Bern, 13 – 17 July 2026
During our first meeting, we worked towards a rigorous definition of the electron superhalo population and identified the main questions that will guide the team’s work. Our central working picture is that the heliosphere contains a reservoir of suprathermal electrons that is continuously replenished. The dominant replenishment mechanism may vary over the solar cycle: direct injections from the Sun may prevail near solar maximum, while interplanetary acceleration of lower-energy electrons, possibly driven by turbulence, may become more important near solar minimum. Testing this hypothesis is a central goal of the project.
We selected the 17 December 2024 halo CME as our first detailed case study of energetic electron injection into the heliosphere. By combining observations from Solar Orbiter, Parker Solar Probe, STEREO and Wind, we started examining how the electrons were released, how their spectra and anisotropy evolved, towards a “superhalo like” population. We then agreed to extend the analysis to a broader sample of around ten electron events, characterising each in terms of spectral shape, density, anisotropy, magnetic connectivity and likely solar source.
A major outcome of the meeting was the need to define “quiet times” consistently across missions. We also recognised that instrumental background is especially critical during these low-intensity intervals and must be carefully characterised before the superhalo can be isolated reliably. We will then use quiet-time observations, particularly near solar minimum, to test whether the superhalo can be sustained by the interplanetary acceleration of lower-energy electrons, possibly through turbulence.
Beyond the science, we also made the most of Bern’s warm summer weather. The team enjoyed “cooling swims” in the Aare, a social dinner with scenic views, and a tour of the city with a special guide. Finally, showing that good international teams remain resilient through difficult moments, we also came together to watch England and France get knocked out of the World Cup.
