Harmonized retrieval of middle atmospheric ozone from two microwave radiometers in Switzerland

Abstract

Abstract. We present new harmonized ozone time series from two ground-based microwave radiometers in Switzerland: GROMOS and SOMORA. Both instruments measure hourly ozone profiles in the middle atmosphere (20–75 km) since more than two decades. As inconsistencies in long-term trends derived from these two instruments were detected, a harmonization project was initiated in 2019. The goal was to understand and reduce the discrepancies between the two data records. The harmonization has been completed for the data from 2009 until 2022 and has been successful at reducing the differences observed between both time series. It also explains the remaining differences between both instruments and flags their respective anomalous measurement periods in order to adapt their consideration for future trend computations. We describe the harmonization and the resulting time series in detail. We also highlight the improvements in the ozone retrievals with respect to the previous data processing. In the stratosphere and lower mesosphere, the seasonal ozone relative differences between both instruments are now within 10 % and show good correlations (R > 0.7) except for summertime. We also perform a comparison of these new data series against measurements from the satellite instruments Microwave Limb Sounder (MLS) and Solar Backscatter Ultraviolet Radiometer (SBUV) over Switzerland. Seasonal mean differences with MLS and SBUV are within 10 % in the stratosphere and lower mesosphere up to 60 km and increase rapidly above.