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A barotropic vorticity budget for the subtropical North Atlantic Based on observations

TitleA barotropic vorticity budget for the subtropical North Atlantic Based on observations
Publication TypeJournal Article
Year of Publication2019
AuthorsLe Bras I.AA, Sonnewald M., Toole J.M
Date Published2019/11
Type of ArticleArticle
ISBN Number0022-3670
Accession NumberWOS:000490741900003
Keywordsassimilation; Barotropic flows; Boundary currents; circulation; data; florida current; gulf-stream; Gyres; North Atlantic Ocean; ocean; oceanography; recirculation; seasonal cycle; sverdrup balance; transport; variability; vorticity; western boundary currents

To ground truth the large-scale dynamical balance of the North Atlantic subtropical gyre with observations, a barotropic vorticity budget is constructed in the ECCO state estimate and compared with hydrographic observations and wind stress data products. The hydrographic dataset at the center of this work is the A22 WOCE section, which lies along 66 degrees W and creates a closed volume with the North and South American coasts to its west. The planetary vorticity flux across A22 is quantified, providing a metric for the net meridional flow in the western subtropical gyre. The wind stress forcing over the subtropical gyre to the west and east of the A22 section is calculated from several wind stress data products. These observational budget terms are found to be consistent with an approximate barotropic Sverdrup balance in the eastern subtropical gyre and are on the same order as budget terms in the ECCO state estimate. The ECCO vorticity budget is closed by bottom pressure torques in the western subtropical gyre, which is consistent with previous studies. In sum, the analysis provides observational ground truth for the North Atlantic subtropical vorticity balance and explores the seasonal variability of this balance for the first time using the ECCO state estimate. This balance is found to hold on monthly time scales in ECCO, suggesting that the integrated subtropical gyre responds to forcing through fast barotropic adjustment.

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