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definition | In the context of tide tables, a port for which sufficient data is available in order for a set of official predictions to be produced. Also known as a "primary port", especially in North America. |
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definition | From the "Australian Hydrographic Office Glossary": The state of a tidal stream when its speed is zero or nearly so, especially the moment when the reversing stream changes its direction. Also known as slack tide or slack. see also streams. |
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definition | From the "Australian Hydrographic Office Glossary": The condition at high or low water when there is no perceptible change in the height of tide for a period of time. Sometimes called platform tide. see also streams. |
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definition | When sea level is referenced to the centre of the Earth, it is sometimes referred to as “absolute”, as opposed to “relative”, which is referenced to a point (eg. a coastal benchmark) whose vertical position may vary over time. |
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definition | A unit which sends an acoustic pulse through free air down a sounding tube to the water’s surface and measures the return time. The return travel time though the air between a transmitter/receiver and the water surface below is converted to sea level. |
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definition | Used in the response method of tidal analysis, response method analysis consists of determining a set of complex weights (typically five), which define the admittance of the response system at a given frequency. Once known, the admittance, combined with the known coefficients on the spherical harmonics representing the tide-generating potential, can be used to deduce the amplitude and phase of the usual harmonics (M2, S2, etc.). Admittance is sometimes defined as the ratio of the spectra of the sea level and the equilibrium tide (or tide-generating potential), and sometimes as the ratio of their cross-spectrum and the spectrum of the equilibrium tide. Being a complex quantity, it has both amplitude and phase. |
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definition | The delay in time between the transit of the moon and the highest spring tide. Normally one or two days, but it varies widely. In other words, in many places the maximum tidal range occurs one or two days after the new or full moon, and the minimum range occurs a day or two after first and third quarter. In a semi-diurnal tidal environment dominated by M2 and S2, the age in hours can be computed using the formula (gS2 – gM2)/(ѠM2 - ѠS2), where gS2 and gM2 are the phase lags (in degrees) from an analysis of the data, and ѠM2 and ѠS2 are the speeds (in °/hour). A similar formula can be devised for a diurnal environment dominated by O1 and K1. |
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definition | Tidal frequencies that contain significant energy and are of higher frequency than the Nyquist frequency, they result from folding of lower frequencies in the power spectrum. |
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definition | Maps of specific tidal constituents (eg. M2) are normally drawn with lines connecting
points of constant amplitude (co-range or co-amplitude lines) and/or phase (co-phase
lines). The co-phase lines often appear like spokes radiating out from a central
hub - the "amphidrome" or "node". Often a single map will show a number of these
"amphidromic systems". The co-range lines more or less encircle the amphidrome, where
the constituent amplitude is least. Amphidromes are resonance phenomena, with higher-frequency constituents tending to have lesser areal extent. Whereas O1 has an amphidrome virtually over the entire North Atlantic Ocean, M2 has two. |
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definition | From the "Australian Hydrographic Office Glossary": One half of the range of a constituent, tide or wave in general. |