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.
The continuous series of sea level at Key West, Florida commenced in 1913, but we have discovered sporadic measurements that date back to 1846. From records at the U.S. Army Corps of Engineers and the U.S. Coast and Geodetic Survey, the sea level series has been connected to a Summary (common) Datum. Thus, a gappy record of monthly and annual mean heights (H[t]), perhaps the United States' longest series over San Francisco (ca. 1854) or New York ( ca. 1856), can be tested to ascertain if the rise in relative sea level at this site is stationary. Applying first and second order least squares and two‐phase regression analyses, we find that dH/dt is 0.19±0.01 cm/yr, and that d²H/dt²= [9.6±8.6]·10−3 cm/yr²; the two‐phase regression shows H[t] rising 0.15±0.03 cm/yr before ca. 1925 and 0.23±0.01 cm/yr afterwards. Neither the second‐order regression coefficient nor d²H/dt² nor the two‐phase calculation are significant above the 75% confidence level, but all three are weakly consistent with accelerated rise. For the epoch 1951–1987, Key West sea level, corrected for post‐glacial rebound, is best explained by concurrent measurements of 0–1,000 db dynamic height anomaly change.
Observations from satellite‐tracked drifting buoys, expendable bathythermograph and conductivity‐temperature‐depth data, and Geosat altimeter data are used to describe anticyclonic eddies that occur in small numbers off the Pacific coast of Central America. These eddies are similar in many respects to the well‐known warm‐core rings that are observed north of the Gulf Stream off the Atlantic coast of North America, except that they occur in an environment that also is warm, and they contain considerably greater kinetic energy. It is hypothesized that they are formed as a result of conservation of potential vorticity when the North Equatorial Countercurrent (NECC) turns northward upon approaching the eastern boundary during its autumnal maximum. The rings so formed have a strongly nonlinear character which causes them to propagate westward between 9°N and 14°N with a speed in excess of that of long Rossby waves. Due to a relatively small available potential energy content, these rings have a dissipation time scale of about 6 months and perhaps end by collision with and reabsorbtion into the NECC. The rings account for the observed enhancement of surface kinetic energy, and probably for the seaward transport of waters enriched in copper.
Twelve years of monthly mean positions of the northern boundary of the Loop Current in the eastern Gulf of Mexico from satellite and in situ data have been compared with coincident 1977-1988 estimates of volume transport in the Straits of Florida in the subseasonal frequency band 15-I to 5-I cycles per month. Volume transport estimated from Cuba minus Florida sea level difference in this frequency band accounts for 69% of the variance in volume transport estimated from the Florida-Grand Bahama Island submarine cable. On average, the Loop Current has a dominant period of II months whereas the volume transport is dominated by annual spectral energy; little significant coherence squared occurs between them. The maximum northward penetration of the Loop Current occurs on average in winter when the volume transport is a minimum, but this is an artifact of the sampling epoch. This negative relationship is most pronounced for 1979-1981 when transport is characterized as unimodal, but for 1984-1985 and 1987 the Loop Current and volume transport are more in phase, bimodal, and transport and position tend to have more semiannual energy. In this subseasonal band, the volume transport undergoes a significant change in the phase of its annual cycle after 1985 as compared with 1977-1984. For the twelve years considered in this study, the ensemble correlation between monthly position of the Loop Current and volume transport is essentially zero.
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