FG: Radiation Belts as a System of Systems

Focus Group leaders: Harriet George, Man Hua, Adam Michael, Luisa Capannolo

Joint GEM / CEDAR Workshop 2025

Details to come!

We are open to organising joint sessions with other GEM and CEDAR Focus Groups, please contact Harriet George if you would like to arrange a joint session with the RB-SoS Focus Group.

Full FG Proposal

Title

Radiation Belts as a System of Systems (RB-SoS)

Abstract

The Earth’s radiation belts are highly variable in terms of both particle dynamics and wave activities, and are a key component of the magnetospheric energy flow. This energy flow is initiated in the solar wind, is transmitted through magnetotail reconnection and enters the radiation belts through processes such as advection or injections, and this energy can then be deposited into the atmosphere to generate aurora and affect atmospheric chemistry. This results in a strong coupling of the radiation belts to multiple other systems. A physically consistent understanding of the radiation belts that includes coupling to these other systems within the global magnetosphere is therefore required to accurately model the radiation belts. The overarching goal of this focus group (FG) is to evaluate the complex variability of Earth’s radiation belts as part of the heliospheric ‘system-of-systems’, determining how the radiation belts affect and are affected by different coupled systems. This FG considers the inner and outer belts, the slot region, and temporary ‘third belt’, the particles (protons, electrons and heavy ion species) populating these belts, and the inner magnetospheric plasma waves that interact with radiation belt particles. This focus group will evaluate how radiation belt particle dynamics, inner magnetospheric plasma waves, wave-particle interactions and system-wide dynamics couple to the following regions:

• A. Solar wind and interplanetary magnetic field (IMF)
• B. Magnetotail
• C. Ionosphere and atmosphere
• D. Other inner magnetospheric plasma populations, such as the ring current and plasmasphere

Topic Description

The science goals that this FG will focus on, with emphasis on coupling to systems A – D, are:

1. Determine and quantify how radiation belt particle dynamics are controlled by and how they affect systems that couple to the terrestrial radiation belts. This includes phenomena such as the rates of acceleration, transport or loss under different solar wind, geomagnetic storm and substorm conditions, radiation belt precipitation as an input to the atmosphere/ionosphere system, and radiation belt particle dynamics following particle injections from the magnetotail. This inherently includes evaluation of the impact of wave-particle interactions that are modulated by the coupled systems, which are elaborated on in Goal 2.
2. Determine how plasma wave activity within the inner magnetosphere is governed by the coupled systems, and quantify the importance of wave activity to particle dynamics via wave-particle interactions. This includes evaluating the role that coupled systems play on the spatial distribution (including magnetic local time distribution), growth rate and intensity of inner magnetospheric plasma waves. For example, magnetotail injections create particle anisotropies that can lead to plasma wave generation. The plasmapause also acts as a boundary between the growth of whistler-mode chorus and hiss waves. The coupled systems, therefore, play a defining role in the generation and characteristics of inner mag- netospheric waves. Radiation belt wave-particle interactions are further modulated by these coupled systems. The distribution of cold plasma can alter both the efficiency of wave-particle interactions and the spatial extent of the region where the interaction takes place, impacting the particle dynamics that are considered in Goal 1, such as the rates of pitch-angle scattering or acceleration.
3. Evaluate how system-wide radiation belt evolution is modulated by the coupled systems, and the effect that these system-wide dynamics have on the coupled systems. This goal specifically evaluates radiation belt dynamics that persist significantly longer than a drift period (≳ hours/days) and affect the entire radiation belt environment, such as long-term dropouts and enhancements. For example, some geomagnetic storms and substorms drive radiation belt enhancements more efficiently than other storms, so determining the solar wind and/or magnetotail conditions that result in this varying enhancement efficiency is an important aspect of accurate geospace modeling that is encompassed by this FG. This science topic includes determining and quantifying the effects that large-scale radiation belt dynamics have on the coupled systems, such as the impact of particle precipitation during radiation belt dropout events on the atmosphere/ionosphere system.

Evaluation of the influence of the solar wind on the Earth’s radiation belt includes the impact that specific solar wind/IMF parameters have on the radiation belts. The FG additionally includes evaluation of the impact of solar wind transients, such as high speed solar wind streams or coronal mass ejections, on long-term, system-wide radiation belt enhancements or dropouts, and variations in the radiation belts on solar-cycle timescales that result from changing solar wind/IMF conditions throughout the solar cycle. The coupling of the magnetotail to the radiation belts includes evaluation of the impact of geomagnetic storms and substorm activity on the radiation belts, as well as transient phenomena such as bursty bulk flows or dipolarization fronts. This FG additionally encompasses studies evaluating the magnetotail as a source of radiation belt particles, such as the evaluation of how often and in which conditions the plasma sheet acts as a source of energetic radiation belt particles, and the effect of these particle injections on inner magnetospheric wave generation and the subsequent wave-particle interactions. The Earth’s inner magnetosphere is composed of a range of plasma population, such as the ring current and plasmasphere, that interact with the radiation belts. For example, different wave modes arise inside and outside the plasmasphere, so the plasmapause plays a key role in defining the spatial extent and key characteristics of inner magnetospheric waves that interact with radiation belt particles, while the ring current results in phenomena such as the Dst effect. Determining the coupling of the atmosphere/ionosphere system on the radiation belt includes both the effects of the radiation belts on the atmosphere/ionosphere and the effects that the atmosphere/ionosphere have on the radiation belt environment. Radiation belt particle precipitation deposits mass and energy into the atmosphere/ionosphere, which can have significant space weather and climatological impacts. This FG therefore encompasses studies related to the pitch-angle scattering of radiation belt particles that results in precipitation, which can occur through a range of interactions (including non-linear interactions) with inner magnetospheric waves. Ionospheric outflow is also a source of inner magnetospheric particles, and multiple current systems couple the inner magnetosphere and ionosphere; evaluation of the impacts of these phenomena, and other ionospheric or atmospheric dynamics, on the radiation belts are in-scope for this FG.

Timeliness

The timeliness of this FG is underscored by:

1. Unprecedented observational datasets: Recent and ongoing missions, such as the Van Allen Probes, Arase, THEMIS, MMS, DSX, an increasing number of current and upcoming CubeSat mis- sions (e.g., ELFIN, CIRBE, FIREBIRD, REAL, AEPEX, CANVAS, GTOSat), and balloons (e.g., BARREL), coupled with long-term data from NOAA/GOES, POES, LANL/GEO, and GPS, provide a unique opportunity for a comprehensive investigation of radiation belt wave and particle dynamics.
2. Recent intense space weather events: Radiation belt dynamics drastically varied during the most intense space weather events in the last 20 years (e.g., the Gannon storm in May 2024 with Dst below -400 nT). The datasets mentioned above cover multiple stages of the solar cycle, allowing for the exploration of whether existing knowledge of radiation belts during solar minimum can be extended to solar maximum, which has both significant scientific and practical interests.
3. New insights into system interactions: Significant advances have been made in understanding the impact of other systems, such as the solar wind and IMF, substorm injections from the magnetotail, and plasma populations from the ring current and plasmasphere on radiation belt dynamics, which in turn, affect the relevant physical processes in their coupling systems (e.g., ionosphere/atmosphere). Therefore, investigating the radiation belts within this system-wide framework is a fundamental and open science question that brings together the community to foster a deeper understanding of radiation belts, and their role within the solar system as a whole.
4. Advancements in modeling: Newly developed cross-scale, self-consistent models, combining the global MHD simulations with simulations of local wave-particle interactions (e.g., MAGE, K2), drift- resolved diffusion models, models including nonlinear effects, and novel machine-learning models, offer new capabilities for simulating radiation belt particle dynamics. These models also enhance our understanding of the correlation of the different domains of the geospace, and the relative importance of different driving factors on the radiation belt dynamics. There is a critical need to explore how radiation belt particles serve as inputs and outputs in these broader geospace processes.
5. Continued community interest: Radiation belt physics is a strong interest within the GEM community. The recently concluded FG, “System Understanding of Radiation Belt Particle Dynamics through Multi-spacecraft and Ground-based Observations and Modeling” (2019–2024), was highly successful in terms of participation, scientific output, and impact. Our proposed FG will build on these achievements by advancing investigations into radiation belt physics, while also emphasizing a holistic understanding of the radiation belts as part of the heliospheric “system-of-systems”, focusing on both their impacts on and interactions with other systems.

Relevance to Existing FGs

This proposed FG will actively collaborate with the following ongoing GEM FGs to achieve a system level understanding of the radiation belt dynamics:

1. Mesoscale drivers of the nightside transition region: ionospheric and magnetotail evaluations (2022 – 2026): Particle dynamics in the magnetotail can have significant impacts on radiation belt dynamics. Investigating the energization of particles within the nightside transition region will provide valuable insights into radiation belt particle acceleration processes.
2. Magnetospheric Sources of Particle Precipitation and Their Role on Electrodynamic Coupling of Magnetosphere-Ionosphere-Thermosphere Systems (2022 – 2026): Particle precipitation to the upper atmosphere is a major loss mechanism for the radiation belt particles, which plays an important role in determining and modeling ionospheric electrodynamics. The proposed FG intends to coordinate joint sessions to investigate the contribution of the radiation belt particle precipitation to the electrodynamics of the M-I-T system.
3. The Impact of the Cold Plasma in Magnetospheric Physics (2020 – 2025): The cold plasma plays a crucial role in controlling waves and wave-particle interactions, which are fundamental to the radiation belt particle dynamics. Collaborative efforts between this FG and the proposed one will enhance understanding of how cold plasma modulates radiation belt processes.
4. Kinetic Plasma Processes in the Magnetotail during Substorm Dynamics (2024 – 2028): This FG focuses on understanding the plasma populations, thin current sheets, and particle energization in the magnetotail region, which provide an important source of particles that will feed into the inner magnetosphere. Joint efforts with the proposed FG will provide invaluable insight about the chain of physical processes from the energized particles during substorm onset in the magnetotail region to the radiation belt electron dynamics.
5. Self-Consistent Inner Magnetospheric Modeling (2020 – 2025): This FG focuses on the under- standing and modeling the wave growth driven by ring current particles and wave-particle interactions across different populations. Joint efforts with the proposed FG, which emphasizes radiation belt particles, are essential for a comprehensive understanding of the dynamics of Earth’s inner magnetosphere.
6. Comparative Planetary Magnetospheric Processes (2023 – 2027): A key topic of this FG is the comparative study of radiation belt physics across drastically different planetary magnetospheres. The proposed FG plans to coordinate joint sessions to explore comparative radiation belt wave and particle dynamics, and their role as input/output to other environments (solar wind and interplanetary magnetic field, magnetotail region, atmosphere/ionosphere, etc.) to unravel missing or poorly understood physical processes.