Editorial Type:
Article
Article Type:
Research Article

The Energetics of a Collapsing Meridional Overturning Circulation

Andrew McC. Hogg Research School of Earth Sciences, and ARC Centre of Excellence for Climate System Science, The Australian National University, Canberra, Australian Capital Territory, Australia

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Henk A. Dijkstra Institute for Marine and Atmospheric Research, Department of Physics and Astronomy, Utrecht University, Utrecht, Netherlands

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Juan A. Saenz Research School of Earth Sciences, The Australian National University, Canberra, Australian Capital Territory, Australia

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Print Publication:
01 Jul 2013
DOI:
https://doi.org/10.1175/JPO-D-12-0212.1
Page(s):
1512–1524
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Abstract

A well-studied example of natural climate variability is the impact of large freshwater input to the polar oceans, simulating glacial melt release or an amplification of the hydrological cycle. Such forcing can reduce, or entirely eliminate, the formation of deep water in the polar latitudes and thereby weaken the Atlantic meridional overturning circulation (MOC). This study uses a series of idealized, eddy-permitting numerical simulations to analyze the energetic constraints on the Atlantic Ocean's response to anomalous freshwater forcing. In this model, the changes in MOC are not correlated with the global input of mechanical energy: both kinetic energy and available potential energy (APE) increase with northern freshwater forcing, while the MOC decreases. However, a regional analysis of APE density supports the notion that local maxima in APE density control the response of the MOC to freshwater forcing perturbations. A coupling between APE input and changes in local density anomalies accounts for the difference in time scales between the recovery and collapse of the MOC.

Corresponding author address: Andrew Hogg, Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia. E-mail: Andy.Hogg@anu.edu.au

Abstract

A well-studied example of natural climate variability is the impact of large freshwater input to the polar oceans, simulating glacial melt release or an amplification of the hydrological cycle. Such forcing can reduce, or entirely eliminate, the formation of deep water in the polar latitudes and thereby weaken the Atlantic meridional overturning circulation (MOC). This study uses a series of idealized, eddy-permitting numerical simulations to analyze the energetic constraints on the Atlantic Ocean's response to anomalous freshwater forcing. In this model, the changes in MOC are not correlated with the global input of mechanical energy: both kinetic energy and available potential energy (APE) increase with northern freshwater forcing, while the MOC decreases. However, a regional analysis of APE density supports the notion that local maxima in APE density control the response of the MOC to freshwater forcing perturbations. A coupling between APE input and changes in local density anomalies accounts for the difference in time scales between the recovery and collapse of the MOC.

Corresponding author address: Andrew Hogg, Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia. E-mail: Andy.Hogg@anu.edu.au
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