Title:
«Multi-Scale Modelling of Magnetic Reconnection in the Solar Corona»
Solar flares are powerful explosions in the Sun’s atmosphere that can disrupt satellites, GPS, and power grids on Earth. They are caused by magnetic reconnection, where magnetic field lines suddenly break and release stored magnetic energy. But the details of how energy is released remain poorly understood.
One key reason is that most models treat plasma as a fluid—a method called magnetohydrodynamics (MHD). This works well on large scales but cannot capture the plasma dynamics near the reconnection site. To see the full picture, more accurate plasma models are needed.
This thesis combines MHD with a particle-in-cell (PIC) model, which tracks individual particles. In our MHD–PIC hybrid solver, MHD captures the global evolution, while PIC is used locally near the reconnection site.
We applied the new model to a solar flare setup using conditions from the solar corona. This is the first time such coupling has been successfully demonstrated in a realistic configuration. The results show how the reconnection site changes depending on physical scaling, and reveal particle acceleration—especially of protons—as well as magnetic field patterns that extend far beyond the PIC region.
This work provides a powerful new tool for understanding solar flares and improving space weather forecasting.
Figure: Illustration showing the use of a hybrid particle-in-cell (PIC) and magnetohydrodynamics (MHD) model. PIC is used inside the dotted square, while MHD captures the global evolution.
Credit: Michael Haahr.
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Trial Lecture: «The multiscale nature of the solar wind»
Time and Place: September 16, 2025 10:15 AM CEST, Auditorium 209 Svein Rosselands hus and Zoom
More information can be found on this webpage:
https://www.mn.uio.no/astro/english/research/news-and-events/events/disputations/2025/Michael_Haahr
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