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  • Stenchikov, Georgiy, Kevin Hamilton, Ronald J. Stouffer, Alan Robock, V. Ramaswamy, Ben Santer, and Hans-F. Graf, 2006: Arctic Oscillation response to volcanic eruptions in the IPCC AR4 climate model. J. Geophys. Res., 111, D07107, doi:10.1029/2005JD006286.

[1] Stratospheric sulfate aerosol particles from strong volcanic eruptions produce
significant transient cooling of the troposphere and warming of the lower stratosphere. The
radiative impact of volcanic aerosols also produces a response that generally includes an
anomalously positive phase of the Arctic Oscillation (AO) that is most pronounced in
the boreal winter. The main atmospheric thermal and dynamical effects of eruptions
typical of the past century persist for about two years after each eruption. In this paper we
evaluate the volcanic responses in simulations produced by seven of the climate models
included in the model intercomparison conducted as part of the preparation of the
Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4).
We consider global effects as well as the regional circulation effects in the extratropical
Northern Hemisphere focusing on the AO responses forced by volcanic eruptions.
Specifically we analyze results from the IPCC historical runs that simulate the evolution of
the circulation over the last part of the 19th century and the entire 20th century using a
realistic time series of atmospheric composition (greenhouse gases and aerosols). In
particular, composite anomalies over the two boreal winters following each of the nine
largest low-latitude eruptions during the period 18601999 are computed for various
tropospheric and stratospheric fields. These are compared when possible with
observational data. The seven IPCC models we analyzed use similar assumptions about
the amount of volcanic aerosols formed in the lower stratosphere following the volcanic
eruptions that have occurred since 1860. All models produce tropospheric cooling and
stratospheric warming as in observations. However, they display a considerable range of
dynamic responses to volcanic aerosols. Nevertheless, some general conclusions can be
drawn. The IPCC models tend to simulate a positive phase of the Arctic Oscillation in
response to volcanic forcing similar to that typically observed. However, the associated
dynamic perturbations and winter surface warming over Northern Europe and Asia in the
post-volcano winters is much weaker in the models than in observations. The AR4
models also underestimate the variability and long-term trend of the AO. This deficiency
affects high-latitude model predictions and may have a similar origin. This analysis allows
us to better evaluate volcanic impacts in up-to-date climate models and to better
quantify the model Arctic Oscillation sensitivity to external forcing. This potentially could
lead to improving model climate predictions in the extratropical latitudes of the Northern
Hemisphere.


Last Updated: 2006-04-15

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