Comparisons between a continuous 3‐year current‐meter observation at the sill of the Yucatan Strait, satellite measurements of Gulf Loop Current area, and regional sea level

Abstract

From October 1977 through November 1980 a current‐meter mooring was maintained in the Yucatan Strait. The meter was moored halfway between Mexico and Cuba, 145 m above the sill or in 1895 m of water. Motions of low frequency (<14−1 cycles/day) are oriented approximately parallel to the isobaths, 021°–030° true. Net drift for 3 years is to the SSW at an average velocity of 1.8 cm/s. Sustained southward flows at intervals of 8 months, which persisted for several months each, have average velocities of 5 cm/s, with randomly spaced bursts as high as 15 cm/s. Energy in subtidal frequency bands has significant peaks near 38−1 and 19−1 cycles/day, with a broad band of energy between 300−1 and 200−1 cycles/day. The latter peak is consistent with the approximately 8‐month interval between the southward flow events. Comparison with weekly areal coverage of the Gulf Loop Current from Geostationary Operational Environmental Satellite infrared observations shows little covariation, except that 8 months is typical of some anticyclonic eddy generation. There is little coherence of sill depth velocities with Naples sea level at subtidal frequencies, but with Miami there is coherence at several frequencies, notably 38−1 and 19−1 cycles/day. In the higher frequencies, the principal tidal motions are diurnal and are oriented somewhat across the isobaths toward the northwest, 346°–349° true, with counterrotating O1 and K1 constituents. No semidiurnal, inertial, or fortnightly energy is observed above the background continuum.

Investigation of the Relationship Between the Yucatan Channel Transport and the Loop Current Area in a Multidecadal Numerical Simulation

“…by Maul et al, [1985] and Maul and Vukovich [1993] to insufficient sampling in the YC. The authors suggested that a longer data set was required to further test and validate Maul's [1977] theory.…”

Simulation of velocities in the Yucatan Channel

“…5 have been smoothed since derivatives are noisy. We note first that there is a significant correlation (R=0.4) between changes in the LC area and the deep outflow below 800 m, so that increase in the deep southward outflow is an indication of growing LC, as proposed in [1]. Also shown in Fig.…”

“…4) are often found. As hypothesized in [1] and shown in [3], the deep return transport is expected to correlate with changes in the LC extension (not with the area averaged elevation L itself, but with its derivative). Therefore, we calculate the daily change in the LC elevation, i.e., the derivative ∆L/∆t; the distribution of this derivative as a function of the deep outflow is shown in Fig.…”

“…Consequently, the excess inflow is returned as a deep outflow in the YC. An early attempt by [1] to find a correlation between the observed deep flow over the center of the YC sill and variations in the LC was unsuccessful. However, the more recent observations in [3] show a significant correlation between the deep flow and the LC extension, but they also indicate that the deep return flows are found along the side slopes of the Channel and not at the center of the sill where the current meter in [1] was located.…”

“…1., our knowledge of the structure and variability of the Channel's flow was limited in the past due to limited direct measurements in the Channel (e.g., [1]). However, recent observations, ( [2], [3]), show a considerably more complex flow field than previously thought, and suggest that the mean Channel transport (~24 Sv; 1Sv=10 6 m 3 s -1 ) is smaller than previous estimates (28-30 Sv; [4]).…”