Trends in short-term variability of total column ozone over Europe for the period 1980-2020 from the ground-based observations and ERA5 reanalysis

The aim of this study is to analyse daily fluctuations in total column ozone (TCO3) to look for trends in char-acteristics of the passage of low/high TCO3 systems across Europe in the period 1980-2020. For each season of the year in the period 1980-2020, the sample of one-day change in TCO3 as the percentage of the mean ozone for two consecutive days is calculated for twelve ground-based stations with long-term and frequent TCO3 obser-vations. For comparison purposes, the corresponding ERA5 reanalysis data are also considered. Using the sea-sonal samples of one-day TCO3 fluctuation, the following metrics for the ozone changes are calculated: standard deviation, frequency of exceeding two arbitrarily selected thresholds (10% and 20% for the absolute value of one-day TCO3 fluctuation), and extremes (minimum and maximum value). Both ground-based and ERA5 data provide similar mean values for these metrics in the period 1980-2020. Statistically significant trends in the metrics are only calculated for-10% and-5% of cases using the ground-based and ERA5 data, respectively. There are both negative and positive trends in the stations' metrics, which make it impossible to find a common direction of changes. Trends in time series averaging the metrics of individual stations indicate a decreasing spread of one-day TCO3 fluctuations in summer seasons using the ground-based data but this is not found in ERA5 data. The increase in intensity and depth of low/high TCO3 areas moving across Europe, expected from global warming, cannot be supported by the present analysis.