Cyclonic eddies in the Gulf of Mexico: Observations by underwater gliders and simulations by numerical model

TitleCyclonic eddies in the Gulf of Mexico: Observations by underwater gliders and simulations by numerical model
Publication TypeJournal Article
Year of Publication2015
AuthorsRudnick D.L, Gopalakrishnan G, Cornuelle BD
JournalJournal of Physical Oceanography
Volume45
Pagination313-326
Date Published2015/01
Type of ArticleArticle
ISBN Number0022-3670
Accession NumberWOS:000347535800017
Keywordsadjoint code; Data assimilation; florida; global; loop current; ocean; ocean model; rings; system
Abstract

Circulation in the Gulf of Mexico (GoM) is dominated by the Loop Current (LC) and by Loop Current eddies (LCEs) that form at irregular multimonth intervals by separation from the LC. Comparatively small cyclonic eddies (CEs) are thought to have a controlling influence on the LCE, including its separation from the LC. Because the CEs are so dynamic and short-lived, lasting only a few weeks, they have proved a challenge to observe. This study addresses that challenge using underwater gliders. These gliders' data and satellite sea surface height (SSH) are used in a four-dimensional variational (4DVAR) assimilation in the Massachusetts Institute of Technology (MIT) general circulation model (MITgcm). The model serves two purposes: first, the model's estimate of ocean state allows the analysis of four-dimensional fields, and second, the model forecasts are examined to determine the value of glider data. CEs have a Rossby number of about 0.2, implying that the effects of flow curvature, cyclostrophy, to modify the geostrophic momentum balance are slight. The velocity field in CEs is nearly depth independent, while LCEs are more baroclinic, consistent with the CEs origin on the less stratified, dense side of the LCE. CEs are formed from water in the GoM, rather than the Atlantic water that distinguishes the LCE. Model forecasts are improved by glider data, using a quality metric based on satellite SSH, with the best 2-month GoM forecast rivaling the accuracy of a global hindcast.

DOI10.1175/jpo-d-14-0138.1
Student Publication: 
No