HR: 1400h
AN: OS23B-01    [Abstracts]
TI: Modulation of shallow water tidal current in a semiarid coastal lagoon
AU: * Dworak, J A
EM: jdworak@cicese.mx
AF: Instituto Tecnologico de Guaymas, Km 4 Carretera al Varadero Nacional, Sector Playitas, Guaymas, Son 85480, Mexico
AU: Gomez-Valdes, J
EM: jgomez@cicese.mx
AF: Centro de Investigacion Cientifica y de Educacion Superior de Ensenada, Km 107 Carretera Tijuana Ensenada, Ensenada, SON 22860, Mexico
AB: Complex demodulation is becoming quite common in coastal oceanography. Using a bottom-moored ADP, sea surface level and velocity profiles records were obtained during the summer and autumn of 2000 at the inlet of Guaymas Bay, a semiarid coastal lagoon with mixed tidal regime located in the Gulf of California. The velocity vectors were projected along the principal-axis component (94 % of the variance). The residual current Z0 showed an anti-estuary circulation with speed of 5 cm/s. The 144-day velocity time series were used to study the modulation of the shallow water components. Continuous complex tidal demodulation showed that for the vertically-integrated current, the fourth-diurnal band was the most energetic with synodyc modulation. The maxima in amplitude occurred during neap tides, which suggest a contribution of friction via triplet's interaction to generate compound tides. For the depth-dependent current, all bands showed two layers with independent oscillations; the bottom one, up to the 5 m, and the upper one, from the 8 to 12 m. The third-diurnal band was modulated by the declination of the Sun and the Moon; near the summer solstice, there is a clear anomalistic modulation, while near the autumn equinox, the modulation is of the synodyc type. For the fourth-diurnal band, the modulation is mainly synodic type with an anomalistic influence; and in contrast to the vertically-integrated current, the maxima in amplitude occurred during spring tides, which suggests that this field was no sensitive to non-linear friction. In order to study the mechanisms responsible for the annihilation of the shallow water tidal currents in the interface of the two layers, cubic velocity dissipation and internal friction were calculated from the velocity field. It was found that internal friction annihilated the third- and fourth-diurnal bands at the interface. Dissipation appears to have contributed to the current amplitude difference between bottom and surface, and near the autumn equinox to originate non-simultaneous maxima current amplitude between the bottom and upper layer.
DE: 4217 Coastal processes
DE: 4235 Estuarine processes (0442)
DE: 4277 Time series experiments (1872, 3270, 4475)
DE: 4560 Surface waves and tides (1222)
SC: Ocean Sciences [OS]
MN: 2007 Joint Assembly