A generalized method for estimating the structure of the equatorial Atlantic cold tongue: Application to drifter observations

TitleA generalized method for estimating the structure of the equatorial Atlantic cold tongue: Application to drifter observations
Publication TypeJournal Article
Year of Publication2013
AuthorsHormann V., Lumpkin R, Perez R.C
JournalJournal of Atmospheric and Oceanic Technology
Volume30
Pagination1884-1895
Date Published2013/08
Type of ArticleArticle
ISBN Number0739-0572
Accession NumberWOS:000323638000021
Keywordsatlantic ocean; front; Fronts; long waves; ocean; pacific; Sea surface temperature; tropical instability waves; vortices
Abstract

A generalized method is developed to determine the position of the Atlantic northern cold tongue front across its zonal extent from satellite sea surface temperature (SST) data. Previous approaches estimated the frontal position subjectively or individually, calling for a more objective technique that is suitable for large datasets. The developed methodology is based on a median frontal SST, and associated positional uncertainties are on the order of 0.3 degrees latitude for the period 1998-2011. Frontal characteristics are generally consistent with tropical instability waves (TIWs) and interannual variations are large. Application to drifter observations shows how the new methodology can be used to better understand circulation features near the northern cold tongue front. A drifter pair deployed on the eastern side of a passing TIW crest north of the front revealed that the trajectories of the drifters were clearly influenced by the shape of the front and they did not cross the front, but rather stayed close together about 2.5 degrees north of the front. In a more complete analysis using all available drifters near the Atlantic northern cold tongue front, only about 12% of the trajectories crossed the front. Analyses in an along- and cross-frontal frame of reference complement isopycnal coordinate mapping, and tropical Atlantic drifter velocities averaged in frontal coordinates indicate a broadened shear zone between the northern branch of the South Equatorial Current and North Equatorial Countercurrent as well as meridional convergence near the front.

DOI10.1175/jtech-d-12-00173.1
Short TitleJ. Atmos. Ocean. Technol.
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