Abstract
Abstract. We present the first spatial analysis of "fingerprints" of the El Niño/Southern Oscillation (ENSO) and atmospheric aerosol load after major volcanic eruptions (El Chichón and Mt. Pinatubo) in extreme low and high (termed ELOs and EHOs, respectively) and mean values of total ozone for the northern and southern mid-latitudes (defined as the region between 30° and 60° north and south, respectively). Significant influence on ozone extremes was found for the warm ENSO phase in both hemispheres during spring, especially towards low latitudes, indicating the enhanced ozone transport from the tropics to the extra-tropics. Further, the results confirm findings of recent work on the connection between the ENSO phase and the strength and extent of the southern ozone "collar". For the volcanic eruptions the analysis confirms findings of earlier studies for the northern mid-latitudes and gives new insights for the Southern Hemisphere. The results provide evidence that the negative effect of the eruption of El Chichón might be partly compensated by a strong warm ENSO phase in 1982–1983 at southern mid-latitudes. The strong west-east gradient in the coefficient estimates for the Mt. Pinatubo eruption and the analysis of the relationship between the AAO and ENSO phase, the extent and the position of the southern ozone "collar" and the polar vortex structure provide clear evidence for a dynamical "masking" of the volcanic signal at southern mid-latitudes. The paper also analyses the contribution of atmospheric dynamics and chemistry to long-term total ozone changes. Here, quite heterogeneous results have been found on spatial scales. In general the results show that EESC and the 11-yr solar cycle can be identified as major contributors to long-term ozone changes. However, a strong contribution of dynamical features (El Niño/Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), Antarctic Oscillation (AAO), Quasi-Biennial Oscillation (QBO)) to ozone variability and trends is found at a regional level. For the QBO (at 30 and 50 hPa), strong influence on total ozone variability and trends is found over large parts of the northern and southern mid-latitudes, especially towards equatorial latitudes. Strong influence of ENSO is found over the Northern and Southern Pacific, Central Europe and central southern mid-latitudes. For the NAO, strong influence on column ozone is found over Labrador/Greenland, the Eastern United States, the Euro-Atlantic Sector, and Central Europe. For the NAO's southern counterpart, the AAO, strong influence on ozone variability and long-term changes is found at lower southern mid-latitudes, including the southern parts of South America and the Antarctic Peninsula, and central southern mid-latitudes.
Highlights
Since the detection of the Antarctic ozone hole in the late 1980s (Farman et al, 1985), interest in total ozone changes has increased strongly in the scientific community and general public, due to the direct link with changes in biologically active UV radiation (e.g., Calboet al., 2005).Multiple linear regression models including independent variables, called explanatory variables or covariates, which represent atmospheric variability have been used to assess and analyze the attribution to long-term total ozone trends
The analysis showed that: (i) throughout all regions, the temporal variability in effective stratospheric chlorine (EESC) and the 11-yr solar cycle are the dominating forces modulating total ozone changes; (ii) there is clear evidence for a strong dynamical contribution (QBO, El Nino/Southern Oscillation (ENSO), North Atlantic Oscillation (NAO)/Antarctic Oscillation (AAO)) to EHOs and ELOs, which is generally more weakly expressed for mean values; (iii) especially for the individual dynamical features, large regional differences in the modulation of EHOs, ELOs, and mean values are found
In this study we focused on the interpretation of the spatial “fingerprints” of ENSO and volcanic eruptions in extreme and mean values of total ozone at northern and southern midlatitudes and the contribution of individual dynamical and chemical covariates to long-term total ozone changes
Summary
Since the detection of the Antarctic ozone hole in the late 1980s (Farman et al, 1985), interest in total ozone changes has increased strongly in the scientific community and general public, due to the direct link with changes in biologically active UV radiation (e.g., Calboet al., 2005). Multiple linear regression models including independent variables, called explanatory variables or covariates, which represent atmospheric variability have been used to assess and analyze the attribution to long-term total ozone trends. The most commonly-used covariates include: the 11-yr solar cycle, the Quasi-Biennial Oscillation (QBO), (linear) trends attributed to anthropogenic ozone depleting substances (ODS), and atmospheric aerosol load after volcanic eruptions (e.g., Fioletov et al, 2002; Steinbrecht et al, 2006; Vyushin et al, 2007; Schnadt Poberaj et al, 2011; WMO, 2003, 2007, 2011). There is broad agreement within the scientific community that negative long-term ozone trends at mid-latitudes between the 1980s and mid-1990s are dominated by changes in ODS, while short-term changes are attributable to dynamical phenomena such as horizontal advection and convergence of mass related to changes in tropospheric and lower stratospheric pressure systems (e.g., Wohltmann et al, 2007; Mader et al, 2007; Koch et al, 2005). We analyze the contribution of individual dynamical and chemical covariates on long-term total ozone changes for several regions of interest at northern and southern midlatitudes
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