Enhanced Atlantic subpolar gyre variability through baroclinic threshold in a coarse resolution model

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München : European Geopyhsical Union

Direct observations, satellite measurements and paleo records reveal strong variability in the Atlantic subpolar gyre on various time scales. Here we show that variations of comparable amplitude can only be simulated in a coupled climate model in the proximity of a dynamical threshold. The threshold and the associated dynamic response is due to a positive feedback involving increased salt transport in the subpolar gyre and enhanced deep convection in its centre. A series of sensitivity experiments is performed with a coarse resolution ocean general circulation model coupled to a statistical-dynamical atmosphere model which in itself does not produce atmospheric variability. To simulate the impact of atmospheric variability, the model system is perturbed with freshwater forcing of varying, but small amplitude and multi-decadal to centennial periodicities and observational variations in wind stress. While both freshwater and wind-stress-forcing have a small direct effect on the strength of the subpolar gyre, the magnitude of the gyre's response is strongly increased in the vicinity of the threshold. Our results indicate that baroclinic self-amplification in the North Atlantic ocean can play an important role in presently observed SPG variability and thereby North Atlantic climate variability on multi-decadal scales.

Atmosphere models, Atmospheric variability, Baroclinic, Climate variability, Coarse-resolution model, Coupled climate model, Deep convection, Dynamical threshold, Model system, North Atlantic, North Atlantic Ocean, Ocean general circulation models, Salt transport, Satellite measurements, Self-amplification, Small amplitude, Subpolar gyres, Time-scales, Statistical-dynamical
Mengel, M., Levermann, A., Schleussner, C.-F., & Born, A. (2012). Enhanced Atlantic subpolar gyre variability through baroclinic threshold in a coarse resolution model (Version publishedVersion, Vol. 3). Version publishedVersion, Vol. 3. München : European Geopyhsical Union. https://doi.org//10.5194/esd-3-189-2012