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Article Type:
Research Article

Impact of Anomalous Northward Oceanic Heat Transport on Global Climate in a Slab Ocean Setting

Blandine L’Hévéder Laboratoire de Météorologie Dynamique, L’Institut Pierre-Simon Laplace, Centre National de la Recherche Scientifiques, Ecole Normale Supérieure, and Université Pierre et Marie Curie, Paris, France

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Francis Codron Laboratoire de Météorologie Dynamique, L’Institut Pierre-Simon Laplace, Centre National de la Recherche Scientifiques, Ecole Normale Supérieure, and Université Pierre et Marie Curie, Paris, France

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Michael Ghil Atmospheric and Oceanic Sciences Department, and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, Los Angeles, California

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Print Publication:
01 Apr 2015
DOI:
https://doi.org/10.1175/JCLI-D-14-00377.1
Page(s):
2650–2664
Restricted access

Abstract

This paper explores the impact of anomalous northward oceanic heat transport on global climate in a slab ocean setting. To that end, the GCM LMDZ5A of the Laboratoire de Météorologie Dynamique is coupled to a slab ocean, with realistic zonal asymmetries and seasonal cycle. Two simulations with different anomalous surface heating are imposed: 1) uniform heating over the North Atlantic basin and 2) concentrated heating in the Gulf Stream region, with a compensating uniform cooling in the Southern Ocean in both cases. The magnitudes of the heating and of the implied northward interhemispheric heat transport are within the range of current natural variability. Both simulations show global effects that are particularly strong in the tropics, with a northward shift of the intertropical convergence zone (ITCZ) toward the heating anomalies. This shift is accompanied by a northward shift of the storm tracks in both hemispheres. From the comparison between the two simulations with different anomalous surface heating in the North Atlantic, it emerges that the global climate response is nearly insensitive to the spatial distribution of the heating. The cloud response acts as a large positive feedback on the oceanic forcing, mainly because of the low-cloud-induced shortwave anomalies in the extratropics. While previous literature has speculated that the extratropical Q flux may impact the tropics by the way of the transient eddy fluxes, it is explicitly demonstrated here. In the midlatitudes, the authors find a systematic northward shift of the jets, as well as of the associated Ferrel cells, storm tracks, and precipitation bands.

Corresponding author address: Blandine L’Hévéder, Laboratoire de Météorologie Dynamique, Université Paris VI, Tour 45-55 3e étage, Case postale 99, 4 place Jussieu, F 75252 Paris CEDEX 05, France. E-mail: blandine.lheveder@lmd.jussieu.fr

Abstract

This paper explores the impact of anomalous northward oceanic heat transport on global climate in a slab ocean setting. To that end, the GCM LMDZ5A of the Laboratoire de Météorologie Dynamique is coupled to a slab ocean, with realistic zonal asymmetries and seasonal cycle. Two simulations with different anomalous surface heating are imposed: 1) uniform heating over the North Atlantic basin and 2) concentrated heating in the Gulf Stream region, with a compensating uniform cooling in the Southern Ocean in both cases. The magnitudes of the heating and of the implied northward interhemispheric heat transport are within the range of current natural variability. Both simulations show global effects that are particularly strong in the tropics, with a northward shift of the intertropical convergence zone (ITCZ) toward the heating anomalies. This shift is accompanied by a northward shift of the storm tracks in both hemispheres. From the comparison between the two simulations with different anomalous surface heating in the North Atlantic, it emerges that the global climate response is nearly insensitive to the spatial distribution of the heating. The cloud response acts as a large positive feedback on the oceanic forcing, mainly because of the low-cloud-induced shortwave anomalies in the extratropics. While previous literature has speculated that the extratropical Q flux may impact the tropics by the way of the transient eddy fluxes, it is explicitly demonstrated here. In the midlatitudes, the authors find a systematic northward shift of the jets, as well as of the associated Ferrel cells, storm tracks, and precipitation bands.

Corresponding author address: Blandine L’Hévéder, Laboratoire de Météorologie Dynamique, Université Paris VI, Tour 45-55 3e étage, Case postale 99, 4 place Jussieu, F 75252 Paris CEDEX 05, France. E-mail: blandine.lheveder@lmd.jussieu.fr
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