On the relationship between total ozone and atmospheric dynamics and chemistry at mid-latitudes – Part 2: The effects of the El Niño/Southern Oscillation, volcanic eruptions and contributions of atmospheric dynamics and chemistry to long-term total ozone changes

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.

Trends in stratospheric ozone profiles using functional mixed models

“…Thirdly, we compare our analysis with the analysis of total ozone data in Rieder et al (2010) and Rieder et al (2013). Our AMM analysis finds a significant contribution of ENSO to Boulder (US) ozone variability for PC score 3 (where ozone is maximum), which is similar to the result of Rieder et al (2010) analysis that also found a positive contribution over the US region.…”

“…Note that the contribution is significant only for Winter and Spring months. According to Rieder et al (2013), over Europe the total ozone analysis showed a negative effect of ENSO, but not significant, which is supported by our analysis of PC score 3 for Arosa that shows the non-significant influence. Rieder et al (2013) also indicated the seasonal difference in the ENSO contribution.…”

“…3), both the US and Europe would gain a positive contribution, but only the US would have a small p value (significant). Since our analysis does not assess the ENSO contribution by season, we cannot fully compare our yearly ENSO results to the Rieder et al (2013) findings. Rieder et al (2013) also gave an analysis of the NAO signal contribution to the total ozone column data set (based on the SBUV satellite time series) and found that negative ozone changes are related to NAO over the US and European region, and that the changes are significant in both areas; see Fig.…”

“…In order to improve the fit, it is important to study dynamical processes to find their effects on long-term changes in ozone distribution in middle latitudes and in the upper stratosphere. Several studies have addressed the significance of contributions of dynamical processes to long-term ozone changes (Appenzeller et al, 2000;Weiss et al, 2001;Wohltmann et al, 2007;Mäder et al, 2007;Rieder et al, 2010;Frossard et al, 2013;Rieder et al, 2013;Nair et al, 2013). Several papers (Harris et al, 2008;WMO, 2007) found that a significant part of the change in total ozone after the middle of the 1990s and until 2005 was caused by dynamical variability.…”

“…Rieder et al (2013) also gave an analysis of the NAO signal contribution to the total ozone column data set (based on the SBUV satellite time series) and found that negative ozone changes are related to NAO over the US and European region, and that the changes are significant in both areas; see Fig. 8 in Rieder et al (2013). Since our analysis uses AO, there may be a difference between AO and NAO patterns.…”