Simulation study for ground-based Ku-band microwave observations of ozone and hydroxyl in the polar middle atmosphere.

The Ku-band microwave frequencies (10.70–14.25GHz) overlap emissions from ozone (O3) at 11.072 GHz and hydroxyl radical (OH) at 13.441GHz. These important chemical species in the polar middle atmosphere respond strongly to high latitude geomagnetic activity associated with space weather. Atmospheric model calculations predict that energetic electron precipitation (EEP) driven by magnetospheric sub storms produces large changes in polar mesospheric O3 and OH. The EEP typically peaks at geomagnetic latitudes ~65° and evolves rapidly with time longitudinally and over the geomagnetic latitude range 60°–80°. Previous atmospheric modelling studies have shown that during sub storms OH abundance can increase by more than an order of magnitude at 64–84km and mesospheric O3 losses can exceed 50%. In this work, an atmospheric simulation and retrieval study has been performed to determine the requirements for passive microwave radiometers capable of measuring diurnal variations in O3 and OH profiles from high latitude northern hemisphere and Antarctic locations to verify model predictions. We show that, for a 11.072GHz radiometer making 6h spectral measurements with 10kHz frequency resolution and root mean square baseline noise of 1mK, O3 could be profiled over 8×10−4–0.22hPa (~98–58km) with 10–17km height resolution and ~1ppmv uncertainty. For the equivalent 13.441GHz measurements with vertical sensor polarisation, OH could be profiled over 3×10−3–0.29hPa (~90–56km) with 10–17km height resolution and ~3ppbv uncertainty. The proposed observations would be highly applicable to studies of EEP, atmospheric dynamics, planetary scale circulation, chemical transport, and the representation of these processes in polar and global climate models. Such observations would provide a relatively low cost alternative to increasingly sparse satellite measurements of the polar middle atmosphere, extending long-term data records and also providing ground truth calibration data. [ABSTRACT FROM AUTHOR]