Mathematics – Logic
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmos32b..06p&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #OS32B-06
Mathematics
Logic
4223 Descriptive And Regional Oceanography, 4263 Ocean Prediction, 4544 Internal And Inertial Waves, 4560 Surface Waves And Tides (1255)
Scientific paper
Tidal harmonic analysis is widely used to describe the regular oscillations observed in sea-level. The technique uses a least-squares approach to calculate the amplitude and phase of the variance at specific frequencies corresponding to astronomical, meteorological and other forcing mechanisms. Here tidal harmonic analysis is used to calculate the tidal constituents for each year of a 10-year timeseries of sea-level data from Santa Barbara on central California coast. Both the amplitude and phase of the constituents are stable between years at the dominant tidal frequencies. The calculated constituents can be used to reconstruct a predicted sea-level which describes 99% of the observed variance. This is consistent with the numerous other observations of sea-level in coastal regions. In contrast, tidal harmonic analysis is not successful in describing the tidal-band oscillations of temperature and velocity in the same coastal region. We calculate the diurnal- and semidiurnal-band variance in the temperature and velocity from 10-year timeseries measured at four locations in the Santa Barbara Channel region. Tidal harmonic analysis is then used to calculate the amplitude and phase at each of the tidal frequencies for each year of data. In the diurnal frequency band, the amplitude of the dominant temperature tidal constituents can vary between years by O(10) and the associated phase by 150o. Reconstructing the timeseries from these constituents only accounts for between 15% and 50% of the observed temperature variance and between 30% and 60% of the observed velocity variance. Tidal harmonic analysis similarly fails to resolve the observed semi-diurnal temperature and velocity variance. We conclude that, unlike sea-level, the temperature and velocity fields in this region are not predictable using the tidal harmonic technique. We suggest that this limitation results from spectral broadening of the tidally-driven temperature and velocity variance into narrow-band peaks which cannot be effectively resolved as variance at a selection of specific frequencies.
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