Discussing the effect of sampling error on the estimation of ozone variability and trend in UT/LS.

The study of ozone in the upper troposphere/lower stratosphere (UT/LS) and of its correlation with temperature is one of the key components for the study of climate change. Various studies have estimated trends both regionally and globally in the UT/LS, using both satellite and ground-based data and different measurements techniques. However, the measurement quality and coverage, in time and space, may significantly affect the estimated trends. This communication discusses the impact of the sampling frequency, estimating its error at different latitudes and vertical layers in the UT/LS, on the estimation of the ozone inter-annual variability and on the trends in the period 1978--2022, using a merged dataset combining the ozone soundings provided by SHADOZ (Southern Hemisphere ADditional OZonesondes), NDACC (Network for the Detection of Atmospheric Composition Change) and WOUDC (World Ozone and Ultraviolet Radiation Data Centre). The available measures are clustered into three groups based on the temporal gaps of the historical time series, providing criteria for selecting the best data for climate studies.