Extreme events in total ozone over the Northern mid-latitudes: an analysis based on long-term data sets from five European ground-based stations

Harald E Rieder,Leonhardt M Jancso,Stefania Di Rocco,Johannes Staehelin,Joerg A Maeder,Thomas Peter,Mathieu Ribatet,Anthony C Davison,Hugo De Backer,Ulf Koehler,Janusz Krzyścin,Karel Vaníiček

doi:10.1111/j.1600-0889.2011.00575.x

Abstract

We apply methods from extreme value theory to identify extreme events in high (termed EHOs) and low (termed ELOs) total ozone and to describe the distribution tails (i.e. very high and very low values) of five long-term European ground-based total ozone time series. The influence of these extreme events on observed mean values, long-term trends and changes is analysed. The results show a decrease in EHOs and an increase in ELOs during the last decades, and establish that the observed downward trend in column ozone during the 1970–1990s is strongly dominated by changes in the frequency of extreme events. Furthermore, it is shown that clear ‘fingerprints’ of atmospheric dynamics (NAO, ENSO) and chemistry [ozone depleting substances (ODSs), polar vortex ozone loss] can be found in the frequency distribution of ozone extremes, even if no attribution is possible from standard metrics (e.g. annual mean values). The analysis complements earlier analysis for the world’s longest total ozone record at Arosa, Switzerland, confirming and revealing the strong influence of atmospheric dynamics on observed ozone changes. The results provide clear evidence that in addition to ODS, volcanic eruptions and strong/moderate ENSO and NAO events had significant influence on column ozone in the European sector.

Highlights

After the detection of the Antarctic ozone hole in the 1980s (e.g. Farman et al, 1985), downward trends in stratospheric ozone and the linked increase in erythemal UV-radiation (e.g. Calbo et al, 2005) became of major interest within the scientific community and the general public
The results confirm that even moderate ElNino Southern Oscillation (ENSO) and Northern Atlantic Oscillation (NAO) events have a significant influence on column ozone changes in the European sector
Influence of major volcanic eruptions on column ozone was reported before in the scientific literature, but the results presented here confirm that the influence of volcanic eruptions can be identified in both distribution tails of the time series

Summary

Introduction

After the detection of the Antarctic ozone hole in the 1980s (e.g. Farman et al, 1985), downward trends in stratospheric ozone and the linked increase in erythemal UV-radiation (e.g. Calbo et al, 2005) became of major interest within the scientific community and the general public. The major importance of dynamical changes is confirmed by studies summarized in Harris et al (2008) and WMO (2007), which indicate that the recent increase in total ozone in Northern mid-latitudes during the late 1990s is mainly due to dynamic changes. Hood and Soukharev, 2005; Harris et al, 2008; Shepherd, 2008; Hegglin and Shepherd, 2009) reported that the change in the stratospheric burden in ODS (decline since 1997) contributed only insignificantly to the observed ozone increase at Northern mid-latitudes in recent years Further studies (e.g. Hood and Soukharev, 2005; Harris et al, 2008; Shepherd, 2008; Hegglin and Shepherd, 2009) reported that the change in the stratospheric burden in ODS (decline since 1997) contributed only insignificantly to the observed ozone increase at Northern mid-latitudes in recent years

Methods

Results

Conclusion