Abstract
Abstract. After major volcanic eruptions the enhanced aerosol causes ozone changes due to greater heterogeneous chemistry on the particle surfaces (HET-AER) and from dynamical effects related to the radiative heating of the lower stratosphere (RAD-DYN). We carry out a series of experiments with an atmosphere–ocean–chemistry–climate model to assess how these two processes change stratospheric ozone and Northern Hemispheric (NH) polar vortex dynamics. Ensemble simulations are performed under present day and preindustrial conditions, and with aerosol forcings representative of different eruption strength, to investigate changes in the response behaviour. We show that the halogen component of the HET-AER effect dominates under present-day conditions with a global reduction of ozone (−21 DU for the strongest eruption) particularly at high latitudes, whereas the HET-AER effect increases stratospheric ozone due to N2O5 hydrolysis in a preindustrial atmosphere (maximum anomalies +4 DU). The halogen-induced ozone changes in the present-day atmosphere offset part of the strengthening of the NH polar vortex during mid-winter (reduction of up to −16 m s-1 in January) and slightly amplify the dynamical changes in the polar stratosphere in late winter (+11 m s-1 in March). The RAD-DYN mechanism leads to positive column ozone anomalies which are reduced in a present-day atmosphere by amplified polar ozone depletion (maximum anomalies +12 and +18 DU for present day and preindustrial, respectively). For preindustrial conditions, the ozone response is consequently dominated by RAD-DYN processes, while under present-day conditions, HET-AER effects dominate. The dynamical response of the stratosphere is dominated by the RAD-DYN mechanism showing an intensification of the NH polar vortex in winter (up to +10 m s-1 in January). Ozone changes due to the RAD-DYN mechanism slightly reduce the response of the polar vortex after the eruption under present-day conditions.
Highlights
Tropical eruptions strong enough to inject into the stratosphere perturb the physical and the chemical states of the climate system for several years and longer (Robock, 2000; Cole-Dai, 2010; Timmreck, 2012)
This study addresses the role of ozone changes for the dynamical perturbations of the stratosphere after strong tropical volcanic eruptions
The results are based on a number of ensemble sensitivity simulations with the atmosphere–ocean–chemistry–circulation model (AOCCM) SOCOLMPIOM, which allows us to separate the effect of heterogeneous chemical reactions from the warming effect of the aerosols for preindustrial and present-day conditions as well as three different eruption intensities
Summary
Tropical eruptions strong enough to inject into the stratosphere perturb the physical and the chemical states of the climate system for several years and longer (Robock, 2000; Cole-Dai, 2010; Timmreck, 2012). A prominent example for this mechanism is the winter warming pattern in the NH observed after several large tropical volcanic eruptions (Robock and Mao, 1992; Stenchikov et al, 2002; Shindell et al, 2004; Fischer et al, 2007; Christiansen, 2008; Zanchettin et al, 2012). Such surface temperature anomalies over Eurasia are related to a positive phase of the Arctic Oscillation, which is forced by interactions between the stratospheric polar vortex and tropospheric circulation patterns (Graf et al, 1993; Kodera, 1994)
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