What is it about?
The ocean is continually affected by atmospheric forcing involving surface winds and exchanges of heat and moisture. The ocean response to any individual atmospheric event is often hard to decipher due to the continual changes in atmospheric forcing. In this study, we identify a large number of atmospheric events in the North Atlantic (defined by a North Atlantic Oscillation index) and align all of these events together, and then examine the ocean response to that characteristic event. We find that there are fast ocean responses to that event involving the effect of local winds and air-sea heat fluxes, as well as slow ocean responses involving the ocean circulation transporting temperature anomalies over the basin.
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Why is it important?
The ocean response to atmospheric events is often explained in terms of the immediate response to forcing. However, there are slower responses involving the circulation transporting temperature anomalies over the basin. These different fast and slow responses can lead to opposing signed-ocean temperature responses. For example, stronger westerly winds can lead to a cooling over the subpolar North Atlantic, which is followed after 3 or 4 years by a surface warming due to the transport of warmer, subtropical waters into the subpolar gyre. Hence, the evolution of the ocean temperature anomalies can only be fully explained by accounting for the fast and slow responses to atmospheric forcing.
Perspectives
This study exploited an atmosphere-ocean model data set of 570 ensembles (based on an ensemble of 10 members from the UK Met office that is integrated for 57 different years). This data set included 114 members that represented a positive extreme of the North Atlantic Oscillation (an atmospheric index) and 133 members that represented a negative extreme. We were then able to align those extreme events and understand the ocean responses to that atmospheric event.
Professor Richard G Williams
University of Liverpool Department of Earth Ocean and Ecological Sciences
Read the Original
This page is a summary of: Fast and Slow Subpolar Ocean Responses to the North Atlantic Oscillation: Thermal and Dynamical Changes, Geophysical Research Letters, December 2022, American Geophysical Union (AGU),
DOI: 10.1029/2022gl101480.
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