Strato-mesospheric ozone measurements using ground-based millimeter-wave spectroscopy at Thule, Greenland

On January 2009 a ground-based millimeter-wave spectrometer (GBMS) was installed at Thule Air Base (76.5°N, 68.8°W), Greenland, for long-term winter monitoring of several stratospheric and mesospheric trace gases in the framework of the Network for the Detection of Atmospheric Composition Change. This work is aimed at characterizing the GBMS O₃ vertical profiles between 35 and 80 km altitude obtained by applying the optimal estimation method to O₃ pressure-broadened spectral line measurements carried out during three winters. In this altitude range, GBMS O₃ retrievals are highly sensitive to variations of the atmospheric state, and their accuracy is estimated to be the larger of 11% or 0.2 ppmv. Comparisons of GBMS O₃ profiles with colocated satellite-based measurements from Aura Microwave Limb Sounder (MLS) and Thermosphere Ionosphere Mesosphere Energetics and Dynamics Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) show a good agreement below 65 km altitude once the known 10%-20% high bias of SABER O₃ profiles is considered, with the GBMS displaying an averaged low bias of ∼9% and 17% with respect to MLS and SABER. In the nighttime mesosphere, the GBMS detects the ozone tertiary maximum within 0.1 ppmv (6%) on average with respect to the convolved MLS, SABER, and global 3-D ROSE model profiles but shifts its position to lower altitudes by 4-5 km compared to the height obtained by the other three data sets. In the 50-80 km altitude range, estimates of mesospheric O₃ diurnal variation obtained from the GBMS and the convolved satellite measurements agree well within the ±1 standard deviation (∼0.6 ppmv) of the GBMS mean profile.