Recipient organisationDurham UniversitySource-published name: Durham University
Funding£422K
PeriodJun 2025 — Jun 2028
In plain English
AI plain-English summary
The Sun’s magnetic field, measured by spacecraft a million miles from Earth, is consistently larger than models predict should be leaving the Sun in the first place. This mismatch, known as the open flux problem, matters because the Sun’s magnetic field extends through the solar system as the heliospheric magnetic field. It controls how the solar wind and coronal mass ejections interact with Earth’s magnetosphere, and it modulates the flux of galactic cosmic rays that can disrupt satellites and pose risks to astronauts. Getting the open flux wrong means space weather forecasts are less accurate than they could be. The researchers have developed a new model that accounts for the effect of solar wind outflow on the coronal magnetic field. Preliminary results suggest this outflow can explain part of the missing flux. They will calibrate the model against two solar cycles of observations, including a recent “ground truth” dataset from spacecraft data with switchbacks removed. The resulting open-source code could improve space weather forecasting and lay the groundwork for more advanced time-dependent coronal models. The approach also applies to modelling other stars.
View original technical description
Our ultimate aim is to resolve the longstanding “open flux problem” whereby more magnetic flux is measured in situ at 1 AU than is predicted to leave the Sun by magnetic extrapolation models. The open solar flux is a crucial quantity for space weather because it extends out as the heliospheric magnetic field, affecting the interaction of the solar wind and coronal mass ejections with the Earth's magnetosphere, and modulating the flux of galactic cosmic rays. Conversely, connecting in situ measurements at 1 AU with the open flux on the Sun is important for long-term investigations of the solar dynamo through historical geomagnetic data. Recognising that the open flux shortfall likely results from multiple causes, we will quantify how much additional flux can be explained purely by the effect of solar wind outflow on the coronal magnetic field (Objective 1). In doing so, we will provide a calibrated "outflow equilibrium" model for the coronal magnetic field, and test the improvement of space weather forecasts versus presently-used models (Objective 2). The resulting code will be made available open source to the community. The project is achievable thanks to our recently-developed outflow equilibrium model that modifies the traditional potential field source surface model to account for an axisymmetric solar wind. Preliminary results suggest that this model enhances the open flux, but it remains to be calibrated against observations. Here we will compare with a recent "ground truth" dataset of open flux inferred from in situ data with switchbacks removed. We will also add further constraints from white-light tomographic observations of the latitude-longitude (pseudo)-streamer structure. Our model retains the numerical efficiency of the potential field model, facilitating a thorough parameter observation against observations over two solar cycles. As well as producing in itself an improved tool for space weather forecasting, isolating the effect of outflow will lay the groundwork for future calibration of the latest generation of time-dependent dynamical coronal models. The results will also be relevant to modelling of other stars.
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