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National Committee on Marine Sciences (NCMS)

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    Tides and currents in a two-inlet coastal lagoon: Laguna de Términos, México
    David, Laura T.; Kjerfve, Björn (Elsevier BV, 1998-08)
    Laguna de Términos, the largest coastal lagoon in México with a surface area of 2500 km2, is connected to the Gulf of México via two major ocean inlets. Fifty percent of the lagoon water volume is renewed every 9 days, mostly as a function of tidal exchange. Two month-long field measurement periods indicate that the tide is mostly mixed, mainly diurnal with a mean range of 0.3 m. In the tidal inlets, peak currents measure 1.3 m s-1, and are mostly mixed, mainly semidiurnal. Processes at tidal frequencies explain approximately 70% of the water level variability; and approximately 95 and 65% of the current variability in the inlets and inside the lagoon, respectively. The remaining low-frequency variability is attributed to meteorological forcing. The lagoon receives a mean freshwater discharge of 378 m3 s-1 from three rivers, but the inlets are still well mixed with only a weak gravitational circulation in one of the inlets. Measurements from a single tidal cycle in March 1995 indicate that the net fluxes of salt and suspended sediment during this period were directed towards the Gulf of México in both inlets, mostly as a result of advective dominance opposed by lagoon-directed tidal dispersion and vertical shear fluxes.
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    Local tide and geoid corrections significantly improve coastal retracked Jason sea surface heights in the Philippines
    Flores, Paul Caesar; Reyes, Rosalie; Amedo-Repollo, Charina Lyn; Rediang, Abegail; Alfante, Rey Mark; Bauzon, Ma. Divina Angela; Pasaje, Nikki; Bringas, Dennis (Science and Technology Information Institute, 2022-11-08)
    Retracking algorithms increase the accuracy of coastal sea surface height (SSH) measurements. However, it is still important to validate these retracking estimates with tide gauge (SSHtg) observations. We downloaded the freely available Jason altimeter SSH processed using the XTRACK-ALES algorithm, then detided the SSH using different tide models. The first model is the default tidal correction based on Finite Element Solution 2014 (SSHfes), and the second model is the T_Tide harmonic analysis of the nearest tide gauge (SSHaltimeter). SSHfes showed a very poor correlation (< 0.31) and very high root mean square error (RMSE, > 29 cm). In contrast, SSHaltimeter generally showed a very high correlation (> 0.91) and low RMSE (< 17.4 cm). A further quality check based on the average and standard deviation of the difference between the SSH readings (SSHfes – SSHtg and SSHaltimeter – SSHtg) also showed the superior performance of SSHaltimeter,which scored < 9.3 and < 16.5 cm, respectively; compared to SSHfes, which scored < 9.3 cm and > 27 cm for the same parameters. The poor performance from the SSHfes likely comes from the complex bathymetry and coastal geomorphology of the country, which is not accounted for in the FES. The Philippines generally has a narrow shelf, and the FES tide corrections may be related to deep-water tides rather than the shallow-water tides observed from tide gauges. Despite the high correlation and agreement between the SSHaltimeter and SSHtg, the rate of sea level rise from the SSHaltimeter in some sites is more than twice the rate from SSHtg, which indicates the possible influence of the vertical land movement.
    This study was supported by grants to R.B. Reyes by the Department of Science and Technology–Philippine Council for Industry, Energy, and Emerging Technology Research and Development through the Coastal Sea Level Rise Philippines Project. We also thank the anonymous reviewers for their feedback on how to improve the manuscript.