FG: Multiscale Dayside Transients and their Effect on Earth's Magnetosphere

Title

Multiscale Dayside Transients and their Effect on Earth’s Magnetosphere

Abstract

The proposed Focus Group (FG) aims to examine multiscale dayside processes and their impact on Earth’s magnetosphere. Our focus includes evaluating how large-scale solar-driven events, such as Coronal Mass Ejections (CMEs) and High-Speed Streams (HSSs), interact with near-Earth dayside transients, as well as comparing their geoeffectiveness to localized shock-generated transients like Hot Flow Anomalies (HFAs), Foreshock Bubbles (FBs), and Magnetosheath High-Speed Jets (HSJs). In addition, we aim to investigate the role of kinetic-scale phenomena, such as magnetosheath current sheets and magnetic holes, in shaping the magnetospheric environment. Such multiscale transients play a key role in solar wind-magnetosphere-ionosphere coupling, influencing magnetopause morphology, field-aligned currents (FACs), auroral dynamics, and magnetopause reconnection processes. Our investigation will focus on the interaction of these transient processes with broader magnetospheric dynamics, addressing critical questions regarding their geoeffectiveness, role in wave-particle interactions, and broader space weather consequences. By utilizing recent advancements in hybrid and fully kinetic simulations, combined with extensive datasets from in-situ missions like MMS, THEMIS, and Geotail. This FG is particularly timely given the approaching solar maximum and upcoming missions such as HelioSwarm, SMILE, and potentially Plasma Observatory. We will collaborate with other GEM groups to bridge knowledge gaps, emphasizing observation-simulation comparisons and expanding our understanding to other planetary systems. Deliverables will include a comprehensive conjunction database and a proposed GEM challenge.

Topic Overview

A variety of transient phenomena occurs within Earth’s dayside plasma environment, spanning a wide range of spatial and temporal scales. These include localized shock processes both upstream at the foreshock and downstream at the magnetosheath, such as Hot Flow Anomalies (HFAs), Spontaneous Hot Flow Anomalies (SHFAs), Foreshock Bubbles (FBs), High-Speed Jets (HSJs), and non-linearly evolved Ultra Low Frequency (ULF) waves (e.g., shocklets and SLAMS). Collectively referred to as shock-generated transients, these processes may be either intrinsic or driven by variable upstream solar wind conditions. While large-scale solar transients are established drivers of geomagnetic storms, mesoscale shock-generated transients play a critical role in solar wind-magnetosphere-ionosphere coupling, contributing to significant magnetopause deformation, the generation of field-aligned currents (FACs), and auroral activity. Furthermore, dayside processes include phenomena such as magnetopause reconnection, driven by strong magnetic field shear, and the Kelvin-Helmholtz Instability (KHI), triggered by velocity shear in plasma flows that can be initiated or influenced by interactions between shock-generated transients and the magnetopause. Kinetic processes occurring at ion and electron scales within the foreshock, bow shock, and magnetosheath can evolve into larger structures or interact with existing transients. SLAMS evolve from ULF waves, while the Kelvin-Helmholtz Instability—an MHD-scale convective instability—cascades down to kinetic scales, involving secondary processes such as reconnection and plasma turbulence. Disentangling these complex, multiscale processes is crucial for assessing their contributions to energy transfer across the magnetosphere, which, in turn, impacts space weather dynamics.

Our proposed Focus Group (FG) will investigate the multiscale nature of these transients, their variability in response to solar transients, and their overall effects on the magnetosphere-ionosphere system. Key questions include:

• How do CMEs and HSSs interact with Earth’s bow shock and influence the generation and evolution of shock-generated transients? How do they modify plasma transport across the magnetopause through magnetopause reconnection and KH instability?

• How do shock-generated transients affect the magnetosphere, such as the magnetopause, ULF waves, particle precipitation, aurora, and geomagnetic field perturbation? How do these effects compare to those of solar transients, both individually and cumulatively?

• What role do shock-generated transients play in wave transmission, particle energization, and turbulence generation between the magnetosheath and magnetosphere?

• How do transients affect magnetopause reconnection in terms of onset and rate? What is the interplay between KHI, shock localized processes and magnetic reconnection?

Timelines

The proposed focus group (FG) is especially timely due to the advancements in hybrid and kinetic simulation codes, alongside the wealth of dayside observations spanning multiple solar cycles.** Recent developments in sophisticated simulations, such as Particle-in-cell (PIC) embedded simulations (e.g., MHD-EPIC) and global hybrid simulations (e.g., Vlasiator, ANGIE3D), have opened new ways towards understanding the 3D structures and processes at Earth’s bow shock, from ion-scale to global-scale dynamics. Further inclusion of electron kinetic scales (e.g., e-Vlasiator) in the coming years will offer an even more comprehensive understanding of multiscale dayside dynamics. Over the years, we have accumulated vast datasets from various in-situ missions such as MMS, THEMIS, ARTEMIS, Cluster, Van Allen Probes, ARASE, and Geotail, as well as ground-based data like SuperMAG under the Heliospheric System Observatory (HSO). Furthermore, recent solar missions, such as Parker Solar Probe (PSP) and Solar Orbiter (SolO), have further enriched our ability to study the Sun-Earth connection, offering unique conjunction capabilities with Earth-orbiting missions. These alignments will allow simultaneous observations of solar transients, such as Coronal Mass Ejections (CMEs) and high-speed streams, during the upcoming solar maximum, projected to peak between 2025-2026. This presents an unprecedented opportunity to explore how dayside processes respond to variable solar wind conditions during periods of heightened solar activity and how they contribute to geomagnetic activity. Moreover, the proposed FG will be essential in preparing for upcoming missions, including HelioSwarm (2029) and SMILE (2024), as well as potential future missions like Plasma Observatory (PO), a finalist ESA M-class mission. HelioSwarm and PO, in particular, being multi-spacecraft and cross-scale missions fit perfectly with the objectives of this FG.

With the conclusion of the previous dayside FG (focused on collisionless shocks) in 2024, there is a pressing need for a new dayside FG to explore the complex, multiscale interactions between solar wind transients and Earth’s magnetosphere.

Scope and Collaborations

Our FG builds on previous efforts by expanding the scope to include multiscale transient processes and their impacts on the magnetosphere. A key goal is to foster collaboration between the broader GEM magnetosphere modeling community and the dayside research community, which has remained somewhat disconnected, to improve our understanding of the geospace environment. The proposed FG aligns with several existing GEM Focus and Resource Groups:

1. Comparative Planetary Magnetospheric Processes (2023-2027): Many dayside phenomena are present across the heliosphere in different planetary environments. We will work with COMP to investigate how these processes operate across planetary magnetospheres, such as those of Mars, Venus, Saturn, and Jupiter.

2. Understanding the Causes of Geomagnetic Disturbances in Geospace for Hazard Analysis on Geomagnetically Induced Currents (2022-2026):This FG investigates the causes and impacts of geomagnetic disturbances. Our research on dayside processes will support this by providing insights into how solar wind-driven transients contribute to periods of strong geomagnetic activity.

3. Self-Consistent Inner Magnetospheric Modeling (2020 – 2025): We will explore how dayside processes, such as foreshock waves and shock-generated transients, affect radiation belt populations and wavefields, aligning directly with SCIMM’s objectives.

4. Magnetospheric Sources of Particle Precipitation and Their Role on Electrodynamic Coupling of Magnetosphere-Ionosphere-Thermosphere Systems (2022-2026): MPEC is also aligned with our group, in a similar manner to SCIMM. With their focus being M-I-T coupling, our objectives link dayside processes from the solar wind first interaction forming a complete SW-M-I-T coupled system.

Additionally, the Machine Learning (ML) Resource Group will benefit from our focus group. Since many ML models rely on data from dayside observations, understanding the processes we explore in this FG is critical to improving both dayside and nightside magnetosphere ML modeling efforts.

Goals and Deliverables

Year 1: Invite experts to identify key knowledge gaps, focusing on observation and simulation comparisons. Year 2: Propose a GEM challenge and hold joint sessions with the GIC and MPEC FGs. Year 3: Continue the GEM challenge and joint sessions with the COMP FG while conducting workshop-style sessions. Year 4: Complete the GEM challenge and publish a session summary including answered and open questions, resulting in a review paper.

Deliverables to the Community:

Conjunction Database:A comprehensive database of spacecraft conjunctions categorized by solar wind conditions and the presence of multiscale transients will be created, offering a valuable resource for investigating dayside processes across different conditions and scales. An example of what can be done with such a database is shown in Figure 1 in which a high-speed jet (shock-generated transient) is observed by three different missions

Chairs

● Savvas Raptis, Johns Hopkins Applied Physics Laboratory, <savvas.raptis@jhuapl.edu>. Expertise: solar wind - magnetosphere coupling, shock physics, kinetic processes, machine learning

● Ivan Vansko, University of Texas at Dallas, <Ivan.Vasko@UTDallas.edu> Expertise: Plasma waves, shock physics, wave-particle interaction, turbulence

● Imogen Gingell, University of Southampton, <I.L.Gingell@soton.ac.uk> Expertise: hybrid simulation modeling, shock physics, kinetic processes, reconnection

● Terry Z. Liu, University of California, Los Angeles <terryliuzixu@ucla.edu> Expertise: particle acceleration, foreshock processes, wave-particle interaction

● Ying Zou, Johns Hopkins Applied Physics Laboratory, <Ying.Zou@jhuapl.edu>. Expertise: solar wind-magnetosphere coupling, aurora dynamics, atmosphere and thermosphere dynamics

Research Area

Primary: Solar Wind - Magnetosphere Interaction (SWMI)

Proposed Length

4 years (2025-2029). The first year will allow us to establish a consensus on the proposed topic, identifying current knowledge gaps from both simulation and observation perspectives. In the second year, we will propose a GEM challenge and organize joint sessions with other focus groups. Third year will continue the challenge while collaborating with the COMP FG to assess the global importance of dayside processes across planetary systems. Finally, we will conclude the project by summarizing the objectives, and provide a detailed report on remaining open questions for future research

Expected Activities

• Organize joint sessions with existing Focus Groups (FGs), ensuring collaborative discussions.

• Experts will be invited for state-of-the-art reviews on specific phenomena (e.g., SLAMs, jets, magnetopause reconnection etc.) to compile a list of critical unanswered questions per process.

• Priority will be placed on early career talks, encouraging participation from graduate students and young researchers, creating an Early Career (EC)-driven session.

• In response to community feedback, we will hold a series of workshop-style hands-on sessions covering various dayside processes. These workshops will emphasize multi-spacecraft techniques and observation-simulation comparisons, addressing topics from kinetic (e.g., magnetosheath current sheets) to fluid scales (e.g., FTEs).