Decadal variability of Eddy Kinetic Energy in the South Pacific Subtropical Countercurrent in an Ocean General Circulation Model.

Rieck, Jan Klaus, Böning, Claus W. and Greatbatch, Richard John (2018) Decadal variability of Eddy Kinetic Energy in the South Pacific Subtropical Countercurrent in an Ocean General Circulation Model. Open Access Journal of Physical Oceanography, 48 (4). pp. 757-771. DOI 10.1175/JPO-D-17-0173.1.

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Abstract

The Eddy Kinetic Energy (EKE) associated with the Subtropical Countercurrent (STCC) in the western subtropical South Pacific is known to exhibit substantial seasonal and decadal variability. Using an eddy-permitting ocean general circulation model, which is able to reproduce the observed, salient features of the seasonal cycles of shear, stratification, baroclinic production and the associated EKE, we investigate the decadal changes of EKE. We show that the STCC region exhibits, uniquely among the subtropical gyres of the world’s oceans, significant, atmospherically forced, decadal EKE variability. The decadal variations are driven by changing vertical shear between the STCC in the upper 300 m and the South Equatorial Current below, predominantly caused by variations in STCC strength associated with a changing meridional density gradient. In the 1970s, an increased meridional density gradient results in EKE twice as large as in later decades in the model. Utilizing sensitivity experiments, decadal variations in the wind field are shown to be the essential driver. Local wind stress curl anomalies associated with the Interdecadal Pacific Oscillation (IPO) lead to up- and downwelling of the thermocline, inducing strengthening or weakening of the STCC and the associated EKE. Additionally, remote wind stress curl anomalies in the eastern subtropical South Pacific, which are not related to the IPO, generate density anomalies that propagate westward as Rossby waves and can account for up to 30–40 % of the density anomalies in the investigated region.

Document Type: Article
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-TM Theory and Modeling
OceanRep > The Future Ocean - Cluster of Excellence
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1175/JPO-D-17-0173.1
ISSN: 0022-3670
Related URLs:
Projects: MiKlip, ATMOS-MODINI, Future Ocean
Expeditions/Models/Experiments:
Date Deposited: 12 Feb 2018 12:51
Last Modified: 27 May 2019 11:12
URI: http://oceanrep.geomar.de/id/eprint/41897

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