Magnar Reistad

Validation and intercomparisons of wave measurements and models during the EuroROSE experiments

The objective of the EuroROSE (European Radar Ocean Sensing) project was to combine area covering ground-based remote-sensed wave and current data with high-resolution numerical forecast models to provide nowcasts and forecasts for coastal marine operators. Two experiments to test and to demonstrate the system took place: one on the coast of Norway, north of Bergen in March 2000 and the second on the north coast of Spain at Gijon in October–November 2000. Qualitative and quantitative intercomparisons of the wave measurements and wave model products from these experiments are presented. These include measurements using the Wellen Radar (WERA) high-frequency (HF) radar, the WaMoS (Wave Monitoring System) Xband radar, a directional Waverider and output from the WAM wave model. Comparisons are made of the full directional spectra and of various derived parameters. This is the first-ever intercomparison between HF and X-band radar wave measurements and between either of these and WAM. It has provided a data set covering a much wider range of storm and swell conditions than had been available previously for radar wave-measurement validation purposes and has clarified a number of limitations of the radars as well as providing a lot of very useful radar wave data for future model-validation applications. The intercomparison has led to improvements in the data quality control procedures of both WaMoS and WERA. The two radar sytems measured significant wave height with mean biases of 3% and 6%, respectively, and mean direction differences of less than 2j in both cases. Limitations in the WAM model implementation are also discussed. D 2002 Elsevier Science B.V. All rights reserved.

Wave Extremes in the Northeast Atlantic

AbstractThe objective of this study is to compute 100-yr return value estimates of significant wave height using a new hindcast developed by the Norwegian Meteorological Institute. This regional hindcast covers the northeast Atlantic and spans the period 1958–2009.The return value estimates are based upon three different stationary models commonly applied in extreme value statistics: the generalized extreme value (GEV) distribution, the joint GEV distribution for the r largest-order statistic (rLOS), and the generalized Pareto (GP) distribution. Here, the qualitative differences between the models and their corresponding confidence intervals are investigated.

Assimilation of ERS SAR wave spectra in an operational wave model

Inverted wave spectra from ERS-1 synthetic aperture radar (SAR) image and wave mode products have been assimilated in the operational wave model for the ocean wave forecast service at the Norwegian Meteorological Institute. Elements of the operational system are explained briefly, and the impact of including the SAR wave data in the operational wave model runs is shown both for individual cases and as overall statistics. Although individual cases clearly show that the satellite observations are able to influence the forecast in a generally positive way, the average improvement is minor for the areas covered by the wave model. Reasons for this are the intermittency of the data, on the average small differences between inverted SAR and model first-guess wave spectra, and to some extent, limitations in the analysis method.

Wave height variations in the North Sea and on the Norwegian Continental Shelf, 1881–1999

Analyses of overlapping Norwegian Meteorological Institute (DNMI) hindcast squared monthly mean wind speeds and monthly mean significant wave heights show a linear relation. Based on available time series of wind speed, computed from sea level pressure (SLP), this enables us to establish long and consistent time series of monthly mean significant wave heights. Data sets of monthly mean 10 m wind speeds from nine locations in the North Sea and on the Norwegian Continental Shelf have been investigated. The data sets include World Meteorological Organization (WMO) data, 1881–1982, DNMI hindcast data, 1955–1999, and National Centers for Environmental Prediction/ National Center for Atmospheric Research (NCEP/NCAR) data, 1948–1999. From these time series it is evident that mean wave heights are subject to significant variations within a variety of time scales. There is a positive trend starting in the 1960s, mainly in northern parts of the North Sea, with significant regional variation. The increase is, however, not more dramatic than the decrease which occurred from 1881 and towards the beginning of the 20th century. Analyses of annual maximum significant wave heights based on 6 h values of DNMI data, 1955–1999, strongly indicate increasing wave heights and rougher wave climate at the stations off the coast of mid-Norway. At the other stations the trends are only weakly positive or not apparent at all. r 2003 Elsevier Science Ltd. All rights reserved.

Projected changes in significant wave height toward the end of the 21st century: Northeast Atlantic

Wind field ensembles from six CMIP5 models force wave model time slices of the northeast Atlantic over the last three decades of the 20th and the 21st centuries. The future wave climate is investigated by considering the RCP4.5 and RCP8.5 emission scenarios. The CMIP5 model selection is based on their ability to reconstruct the present (1971–2000) extratropical cyclone activity, but increased spatial resolution has also been emphasized. In total, the study comprises 35 wave model integrations, each about 30 years long, in total more than 1000 years. Here annual statistics of significant wave height are analyzed, including mean parameters and upper percentiles. There is general agreement among all models considered that the mean significant wave height is expected to decrease by the end of the 21st century. This signal is statistically significant also for higher percentiles, but less evident for annual maxima. The RCP8.5 scenario yields the strongest reduction in wave height. The exception to this is the north western part of the Norwegian Sea and the Barents Sea, where receding ice cover gives longer fetch and higher waves. The upper percentiles are reduced less than the mean wave height, suggesting that the future wave climate has higher variance than the historical period.

Comparisons of Wave Measurements from the Eurorose Fedje Experiment

The objective of the EuroROSE project was to combine area covering ground-based remote-sensed wave and current data with high resolution numerical forecast models to provide now- and forecasts for coastal marine operators. The first experiment to test and demonstrate the system took place on the coast of Norway, north of Bergen in March 2000. Qualitative and quantitative intercomparisons of the wave measurements and wave model products from this experiment are presented. These include measurements using the WERA HF radar, the WaMoS X-band radar, a directional waverider and output from the WAM wave model. Comparisons are made of the full directional spectra and of various derived parameters. This is the first ever intercomparison between HF and X-band radar wave measurements and between either of these and WAM.