Modeled and observed empirical orthogonal functions of currents in the Yucatan Channel, Gulf of Mexico

Abstract

Candela et al. [2003] have reported empirical orthogonal function (EOF) analyses based on 23‐month current‐meter and acoustic Doppler current profiler measurements in the Yucatan Channel. Those authors noted the difference between EOFs obtained from observations and their z‐level models and EOFs calculated by Ezer et al. [2003] from the results of a terrain‐following model. Here a new analysis is reported that explains this difference, and that also suggests the importance of shelf‐edge meander mode of the core Loop Current in the channel. We show that the terrain‐following model gives EOFs with characteristics similar to those observed when data from the upper slope and shelf in the western portion of the model channel are omitted. Modes 1 and 2 have tripole and dipole structures with energies (35%, 26%), respectively, of total energy, and correlate with “slow” vacillation of the core‐current for periods >50 days. Exclusion of upper‐slope and shelf data eliminates a short‐period and energetic component inherent in Ezer et al.'s original mode 1 EOF. This mode correlates with frontal meanders of the core current over the shelf edge in the western portion of the channel. The short‐period mode may be missing or underestimated in observational and z‐level models' analyses, since there were only a few moorings over the upper slope and shelf, and z‐level models have step‐like topography with generally lower resolution in shallower seas.