Stratosphere-troposphere coupling at inter-decadal time scales: Implications for the North Atlantic Ocean

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Abstract

[1] Evidence of stratosphere-troposphere coupling at inter-decadal time scales is searched for in a 260-year simulation performed with a climate model including a state-of-the-art stratosphere. The boundary conditions of the simulation are specified according to preindustrial conditions and are kept constant from year to year. It is shown that long lasting (∼20 years) positive and negative anomalies of the northern winter stratospheric polar vortex exist in the simulation. Given that there are no externally imposed low frequency time variations, these persistent variations are due to internal dynamical processes of the modeled coupled atmosphere ocean system. By composite analysis, it is shown that the long lasting stratospheric vortex anomalies are connected through the troposphere to mean sea level pressure, surface temperature and sea ice cover anomalies. These connections are reminiscent of intra-seasonal stratosphere–troposphere coupling. Over the ocean, the surface temperature and sea ice cover anomalies are indicative of the delayed Atlantic meridional overturning circulation response to atmospheric forcing. The latter is indeed found to be anomalously strong/weak during the long lasting positive/negative stratospheric vortex anomalies, providing evidence for a potential role of the stratosphere in decadal prediction.

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