Analysis of flow variability in the Yucatan Channel

Abstract

[1] The structure and variability of the velocity and temperature fields in Yucatan Channel are analyzed using data from an eight-mooring array deployed from August 1999 to June 2000. The area-averaged kinetic energy and transport fluctuations spectra show that the extrema of these quantities do not coincide, and that flow variability is dominated by highly energetic processes with weak transport contributions. Transport fluctuations peak in the 20-40 and 5-10 day period bands, but show no clear correlation with the local wind-stress forcing. Empirical orthogonal function (EOF) analysis of the along-channel velocity component shows that approximately 55% of the total velocity variance is retained in the first two EOFs, which depict tripolar (the center of the channel is out of phase with the sides) and dipolar structures. A multivariate complex EOF analysis of low-passed temperature and velocity components suggests the tripole-dipole structures are the components of irregular oscillations of the flow, related to the northwestward propagation of anticyclones and cyclones through the channel. The weak transport signal in these modes is consistent with the eddies being advected by the mean flow. In contrast to other western boundary current regions, the passage of eddies provides the predominant explanation for the variability in the Yucatan Channel. However, the processes controlling transport variability remain unclear.

Loop Current, Rings and Related Circulation in the Gulf of Mexico: A Review of Numerical Models and Future Challenges

“…The strong variability are also seen in the cross-channel flows. As mentioned previously, Abascal et al [2003] reported mean cross-channel speeds of O(0. m s -) and standard deviation ≈ 0.5 m s -near the surface. The cross-channel currents are clearly time-dependent and not always negligible.…”

“…There is not (yet?) direct observational evidence of Caribbean eddies squeezing through the Yucatan Channel (though the Canek moorings across the channel suggest such a possibility; Abascal et al [2003]), but Murphy et al's numerical finding is interesting and potentially significant. Oey et al [2003] expanded upon Murphy et al's ideas, but instead of looking at the progression of individual eddies, they asked if forcing by winds (six-hourly ECMWF was used) and/or by Caribbean eddies (satellite SSH anomaly was used) would affect the statistics of ring-shedding, the periods in particular.…”

“…The observed EOF mode (3%) is tri-polar, coherent currents on both sides and opposing currents in the center of the channel, while mode 2 (23%) exhibits a bipolar structure that extends deeper to z ≈ −000 m. Abascal et al [2003] interpreted both modes in terms of passages of eddies (anticyclones and cyclones) or anomalies, through the channel (their Figure 8). These anomalies give rise to meanders of the core current in the channel.…”

U.S. GODAE: Global Ocean Prediction with the Hybrid Coordinate Ocean Model (HYCOM)

“…Figure 1a shows the vertical section of the mean velocity across the Yucatan Channel from the 1/12° Atlantic system over the time period of September 2003 through August 2004. Observations of velocities from Abascal et al (2003) are shown in Figure 1b. The mean velocity/transport across 35°W between 5°S and 5°N from the model is shown in Figure 2a, while a corresponding plot of observations from Schott et al (2003) is shown in Figure 2b.…”

The HYCOM (HYbrid Coordinate Ocean Model) data assimilative system

“…It is left to the user to model where the continuity (thickness tendency) equadefine the coordinate separation constraints that control tion is solved prognostically throughout the domain, regional transitions among the three coordinate choices with the Arbitrary Lagrangian-Eulerian (ALE) technique as described in the appendix. used to remap the vertical coordinate and maintain difAfter the model equations are solved, the hybrid ferent coordinate types within the domain (Adcroft and coordinate generator then relocates vertical interfaces to Hallberg, 2006). This differs from Eulerian Vertical restore isopycnic conditions in the ocean interior to the Direction (EVD) models with fixed z-and a-coordinates greatest extent possible while enforcing the minimum that use the continuity equation to diagnose vertical thickness requirements specified by (1) in the appendix.…”