Methodology:

Ny Ålesund Ozone in the Mesosphere Instrument (NAOMI) data were binned according to the local solar zenith angle (SZA) at 90 km into night time (SZA >110°), twilight (75° < SZA < 110°), and daytime (SZA <75°) observations. Binned ozone (O3) records between 15 August 2017 and 15 March 2020 were averaged for the following three periods: 15 December-15 March, 15 April-15 July, and 15 August-15 November, hereafter identified as 'winter', 'summer', and 'autumn' respectively. Mesospheric O3 profiles were retrieved from the NAOMI observations during 'winter' night and twilight, and 'autumn' twilight periods using version 2.2.58 of the Atmospheric Radiative Transfer Simulator (ARTS) (available at http://www.radiativetransfer.org/ ) and the Qpack2 (a part of atmlab v2.2.0) software package using the optimal estimation method (OEM). Vertical profiles of O3 VMR were calculated using a 10-year dataset from WACCM-D covering 2000-2009. WACCM-D is a 3-D global atmospheric model that incorporates a detailed representation of D-region chemistry in the specified dynamics (SD) version of the Whole Atmosphere Community Climate Model (WACCM 4). The WACCM-D data at 78.632 °N and 12.500 °E, the model grid point closest to Ny Ålesund, were used. Water vapour (H2O) VMR profiles were a combination of 6 hourly, model level Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) data and WACCM-D data. Temperature profiles were constructed by combining MERRA-2 data, SABER version 2.0 data, and WACCM D data. SABER temperature, O3 VMR, and water vapour VMR profiles overlapping NAOMI observations were binned into night time, twilight, and daytime datasets for 'winter', 'summer', and 'autumn', as was done for the NAOMI data. The 'winter' night and twilight, and 'autumn' twilight O3 VMR profiles from NAOMI and SABER 9.6 µm observations were compared, as well as the SABER 9.6µm and 1.27µm observations for 'summer' day and twilight, and 'autumn' twilight periods.

Data quality:

Ozone (O3) vertical profile uncertainties for NAOMI and SABER have been estimated from the retrieval diagnostics and published SABER validation data respectively.