A model intercomparison study of climate change‐signals in extratropical circulation

• Published in: International Journal of Climatology
• Main Authors: Rauthe, Monika, Hense, Andreas, Paeth, Heiko
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2004
• Subjects: aleutian low; Antarc*; Antarctic; Climate change; Global warming; North Atlantic; North Atlantic oscillation
• Online Access: http://dx.doi.org/10.1002/joc.1025; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fjoc.1025; https://rmets.onlinelibrary.wiley.com/doi/pdf/10.1002/joc.1025

Abstract Since 1970, the observed time series of various extratropical circulation modes have revealed remarkable trends. In many studies it has been suggested that these trends may be related to global warming due to increasing greenhouse gas (GHG) concentrations. Coupled climate model scenario experiments may give a hint of such a relationship. Here, a large model intercomparison study is presented, incorporating most state‐of‐the‐art models of the international modeller community with GHG and GHG plus sulphate aerosol (SUL) forcing, in order to quantify the signals common to different climate models and to determine the degree of uncertainty. The extratropical circulation candidates are the Arctic oscillation (AO), the North Atlantic oscillation (NAO), the Aleutian low (AL) and the Antarctic oscillation (AAO). Most climate models agree in predicting positive AO and AAO trends into the 21st century, these being different from the respective results of long‐term control experiments. The NAO appears to be less sensitive to radiative forcing, with slightly positive and negative trends occurring in different models. The AL tends to strengthen in several models with GHG + SUL forcing. Projecting the spatial structure of the circulation modes onto the trend patterns of mean sea‐level pressure (SLP) indicates that, in particular, the AO and AAO contribute considerably to the simulated long‐term trends in SLP. Intermodel variations in Northern Hemisphere SLP trends become predominantly apparent over the mountainous regions and the North Pacific. In the Southern Hemisphere, the Antarctic region is subject to large model uncertainties. The multi‐decadal trends of all circulation modes except the NAO are statistically significant in the majority of the climate‐change experiments. At the interannual time scale, external radiative forcing does account for a small but statistically significant part of total multi‐model variability, but this part is of the same order of magnitude as the systematic differences between the ...