Microwave radiometric measurements and simulations of the Zeeman-affected rotational transition of oxygen at 233.95 GHz

In this study, we present measurements of the Zeeman affected rotational transition of atmospheric oxygen (${}^{16}{O}^{18}O$) at 233.95 GHz. These observations were conducted using the KIruna Microwave RAdiometer (KIMRA) at the Swedish Institute of Space Physics (IRF) in Kiruna, Sweden. The data presented here are an example set of our continuous observations collected during a calm period of Earth’s magnetosphere on January 4, 2024, in four different lines of sight. All measurements were taken at a fixed zenith angle of $77.6°$, while the azimuth angle varied from 0° to 270° in steps of 90°. The measurements successfully resolved each sub-line of the transition, and comparisons with simulations performed using PyARTS showed excellent agreement between the observations and simulations in all directions. Oxygen emission lines at lower frequencies have been used to retrieve temperature profiles in the stratosphere. We found, however, that the signatures at this particular frequency at 233.95 GHz are not suited for atmospheric temperature profiling unlike those at lower frequencies, such as 118 GHz or signatures in the 50–60 GHz Oxygen band.