Updated Zeeman effect splitting coefficients for molecular oxygen in planetary applications
In one sentence
A first-principles Zeeman-effect treatment of the molecular oxygen lines used by satellite missions to sound the Earth’s atmosphere, showing that field-induced broadening is small but not negligible — and easy to mis-attribute to temperature.
What’s the question?
Satellite remote sensing of the Earth’s atmosphere routinely retrieves vertical temperature profiles by fitting the shape of molecular oxygen rotational lines. Those lines sit in the Earth’s magnetic field, which broadens them via the Zeeman effect. If you don’t model that broadening explicitly, it leaks into the temperature retrieval — you’d attribute Zeeman broadening to thermal motion and get the wrong number.
What did we do?
We computed updated Zeeman splitting coefficients for the relevant O₂ lines and quantified how much the field-induced broadening biases the inferred temperature. For several practical sounding bands, we showed the Zeeman contribution is comparable in magnitude to the temperature signal that operational missions are trying to recover.
Why does it matter?
The coefficients we tabulated drop directly into operational radiative-transfer codes used by atmospheric remote-sensing groups, removing a known source of systematic error from temperature retrievals. They later showed up in a quite different context, too: the CLASS collaboration (Petroff et al. 2020) used them to model — and detect, at Q band — the polarized atmospheric foreground that the Zeeman effect in O₂ produces for ground-based CMB experiments. A small piece of molecular physics that has turned out to matter from satellite weather sounding all the way up to the cosmic microwave background.
My role
Co-author. Set up the model of O₂’s Zeeman effect and wrote the underlying molecular-physics sections.