28 Mar 2023
 | 28 Mar 2023

Microwave radiometer observations of the ozone diurnal cycle and its short-term variability over Switzerland

Eric Sauvageat, Klemens Hocke, Eliane Maillard Barras, Shengyi Hou, Quentin Errera, Alexander Haefele, and Axel Murk

Abstract. In Switzerland, two ground-based ozone microwave radiometers are operated in the vicinity of each other (ca. 40 km): GROMOS in Bern (Institute of Applied Physics) and SOMORA in Payerne (MeteoSwiss). Recently, their calibration and retrieval algorithms have been fully harmonized and updated time series are now available since 2009. Using these harmonized ozone time series, we investigate and cross-validate the strato-mesospheric ozone diurnal cycle derived from the two instruments and compare it with various model-based datasets: a dedicated GDOC ozone diurnal cycle climatology based on the Goddard Earth Observing System (GEOS-5) general circulation model, the Belgian Assimilation System for Chemical ObsErvations (BASCOE) a chemical transport model driven by ERA5 dynamics, and a set of free-running simulations from the Whole Atmosphere Community Climate Model (WACCM). Overall, the two instruments show very similar ozone diurnal cycles at all seasons and pressure levels and the models compare well with each other. There is a good agreement between the models and the measurements at most seasons and pressure levels and the largest discrepancies can be explained by the limited vertical resolution of the microwave radiometers. However, as in a similar study over Mauna Loa, some discrepancies remain near the stratopause, at the transition region between ozone daytime accumulation and depletion. We report similar delays in the onset of the modelled ozone diurnal depletion in the lower mesosphere.

Using the newly harmonized time series of GROMOS and SOMORA radiometers, we present the first observations of short-term (sub-monthly) ozone diurnal cycle variability at mid-latitudes. The short-term variability is observed in the upper stratosphere during wintertime, when the mean monthly cycle has a small amplitude and when the dynamics is more important. It is shown in the form of strong enhancements of the diurnal cycle, reaching up to 4–5 times the amplitude of the mean monthly cycle. We show that BASCOE is able to capture some of these events and present a case study of one such event following the minor sudden stratospheric warming of January 2015. Our analysis of this event supports the conclusions of a previous modelling study, attributing regional variability of the ozone diurnal cycle to regional anomalies in nitrogen oxide (NOx) concentrations. However, we also find period with enhanced diurnal cycle that do not show much change in NOx and where other processes might be dominant (e.g. atmospheric tides). Given its importance, we believe that the short-term variability of the ozone diurnal cycle should be further investigated over the globe, for instance using the BASCOE model.

Eric Sauvageat et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on egusphere-2023-436', Adrian Tuck, 31 Mar 2023
    • AC1: 'Reply on CC1', Eric Sauvageat, 31 Mar 2023
      • CC2: 'Reply on AC1', Adrian Tuck, 31 Mar 2023
  • RC1: 'Comment on egusphere-2023-436', Anonymous Referee #1, 08 Apr 2023
    • AC2: 'Reply on RC1', Eric Sauvageat, 12 Apr 2023
  • RC2: 'Comment on egusphere-2023-436', Anonymous Referee #2, 26 Apr 2023
    • AC3: 'Reply on RC2', Eric Sauvageat, 05 May 2023

Eric Sauvageat et al.


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Short summary
In Switzerland, two instruments can measure continuous ozone profiles in the middle atmosphere. From these instruments, we can study the daily variation of ozone which are difficult to observe otherwise. It is valuable to validate the simulations of ozone in this region. We present new results obtained during the last decade and compare it against various models. For the first time, we are also able to show how the daily variations are impacted by short-term fluctuations in the atmosphere.