Other
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmos31b0428m&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #OS31B-0428
Other
4235 Estuarine Processes, 4263 Ocean Prediction, 4546 Nearshore Processes, 4556 Sea Level Variations, 4560 Surface Waves And Tides (1255)
Scientific paper
Mixed semi-diurnal tides and associated processes in estuaries and other coastal waters are substanially modulated by variations in lunar declination, which has a 27.21 day "nodical month" period, although these influences are generally ascribed to the more obvious changes in lunar phase, which varies with the 29.53 day synodical month. Analyses of archival sea level data, primarily in the San Francisco (California) Estuary, demonstrate previously undescribed patterns at a range of temporal scales. First, "ambiguous" high and low tides (neither HHW, LHW, HLW, nor LLW) recur in a consistent 13.61 day pattern of 1, 3, 5, or 7 adjacent ambiguous HW followed by 1 or 3 ambiguous LW. Thus, the dominant tidal current (LLW-HHW or HHW-LLW) of any mixed semi-diurnal estuary reverses every 13.61 days for a few days, with potentially dramatic influences on water body and sediment fluxes. Second, while the diurnal timing of HHW or LLW typically advances about 50 minutes each solar day, the "tidal pattern cross-over" resets the timing of HHW and LLW by 12.42 hours every 13.61 days, resulting in a strong apparent seasonality in the diurnal timing of tidal maxima and minima. This seasonality significantly controls the temporal and spatial distribution of processes influenced both by hydroperiod and temperature or solar insolation. Finally, while the resulting "seasonal" pattern is stable over short series of observations, it in fact reflects a 366.34 day pattern, which means that the seasonality itself has a 335 year period. Thus, coastal areas which are now generally flooded (HHW) at night in the summer and during the day in the winter had the opposite pattern about 170 years ago. This means that many century-scale physical and biotic changes in estuaries may be due to nodical tidal phenomena rather than solely to anthropogenic causes.
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