The impact of hemispherically asymmetrical volcanic aerosol injections on the North Atlantic Oscillation.

Volcanic eruptions exert a considerable influence on global climate and may impact large scale modes of atmospheric variability, including the North Atlantic Oscillation (NAO). However, little consensus on the nature of this relationship exists, partially because of the numerous possible NAO forcing mechanisms, the large number of variables associated with eruptions (e.g., size, time of year, latitude, etc), the small number of large eruptions across the instrumental era, and conflicting climate model simulations. This study leverages statistical techniques to evaluate the relationship between historical volcanic eruptions and the observed NAO response since the beginning of the twentieth century. Monte Carlo analyses show that large northern hemisphere eruptions (VEI 5 or greater) are significantly related to a positive NAO response at the 1% significance level across the twentieth century, whereas no significant association is found for southern hemisphere eruptions, though this may reflect a low sample size. Furthermore, results suggest an increasing NAO response amplitude to northern hemisphere eruptions across recent decades, possibly illustrating dynamic changes in the atmospheric phenomenon resulting from anthropogenic activity.