KARADENİZ DALGA MODELLEMESİ

Van vledder, G.Ph., Akpınar, A., Wave model predictions in the Black Sea: Sensitivity to wind fields. Applied Ocean Research, Volume 53, October 2015, Pages 161–178.
 

This paper evaluates the impact of using different wind field products on the performance of the third generation wave model SWAN in the Black Sea and its capability for predicting both normal and extreme wave conditions during 1996. Wind data were obtained from NCEP CFSR, NASA MERRA, JRA-25, ECMWF Operational, ECMWF ERA40, and ECMWF ERA-Interim. Wave data were obtained in 1996 at three locations in the Black Sea within the NATO TU-WAVES project. The quality of wind fields was assessed by comparing them with satellite data. These wind data were used as forcing fields for the generation of wind waves. Time series of predicted significant wave height (Hmo), mean wave period (Tm02), and mean wave direction (DIR) were compared with observations at three offshore buoys in the Black Sea and its performance was quantified in terms of statistical parameters. In addition, wave model performance in terms of significant wave height was also assessed by comparing them against satellite data.

The main scope of this work is the impact of the different available wind field products on the wave hindcast performance. In addition, the sensitivity of wave model forecasts due to variations in spatial and temporal resolutions of the wind field products was investigated. Finally, the impact of using various wind field products on predicting extreme wave events was analyzed by focussing on storm peaks and on an individual storm event in October 1996. The numerical results revealed that the CFSR winds are more suitable in comparison with the others for modelling both normal and extreme events in the Black Sea. The results also show that wave model output is critically sensitive to the choice of the wind field product, such that the quality of the wind fields is reflected in the quality of the wave predictions. A finer wind spatial resolution leads to an improvement of the wave model predictions, while a finer temporal resolution in the wind fields generally does not significantly improve agreement between observed and simulated wave data.

 

Akpınar, A., Ponce de Leon, S., An assessment of the wind re-analyses in the modelling of an extreme sea state in the Black Sea. Dynamics of Atmospheres and Oceans, Volume 73, March 2016, Pages 61–75.
 

This study aims at an assessment of wind re-analyses for modelling storms in the Black Sea. A wind-wave modelling system (Simulating WAve Nearshore, SWAN) is applied to the Black Sea basin and calibrated with buoy data for three recent re-analysis wind sources, namely the European Centre for Medium-Range Weather Forecasts Reanalysis-Interim (ERA-Interim), Climate Forecast System Reanalysis (CFSR), and Modern Era Retrospective Analysis for Research and Applications (MERRA) during an extreme wave condition that occurred in the north eastern part of the Black Sea. The SWAN model simulations are carried out for default and tuning settings for deep water source terms, especially whitecapping. Performances of the best model configurations based on calibration with buoy data are discussed using data from the JASON2, TOPEX-Poseidon, ENVISAT and GFO satellites. The SWAN model calibration shows that the best configuration is obtained with Janssen and Komen formulations with whitecapping coefficient (Cds) equal to 1.8e−5 for wave generation by wind and whitecapping dissipation using ERA-Interim. In addition, from the collocated SWAN results against the satellite records, the best configuration is determined to be the SWAN using the CFSR winds. Numerical results, thus show that the accuracy of a wave forecast will depend on the quality of the wind field and the ability of the SWAN model to simulate the waves under extreme wind conditions in fetch limited wave conditions.

 

 

Akpınar, A., Bingölbali, B., Long-term variations of wind and wave conditions in the coastal regions of the Black Sea. Natural Hazards, Volume 84, October 2016, Pages 69–92.
 

Spatial and temporal variations of significant wave height (Hm0) and wind speed (WS) at selected locations over the Black Sea are studied based on 31-year long-term SWAN simulations forced with Climate Forecast System Reanalysis dataset. The objective was to investigate whether or not there is a possible increase in wind and wave conditions along the Black Sea shelves. Wind and wave parameters are obtained at 33 locations enclosing the Black Sea coast line from SWAN simulations and annual mean and maximum Hm0 and WS values as the climatological variables are computed for these locations. Using these data, long-term trends and their significance at these locations are investigated based on Mann–Kendall trend test. To quantify the trends, Sen’s slope estimator and least square linear regression (the slope of the linear best-fit curve) are used. Variation of monthly mean Hm0 and WS values at these locations are also discussed. Besides, decadal variations of these four climatological variables at 33 locations are studied. The results show that higher wind speeds and wind wave heights are monitored in the winter season in all locations, while during the summer months, there is a significant drop in both Hm0 and WS. In the western Black Sea, average Hm0 is highest (about 1.02 m) at locations 23 and 25. During the period of 1979 and 2009, it is determined that mean WS has a weak significant increasing trend (maximum 1.29 cm/s/year) along the north-eastern coasts of Turkey and the Crimean peninsula, while there is no statistically significant Hm0 trend in the Black Sea except at location 11, offshore Sochi in the north-eastern part of the Black Sea. A weak decreasing trend (maximum 0.24 cm/year) in mean Hm0 is seen along the north-western coasts of Turkey, while maximum Hm0 and WS show no statistically significant increasing or decreasing trend except location 2, which has a weak significant increasing trend for maximum WS. All the trends at other locations for four variables are statistically insignificant, and they have no trend. The most significant difference is observed in maximum WS as 6.14 m/s in different decades in the north-western part of the Black Sea. The difference in the decades is very low in mean Hm0 at all locations. Mean wind and wave conditions at all locations have almost negligible difference, whereas decadal variations of maximum Hm0 and WS show high differences. This may be probably due to storms and cyclones conditions.

 

 

Akpınar, A., Bingölbali, B., Van vledder, G.Ph., Wind and wave characteristics in the Black Sea based on the SWAN wave model forced with the CFSR winds. Ocean Engineering, Volume 126, November 2016, Pages 276–298.
 

Wind and wave characteristics and their long-term variability in the Black Sea over a period of 31 years are investigated in this study. The state-of-the art spectral wave model SWAN is implemented to perform a 31- year wave hindcast in the area of interest. The simulation results are used to assess the inter-annual variability and long-term changes in wind and wave climate in the Black Sea for the period 1979–2009. The SWAN model is forced with the Climate Forecast System Reanalysis (CFSR) winds. The model is calibrated and validated against available wave measurements at six offshore and near-shore locations spread over a large region in the Black Sea. The calibration was performed by tuning parameters in the white-capping and wind input formulations against available measurements for 1996 at three offshore locations (Gelendzhik, Hopa, and Sinop). The validation was carried out using measured data, at Gelendzhik, Hopa, and Sinop offshore locations, Gloria drilling platform and Karaburun and Filyos near-shore locations. From the 31-year simulation results, the long-term spatial distributions and changes of the mean wind and mean and maximum wave characteristics and their inter-annual variabilities were determined. The calibration improved SWAN model performance by 11.6% for Hm0 and 3.3% for Tm02 on average at three locations. The mean annual significant wave height (Hm0) and mean wind speed (WS) indicate the occurrence of higher wave heights and wind speeds in the western Black Sea compared to the south eastern coasts of the Black Sea. The coefficient of variation over the Black Sea for Hm0 and WS shows that the variability for Hm0 is higher than that of WS. It is also observed that the variability for Hm0 is higher in areas (such as offshore Gelendzhik, Russia) where the variability of WS is high. Besides, the storms mentioned in the previous studies (such as Galabov and Kortcheva, 2013; Tarakcioglu et al., 2015) are observed in four interesting characteristic areas with maximum Hm0 determined in this study over the Black Sea.

 

Akpınar, A., Bingölbali, B., Van vledder, G.Ph., Long-term analysis of wave power potential in the Black Sea, based on 31-year SWAN simulations. Ocean Engineering, Volume 130, January 2017, Pages 482–497.
 

This study analyzes the wave energy potential in the Black Sea based on long-term model simulations. A dataset covering the period of 1979–2009 is produced using a calibrated numerical wave prediction model (SWAN). This dataset was analyzed in detail to determine the wave energy potential to enable a reliable and optimal design of wave energy conversion devices in the Black Sea. This analysis provides information on the long-term variability as well as on the annual, seasonal and monthly averages. The analysis of the hindcast results is conducted on a spatial and a location scale. The spatial analysis provides information for the entire Black Sea on; the averaged mean wave energy flux over the period 1979–2009, and the decades 1980–1989, 1990–1999, and 2000–2009, seasonal and monthly averages of wave energy flux during 31 years, variability indices for the 1979−2009 period, and variabilities on monthly and seasonality basis based on inter-annual averages during 31 years. The location scale considered nine locations providing information on; wave power roses, probabilities of occurrence and cumulative distribution functions of wave power in different power ranges, variation and trend of yearly average wave power, seasonal average wave power and its annual variations, and quantities of wave energy flux for different Hm0 and Tm-10 ranges. Results show that areas with the highest wave energy potential are located in the south-western part of the Black Sea. These areas are; Burgas – Rezovo (BR) with an average annual total energy of 43.9 MW h/m followed by Dolni Chiflik – Shkorpilovtsi (DCS) with 37.3 MW h/m and Istanbul – Alacali (IA) with 36.1 MW h/m.