Remote Sensing of CME Magnetic Field Across the Corona to Heliosphere Using Coordinated Wide Field of View Radio Polarimetric and PUNCH Observations

Measuring magnetic fields of coronal mass ejections (CMEs) in the outer corona and inner heliosphere through remote sensing is vital for advancing space-weather prediction. While routine white-light coronagraphs and heliospheric imagers provide insights into the geometry of CME magnetized plasma, they are not capable of directly measuring magnetic fields. At radio wavelengths, Faraday rotation (FR) — the polarization angle change of background linearly polarized astronomical sources — can be used to estimate line-of-sight (LoS) integrated magnetic fields when a plasma structure intersects the LoS. However, this technique has traditionally been restricted to coronal heights below 15 𝑅⊙ (R⊙​ = Solar radii), utilizing high-frequency telescopes like the JVLA, which have narrower fields of view (FoVs) and reduced sensitivity to magnetic field strength.

In recent years, the advent of new-generation ground-based radio telescopes such as MWA, LOFAR, ASKAP, and MeerKAT has provided a significant opportunity. These instruments, with their wide FoVs and lower observing frequencies, are well-suited for measuring CME magnetic fields from the corona to the inner heliosphere. Despite their potential, challenges remain, including calibration and the need for precise, time-sensitive observations using non-solar-dedicated telescopes during space-weather events. Additionally, extracting magnetic field estimations from radio measurements requires accurate knowledge of the electron density distribution along the LoS to the background radio sources. The PUNCH mission's white-light polarization observations offer a complementary solution by providing electron density measurements from the outer corona to the inner heliosphere. This synergy enables the extraction of magnetic field estimates from wide-FoV radio observations.

This presentation highlights recent successes in detecting FR signatures caused by CMEs from coronal to heliospheric heights, leveraging cutting-edge radio telescopes. These efforts are especially timely as they align with the early operational phase of PUNCH, paving the way for coordinated radio and white-light wide-FoV polarimetric observations to provide complimentary pieces of information to measure CME vector magnetic fields. The ultimate goal is to strengthen space-weather research and improve predictive capabilities by combining these advanced observational techniques.