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GEM Focus Group: Multiscale Dayside Transients (MDT) and their Effect on Earth’s Magnetosphere

Savvas Raptis1, Ivan Vansko2, Imogen Gingell3, Terry Z. Liu4, Ying Zou1 Runyi Liu4, David Tonoian2

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1 APL/JHU, Laurel, MD, USA

2 University of Texas at Dallas

3 University of Southampton

4 University of California, Los Angeles

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Credit: © Naeblys/Shutterstock

Primary: Solar Wind - Magnetosphere Interaction (SWMI)

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  1. Shocks and foreshocks in 3 mins

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  • Dayside Transient Processes

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  • Effects on the Magnetosphere-Ionosphere system

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  • Team & Goals

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  • Our first GEM sessions & Next Steps

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Earth’s magnetosphere & shock environment

L. B. Wilson (2016)

Dayside Transients

ULF waves

Shock waves:

Formed when structure moves with speed above local wave speed

(e.g., sound, magnetosonic)

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Heating, accelerating particles and converting energies

+ forming transient phenomena upstream and downstream

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Fast shock transition (Theory & initial data)

1964. Initial results of IMP-1 magnetic field experiment.

Rankine Hugoniot relations / Jump Conditions

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Thermalization, Compression, Breaking

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1D Isotropic and adiabatic one fluid plasma shock transitions

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The Supercritical Bow Shock & foreshock

Reproduced from [Balogh and Treumann, 2013].

Assuming Specular Reflection

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Quasi-parallel and Quasi-perpendicular shocks

Qpar

Qperp

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Multiscale Dayside Transients (MDT) and their Effect on Earth’s Magnetosphere

  1. Dayside Transient Processes
  2. Effects on the Magnetosphere-Ionosphere system
  3. Team & Goals
  4. Our first GEM sessions & Next Steps

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What is a “Dayside” Transient?

  • Global (Solar):
    • Coronal Mass Ejection (CME)
    • High-Speed Stream (HSS)
    • Pressure Pulse / IP Shocks
  • Fluid scale:
    • Flux Transfer Event (FTE)
    • Magnetopause (bursty) Reconnection
  • Mesoscale:
    • Hot Flow Anomalies (HFAs)
    • Foreshock Bubbles (FBs)
    • Magnetosheath jets
  • Kinetic:
    • ULF waves
    • Shocklets
    • SLAMS

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

Transient phenomena are events that disrupt the steady-state plasma conditions, occurring temporarily and introducing dynamic changes to the physical system

Figure adapted from Krämer+ (2025; sketch by Florian Koller)

NOTE: Transients can be intrinsic (e.g., ULF waves) or driven (e.g., HFAs)

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What is a “Dayside” Transient?

  • Global (Solar):
    • Coronal Mass Ejection (CME)
    • High-Speed Stream (HSS)
    • Pressure Pulse / IP Shocks
  • Fluid scale:
    • Flux Transfer Event (FTE)
    • Magnetopause (bursty) Reconnection
  • Mesoscale:
    • Hot Flow Anomalies (HFAs)
    • Foreshock Bubbles (FBs)
    • Magnetosheath jets
  • Kinetic:
    • ULF waves
    • Shocklets
    • SLAMS

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

Transient phenomena are events that disrupt the steady-state plasma conditions, occurring temporarily and introducing dynamic changes to the physical system

Figure adapted from Krämer+ (2025; sketch by Florian Koller)

NOTE: Transients can be intrinsic (e.g., ULF waves) or driven (e.g., HFAs)

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The anatomy of an HFA

Figure by Nick Omidi

Density compressions and cavity

Strong plasma flow

deflections in core

Crater-like B-field and IMF discontinuity

Solar wind beam disrupted

Upstream

shock

Upstream

shock

Superheated core plasma

Figure by Drew Turner

Kajdič+ (2024)

Hot Flow Anomalies (HFA)

Discontinuity intersects the bow shock and the convection electric field

(−V X B) points towards the sheet on at least one side.

How many: ~several per day!

How big: ~up to 10s of Re

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Universality of shock-generated transients

Yes!*

Yes!*

Hietala et al. ISSI 2019

*Gunell+ 2023, Zhou+ 2024, Mohammed-Amin+ 2025 (Poster of Abigail Tadlock #2)

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Transients Scaling Across Systems

Adapted form Valek et al. (2017) | JGR

Zhou, et al. 2024

HFA Scaling

Jet Scaling

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Multiscale Dayside Transients (MDT) and their Effect on Earth’s Magnetosphere

  1. Dayside Transient Processes
  2. Effects on the Magnetosphere-Ionosphere system
  3. Team & Goals
  4. Our first GEM sessions & Next Steps

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Transient and Wave transmission

How are the ULF waves transmitted from the magnetosheath to magnetosphere?

Turc+ 2024

 Evidence of Pc3 waves generated by a large HFA (Zhao+ 2017)

Pi2 Pulsations transmitted associated to jets/foreshock transients (Katsavrias+ 2021)

Foreshock transients driving Pc5 waves (Hartinger+ 2013)

Liu+ 2025 (Under Review)

GMAG correlation with foreshock waves

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Magnetopause Reconnection and Displacement

Němeček+ 2023

Wang+ 2021

Zhou+ 2025 (under review)

Jets ~ 4Re localized

HFAs ~6Re over the whole MSH

Open question: How “important” is this for preconditioning the magnetosphere?

Transient localized processes drive and adapt MP bursty reconnection

Hietala+ 2018, Escoubet+ 2020, Vuorinen+ 2021

Ng+2021

”Jets can have bursts of southward Bz”

Open question: Is this sufficient?

Yang+2023, Guo+ 2023

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Inner magnetosphere and Ionosphere effects

Shen+2018, Wang+ 2018

Murr+ 2003

Which shock-generated transients cause ground perturbations?

How do shock-generated transients drive localized aurora brightening?

Liu+ 2024

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Team & Goals

  1. Dayside Transient Processes
  2. Effects on the Magnetosphere-Ionosphere system
  3. Team & Goals
  4. Our first GEM sessions & Next Steps

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Multiscale Dayside Transients (MDT) FG

Savvas Raptis

(Johns Hopkins University APL)

- Collisionless shocks

- Transient processes

Ivan Vasko

(University of Texas at Dallas)

- Plasma waves

- Wave-particle interactions

Imogen Gingell

(University of Southampton)

- Hybrid & PIC simulations

- Shock, turbulence, reconnection

Terry Liu

(University of California)

- Particle acceleration

- Foreshock processes

Ying Zou

(Johns Hopkins University APL)

- Solar wind – Magnetosphere coupling

- Magnetosphere- ionosphere coupling

Runyi Liu

(University of California)

- ULF Waves

- Foreshock

David Tonoian

(University of Texas at Dallas)�- Wave-particle interactions

- Particle scattering

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Relevance to Existing GEM Focus Groups

COMP

    • How do dayside transients manifest in other planets?

RX

    • How do transient phenomena modulate dayside reconnection?
    • How does reconnection processes modulate dayside transient processes?

GIC

    • How are large scale solar transients change at Earth?
    • How do mesoscale transients drive currents?

Multiscale Dayside Transients

RG: Machine Learning

How do we these incorporate dayside processes to ML models?

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Recent history of Transients’ efforts (From Mike Hartinger)

  • GEM FG 2019-2024, “Particle Heating and Thermalization in Collisionless Shocks in the MMS Era”
  • GEM FG 2016-2021, “Dayside Kinetic Processes in Global Solar Wind-Magnetosphere Interaction”
  • GEM FG 2012-2016, “Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures”

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  • ISSI team, “Global study of the transmission of foreshock ULF waves into the magnetosheathand the magnetosphere”
  • ISSI team, “Foreshocks Across The Heliosphere: System Specific Or Universal Physical Processes?”
  • ISSI team, “Future directions for understanding surface waves throughout Earth’s magnetosphere and beyond”
  • ISSI team, “Jets Downstream of CollisionlessShocks”
  • ISSI team, ”Impact of Upstream Mesoscale Transients on the Near-Earth Environment”

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Why then do it again ?

Oliveira et al., 2024

ANGIE3D

Vlasiator

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Expected Activities

Goals and Deliverables

  • Year 1: Invite experts and identify knowledge gaps
  • Year 2:  A GEM challenge on TBD topic
  • Year 3: Update and continuation of GEM challenge
  • Year 4: GEM challenge completion along with:
    • Session Summary
    • Review paper
    • Future goals (i.e., what was not addressed)
    • Database of in-situ events for cross-scale studies via multi-mission observations
  • Collaborative Sessions: Host joint meetings with existing Focus Groups to foster cross-disciplinary discussions.
  • Expert Reviews: Invite specialists to provide state-of-the-art insights and compile critical unanswered questions.
  • Early Career Focus: Prioritize talks from graduate students and young researchers to encourage active participation and form an EC driven session.
  • Hands-on Workshops: Offer practical sessions on dayside processes, emphasizing multi-spacecraft techniques and observation-simulation comparisons across kinetic to fluid scales (e.g., magnetosheath current sheets to FTEs).

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Please provide feedback and what you want to see in the future

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Expected Activities

Goals and Deliverables

  • Year 1: Invite experts and identify knowledge gaps
  • Year 2:  A GEM challenge on TBD topic
  • Year 3: Update and continuation of GEM challenge
  • Year 4: GEM challenge completion along with:
    • Session Summary
    • Review paper
    • Future goals (i.e., what was not addressed)
    • Database of in-situ events for cross-scale studies via multi-mission observations
  • Collaborative Sessions: Host joint meetings with existing Focus Groups to foster cross-disciplinary discussions.
  • Expert Reviews: Invite specialists to provide state-of-the-art insights and compile critical unanswered questions.
  • Early Career Focus: Prioritize talks from graduate students and young researchers to encourage active participation and form an EC driven session.
  • Hands-on Workshops: Offer practical sessions on dayside processes, emphasizing multi-spacecraft techniques and observation-simulation comparisons across kinetic to fluid scales (e.g., magnetosheath current sheets to FTEs).

​

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Please provide feedback and what you want to see in the future

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Our First Year Highlights

  1. Dayside Transient Processes
  2. Effects on the Magnetosphere-Ionosphere system
  3. Team & Goals
  4. Our first GEM sessions & Next Steps

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Our first GEM (Monday – Tuesday)

2 standalone session, 1 joint with RX,

23 contributed talks, 2 invited scene setting talks, 10 posters

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Special thanks to Mike Hartinger and Yu Lin!

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Let’s see some highlight from this week!

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Highlights Monday 13:30 – 15:30

Counteract reporting bias by studying transients associated with large magnetopause displacements that produce no ionospheric/ground response –we can learn the most from these!

M. Hartinger

Y. Lin

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Highlights Monday 16:00 – 18:00 | Shock Physics

Toy-Edens+ [JGR 2024] :

Full list of dayside environments, magnetopause, bow shock list (Drew Turner)

Non-stationarity of a SLAMS (Mengmeng Wang)

Electron VDF

Xi Lu

Remote Gyrosensing of the Earth's Bow Shock�

Mohammad Barani

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Simulations of HSJs behind quasi-parallel shocks: Test particles/hybrid simulations

Yufei Hao

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Highlights Monday 16:00 – 18:00� Magnetosphere/Ionosphere Effects

Compressional ULF waves

Wang et al., (2018a, 2018b); Xu et al., 2024 (about to submit)

FLRs

Wang et al., (2019, 2020)

FACs/TCVs

Wang et al., (2025)

Yuda Zhi

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Monday (16:00 – 18:00) Gannon Storm Success Stories

This density enhancement may play a crucial role

Orange – THEMIS/MMS

Blue - WIND

Old SW (OMNI)

New SW (MMS/ARTEMIS)

Bz (nT)

Bz (nT)

  • Introduced local upstream (~10 min) transient variability from local in-situ observations

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  • Data–model agreement increased drastically

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  • Physical interpretation of ground data changed significantly

Ohtani+ (2025)

Pham+ (ongoing)

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Highlights Tuesday 10:00 – 12:00

Jonthan Ng

Rachel Rice

Naoki Bessho

Katy Goodrich & Robert Strangeway

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Some quotes I read/heard for our FG

“What role do transients play in

space weather?”

-M. Hartinger, (Monday) 2025 GEM

“What role do transients play in

the development of storms?”

-B. Walsh, (Tuesday) 2025 GEM

“What’s your focus group again?”

- Same Anonymous APL colleague, (Sunday) 2025 GEM

“….Daaaaaysiiiide what? …”

- Visibly confused Anonymous, (Tuesday) 2025 GEM

“Should we try to gather all lists of transient events to provide targets for modelers? To have examples that have both a space weather impact but also for these that don’t?”

-Me, (Monday) 2025 GEM

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Reply: “Asynchronous head nodding across the room”

“Oh, nice, I didn’t know people work on this?”

- Anonymous, (Tuesday) 2025 GEM

“..aah ye ye.. you have a focus group?”

- Anonymous APL colleague, ~1 week before GEM

“I am so happy about this focus group! It’s very relevant to my research!”

- Several people, 2025 GEM

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“This focus group has perfect timing with my PhD topic!”

- Anonymous, 2025 GEM

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Upcoming Actions

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Join our Google Group to (at some point…) get updates and information for our telecons and meetings: https://groups.google.com/g/helio-day-research (We will discuss our online activities during GEM/CEDAR 2025 workshop)

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Extra Backup Slides

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Example of a Transient Event (High-speed jet)

Example of High-Speed jet (MMS Data)

Krämer+ (2025)

MMS helped bridging fluid to ion/electron scales

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Clarified transient processes:

    • Formation
    • Particle acceleration
    • Propagation
    • Distribution-function evolution

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Remaining challenge: co-existing phenomena (HFAs, jets, SLAMS) are interconnected and need deeper investigation

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We need more than 4-point measurements and in various scales

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Spatial and Temporal Solar Wind Variability

O’ Brien+ 2023

Burkholder+ 2020

Borovsky 2017

Walsh 2019

MMS (MSH)

OMNI

Bz

WIND

ACE

Walsh 2019

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What are we dealing with?

All our modeling efforts

An 1D, planar solar wind without foreshock, realistic magnetosheath or shock-generated transients

Two challenges:

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Solar wind information limitations:

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    • Reality has complex 3D structure and spatial variability.

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    • It is easier to rely on simple 1D picture that is available than do the extra effort.

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Neglected foreshock and magnetosheath transients:

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    • These transients can affect magnetopause reconnection, and more.

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    • They are often omitted because they are difficult to include.

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