Search

Research indicates that transport variability within the Strait of Gibraltar is primarily affected by the cross strait sea level, using data obtained with an acoustic doppler current profiler. The cross strait sea level accounts for 57% of transport record variability, and increases to 78% with the addition of semimonthly and monthly cycles to the linear regression.

Abstract: Large waves pose risks to ships, offshore structures, coastal infrastructure and ecosystems. This paper analyses 10 years of in-situ measurements of significant wave height (H s ) and maximum wave height (H max ) from the ocean weather ship Polarfront in the Norwegian Sea. During the period 2000 to 2009, surface elevation was recorded every 0.59s during sampling periods of 30min. The H max observations scale linearly with H s on average. A widely-used empirical Weibull distribution is found to estimate average values of H max /H s and H max better than a Rayleigh distribution, but tends to underestimate both for all but the smallest waves. In this paper we propose a modified Rayleigh distribution which compensates for the heterogeneity of the observed dataset: the distribution is fitted to the whole dataset and improves the estimate of the largest waves. Over the 10-year period, the Weibull distribution approximates the observed H s and H max well, and an exponential function can be used to predict the probability distribution function of the ratio H max /H s . However, the Weibull distribution tends to underestimate the occurrence of extremely large values of H s and H max . The persistence of H s and H max in winter is also examined. Wave fields with H s >12m and H max >16m do not last longer than 3h. Low-to-moderate wave heights that persist for more than 12h dominate the relationship of the wave field with the winter NAO index over 2000–2009. In contrast, the inter-annual variability of wave fields with H s >5.5m or H max >8.5m and wave fields persisting over ~2.5 days is not associated with the winter NAO index. [Copyright &y& Elsevier]

Abstract: The nodal modulation of the diurnal (K 1 and O 1) and semi-diurnal (M 2 and K 2) tidal constituents at the coasts of the Mediterranean Sea and the eastern Atlantic is estimated and its spatial variability mapped. Fourteen hourly tide gauge records each spanning more than 18 years are considered in this analysis. Ten tide gauges are located in the Mediterranean Sea and four in the Bay of Biscay. The nodal modulation of the most energetic tidal constituent (M 2) reaches up to 5cm at the eastern Atlantic coasts, while within the Mediterranean Sea its modulation is in general less than 1.1cm. The largest K 2 nodal modulation found is 3.7cm in the eastern Atlantic coasts. In the Mediterranean Sea, smaller modulation amplitudes, ranging between 0.4 and 1.4cm are found. The K 1 tide constituent has the largest amplitude nodal modulation within the Mediterranean Sea of 1.9cm in the north Adriatic Sea, which is also larger than the modulation of this constituent at the eastern Atlantic coasts. The O 1 tide constituent has the highest amplitude nodal modulation (1.4cm) at the eastern Atlantic coasts. In the Mediterranean Sea the maximum value is 1cm in the north Adriatic Sea. The derived nodal modulations of the diurnal and semi-diurnal constituents follow, in general, the equilibrium tidal theory. The tidal amplitudes for all four components do not indicate significant secular trends for most tide gauges. The tidal phases indicate significant negative trends for all four tidal constituents within the central and eastern Mediterranean Sea. [Copyright &y& Elsevier]

Abstract: Estimates of extreme sea levels and return periods have been based mainly on hourly sampling rates. Technological development has enabled the sampling rates to increase and sampling rates of 5–10min are becoming increasingly common. In this paper we explore the relationship between extreme sea levels and estimated return periods based on hourly and shorter sampling periods in three tide-gauges one at the Atlantic coasts of Spain (Coruña), one in the western Mediterranean (Malaga) and one in the N. Adriatic (Trieste). Significant differences of several centimetres are found in the hourly and 5min extremes. These reflect in significant underestimation of the 50-year return levels which in Trieste reach 38cm. A theoretical relationship between the high and the low sampling rate of extremes is also tested. Thus updated 50-year return levels for the Mediterranean and the coasts of the Iberian peninsula are produced assuming that the differences identified in the various stations generalise to other tide-gauge (hourly) records for which hourly values have been analysed earlier. [Copyright &y& Elsevier]

Investigates the trends in the British Isles mean sea level data measured by tide gages. Analysis of data; Use of sea level indices; Recommendations for the development of tide gage and global positioning system recording.