Results from the validation campaign of the ozone radiometer GROMOS-C at the NDACC station of Réunion island

Abstract

Abstract. Ozone performs a key role in the middle atmosphere and its monitoring is thus necessary.At the Institute of Applied Physics of the University of Bern, Switzerland, we built a new ground-based microwave radiometer, GROMOS-C (GRound based Ozone MOnitoring System for Campaigns). It has a compact design and can be operated remotely with very little maintenance requirements, being therefore suitable for remote deployments. It has been conceived to measure the vertical distribution of ozone in the middle atmosphere, by observing pressure-broadened emission spectra at a frequency of 110.836 GHz. In addition, meridional and zonal wind profiles can be retrieved, based on the Doppler shift of the ozone line measured in the four directions of observation (north, east, south and west).In June 2014 the radiometer was installed at the Maïdo observatory, on Réunion island (21.2 • S, 55.5 • E). Highresolution ozone spectra were recorded continuously over 7 months. Vertical profiles of ozone have been retrieved through an optimal estimation inversion process, using the Atmospheric Radiative Transfer Simulator ARTS2 as the forward model. The validation is performed against ozone profiles from the Microwave Limb Sounder (MLS) on the Aura satellite, the ozone lidar located at the observatory and with ozone profiles from weekly radiosondes. Zonal and meridional winds retrieved from GROMOS-C data are validated against another wind radiometer located in situ, WIRA. In addition, we compare both ozone and winds with ECMWF (European Centre for Medium-Range Weather Forecasts) model data. Results show that GROMOS-C provides reliable ozone profiles between 30 and 0.02 hPa. The comparison with lidar profiles shows a very good agreement at all levels. The accordance with the MLS data set is within 5 % for pressure levels between 25 and 0.2 hPa. GROMOS-C's wind profiles are in good agreement with the observations by WIRA and with the model data, differences are below 5 m s −1 for both.

Diurnal variation in middle-atmospheric ozone observed by ground-based microwave radiometry at Ny-Ålesund over 1 year

“…The settings for the GROMOS-C retrieval are described in Fernandez et al (2015). The results of a validation campaign at the NDACC station of La Réu-nion (Fernandez et al, 2016) show the good performance of GROMOS-C. In the altitude range of 25-60 km the relative difference to MLS observations lies within 5 %.…”

“…For microwave radiometry as described in this paper the average optical depth at the GROMOS-C measurement frequency of 110.8 GHz was 0.7 in winter and increased to 1.2 in summer. An opacity value lower than 0.5 is considered to be ideal for such observations (Fernandez et al, 2016). OZORAM measures at 142.2 GHz which is at the wing of a water vapour line.…”

Diurnal variation in middle atmospheric ozone by ground based microwave radiometry at Ny-Ålesund over 1 year

“…For microwave radiometry as described in this paper the average optical depth at 110.8 GHz was 0.7 in winter and almost doubled to 1.2 in summer. An opacity value lower than 0.5 is considered to be very good for such observations (Fernandez et al, 2016).…”

“…The settings for the GROMOS-C retrieval are described in Fernandez et al (2015). The results of a validation campaign at the NDACC station of La Réunion island (Fernandez et al, 2016) show a good performance of GROMOS-C. In the altitude range of 25-60 km the southward direction while the ozone VMR stayed constant inside the vortex in north and eastward direction (Fig.…”

“…A tropospheric correction has been applied to the GROMOS-C spectra, such that the retrieval starts at the tropopause level according to Fernandez et al (2015). This treatment of the troposphere proved to be robust (Fernandez et al, 2016). For OZORAM an other retrieval concept is used where the opacity of the troposphere is retrieved together with the ozone profile.…”