Liliana Rusu

An operational wave forecasting system for the Portuguese continental coastal area

An operational system based on numerical models for wind and wave forecasting in the Portuguese coastal area is presented. It is based on the wave models WAM (WAve prediction Model) and SWAN (Simulating WAves Nearshore), driven by the wind fields provided by the atmospheric models GFS (Global Forecast System) from NCEP (National Centers for Environmental Prediction) and MM5 (Mesoscale Meteorological Model), respectively.The system is operational since October 2008 and runs automatically on Linux and Windows environments. Forecast products for four days ahead are produced daily. Graphical outputs of the wave parameters (fields and temporal series) are made available in a restricted domain internet site. The validation of the results provided by the forecasting system is carried out by performing comparisons with both wind and wave measurements.

Wind and wave modelling in the Black Sea

The performance of a wind-wave modelling system applied to the Black Sea basin is evaluated. The models considered are WRF (Weather Research and Forecasting) for wind and SWAN (Simulating Waves Nearshore) for waves. Model system simulations are carried out for a four-month period at the beginning of 2002. The accuracy of the predictions is further assessed by comparing the main modelled wind and wave parameters with both in-situ and remotely sensed measurements. In statistical terms, the performance of the modelling system is, in general, in line with the results obtained by other studies made in similar environments. Janssen’s formulation for the wind-wave generation, recently improved in SWAN, makes this approach the most effective in the Black Sea from the point of view of the numerical accuracy. Subsequently, the geographical variability of the model predictions is assessed together with an evaluation of the wave model results in the spectral space.

Local data assimilation scheme for wave predictions close to the Portuguese ports

The present work describes developments in improving the wave predictions close to the most important Portuguese ports. A wave modelling system was implemented and focused on the Portuguese continental nearshore. It is based on WAM, for the wave generation and on SWAN, for the coastal transformation. The system has been operational since October 2008 and delivers daily forecast products corresponding to four days ahead. Validations of the results were performed against both buoys and satellite data. In order to improve the wave predictions in the nearshore areas neighbouring the Portuguese harbours targeted, two new steps were performed and they are presented in this work. Firstly, high resolution computational domains covering the vicinities of the ports were connected to the wave prediction system. As a further step, a data assimilation scheme was also implemented. The procedure considered uses the data provided by the buoys that are operating in the vicinity of the main Portuguese ports and gives real time estimations of the significant wave height. A recursive successive correction algorithm was developed to improve the model predictions close to the locations of the buoys. The assimilation of the buoy data was performed on three levels – time, geographical and spectral spaces. This procedure allows corrections to the boundary conditions considered for the high resolution computational domains implemented in the vicinity of the harbour areas. The results show that data assimilation makes the wave prediction system more accurate, particularly in conditions where waves are usually less well modelled such as during storms.

Influence of the Wind Fields on the Accuracy of Numerical Wave Modelling in Offshore Locations

The influence of the wind field resolution in the accuracy of the wave predictions is studied using spectral numerical models in highly non-stationary situations. The main area of interest is the port of Sines, located in the Portuguese continental coastal environment south of Lisbon. An implementation of the MM5 atmospheric model was developed for the area of study, starting from a large area of the Atlantic Ocean and nesting successively with finer grid towards the point of interest, so as to provide wind fields with increasing level of detail. The SWAN model was forced with wind fields simulated by different models and with different resolutions. A wave rider type directional buoy located offshore the Sines port at approximately 100 meters water depth was used as check point. In a first approach, two different wind fields simulated by REMO and MM5 were considered for forcing the SWAN based transformation module. Both wind fields have a spatial resolution of 0.5 degrees and were obtained using the global NCEP reanalysis data as wind driver. Initial wave boundary conditions are provided by WAM simulations for the entire North Atlantic basin. Afterwards, three successive SWAN areas were implemented. The three spatial resolutions defined for these SWAN computational domains were 0.05, 0.02 and 0.005 degrees. Corresponding special resolutions for the wind fields produced by MM5 ranged from 0.15 to 0.015 degrees. Simulations were performed from the beginning of December 2000 till the end of February 2001, which is one of the most energetic periods registered close to this coast and the results in terms of significant wave height, mean period and wave direction were compared with the in situ measured data.Copyright

Evaluation of the wind energy potential along the Mediterranean Sea coasts

The objective of the present work is to evaluate the wind potential in the nearshore of the Mediterranean Sea. Thus, a comprehensive picture of the wind conditions is provided by considering 15-year of cumulative information coming from remotely sensed data and from two numerical models. These are provided by the European Center for Medium-Range Weather Forecasts (ECMWF) and the National Centers for Environmental Prediction (NCEP). Since most of the offshore wind turbines usually operate at about 80 m height, the initial wind conditions (reported at 10 m) were adjusted to this height and various wind parameters were evaluated. Besides these, the characteristics of the Vestas V90-3.0MW wind turbine were used to identify the efficiency of this type of generator in terms of operating capacity, rated capacity and capacity factor. From the analysis of these data, it can be noticed that more energetic wind conditions are encountered in the northern part of the basin (close to the Spain–France border and south of Greece) and also in the southern part of the sea (Tunisia sector). In the final part of the paper, based on satellite measurements, the wind conditions (monthly and seasonal) coresponding to some representative locations in the Mediterranean Sea were compared to those from several offshore locations where wind farms already operate.

A joint evaluation of wave and wind energy resources in the Black Sea based on 20-year hindcast information

In this study, a joint evaluation of the wind and wave energy over the Black Sea basin is performed for a 20-year time interval. The importance of such a study is enhanced by the fact that the potential of the wave energy cannot be considered high compared to the large oceans, while the wind conditions over the Black Sea can be considered significant in various areas. The wind fields from the U.S. National Centers for Environmental Prediction were used for wind energy estimation. A high resolution wave hindcast database, as resulted from the simulations performed with the Simulating WAves Nearshore model, is used for a detailed analysis of the wave energy potential in the basin of the Black Sea. The reliability of the wave simulation results was increased by means of some data assimilation methodologies. The variability and complementarity of these renewable energy resources was investigated. The analysis showed that there exist some suitable areas for combined wind-wave exploitation.

Data assimilation with the ensemble Kalman filter in a high-resolution wave forecasting model for coastal areas

ABSTRACT The present work describes a post-processing implementation of the ensemble Kalman filter (EnKF) that is used to improve the wave predictions in a high-resolution Simulating Waves Nearshore computational domain implemented in the Portuguese continental nearshore. The approach consists in applying the EnKF algorithm directly to the parameter to be predicted, replacing the observation at the forecast time by the analysis previously obtained. This technique has already led previously to good results when applied to the significant wave height, and an improved algorithm is used now to increase the accuracy both of the predicted significant wave height and mean wave period. The results of this new approach indicate a visible enhancement of the wave predictions reliability. It can be thus concluded that the work continues the effort to find a better post-processing algorithm in order to improve the results of the numerical wave models near the harbour areas by means of data assimilation methods.

Numerical Modelling of the Wave Propagation Close to the Sacalin Island in the Black Sea

The target area of the present work is the nearshore neighbouring the Sacalin Island in the Black Sea, right off the Danube Delta and close to the Saint George branch of the Danube River. Being a newly formed island, this is a very special coastal environment. Moreover, because it has a great variety of rare fauna, the area was declared as an ecological reserve. A multilevel wave modelling system, based on the Simulating Waves Nearshore (SWAN) spectral model, was focused on the target area. In the final computational domain, with the highest resolution in the geographical space, the effect of the current induced by the Danube River outflow was also accounted for in the modelling process. The wave propagation patterns characteristic to this side of the sea, together with some parameters related to the shoreline conditions, were evaluated. Four different case studies were considered for a detailed analysis. The results provided by the modelling system revealed two antagonist processes. The first process, which is dominant, and that can be defined as a constructive process, corresponds to the waves coming from the northeast. The second process, which can be defined as a destructive process, corresponds to the conditions of extremely strong storms with waves coming from the southeast. Although such situations are quite rare, they might occur however from time to time and this is actually the case that generated in the winter of 2013 a strong penetration of the waves through the Sacalin Island changing the coastal configuration.