The evolution of the upwelling regime off west Portugal between 1941 and 2000 was investigated. Monthly averages of the longshore (meridional) wind component at four coastal stations of the Institute for Meteorology were computed and subject to linear regression analysis. Several comparisons were made among stations until a final regression model was reached. The resulting residuals were checked for the presence of red noise, and pairwise correlation coefficients were estimated for residuals of different stations. To complement this study, monthly sea-surface temperature averages were computed for six regions off west Portugal and subject to a similar procedure. In both analyses, it was concluded that the Portuguese upwelling regime has weakened since the 1940s. The waning of the northerly, upwelling-favourable winds was significant throughout the traditional upwelling season (April-September). Sea-surface temperature showed a steady year-round increase from 1941 onwards, in both offshore (+0.002°C/year) and coastal (+0.010°C/year) regions.

The nearshore wave energy resource in Portugal has been assessed through the development of ONDATLAS. This is an electronic atlas, compatible with Internet access, containing comprehensive wave climate and wave energy statistics for 78 points at about 20m water depth spaced variably ca.5-30km, 5 points at deep water, and 2 points at open ocean locations. The data were produced by a third-generation wind-wave model, complemented by an inverse-ray model that computes the directional spectra transformation from open ocean to the nearshore. Shoaling, refraction, bottom dissipation, and shelter by the coastline and/or neighboring islands are taken into account. ONDATLAS statistics comprise yearly and monthly values, variability and probability data for significant wave height, energy (mean) period, peak period and wave power, and directional histograms for wave and power direction. Joint probability distributions for various combinations of the above parameters are also available, as well as extreme values and return period for wave height and period parameters. A summary of the detailed verification of this model using long-term buoy measurements at four sites is presented. The main characteristics of ONDATLAS are described. The strong spatial variability that wave conditions exhibit at the coastal area are illustrated and a brief assessment of the nearshore resource at the Portugal mainland is presented.

No abstract

The goals of the present work are to compare TOPEX/Poseidon (T/P) significant wave height (HS) with buoy data off the West Coast of Portugal and to evaluate the performance of wave period algorithms. Altimeter and buoy data are compared according to co-location criteria proposed in literature. A new method for analysing the variation of quality parameters in the space and time domains is presented. The use of wave group velocity as a way of relating space and time lags is also proposed. Local calibrations for T/P HS are computed, with the interval of degradation of TOPEX altimeter considered separately. It is found that an algorithm for mean wave zero-crossing period (ZT) can be used in the region under consideration, the root mean square error (Erms) being lower than 0.7 s if local coefficients are used.

In this paper a methodology for assessing the accuracy of full directional wave spectra produced by wind-wave models is presented and tested. This methodology includes graphical and parametric comparisons of model directional spectra against data obtained from directional buoys. Results of the verification of 3rd generation wind-wave models using directional buoy data show that in general the accuracy of model directional results is good. In addition it was found that this methodology is well suited to identify the occurrence of different wave systems in the same sea state, namely swells within the same frequency band but with different origins.

The nearshore wave energy resource in Portugal has been assessed through the development of ONDATLAS. This is an electronic atlas, compatible with Internet access, containing comprehensive wave climate and wave energy statistics for 78 points at about 20 m water depth spaced variably ca. 5 km to 30 km, 5 points at deep water and 2 points at open ocean locations. The data were produced by a third-generation wind-wave model, complemented by an inverse-ray model that computes the directional spectra transformation from open ocean to the near-shore. Shoaling, refraction, bottom dissipation and shelter by the coastline and/or neighbouring islands are taken into account. ONDATLAS statistics comprise yearly and monthly values, variability and probability data for significant wave height, energy (mean) period, peak period and wave power, and directional histograms for wave and power direction. Joint probability distributions for various combinations of the above parameters are also available, as well as extreme values and return period for wave height and period parameters. A summary of the detailed verification of this model using long-term buoy measurements at four sites is presented. The main characteristics of ONDATLAS are described. The strong spatial variability that wave conditions exhibit at the coastal area are illustrated and a brief assessment of the nearshore resource at the Portugal mainland is presented.