Vorticity flux through the Yucatan Channel and Loop Current variability in the Gulf of Mexico
[1] Recent observations (the CANEK Program [Candela et al., 2002]) suggest that potential vorticity (PV) flux anomaly (VFA) at Yucatan Channel may serve as a useful indicator of Loop Current variability, including Loop Current extension, retraction, and eddy shedding. Intuitively, anticyclonic VFA extends the Loop Current into the Gulf of Mexico and cyclonic VFA causes retraction or even shedding. However, this intuition is inconsistent with PV conservation. The problem is reexamined here by careful analyses of the relation between VFA and Loop Current variability using (1) the results of a 15-year numerical simulation of shedding specified with simple forcing, and (2) CANEK and satellite observations. Both model and observations indicate that Loop Current eddy shedding or retraction tends to occur shortly (1� 2 months) after the influx of VFA at Yucatan has turned anticyclonic, and that these events are sometimes preceded by a more prolonged period of influx of cyclonic VFA. These findings suggest that contrary to intuition, influx of cyclonic VFA tends to extend the Loop Current into the Gulf, thus making the Loop Current more susceptible to retract or shed an eddy, and influx of anticyclonic VFA may then ‘‘trigger’’ retraction or eddy shedding. However, the Loop Current’s behaviors are much more complex than can be prescribed by these simple rules. A much longer observational data set, coupled with more refined model experiments and sophisticated analyses, is required to further quantify the phenomenon. INDEX TERMS: 4520 Oceanography: Physical: Eddies and mesoscale processes; 4255 Oceanography: General: Numerical modeling; 4576 Oceanography: Physical: Western boundary currents; 4243 Oceanography: General: Marginal and semienclosed seas; KEYWORDS: vorticity flux, Loop Current, Yucatan Channel Citation: Oey, L.-Y. (2004), Vorticity flux through the Yucatan Channel and Loop Current variability in the Gulf of Mexico, J. Geophys. Res., 109, C10004, doi:10.1029/2004JC002400.
Loop Current warming by Hurricane Wilma
Hurricanes mix and cool the upper ocean, as shown here in observations and modeling of the Caribbean Sea and the Gulf of Mexico during the passage of hurricane Wilma. Curiously, the upper ocean around the Loop Current warmed prior to Wilma's entrance into the Gulf. The major cause was increased volume and heat transports through the Yucatan Channel produced by storm‐induced convergences in the northwestern Caribbean Sea. Such oceanic variability may have important impacts on hurricane predictions.
The separation of the Yucatan Current from the Campeche Bank and the intrusion of the Loop Current into the Gulf of Mexico
Data collected in the eastern Gulf of Mexico during 1974, 1975, and 1976 show that the penetration of the Loop Current into the gulf is strongly correlated with the location of the Yucatan Current on the Campeche Bank. The Loop does not penetrate far into the gulf when the Yucatan Current separates from the bank in the vicinity of the Catoche Tongue (i.e., the eastern Campeche Bank). Deep Loop penetrations are correlated with separations farther west on the bank. The angle of the Yucatan Current at separation is also correlated with the location of separation (i.e., smaller angles relative to due east are correlated with separations from farther east on the bank). Thus small angles at separation are correlated with shallow intrusions of the Loop. Historical temperature data collected in the eastern gulf are reviewed and support these correlations. Simple conservation of potential vorticity considerations can explain the correlation between the angle at separation and the penetration of the Loop.