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GEOPHYSICAL RESEARCH LETTERS, VOL. 32, L18715, doi:10.1029/2005GL023226, 2005

A stratospheric influence on the winter NAO and North Atlantic surface climate

Adam A. Scaife

Hadley Centre for Climate Prediction and Research, Met Office, Exeter, UK


Jeff R. Knight

Hadley Centre for Climate Prediction and Research, Met Office, Exeter, UK


Geoff K. Vallis

Geophysical Fluid Dynamics Laboratory, Princeton University, Princeton, New Jersey, USA


Chris K. Folland

Hadley Centre for Climate Prediction and Research, Met Office, Exeter, UK


Abstract

The North Atlantic Oscillation (NAO) has a profound effect on winter climate variability around the Atlantic basin. Strengthening of the NAO in recent decades has altered surface climate in these regions at a rate far in excess of global mean warming. However, only weak NAO trends are reproduced in climate simulations of the 20th Century, even with prescribed climate forcings and historical sea-surface conditions. Here we show that the unexplained strengthening of the NAO can be fully simulated in a climate model by imposing observed trends in the lower stratosphere. This implies that stratospheric variability needs to be reproduced in models to fully simulate surface climate variations in the North Atlantic sector. Despite having little effect on global mean warming, we show that downward coupling of observed stratospheric circulation changes to the surface can account for the majority of change in regional surface climate over Europe and North America between 1965 and 1995.

Received 13 April 2005; accepted 26 August 2005; published 28 September 2005.

Index Terms: 1616 Global Change: Climate variability (1635, 3305, 3309, 4215, 4513); 3337 Atmospheric Processes: Global climate models (1626, 4928); 3339 Atmospheric Processes: Ocean/atmosphere interactions (0312, 4504); 3362 Atmospheric Processes: Stratosphere/troposphere interactions.

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Citation: Scaife, A. A., J. R. Knight, G. K. Vallis, and C. K. Folland (2005), A stratospheric influence on the winter NAO and North Atlantic surface climate, Geophys. Res. Lett., 32, L18715, doi:10.1029/2005GL023226.