Arctic Oscillation response to the 1991 Mount Pinatubo eruption: Effects of volcanic aerosols and ozone depletion

Abstract

[1] Observations show that strong equatorial volcanic eruptions have been followed by a pronounced positive phase of the Arctic Oscillation (AO) for one or two Northern Hemisphere winters. It has been previously assumed that this effect is forced by strengthening of the equator-to-pole temperature gradient in the lower stratosphere, caused by aerosol radiative heating in the tropics. To understand atmospheric processes that cause the AO response, we studied the impact of the 1991 Mount Pinatubo eruption, which produced the largest global volcanic aerosol cloud in the twentieth century. A series of control and perturbation experiments were conducted with the GFDL SKYHI general circulation model to examine the evolution of the circulation in the 2 years following the Pinatubo eruption. In one set of perturbation experiments, the full radiative effects of the observed Pinatubo aerosol cloud were included, while in another only the effects of the aerosols in reducing the solar flux in the troposphere were included, and the aerosol heating effects in the stratosphere were suppressed. A third set of perturbation experiments imposed the stratospheric ozone losses observed in the post-Pinatubo period. We conducted ensembles of four to eight realizations for each case. Forced by aerosols, SKYHI produces a statistically significant positive phase of the AO in winter, as observed. Ozone depletion causes a positive phase of the AO in late winter and early spring by cooling the lower stratosphere in high latitudes, strengthening the polar night jet, and delaying the final warming. A positive phase of the AO was also produced in the experiment with only the tropospheric effect of aerosols, showing that aerosol heating in the lower tropical stratosphere is not necessary to force positive AO response, as was previously assumed. Aerosol-induced tropospheric cooling in the subtropics decreases the meridional temperature gradient in the winter troposphere between 30°N and 60°N. The corresponding reduction of mean zonal energy and amplitudes of planetary waves in the troposphere decreases wave activity flux into the lower stratosphere. The resulting strengthening of the polar vortex forces a positive phase of the AO. We suggest that this mechanism can also contribute to the observed long-term AO trend being caused by greenhouse gas increases because they also weaken the tropospheric meridional temperature gradient due to polar amplification of warming.

Effects of Arctic geoengineering on precipitation in the tropical monsoon regions

“…To compare the amounts of sulfate aerosols used in our geoengineering simulations to a major volcanic eruption, it may be noted that the 1991 Pinatubo eruption injected about 20 Mt of SO 2 (30 Mt of SO 4 ; Stenchikov et al 2002) into the stratosphere. Further, it should be noted that we do not inject aerosols in our simulations.…”

Volcanic forcing of climate over the past 1500 years: An improved ice core‐based index for climate models

“…Observations and modeling studies [Hansen et al, 1992;Mao, 1992, 1995;Solomon et al, 1996;Mao and Robock, 1998;Stenchikov et al, 1998;Solomon, 1999;Stenchikov et al, 2002;Briffa et al, 2004] have shown that large tropical volcanic eruptions such as these two recent events produced general cooling effect especially in NH summers, whereas dynamically induced warming over NH continents for the next couple winters following the eruptions. The cooling is the direct result of the 4 stratospheric volcanic aerosols scattering some solar radiation back to space.…”

Ocean Response to the Pinatubo and 1259 Volcanic Eruptions

“…There have been many studies on the effect of volcanic eruptions on global climate change (Robock 2000;Stenchikov et al 1998Stenchikov et al , 2002Stenchikov et al , 2004Stenchikov et al , 2009Kirchner et al 1999;Yang and Schlesinger 2002;Shindell et al 2004;Gleckler et al 2006;Frölicher et al 2011;Mignot et al 2011;Ottera et al 2010;Zanchettin et al 2012). The studies showed that large volcanic eruptions emit sulphur gases into the stratosphere, which become sulphate aerosols.…”