MIST
Magnetosphere, Ionosphere and Solar-Terrestrial
Global Morphology of Chorus Waves in the Outer Radiation Belt and the Effect of Geomagnetic Activity and fpe/fce
Global Morphology of Chorus Waves in the Outer Radiation Belt and the Effect of Geomagnetic Activity and fpe/fce
By Kaine Bunting (British Antarctic Survey)
Chorus waves are naturally occurring plasma waves often observed in the Earth’s outer radiation belt that strongly influence the behaviour of energetic electrons. These waves can both accelerate electrons to relativistic energies, which poses a threat to satellites, as well as scatter electrons into Earth's atmosphere, where they are consequently lost.
The ratio between the electron plasma frequency (fpe) and electron gyrofrequency (fce) holds information on both electron density and magnetic field strength and significantly influences the efficiency of these processes, with electron acceleration being most effective during periods of low fpe/fce.
Bunting et al. (2026) analyses a combined 24.5 years of wave data from three THEMIS satellites to investigate the effect of fpe/fce, geomagnetic activity and normalized frequency on the spatial distribution and intensity of chorus waves.
The strongest waves are generally observed on the dawn-side of the Earth during active geomagnetic conditions. Figure 1 shows global plots of the equatorial (|MLAT| < 9°) chorus wave intensity during active conditions (AE > 200nT). At intermediate relative frequencies (0.3fce < f < 0.4fce), chorus is largely independent of fpe/fce. However, at low frequencies (flhr < f < 0.1fce), strong waves are most often associated with high fpe/fce (>10) and at high frequencies (0.5fce < f < 0.7fce), chorus is strongest at low fpe/fce (<6).
Overall, this study highlights the critical role of fpe/fce on the spatial distribution and dynamic behaviour of chorus waves under varying geomagnetic conditions, as well as its influence on wave-particle interactions. During a geomagnetic storm fpe/fce outside of the plasmapause may gradually change from low to high values over the course of the recovery phase, suggesting that the role of chorus may change from efficient acceleration early in the recovery phase to little or no acceleration and even loss toward the end of the recovery phase.
See publication for details:
Bunting, K. A., Meredith, N. P., Bortnik, J., Ma, Q., Matsuura, R., & Shen, X.-C. (2026). Global morphology of chorus waves in the outer radiation belt and the effect of geomagnetic activity and fpe/fce. Journal of Geophysical Research: Space Physics, 131, e2025JA034737. https://doi.org/10.1029/2025JA034737
Figure 1 - Global maps of the average chorus wave intensity during active geomagnetic conditions (AE > 200nT) in the equatorial region (MLAT < 9°) as a function of L* and magnetic local time for, from top to bottom, increasing relative frequency, and, from left to right, increasing fpe/fce. The maps extend linearly out to L* = 10 with noon at the top and dawn to the right. The average intensities are shown in the large panels and the corresponding sampling distributions in the small panels to the bottom right of each large panel.
Statement from MIST Council regarding the STFC Funding Situation
Statement from MIST Council regarding the STFC Funding Situation
MIST Council is deeply concerned by the ongoing STFC funding uncertainty and its impact on our community and beyond.
The current combination of prospective delayed and reduced funding, together with already volatile financial situations at universities across the UK, is placing significant strain on research groups. In some cases, institutions may be unable to support researchers through gaps between projects, increasing precarity across the community and adding significant pressure on early-career researchers.
We are concerned that continued uncertainty risks accelerating a brain drain from the UK, as skilled researchers reconsider their future in a system offering limited stability. The loss of expertise at any career stage would have lasting consequences for UK space science.
What is going on?
For those that are unaware of the situation, it is complex and evolving. We suggest the following sources to get up to speed on the current developments.
https://ras.ac.uk/news-and-press/news/proposed-budget-cuts-catastrophe-uk-astronomy
What are we doing about it?
Behind the scenes, MIST Council is actively engaging with relevant parties to understand the scale of the challenge and to identify constructive ways forward.
- We are seeking seasoned members of the community to join MIST Council on a task force to help develop options and represent the needs of our community. If you would like to be involved, please reach out to us via the MIST Council email (This email address is being protected from spambots. You need JavaScript enabled to view it.) by the end of this week (13th February 2026).
- In addition to the task force, we want to provide an open forum for discussion and collective input among all members of the wider MIST community. We are exploring options and will be in touch as soon as possible with further details.
- We believe in working together in the face of the current challenges and we are collaborating with UKSP and others to strive for a fair and positive outcome for all. We are reaching out to members of the SSAP (Solar System Advisory Panel) to explore the hosting of a community town hall meeting, like the one already being organised by the AAP (Astronomy Advisory Panel), to provide an open forum for discussion and collective input.
What can you do to help?
There are several open letters representing people in various career stages that have been made available to sign. We encourage you to read the relevant letter(s) and to sign them if you support them:
- Fellowship Holders: https://advancedfellows-openletter-stfc.github.io/index.html
- Early Career Researchers: https://ecr-openletter-stfc.github.io/
The Royal Astronomical Society are also urging Fellows to lobby their MPs against the cuts, and have included a template letter that can be used to do so:
https://ras.ac.uk/news-and-press/news/ras-fellows-urged-lobby-against-unprecedented-cuts
MIST Council will continue to advocate for transparency, stability, and funding structures that recognise both the long-term nature of our science and the people who deliver it.
We thank you for your continued support in this period of uncertainty.
Please contact This email address is being protected from spambots. You need JavaScript enabled to view it. if you have further suggestions.
MIST Council
Energetic Proton Dropouts During the Juno Flyby of Europa Strongly Depend on Magnetic Field Perturbations
Energetic Proton Dropouts During the Juno Flyby of Europa Strongly Depend on Magnetic Field Perturbations
By Hans Huybrighs (DIAS)
In September 2022 NASA's Juno spacecraft flew by Jupiter's ocean moon Europa. In this study we analyzed energetic ion dropouts measured near Europa. We care about energetic ions because they bombard Europa's icy surface . While they make the surface inhospitable, they might also help produce oxidants from the ice that could form a source of energy for life in the ocean.
The Juno measurements show what happens with the energetic protons at 350 km above the surface, in Europa’s wake (considering the general sense of motion of the protons). There, protons have disappeared, compared to further away where they are abundant. The cartoon below shows some classical ideas about what happens to the protons near Europa (panel 1-2).
Using particle tracing simulations of the ions we can show that the deflections by magnetic fields (3) are also important. In fact, at 100 keV magnetic deflections are the dominant factor that determine the ion abundance. At 1 MeV its a combination of magnetic deflections and the effect shown in panel 2. The simulations also show that the shape of the proton dropout region depends on the exact configuration of the magnetic field, which can vary depending on the atmosphere and electron beams in the wake. All this helps us better understand what happens with the energetic ions and shows us that our ideas of Europa's atmosphere and magnetic fields are reasonable but that improvements can be made.
See publication for details:
, , , , , , et al. (2025). Energetic proton dropouts during the Juno flyby of Europa strongly depend on magnetic field perturbations. Journal of Geophysical Research: Space Physics, 130, e2025JA034000. https://doi.org/10.1029/2025JA034000