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Spectral quantification of nonlinear behaviour of the nearshore seabed and correlations with potential forcings at Duck, N.C., U.S.A.

Magar V, Lefranc M, Hoyle RB, Reeve DE - PLoS ONE (2012)

Bottom Line: The patterns within these forcings are compared to the local bathymetric patterns; it is found that the patterns extracted using SSA and MSSA agree well with previous patterns identified using wavelets and confirm the highly non-stationary behaviour of beach levels at Duck.Annual and semi-annual cycles within the bathymetry are found to be strongly correlated with the monthly wave height, in agreement with the SSA findings.Other collective intra-annual cycles besides the semi-annual were identified; they were all correlated with the North Atlantic Oscillation.

View Article: PubMed Central - PubMed

Affiliation: Coastal Engineering Research Group, Marine Institute, School of Marine Science and Engineering, University of Plymouth, Plymouth, Devon, United Kingdom. vanesa.magar@plymouth.ac.uk

ABSTRACT
Local bathymetric, quasi-periodic patterns of oscillation are identified from 26 years of monthly profile surveys taken at two shore-perpendicular transects at Duck, North Carolina, USA. The data cover both the swash and surf zones. Singular Spectrum Analysis (SSA) and Multi-channel Singular Spectrum analysis (MSSA) methods are applied, on the shoreface, to three potential forcings: the monthly wave heights, the monthly mean water levels and the large scale atmospheric index known as the North Atlantic Oscillation. The patterns within these forcings are compared to the local bathymetric patterns; it is found that the patterns extracted using SSA and MSSA agree well with previous patterns identified using wavelets and confirm the highly non-stationary behaviour of beach levels at Duck. This is followed by analysis of potential correlations between the local bathymetry (at the two transects) and hydrodynamic and atmospheric patterns. The study is then extended to all measured bathymetric profiles, covering an area of 1100 m (alongshore) by 440 m (cross-shore). MSSA showed no collective inter-annual patterns of oscillations present in the bathymetry and the three potential forcings. Annual and semi-annual cycles within the bathymetry are found to be strongly correlated with the monthly wave height, in agreement with the SSA findings. Other collective intra-annual cycles besides the semi-annual were identified; they were all correlated with the North Atlantic Oscillation.

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Spectral density plot for the reconstructed component of the SPOs at x = 160 m for transect 58.The thin lines indicate the 95% confidence interval for the spectral estimates. The horizontal line shows the error of the peak frequency estimate for the quasi-yearly cycle.
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pone-0039196-g003: Spectral density plot for the reconstructed component of the SPOs at x = 160 m for transect 58.The thin lines indicate the 95% confidence interval for the spectral estimates. The horizontal line shows the error of the peak frequency estimate for the quasi-yearly cycle.

Mentions: The periods of the underlying cycle were computed all along transects 58 and 190; Table 2 shows the results at selected locations along the profiles. The uncertainties in the periods were estimated from figures of the power spectrum, as well as from the uncertainty of the power values at each frequency. An example of a power spectrum is shown in Fig. 3, corresponding to position x = 160 m at transect 58. If the uncertainty interval of the power value extends to, or beyond, the peak power value, then the uncertainty of the position of the peak also extends to the frequency at that power value. Figure 3 complements Table 2, which shows the uncertainties for the cycle periods in square brackets.


Spectral quantification of nonlinear behaviour of the nearshore seabed and correlations with potential forcings at Duck, N.C., U.S.A.

Magar V, Lefranc M, Hoyle RB, Reeve DE - PLoS ONE (2012)

Spectral density plot for the reconstructed component of the SPOs at x = 160 m for transect 58.The thin lines indicate the 95% confidence interval for the spectral estimates. The horizontal line shows the error of the peak frequency estimate for the quasi-yearly cycle.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3383760&req=5

pone-0039196-g003: Spectral density plot for the reconstructed component of the SPOs at x = 160 m for transect 58.The thin lines indicate the 95% confidence interval for the spectral estimates. The horizontal line shows the error of the peak frequency estimate for the quasi-yearly cycle.
Mentions: The periods of the underlying cycle were computed all along transects 58 and 190; Table 2 shows the results at selected locations along the profiles. The uncertainties in the periods were estimated from figures of the power spectrum, as well as from the uncertainty of the power values at each frequency. An example of a power spectrum is shown in Fig. 3, corresponding to position x = 160 m at transect 58. If the uncertainty interval of the power value extends to, or beyond, the peak power value, then the uncertainty of the position of the peak also extends to the frequency at that power value. Figure 3 complements Table 2, which shows the uncertainties for the cycle periods in square brackets.

Bottom Line: The patterns within these forcings are compared to the local bathymetric patterns; it is found that the patterns extracted using SSA and MSSA agree well with previous patterns identified using wavelets and confirm the highly non-stationary behaviour of beach levels at Duck.Annual and semi-annual cycles within the bathymetry are found to be strongly correlated with the monthly wave height, in agreement with the SSA findings.Other collective intra-annual cycles besides the semi-annual were identified; they were all correlated with the North Atlantic Oscillation.

View Article: PubMed Central - PubMed

Affiliation: Coastal Engineering Research Group, Marine Institute, School of Marine Science and Engineering, University of Plymouth, Plymouth, Devon, United Kingdom. vanesa.magar@plymouth.ac.uk

ABSTRACT
Local bathymetric, quasi-periodic patterns of oscillation are identified from 26 years of monthly profile surveys taken at two shore-perpendicular transects at Duck, North Carolina, USA. The data cover both the swash and surf zones. Singular Spectrum Analysis (SSA) and Multi-channel Singular Spectrum analysis (MSSA) methods are applied, on the shoreface, to three potential forcings: the monthly wave heights, the monthly mean water levels and the large scale atmospheric index known as the North Atlantic Oscillation. The patterns within these forcings are compared to the local bathymetric patterns; it is found that the patterns extracted using SSA and MSSA agree well with previous patterns identified using wavelets and confirm the highly non-stationary behaviour of beach levels at Duck. This is followed by analysis of potential correlations between the local bathymetry (at the two transects) and hydrodynamic and atmospheric patterns. The study is then extended to all measured bathymetric profiles, covering an area of 1100 m (alongshore) by 440 m (cross-shore). MSSA showed no collective inter-annual patterns of oscillations present in the bathymetry and the three potential forcings. Annual and semi-annual cycles within the bathymetry are found to be strongly correlated with the monthly wave height, in agreement with the SSA findings. Other collective intra-annual cycles besides the semi-annual were identified; they were all correlated with the North Atlantic Oscillation.

Show MeSH