On the Feasibility of Remotely Sensing the Earth's Magnetic Field Using a Ground-Based Fully Polarimetric Microwave Radiometer

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Abstract
The Zeeman effect affects millimeter-wave emission lines from atmospheric oxygen through the interaction between the molecular magnetic dipole moment and the geomagnetic field, leading to characteristic line splitting and polarization signatures. Depending on the total angular momentum quantum number, the split components may appear as distinct peaks or as effective line broadening when unresolved. These signatures are observable in molecular oxygen emissions from the stratosphere and mesosphere, where pressure broadening is weak compared to the troposphere. The resulting line shape5 depends on magnetic field strength, viewing geometry, and polarization. The impact of the magnetic field on the line-spectra provides a potential pathway to remotely sense geomagnetic field perturbations. In this study, we examine the feasibility of such measurements using two oxygen fine-structure transitions at 53.067 GHz and 53.596 GHz. Radiative transfer simulations and synthetic retrievals indicate sensitivity to magnetic field perturbations at altitudes between 30 and 75 km. The method is further evaluated using fully polarimetric observations from the Campaign Temperature Radiometer (TEMPERA-C) during a10 geomagnetic storm associated with a strong solar flare in January 2026. Applying the developed inversion scheme, we retrieve a perturbation of the vertical magnetic field component of −130 ± 62 nT for the event.
Funding Information
  • Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung (200021L-228107)