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Abstract: This paper analyses 10years of in-situ measurements of significant wave height (Hs ) and maximum wave height (H max) from the ocean weather ship Polarfront in the Norwegian Sea. The 30-minute Ship-Borne Wave Recorder measurements of H max and Hs are shown to be consistent with theoretical wave distributions. The linear regression between H max and Hs has a slope of 1.53. Neither Hs nor H max show a significant trend in the period 2000–2009. These data are combined with earlier observations. The long-term trend over the period 1980–2009 in annual Hs is 2.72±0.88cm/year. Mean Hs and H max are both correlated with the North Atlantic Oscillation (NAO) index during winter. The correlation with the NAO index is highest for the more frequently encountered (75th percentile) wave heights. The wave field variability associated with the NAO index is reconstructed using a 500-year NAO index record. Hs and H max are found to vary by up to 1.42m and 3.10m respectively over the 500-year period. Trends in all 30-year segments of the reconstructed wave field are lower than the trend in the observations during 1980–2009. The NAO index does not change significantly in 21st century projections from CMIP5 climate models under scenario RCP85, and thus no NAO-related changes are expected in the mean and extreme wave fields of the Norwegian Sea. [Copyright &y& Elsevier]

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: Sea level observations from tide-gauge records located at the Adriatic coasts are analysed. The estimated sea level trends show variability in time and space. Spatial variability is assessed by estimating the differential trends by reference to Trieste. For many of the stations the differential trends become smaller than the corresponding error bars. This indicates that the land, atmospheric and oceanic contributors to sea level change are, at long scales, uniform in the basin. Observed trends in the longer records differ significantly for the periods before 1960 and after 1960. Atmospheric forcing has been a significant contribution in sea level variability for the period 1960 onwards. The atmospheric trends account for −0.8mm/year for the period 1960–2000. No significant atmospheric trends appear to be present at the period 1900–1960. Changes in the atmospheric forcing alone are not capable of explaining fully the difference in the sea level trends for the periods before and after 1960. Steric trends for the period 1960–2000 have also been identified. Their magnitude depends on the depth used for their estimation. Steric trends range between −0.4mm/year for the upper 100m to −2.4mm/year for the whole water column. The residual sea level after the removal of atmospheric and steric effects ranges between 2 and 3.4mm/year at various stations with an associated error bar of 1mm/year. This residual must be accounted for by land movements and incoming signals through the strait of Otranto. The coherence of high frequency sea level signals in the north part of the Adriatic Sea is also analysed for the period 2002–2005 using eight tide gauges. The first empirical orthogonal function contains 71% of the variability indicating that the known coherency at inter-annual and inter-decadal scales extends partly to the higher frequency too. [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]

Presents information on a study which used an acoustic doppler current profiler to measure the currents and estimate the water transport over the Camarinal Sill at the Strait of Gibraltar. Significance of the study; Details concerning the Canary Islands Azores Gibraltar Observations; Data and results.

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.