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

Abstract

The aim of this study is to analyse daily fluctuations in total column ozone (TCO3) to look for trends in characteristics 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 observations. For comparison purposes, the corresponding ERA5 reanalysis data are also considered. Using the seasonal 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.