A subharmonic lunar tide in the seas off Western Europe

Cartwright, David E.

doi:10.1038/257277a0

Cited by 33 publications

(80 citation statements)

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“…For the most part, isolated peaks in the original spectrum have been almost completely removed. A small one still noticeable in the diurnal band has a frequency of approximately 14.50° h-' and is, we conjecture, caused by the degree-3 M, tide which we cannot separate cleanly from the degree-2 MJ without the time series approaching 8 years in duration (Cartwright 1975). There is, in addition, a strong cusp of residual energy remaining across the semidiurnal band and a somewhat smaller cusp across the diurnal band.…”

Section: Tides In Ocean Bottom Pressurementioning

confidence: 94%

Bottom pressure tides along a line in the southeast Atlantic Ocean and comparisons with satellite altimetry

Ray

Byrne

2010

Ocean Dynamics

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Seafloor pressure records, collected at 11 stations aligned along a single ground track of the Topex/Poseidon and Jason satellites, are analyzed for their tidal content. With very low background noise levels and approximately 27 months of high-quality records, tidal constituents can be estimated with unusually high precision. This includes many high-frequency lines up through the seventh-diurnal band. The station deployment provides a unique opportunity to compare with tides estimated from satellite altimetry, point by point along the satellite track, in a region of moderately high mesoscale variability. That variability can significantly corrupt altimeter-based tide estimates, even with 17 years of data. A method to improve the alongtrack altimeter estimates by correcting the data for nontidal variability is found to yield much better agreement with the bottom-pressure data. The technique should prove useful in certain demanding applications, such as altimetric studies of internal tides.

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Section: Tides In Ocean Bottom Pressurementioning

confidence: 94%

Bottom pressure tides along a line in the southeast Atlantic Ocean and comparisons with satellite altimetry

Ray

Byrne

2010

Ocean Dynamics

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“…In the equilibrium tide the term of MI, with argument (1 0 0 0 0 0) being smaller than the principal terms, is commonly omitted but analysis has shown that in the Thames, it has a greater magnitude than the usual terms. Cartwright (1975) has shown that this feature is widespread round Northwest European seas. The yearly EHM analyses have shown scatter in amplitudes and phase lags of many constituents.…”

Section: Astronomical Component Shallow Water Componentmentioning

confidence: 97%

The Fine Resolution of Tidal Harmonics

Amin

1976

Geophysical Journal International

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The tides of deep seas are mainly due to the astronomical forces and these tides can be expressed mathematically by relating the laws of planetary motion with hydrodynamics. Such tides are simple and can be explained in terms of a small number of harmonic components which arise directly from astronomical origins or else indirectly through low order interaction between such terms. The terms developed by mutual interaction are few and are found in significant amplitudes only in the lower frequencies of the spectrum up to sixth-diurnal species. The effects of hydrographical conditions become significant in shallow water where the tide range is comparable with the depth. In the case of shallow coastal areas and estuaries, water in motion is subjected to forces, like bottom friction which change within the tidal cycle as a function of depth. Under these circumstances the rate of convergence of amplitudes of terms developed from high-order interaction becomes slow and the existence of more terms can be identified. These new terms are spread over the whole spectrum thus making it essential to scan it completely and in depth. The tidal characteristics of the Thames represent one such complex. Here the fact that the tide progresses for a long time in a shallow area before entering into the estuary, where it thus meets freshwater flow and a salinity gradient all result in severe distortion of the tide. In the Fine Resolution of Tidal Harmonics method (FRTH), nodal terms of the principal constituents are separated by analysing a data set from Southend of a length exceeding the lunar nodal period of 18.61 years. It is established that the nodal parameters ' f ' and u ' differ from those computed by using the equilibrium tide. This deviation appears to be a significant factor in the generation of humps ' in the residual spectrum discussed by Rossiter & Lennon. The analysis of a long span of data made it possible to resolve directly separable shallow water constituents whose speeds are as close as 0.0022 deg/hr to the speeds of astronomical terms and an attempt has been made to resolve those constituents which are not directly separable, with the help of the ' response function '. The existence of some new shallow water constituents has been confirmed, the most significant of these are in the semi-diurnal, third-diurnal and quarter-diurnal species. The relatively high level of background noise in the long period and diurnal species prohibits the separation of many small nodal terms and consequently their presence cannot be confirmed. No significant change was found in constituents of the sixth-diurnal and higher species. Redefinition of some shallow water * A 294 M. Amin constituents is required in order to facilitate their distinction from associated terms in the same narrow spectral band. However, due to practical problems this is not possible for every place. It has been found better to leave some indirectly separable constituents unresolved. The variance and spectrum of residuals show that predictions are considerably impr...

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“…Doodson's (1 928) original formulation about the composition of the constituent MI is unrealistic in explaining the actual behaviour of terms in it. Cartwright (1975) gave a theoretical explanation of abnormal behaviour of the MI tide at the western European ports. It is the purpose of this research to examine these problems in conjunction with the tides of the western coast of Britain.…”

Section: Introductionmentioning

confidence: 99%

On analysis and prediction of tides on the west coast of Great Britain

Amin

1982

Geophysical Journal International

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Long-period tidal records from eight ports on the west coast of Great Britain are analysed, using both the harmonic method and the response function. Time series up to 9.5 yr were used so that fine structure of certain regions of high energy in the tidal residual spectrum may be examined. This also assisted in accurate separation of tides from surges. According to the currently accepted formulation of MI, its composition is not compatible with its actual composition in the real tide and, as such, has no useful purpose to serve in computation of predictions. Constituents Sa, Ssa, MA, and MB, are adversly affected by weather and long records are essential for their accurate separation. It has been observed that annual perturbations of Sz, similar to those confirmed in recent years for M2, also exist but these are not readily recognisable because their speeds are the same as those of constituents T, and R,. These perturbations, being highly sensitive to meteorological forces, are mainly responsible for cusps or humps in the vicinity of major tidal constituents in tidal residual spectra. The relationship of radiational and gravitational tides is found to be in very good agreement with theoretical results. In summer months non-predictable variance reduces to about half of the annual variance, reflecting the regional weather conditions of summer and winter.

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A subharmonic lunar tide in the seas off Western Europe

Cited by 33 publications

References 1 publication

Bottom pressure tides along a line in the southeast Atlantic Ocean and comparisons with satellite altimetry

Bottom pressure tides along a line in the southeast Atlantic Ocean and comparisons with satellite altimetry

The Fine Resolution of Tidal Harmonics

On analysis and prediction of tides on the west coast of Great Britain

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