Validation of the Long-term (1993－2023) Reanalysis of Total Ozone Column and Their Trends at Zhongshan Station in Antarctica

Based on the Brewer ozone spectrophotometer long-term (1993－2023) observations at Zhongshan Station, Antarctica, the atmospheric Total Ozone Column (TOC) of the MERRA2 and ERA5 reanalysis are compared, evaluated, and their trends are analyzed. The results show that the reanalysis is generally in good agreement with the ground-based data in the context of occurrence of the ozone hole and the TOC seasonality. The TOC bias (ΔΩ) on the daily mean scale is –2.0±9.6 DU and 3.2±7.8 DU for MERRA2 and ERA, respectively. Both the probability distributions of the reanalysis ΔΩ exhibit normal random processes and their large variations occurred at the end of March and during the ozone hole period. The reanalysis data were divided into two periods, 1993－2004 and 2005－2023, based on the changes of satellites to which the reanalysis data were assimilated, but the ΔΩ values (including ERA5) during the ozone hole increases with decreasing of the TOC in the both periods, and the ΔR values for MERRA2/ERA5 were 6.9%±4.6%/4.6%±2.0% and –0.4%～2.3%/6.4%±3.1%, respectively. The ΔR of MERRA2 and ERA5 show an increasing trend with the Solar Zenith Angle (SZA) during 1993－2004, with each magnitude of 3% and 2%, while the opposite trend is observed from 2005 to 2023, with magnitudes of –2% and 2% for MERRA2 and ERA5, respectively. The quality of reanalysis TOC data from 2005 to 2023 is superior to that from 1993 to 2004. Both the reanalysis TOC data validated by Brewer show their consistent recovery trends of TOC, and the linearly fitted recovery rate of ERA5 is 1.3 DU per decade. The study suggests that raw reanalysis TOC data should be used with much caution before evaluating the long-term trends of the ozone layer, and the data from the ground-based observations, although the number of the data is much less than that of reanalysis outputs due to seasonal SZA or weather conditions, is critical for the reanalysis TOC validation and conclusions of the TOC trend.