced portion of the energy flux can cascade past the proton gyro-scale, resulting in a “helicity barrier”.

Numerical evidence: FLR-MHD simulations show an increase of turbulent energy above — and a flux past — proton scales which are consistent with the helicity barrier. However, these simulations reach amplitudes where the FLR-MHD ordering is violated. Subsequently, imbalanced hybrid-PIC simulations were run, which also show robust features of the helicity barrier. These simulations have confirmed the existence of the barrier in a model with less restrictive assumptions.

Part 2:

Observational Evidence: There is significant statistical and observational evidence for the helicity barrier from Parker Solar Probe. The main observable is the transition region, which is also predicted by theory and observed in numerical simulations. Spacecraft observations of the transition region spectral index have been shown to vary with plasma beta and cross helicity in a way that is consistent with the helicity barrier. However, a clear, quantitative theory of the transition region position and slope has not emerged from observations.

Questions and discussion:

What happens to FLR-MHD invariants as the turbulence approaches proton inertial length scales?

• This is an open question; however, hybrid-PIC results suggest the helicity barrier is robust outside the FLR-MHD framework.

Is FLR-MHD a limit of the Vlasov equations?

• Yes, it’s a limit of the gyro-kinetic equations.

What is the effect of the helicity barrier on intermittency at electron scales?

• The barrier results in lower amplitudes at electron scales and “re-Gaussianising” the turbulence, resulting in monofractal scalings which are consistent with the weak turbulence regime.

What effect does the helicity barrier have on minor ion heating?

• Results on PIC simulations of minor ion heating in the presence of the barrier were presented and showed that minor ion heating is significant relative to proton heating.

What effect does electron Landau damping have on the helicity barrier?

• This is also an open question; the linear Landau damping rates would significantly impact the formation of the barrier, but a plasma echo might reduce this effect. Work is underway to quantify the effect of electron Landau damping on the barrier. The work is expected to have implications for the electron/proton heating ratio in the imbalanced solar wind.

What observations would we need to validate the presence of the helicity barrier in the solar wind?

• Observations of the turbulent flux at sub-proton scales, if measured to be the balanced portion, would be a very strong indication of the barrier that would be difficult to explain with other theories.

Organizers: Laxman Adhikari (University of Alabama, Huntsville), Lulu Zhao (Michigan), Junxiang Hu (NASA-GSFC), William H. Matthaeus (University of Delaware)

In recent years global heliospheric simulation has emerged as an important tool in connecting boundary conditions, very large scale structure and observable properties across wide ranges of heliocentric position. Including turbulence transport and its effects (sometimes self consistently) on the inhomogeneous background solar wind further expands the possibilities for explaining observations and improves potential for prediction. Our session aims to highlight and discuss this interaction between large-scale heliospheric structure and the evolution of interplanetary turbulence, both in the inner and outer regions of the heliosphere. Topics we aim to discuss include the use of global models to establish connections between different heliospheric domains and boundaries, and the interplay of turbulence transport with processes such as energetic particle transport, magnetic connectivity, and “critical surfaces” in the young solar wind. Observational studies including existing spacecraft such as Parker Solar Probe, Solar Orbiter, Ulysses, and Voyager as well as upcoming missions such as PUNCH, Helioswarm, and IMAP are relevant to these goals. We welcome observational, numerical, and theoretical studies from the inner to outer heliosphere.

1) Which features and capabilities of global modeling provide optimized accounting for existing observations and how can this performance be improved?

2) How do global heliospheric turbulence transport models compare with spacecraft observations, and how can these models better meet the challenge of accurately representing the coupling of large-scale physics with turbulence?

3) How do large-scale plasma conditions influence smaller scale MHD features and turbulence in theoretical models and in observations?

Progress and Prospects Summary Report

Organized by Laxman Adhikari (University of Alabama in Huntsville), Lulu Zhao (University of Michigan), Junxiang Hu (NASA- GSFC), William H. Matthaeus (University of Delaware)

The main aim of this session was to discuss the use of global models to establish linkages between different heliospheric domains and boundaries, and the interplay of turbulence transport with processes such as particle acceleration and magnetic connectivity.

The first scene-setting speaker was Dr. Rohit Chhiber from the University of Delaware and NASA-GSFC. The title of the presentation was “Recent Progress in Modeling and Representation of Turbulence in the Global Inner-Heliospheric Solar Wind.” Dr. Chhiber discussed significant advances in global models of solar wind in the inner heliospheric turbulence. Dr. Chhiber’s talk raised important science questions for the community. 1) What are the crucial elements of turbulence transport models for global solar wind simulations? 2) How can the representation of kinetic scale and dissipation be improved? 3) How can we better understand Sun-heliosphere connections via turbulence modeling and data? The community remains uncertain whether solar wind turbulence is primarily dominated by slab (Alfven) turbulence or 2D turbulence, how the radially varying proton and electron heating rates are integrated into the global solar wind model, and how the refined and optimized turbulence boundary conditions at the Sun can be obtained. There was a discussion of the development of turbulence transport model, such as the residual energy transport equation which describes the radially varying residual energy with increasing heliocentric distance.

The second scene-setting speaker was Dr. Federico Fraternale from the University of Alabama in Huntsville. The title of the presentation was “Turbulence in the outer heliosphere and global modeling of the SW-LISM interaction.” Dr. Franternale focused on the important question: “Why is turbulence important for global heliospheric models, and vice versa? This talk highlighted the incompleteness of turbulence transport models for the inner heliosheath (IHS) and very local interstellar medium (VLISM), coupling with global SW-LISM. This talk discussed the following science questions. Do turbulence and reconnection provide the required dissipation, in the real system? How can we include these effects in turbulence models? How can turbulence models account for the transmission across the heliopause (HP)?

A graduate student, Caroline Evans, presented her poster entitled “Quantifying how surface complexity influences properties of the solar corona and solar wind.” A fruitful discussion took place between the speaker and the audience, addressing various scientific questions raised by the speakers.

Organizers: W. Matthaeus (Delaware), Alex Chasapis (Colorado), Riddhi Bandyopadhyay (Princeton), Francesco Pecora (Delaware).

Current generation heliospheric missions and modern simulations enable the investigation of space plasma turbulence across a broad range of scales ranging from the injection scales to ion and electron scales. Properties across all these scales are important in understanding fundamental space plasma phenomena ranging from coronal heating and acceleration to energetic particle propagation. Yet the scales are linked dynamically through time-dependence, turbulent cascade and cross-scale energy transfer, leading to energy conversion processes including production of internal energy. This complexity necessitates study of the turbulence at both microscopic and system levels. This session addresses broad aspects of the observed heliospheric turbulence using in situ and remote sensing measurements from Parker Solar Probe, Solar Orbiter, Magnetoshperic MultiScale, ACE, WIND, and Voyager, as well as future missions such as HelioSwarm and Plasma Observatory. These are complemented by increasingly capable magnetohydrodynamic (MHD) simulations with large grid resolution, particle-in-cell (PIC) simulations with large particle numbers, and Eulerian Vlasov models with improving velocity space resolution. Novel scale filtering and multi-spacecraft analysis techniques are providing new and compelling insights into the pathways of turbulent energy conversion in space. Contributions are welcome from the simulation, observation and theory perspectives.

What controls the ion versus electron energy cascade across the inertial range of scale and their heating rates in the dissipation scale?

Do inertial range properties vary with large-scale driving and plasma parameters, such as the involvement of velocity shear and reconnection?

How do these large scale properties and driving mechanisms affect the termination of the inertial range and related heating and dissipation?

Organizers: Lingling Zhao (UAH), Gary Zank (UAH)

This session aims to explore the dynamic interplay between the nature of turbulence and its evolution in the Very Local Interstellar Medium (VLISM). Turbulence in the VLISM appears to be generated in part by heliospheric processes ranging from the interaction of (inner) heliosheath turbulence and its transmission the heliopause to the role of interplanetary shocks propagating into the VLISM. This in turn is superimposed on possibly pre-existing interstellar turbulence. As a result, the turbulent state immediately upwind of the heliopause that appears to be quite distinct from turbulence in heliospheric plasma. The evolution and dissipation of VLISM turbulence is not clearly understood theoretically or observationally and its implications for particle transport, particularly within the context of heliophysics, remain largely unexplored. By focusing on turbulence within the VLISM, we aim to deepen our understanding how the heliosphere influences the VLISM and conversely how it influences the heliosphere, especially in its role in modulating the transport of energetic particles, including cosmic rays, and its relevance to phenomena such as the Interstellar Boundary Explorer (IBEX) Ribbon.

1. What are the characteristics of turbulence in the VLISM and how does the heliosphere act to mediate turbulence in the VLISM?

2. How does turbulence within the VLISM affect the transport and modulation of energetic particles, including cosmic rays, in the heliosphere?

3. What insights can turbulence dynamics within the VLISM provide into the origin and characteristics of observational features such as the IBEX ribbon?

Progress and Prospects Summary Report

Organized by Lingling Zhao (University of Alabama in Huntsville) and Gary Zank (University of Alabama in Huntsville).

This session aims to explore turbulence in the very local interstellar medium, which is the region of the interstellar medium strongly affected by the Sun and the heliosphere, also known as the outer heliosheath. There is a diverse audience with expertise in both the inner heliosphere, outer heliosphere, and astrophysics. We discussed turbulence observations by Voyagers as well as the astrophysical observations of the general interstellar medium. Vladimir Florinski from the University of Alabama in Huntsville was the first scene-setting speaker and gave a presentation on “Turbulence in the very local interstellar medium and its consequences for cosmic ray transport”. His talk introduced the heliosphere and interstellar medium, waves and turbulent fluctuations through compressibility and spectral density, as well as the implications for cosmic ray transport and the role of turbulence and pickup ions in the formation of the IBEX ribbon. The second scene- setting speaker was Siyao Xu from the University of Florida. She gave a talk on turbulence in the partially ionized very local interstellar medium (VLISM) and its implication on the IBEX ribbon and discussed the driving and damping scales of turbulence in the VLISM and the components of turbulence in the VLISM. Finally, the audience discussed how instabilities, shocks, and reconnection affect turbulence in VLISM? In addition to the two scene-setting speakers, we also have contributed presentations from Gary Zank (UAH) and Federico Fraternale (UAH). They discussed the magnetic power spectrum observed in the heliosheath and VLISM and their variations with distance away from the heliopause. Some possible physical explanations were explored.

Main points of discussion during the session include the following:

(1) The magnetic power spectrum observed by Voyagers. Flattening of the power spectrum in the high frequency range was observed. The effects of instrument noise were discussed and it appears likely that the flattening is physical. Discussions are also made regarding the relation between the magnetic spectrum and the density spectrum measured by the plasma wave instrument.

(2) Properties of the turbulence and the evolution in space or time. The turbulence is observed to evolve from compressible to incompressible as the Voyagers travels further away from the heliosphere. Mode conversion provides a possible explanation, but it may not explain all aspects of observations and further investigations are still needed. The effects of solar activity changes are also discussed as simulations with time-dependent inner boundary conditions set according to observations suggest that the variation in the Voyager measurements is qualitatively consistent with the solar or solar wind conditions such as the dynamic pressure at 1 au.

(3) Insights from astrophysical observations. Turbulence is ubiquitous in the interstellar medium, but the Voyager observations are the only in situ measurements. Comparisons between the remote observation of turbulence and the Voyager observed turbulence are discussed. Voyager observations are also consistent with the regime of viscous damped turbulence due to neutral viscosity.

(4) The scattering of particles and the formation of IBEX ribbon. The mechanism of turbulence mirroring is discussed. The idea still needs to be explored more quantitatively in the future to compare with the IBEX observations.

Organizers: Alicia K. Petersen (University of Florida), K.D. Leka (North West Research Associates), Samuel Schonfeld (Air Force Research Lab)

Whether its modelers not understanding the intricacies of the data their models rely on, limitations of models that don’t get described in their publications, analogies in theories that get taken as fact, or one of many other “mistakes” that linger in our cross-disciplinary research community, there are times when you don’t know what you don’t know. If you’re rolling your eyes when reviewing yet another proposal making the same mistake you see time and time again, or you are a student/early career researcher eager to hear the secrets of the trade that don’t make it into the papers and the readme files, this is the session for you. When readme files and instrument papers aren’t enough, when living reviews are not so “living,” when crucial minds leave the field, what can we do to disseminate wisdom across subfields and pass it between generations of researchers? Join us for an open and fruitful discussion; come help brainstorm new solutions for knowledge dissemination.

1. Wisdom Dissemination: How do we create avenues for communicating knowledge and detailed information for users of our research that go beyond the limitations of journal publications and are more open than private discussions between those already in-the-know?

2. PSAs: From the perspective of a modeler, data expert, etc, what are some of the common “mistakes” made by the community?

3. Challenges: What are the challenges and concerns that face our growing and cross-generational research community, as for example, available methods of communicating and collaborating expand and as some long-standing members of our research community leave the field?

Organizers: Bennett A. Maruca (University of Delaware) Niharika H. Godbole (American University and NASA Goddard) Ramiz Qudsi (Boston University)

Low-cost flight platforms — including high-altitude balloons, suborbital (sounding) rockets, and CubeSats — occupy a unique role in heliophysics. Many of these missions have produced substantial scientific results in their own rights, but because of their modest costs, they also serve as important opportunities for technology development and education. Larger missions often draw substantial heritage from these sorts of small missions, and small missions typically provide far more opportunities for student involvement. This session will highlight the strengths and weaknesses of each type of flight platform, discuss best practices for successful missions, and encourage participation in these missions (especially by students and those new to mission development). — What are the unique strengths and weaknesses of each type of flight platform? — What are the most effective strategies for designing, funding, and implementing successful missions (scientific, technological, and/or educational) with these platforms? — How can students and members of the community new to hardware/mission development best become involved in these missions?

Progress and Prospects Summary Report

Organizers:

• Bennett A. Maruca (University of Delaware; Bartol Research Institute)
• Niharika Godbole (NASA/Goddard; American University)
• Ramiz Qudsi (Boston University)

Description:

Low-cost flight platforms – including high-altitude balloons, suborbital (sounding) rockets, and CubeSats – occupy a unique role in heliophysics.  Many of these missions have produced substantial scientific results in their own rights, but because of their modest costs, they also serve as important opportunities for technology development and education.  Larger missions often draw substantial heritage from these sorts of small missions, and small missions typically provide far more opportunities for student involvement.  This session served as an introduction to these flight platforms, highlighted best practices, and showcased past and current missions.

Scene-Setting Speakers:

• CubeSats: Juan Carlos Martinez Oliveros (UC Berkeley, Space Sciences Laboratory)
  Juan Carlos’s presentation was a case study of the PADRE (PolArization and Directivity X-Ray Experiment) Mission, which he serves as PI.  Slated for launch in June, 2025, PADRE will consist of a 12U CubeSat and will be dedicated to the observation of solar flares.  Juan Carlos’s presentation and related discussion also highlighted some of the key challenges of building a CubeSat mission — notably the condensed timeline for instrument development compared to other platforms (and constraints therein), and integration of off-the-shelf components.
• High-altitude balloons: John Clem (University of Delaware; Bartol Research Institute)
  John gave a broad overview of scientific ballooning.  He described different types of balloons (including sizes and pressurization), different use cases (e.g., solar physics, astrophysics, and atmospheric sciences), and different launch sites and flight paths (e.g., circumpolar).  His presentation highlighted several missions as case studies, including AESOP, BITSE, BARREL, and GRIPS.  The capabilities and physical limitations of high-altitude balloon platforms were also discussed.
• Sounding rockets: Kelly Korreck (NASA/Headquarters)
  Kelly’s presentation gave a broad overview of NASA’s sounding rocket program, which dates back over forty years.  Sounding-rocket flights are relatively short but can reach a wide range of altitudes (depending on the launch vehicle).  A wide range of launch locations and trajectories are available, and Kelly strongly recommended consultation of NASA’s Sounding Rocket Handbook for details.

General Discussion:

Following these scene-setting talks (and after the session concluded), we received questions about student opportunities, funding availability, resources for proposal-writing, and data availability from prior missions.

Organizers: Nikolai Pogorelov (University of Alabama in Huntsville), Ameneh Mousavi (Space Science Institute), Eric Zirnstein (Princeton University)

Pickup ions (PUIs) are created in the heliosphere and in the very local interstellar medium (VLISM) due to charge exchange, photoionization, and electron impact ionization of neutral atoms, especially hydrogen (H) and helium (He). In principle, there exist several populations of PUIs, depending on the region of their origin and the parent neutral atom population they derive from. It is common to subdivide the domain of the solar wind (SW) interaction with the interstellar medium into 4 regions: (1) the unperturbed local interstellar medium (LISM); (2) the LISM affected by the presence of the heliosphere (VLISM); (3) the heliosheath, i.e., the SW region between the heliopause (HP) and the heliospheric termination shock (TS), and (4) the supersonic SW. Neutral atoms are also commonly classified according to their origin in the above-mentioned regions. PUIs carry most of internal energy of the SW plasma and constitute its non-thermal population. They also give birth to energetic neutral atoms (ENAs), some of them being observed by the Interstellar Boundary Explorer (IBEX). While the properties of PUIs were observed in situ by Ulysses and are currently being measured by New Horizons at far distances from the Sun, they also have a profound effect on interpreting Voyager measurements. It is also becoming increasingly evident that Ulysses SWICS measurements require reevaluation based on a more accurate approach of transferring the count rates into the distribution functions.

We call for data, theory, and modeling presentations addressing the following questions:

1. How the space-time evolution of PUI distribution functions, especially at collisionless shocks, affects the global heliosphere?

2. What are the physical processes influencing the IBEX ribbon and the heliosheath ENA fluxes, and the methods for improving the energy resolution of ENA models.

3. What are the theoretical challenges in our understanding of the PUI physics from the perspective of the upcoming Interstellar Mapping and Acceleration Probe (IMAP) mission.

Progress and Prospects Summary Report

Organizers: Nikolai Pogorelov (University of Alabama in Huntsville), Ameneh Mousavi (Space Science Institute, Boulder, CO), Eric Zirnstein (Princeton University)

The session took place on August 13, 2024 and was focused on the following topics: (1) How the space-time evolution of pickup ion (PUI) distribution functions, especially at collisionless shocks, affects the global heliosphere? (2) What are the physical processes influencing the IBEX ribbon and the heliosheath ENA fluxes, and the methods for improving the energy resolution of ENA models. (3) What are the theoretical challenges in our understanding of the PUI physics from the perspective of the upcoming Interstellar Mapping and Acceleration Probe (IMAP) mission.

The first half of the session was dedicated to observational data involving PUIs. The scene setting presentation was given by David McComas. A historical introduction was given that included ACE/Wind/STEREO data at 1 au, Ulysses data between 1 and 5.4 au, Pioneer 10 at 8.3 au, and Cassini between 6.4 and 10 au. There was a discussion (Joe Giacalone and others) about the details of identification of He+ and He2+ ions, and corresponding PUIs, by fitting 24-hour New Horizons SWAP measurements. Further focus was on the PUI behavior at shocks and derivation of PUI distribution functions from NH’s 30-minute data. In particular, the possibility of the solar wind plasma (mixture of the thermal core protons and PUIs) temperature to increase to such an extent that transient shock propagating through it disappear. Additional discussion addressed the radial distribution of PUIs as NH approaches the heliospheric termination shock. A question about the necessity of reconstruction of magnetic field along the NH trajectory. A summary of IBEX ENA measurements, which are of critical importance for deriving information about PUI behavior in the heliosphere, was given. The capabilities of the IMAP mission were discussed. As a follow-up, Nikolai Pogorelov attracted attention to the new interpretation of Ulysses SWICS data performed by Ming Zhang (Florida Institute of Technology). Formerly a Co-I on SWICS, he proposed to improve the derivation of PUI distribution functions (for H+ and He+) by avoiding simplifications associated with the previously used narrow-beam approximation. This resulted in a set of distribution functions with 6-hour cadence during the 2 months around the 2003 Halloween events. This work was further used by Smith et al. (2022) to obtain the distributions of PUI bulk properties. Comparison of the new results with the old ones shows substantial differences, suggesting a necessity to reevaluate Ulysses SWICS data.

Federico Fraternale gave a scene-setting talk about the community progress in modeling the solar wind interaction with the local interstellar medium (LISM). In particular, the importance of performing kinetic, time-dependent simulations that would make it possible to interpret IBEX and IMAP ENA and PUI observations with higher accuracy. Such simulations can be used also to derive the properties on the unperturbed LISM through He atom observations in the inner heliosphere. The importance of an adequate treatment of electrons was also emphasized. New approaches to analyze turbulence in the solar wind and LISM were outlined. In discussion, an opinion was expressed that modeling should focus on reproducing, interpreting, and predicting spacecraft observations. There was also a comment about the application of fitting TeV cosmic ray anisotropy measurements to infer the global structure of the heliosphere. Ameneh Mousavi further focused on the physical mechanism responsible for the IBEX ribbon, particularly involving mirror-mode instabilities. Fan Guo and Vladimir Florinski made related comments based on their experience. Parisa Mostafavi pointed out the importance of proper description of PUIs crossing the termination shock. In the discussion, it was emphasized that the PUI behavior at shocks is entirely kinetic.

Eric Zirnstein further commented commented that solving the Parker transport equation in the heliosheath, with flow advection, velocity diffusion, flow divergence, production and loss source terms, improves the model agreement with IBEX data. The session was lively and with a good attendance of students and young scientists.