Hindcast Wind Research Articles

Assessment of the use of scatterometer wind data to force wave models in the North Atlantic Ocean

The present work uses for the first time scatterometer wind fields to force a wave model and compares the accuracy of the resulting wave conditions with the ones obtained when using two different sources of hindcast wind fields forcing the same wave spectral model in the Atlantic Ocean. For this purpose, a 5-year hindcast (2010–2014) is performed with the wave spectral model SWAN for the Madeira and Azores archipelagos. The model uses as input the bathymetry from GEBCO, the wave boundary conditions from the WAVEWATCH III wave model provided by Ifremer and winds from the ERA-Interim and ERA5 databases, and remotely sensed winds from scatterometers. A quantitative analysis of the results is performed, and the numerical results are validated against altimeter data and buoy measurements. Globally, ERA-Interim, ERA5 and scatterometer wind data provided similar accuracy of the generated wave fields, as expressed in the error statistics, which are very close to each other, but in the case of extreme events, the scatterometer data reveals more intense winds and consequently lead to sea states with higher significant wave height. This is more visible in the Azores area than in Madeira. The results demonstrate that, in general, the significant wave height is well reproduced by SWAN.

Evaluation of regional climate models and future wave characteristics in an enclosed sea: A case study of the Black Sea

The main objective of this study is to evaluate a possible climate change impact on wave climate in an enclosed sea (Black Sea) until the end of the 21st century. To achieve the goal, the wave data are generated from a third-generation wave model forced with the widely used reanalysis data (Climate Forecast System Reanalysis), and the hindcast wind fields simulated by a Regional Climate Model, namely Rossby Centre regional atmospheric model (version RCA4). The pattern of change in the wave climate is discussed by comparing the historical (1970–2005) with the future for periods 2021–2060 and 2061–2100 under two climate scenarios. The projected changes in the mean wave characteristics are characterized by an increase in the near future for both RCP scenarios that is more prominent under RCP8.5 scenario in the eastern basin. The middle future under RCP8.5 scenario suggests more significant changes in annual mean values than those obtained under RCP4.5 scenario. In the context of climate change, the possible effects are more prominent on extreme wave heights. For example, the increases in the wave heights for the 100-year return period reach the value of 5% and 25% in the western and eastern Black Sea, respectively.

Multivariate spatial conditional extremes for extreme ocean environments

The joint extremal spatial dependence of wind speed and significant wave height in the North East Atlantic is quantified using Metop satellite scatterometer and hindcast observations for the period 2007–2018, and a multivariate spatial conditional extremes (MSCE) model, ultimately motivated by the work of Heffernan and Tawn (2004). The analysis involves (a) registering individual satellite swaths and corresponding hindcast data onto a template transect (running approximately north-east to south-west, between the British Isles and Iceland), (b) non-stationary directional-seasonal marginal extreme value analysis at a set of registration locations on the transect, (c) transformation from physical to standard Laplace scale using the fitted marginal model, (d) estimation of the MSCE model on the set of registration locations, and assessment of quality of model fit. A joint model is estimated for three spatial quantities: Metop wind speed, hindcast wind speed and hindcast significant wave height. Results suggest that, when conditioning on extreme Metop wind speed, extremal spatial dependence for all three quantities decays over approximately 600–800 km.

Mapping of the levelised cost of energy for floating offshore wind in the European Atlantic

Understanding the spatial variation of the levelised cost of energy (LCOE) of offshore wind is fundamental for identifying potential areas for the development of this technology. With this in view, this paper presents a large-scale mapping of the LCOE of floating offshore wind over the European Atlantic, with a focus on floating semi-submersible platforms. The energy production is estimated accurately at every site using hindcast wind data combined with the power curve of an exemplar wind turbine. Furthermore, this work presents an analysis of the different costs incurred in the lifetime of the project using expressions depending on site-specific variables, i.e., water depth and distance to shore. The results highlight the paramount influence of the energy production and, therefore, the wind resource on the final cost of energy. The lowest LCOE values (∼95 €/MWh) correspond to the areas where the wind resource is most abundant: off Great Britain and Ireland, in the North Sea and off NW Spain. The influence of the resource leads inevitably to LCOE values somewhat higher off Portugal and Norway (∼125 €/MWh), and much higher in the Gulf of Biscay and south of the Iberian Peninsula (>160 €/MWh). Within regions with a similar resource, e.g., the North Sea (LCOE in the range 95–135 €/MWh), the distance to shore is found to be the main variable affecting the LCOE. By comparison, the costs related to water depth (primarily, mooring costs) are of little significance – unlike with bottom-fixed technologies.

Surface Currents Derived from SAR Doppler Processing: An Analysis over the Naples Coastal Region in South Italy

Several studies have shown the capabilities of Synthetic Aperture Radar to map sea currents in ocean regions mainly characterized by large flows. We consider the well known method based on the analysis of the Doppler Centroid. The Doppler, as, in general, the scattering from the sea, is sensitive to several phenomena, occurring between the upper ocean and atmospheric boundary layers. To investigate such phenomena, we considered the combined use of both ENVISAT calibrated amplitude and Doppler data in conjunction with hindcast wind information provided by atmospheric models as well as Wind and Doppler Geophysical Model Functions (W/D-GMF) developed, in the literature, for C-Band systems. This integrated analysis for the interpretation of the Doppler surface currents measurements was carried out on a case study located in the Mediterranean Sea which is characterized by a general low circulation regime: specifically, the coastal region around the city of Naples. In this case study, we show that generally, wind plays a direct significant role in the observed Doppler surface current. The availability of an oceanographic numerical model for one of the analyzed cases also allowed us to attempt to interpret the effect of the typical thermohaline circulation pattern on the Doppler anomaly.

An Improved Method to Estimate the Probability of Oil Spill Contact to Environmental Resources in the Gulf of Mexico

The oil spill risk analysis (OSRA) model is a tool used by the Bureau of Ocean Energy Management (BOEM) to evaluate oil spill risks to biological, physical, and socioeconomic resources that could be exposed to oil spill contact from oil and gas leasing, exploration, or development on the U.S. Outer Continental Shelf (OCS). Using long-term hindcast winds and ocean currents, the OSRA model generates hundreds of thousands of trajectories from hypothetical oil spill locations and derives the probability of contact to these environmental resources in the U.S. OCS. This study generates probability of oil spill contact maps by initiating trajectories from hypothetical oil spill points over the entire planning areas in the U.S. Gulf of Mexico (GOM) OCS and tabulating the contacts over the entire waters in the GOM. Therefore, a probability of oil spill contact database that stores information of the spill points and contacts can be created for a given set of wind and current data such that the probability of oil spill contact to any environmental resources from future leasing areas can be estimated without a rerun of the OSRA model. The method can be applied to other OCS regions and help improve BOEM’s decision-making process.

Estimation of the Near Future Wind Power Potential in the Black Sea

The main objective of the present study is to quantify the recent past and explore the near future wind power potential in the Black Sea basin, evaluating the possible changes. Furthermore, an analysis of the wind climate in the target area was also performed. The wind resources have been assessed using the wind fields provided by various databases. Thus, the wind power potential from the recent past was assessed based two different sources covering each one the 30-year period (1981–2010). The first source is the ERA-Interim atmospheric reanalysis provided by the European Centre for Medium-Range Weather Forecasts (ECMWF), while the second source represents the hindcast wind fields simulated by a Regional Climate Model (RCM) and provided by EURO-CORDEX databases. The estimation of the near future wind power potential was made based on wind fields simulated by the same RCM under future climate projections, considering two Representative Concentration Pathways (RCPs) scenarios (RCP4.5 and RCP8.5) and they cover also a 30-year time interval (2021–2050). Information in various reference points were analyzed in detail. Several conclusions resulted from the present work. Thus, as regards the mean wind power potential in winter season, in 51% of the locations a significant increase is projected in the near future (both scenarios). Besides providing a detailed description of the wind conditions from the recent past over the Black Sea basin considering two major sources, the novelty of the present work consists in the fact that it gives an estimation of the expected wind climate in the target area for the near future period and at the same time an evaluation of the climate change impacts on the wind speed and wind power potential.

Forecasting Storm Surge and Inundation: Model Validation

Abstract Coastal regions are increasingly vulnerable to damage from storm surge and inundation. Delft3D is used by the Naval Oceanographic Office to model the ocean dynamics in the near shore. In this study, the performance of Delft3D in predicting the surge and inundation during Hurricane Ike, which impacted the northern Gulf of Mexico in September 2008, is examined. Wave height, water level, and high-water mark comparisons with a number of observations confirm that the model does well in predicting the surge and inundation during extreme events. The impact of using forecast winds based on the best-track data as opposed to hindcast winds is also investigated, and it is found that the extent of inundation is represented reasonably well with the forecast winds. In Delft3D, waves can be coupled to the hydrodynamic component using the radiation stress gradient method or the dissipation method. Comparing the results of using the two shows that for low-resolution grids such as that needed for a forecast model the dissipation method works better at reproducing the water levels and inundation.

Downscaling wind and wavefields for 21st century coastal flood hazard projections in a region of complex terrain

AbstractWhile global climate models (GCMs) provide useful projections of near‐surface wind vectors into the 21st century, resolution is not sufficient enough for use in regional wave modeling. Statistically downscaled GCM projections from Multivariate Adaptive Constructed Analogues provide daily averaged near‐surface winds at an appropriate spatial resolution for wave modeling within the orographically complex region of San Francisco Bay, but greater resolution in time is needed to capture the peak of storm events. Short‐duration high wind speeds, on the order of hours, are usually excluded in statistically downscaled climate models and are of key importance in wave and subsequent coastal flood modeling. Here we present a temporal downscaling approach, similar to constructed analogues, for near‐surface winds suitable for use in local wave models and evaluate changes in wind and wave conditions for the 21st century. Reconstructed hindcast winds (1975–2004) recreate important extreme wind values within San Francisco Bay. A computationally efficient method for simulating wave heights over long time periods was used to screen for extreme events. Wave hindcasts show resultant maximum wave heights of 2.2 m possible within the Bay. Changes in extreme over‐water wind speeds suggest contrasting trends within the different regions of San Francisco Bay, but 21th century projections show little change in the overall magnitude of extreme winds and locally generated waves

Evaluation of two spectral wave models for wave hindcasting in the Mackenzie Delta

Climate change, reduced sea ice and increased ice-free waters over extended areas for longer summer periods potentially lead to increased wave energy in the Beaufort Sea (Wang et al., 2015; Khon et al., 2014) [1,2], which is a major concern for coastal and offshore engineering activities. We compare two spectral wave models SWAN (Simulating WAves Nearshore) and MIKE 21 SW (hereafter MIKE21) in simulations of storm-generated waves in the Mackenzie Delta region of the southern Beaufort Sea. SWAN model simulations are performed using two nested grids system, whereas MIKE21 uses an unstructured grid system. Forcing fields are defined by hourly hindcast winds. Moving ice edge boundaries are incorporated during storm simulations. Modelled wave spectra from four storms are shown to compare well with field observations. Two established whitecapping formulations in SWAN are investigated: one dependent on mean spectral wave steepness, and the other on local spectral steepness. For the Beaufort Sea study area, we suggest that SWAN wave simulations using the latter local spectral steepness formulation are better than those using the former mean spectral steepness formulation. MIKE21 simulations also tend to agree with SWAN results using the latter whitecapping formulation.

The effect of wind variability and domain size in the Persian Gulf on predicting nearshore wave energy near Doha, Qatar

Wind-wave generation and propagation processes in the Persian Gulf during October and November 2010 were simulated with a third-generation numerical wave model. Several different numerical configurations were used, with output at an instrument pier near the Doha, Qatar coast used to examine the efficacy of these approaches. Three wind sources were used: two sets of wind hindcasts which span the extent of the Gulf; and 15-min averaged winds measured at the pier and distributed as a spatially constant wind field for the model. Domain size, and its nearshore effect, was examined by using three domains of varying sizes and resolutions. Boundary conditions from nesting between larger and smaller domains were also varied to determine how incoming wave conditions from larger domains located further offshore can affect nearshore wave conditions. The effect of wind field, boundary conditions and domain size were quantified by examining the histograms, correlation coefficient, and root-means-square differences, of various parameters (significant wave height, wave height due to swells, peak period, and mean approach direction) for each wave condition at the site. It is determined that significant wave heights at the pier are strongly dependent on the wind fields used and also have some dependence on the use of boundary conditions, while nearshore peak periods are very dependent on the use of boundary conditions. Furthermore, the distribution of wave mean angles tends to be narrower for cases in which hindcast winds and boundary conditions were used. These results are consistent with the sporadic appearance of a strong, unidirectional wind field over the Persian Gulf basin.

Nearshore SWAN model sensitivities to measured and modelled offshore wave scenarios at an embayed beach compartment, NSW, Australia

Spectral wave modelling is a common dynamical approach to transform offshore wave climates to the nearshore zone for coastal hazard definition and engineering design. Knowledge of model limitations and sensitivities are thus of paramount importance to appropriate use for coastal engineering. This study reports the calibration and nearshore sensitivities of a SWAN model at Wamberal-Terrigal on the central New South Wales coast, when the model is forced with wave information from a regional WaveWatch III (WW-III) model, compared to model forcing from simultaneous offshore buoy observations. SWAN achieved good results for nearshore wave heights (R2 = 0.86, RMSE = 0.2 m), but under-estimated mean wave period by approximately 1 s. Default SWAN physics were found to be largely appropriate. The inclusion of hindcast winds introduced a systematic over-estimation of high frequency (low period) wind-sea but improved the shape of the wave period distribution. Transformations of WW-III spectra through SWAN suggests that oblique swell is under-represented by WW-III at this location, with only wave directions between 80 degrees and 150 degrees accounted for. In modelling cases, the long shore transport component, typically driven by oblique long-period wave energy, would likely be under-estimated while shorter-period wind-waves that favour cross-shore sediment transport is preferenced.

Nearshore SWAN model sensitivities to measured and modelled offshore wave scenarios at an embayed beach compartment, NSW, Australia

Spectral wave modelling is a common dynamical approach to transform offshore wave climates to the nearshore zone for coastal hazard definition and engineering design. Knowledge of model limitations and sensitivities are thus of paramount importance to appropriate use for coastal engineering. This study reports the calibration and nearshore sensitivities of a SWAN model at Wamberal-Terrigal on the central New South Wales coast, when the model is forced with wave information from a regional WaveWatch III (WW-III) model, compared to model forcing from simultaneous offshore buoy observations. SWAN achieved good results for nearshore wave heights (R2 = 0.86, RMSE = 0.2 m), but under-estimated mean wave period by approximately 1 s. Default SWAN physics were found to be largely appropriate. The inclusion of hindcast winds introduced a systematic over-estimation of high frequency (low period) wind-sea but improved the shape of the wave period distribution. Transformations of WW-III spectra through SWAN suggests that oblique swell is under-represented by WW-III at this location, with only wave directions between 80° and 150° accounted for. In modelling cases, the long shore transport component, typically driven by oblique long-period wave energy, would likely be under-estimated while shorter-period wind-waves that favour cross-shore sediment transport is preferenced.

Circulation on the central Bering Sea shelf, July 2008 to July 2010

We examine the July 2008 to July 2010 circulation over the central Bering Sea shelf using measurements at eight instrumented moorings, hindcast winds and numerical model results. At sub‐tidal time scales, the vertically integrated equations of motion show that the cross‐shelf balance is primarily geostrophic. The along‐shelf balance is also mainly geostrophic, but local accelerations, wind stress and bottom friction account for 10–40% of the momentum balance, depending on season and water depth. The shelf exhibits highly variable flow with small water column average vector mean speeds (<5 cm s−1). Mean/peak speeds in summer (3–6 cm s−1/10–30 cm s−1) are smaller than in winter and fall (6–12 cm s−1/30–70 cm s−1). Low frequency flows (<1/4 cpd) are horizontally coherent over distances exceeding 200 km. Vertical coherence varies seasonally, degrading with the onset of summer stratification. Because effects of heating and freezing are enhanced in shallow waters, warm summers increase the cross‐shelf density gradient and thus enhance northward transport; cold winters with increased ice production and brine rejection increase the (now reversed) cross‐shelf density gradient and enhance southward transport. Although the baroclinic velocity is large enough to influence seasonal transports, wind‐forced Ekman dynamics are primarily responsible for flow variations. The system changes from strong northward flow (with coastal convergence) to strong southward flow (with coastal divergence) for northerly and easterly winds, respectively. Under northerly and northwesterly winds, nutrient‐rich waters flow toward the central shelf from the north and northwest, replacing dilute coastal waters that are carried south and west.

A comparison of remote vs. local influence of El Niño on the coastal circulation of the northeast Pacific

Abstract A set of spatially nested circulation models is used to explore interannual change in the northeast Pacific (NEP) during 1997–2002, and remote vs. local influence of the 1997–1998 El Nino on this region. Our nested set is based on the primitive equations of motion, and includes a basin-scale model of the north Pacific at ∼40-km resolution (NPac), and a regional model of the Northeast Pacific at ∼10-km resolution. The NEP model spans an area from Baja California through the Bering Sea, from the coast to ∼2000-km offshore. In this context, “remote influence” refers to effects driven by changes in ocean velocity and temperature outside of the NEP domain; “local influence” refers to direct forcing by winds and runoff within the NEP domain. A base run of this model using hindcast winds and runoff for 1996–2002 replicates the dominant spatial modes of sea-surface height anomalies from satellite data, and coastal sea level from tide gauges. We have performed a series of sensitivity runs with the NEP model for 1997–1998, which analyze the response of coastal sea level to: (1) hindcast winds and coastal runoff, as compared to their monthly climatologies and (2) hindcast boundary conditions (from the NPac model), as compared to their monthly climatologies. Results indicate penetration of sea-surface height (SSH) from the basin-scale model into the NEP domain (e.g., remote influence), with propagation as coastal trapped waves from Baja up through Alaska. Most of the coastal sea-level anomaly off Alaska in El Nino years appears due to direct forcing by local winds and runoff (local influence), and such anomalies are much stronger than those produced off California. We quantify these effects as a function of distance along the coastline, and consider how they might impact the coastal ecosystems of the NEP.

A 44-year (1958–2001) sea level residual hindcast over the Mediterranean Basin

The present work describes a 44-year integration of a two dimensional sea level model forced by atmospheric pressure and wind over the Mediterranean Sea. As an output of such long-term hindcast a sea surface residual database containing storm surge events was created. Storm surge is a critical parameter in different kinds of studies, from harbor design to coastal dynamics. This work focuses on studying the regional evolution of the atmospheric forcing contribution to the residual sea surface variation. Modeling sea level residual in the Mediterranean Sea is of particular interest because the response of the sea to the atmospheric forcing may be important in comparison to the tidal amplitudes. The integration was performed by means of the HAMSOM numerical model in a barotropic mode. Hourly HIPOCAS hindcast wind and atmospheric sea level pressure fields were used to force the sea level model. These forcing fields were generated by dynamical downscaling from the NCEP/NCAR global reanalysis through the atmospheric REMO model. Measured residual sea surface is well reproduced by the model with a coefficient of correlation of the order of 0.82 at various Spanish harbor locations. On the other side, the study of the climatological sea surface elevation shows that the Mediterranean Basin has undergone negative trends over the past 44 years: a mean negative rate of −0.8 mm/yr is found in the central basin and extreme values as large as −2.0 mm/year in the Adriatic Basin.

Numerical and Experimental Analysis of Rapid Delta Formation, Turkish coast

The morphology of river mouths can be completely changed by dramatic flow changes caused by climate changes in catchment basins. Agricultural activities that overexploit water produce changes in sediment discharge that are reflected in sedimentation rates in dams. The basic aim of this study is to assess the causes and effects of rapid delta formation in Gomec (an important tourism centre on the Aegean Sea coast of Turkey), as a result of river catchment changes between 1998 and 2001. The rapidly developing delta covers an area of approximately 2 km length and 100 m width and was studied using numerical simulation and field studies. Bathymetric measurement, flow velocity and oceanographic parameters were measured. Bottom sediment samples were taken from the river and adjacent sea and sources were determined by mineral analysis. River flows and wave properties (determined from hindcast wind data) were used in the numerical model studies. The development of the delta was predicted for different scenarios. It is concluded that unless remedial action is taken, the delta will continue to develop rapidly and will produce both morphological and ecological impacts.

Sea-breeze forced diurnal surface currents in the Thermaikos Gulf, North-west Aegean

Energetic rotary diurnal surface currents of up to 40 cm/s are observed in the Thermaikos Gulf, North-west Aegean. They are principally confined above the pycnocline in the upper 3 m of the water column. Beneath this depth they are much weaker, less regular and oscillate in anti-phase with those at the surface. Averaged over 10-days, the current cycles are seen to vary sinusoidally with the northward component leading the eastward by 0.2 of a cycle (0.4 π), corresponding to clockwise rotating current ellipses. The mean amplitude ratio between the northward and eastward component amplitudes ( u/ v) is 0.83. A simple analytical model, representing the dynamical balance of a homogeneous surface layer, predicts diurnal wind forcing, i.e. a sea-breeze, should drive diurnal currents whose amplitude will be particularly energetic close to 30° latitude, where the diurnal and inertial periods are similar. Assuming that a 3 m deep surface layer is subject to linear frictional drag, the model is used to hindcast the phase of a northward diurnal wind required to force the observed current components. A linear friction coefficient (of 0.6 ω) is derived from the phase difference between the eastward and northward current components. Using this friction coefficient the phase of a diurnal northward wind is hindcast from the absolute phase of the current components. This hindcast wind phase of 1.70 rad is consistent with the observed northward wind of 1.66 rad with a phase difference of 0.04 rad (<10 min), which provides confirmatory evidence of the role of the sea-breeze wind stress cycle in forcing these motions. The model is finally used to predict the variation in the amplitude, ellipticity and rotation of these currents with latitude.

Potential Impact of Twenty Year Hindcast Wind and Wave Climatology on Ship Design

This paper highlights some features of the Navy's new climatology which appear to extend the designer's capability to realistically assess ship performance. The climatology provides global wave and wind parameter statistics, identifies the occurrence and persistence of some heavy weather conditions, and promises to permit a substantial upgrading of wave directionality and spectral shape models. Effects of these features are summarized in terms of predicted performance of several naval combatants.

Computer model of wind, waves, and longshore currents during a coastal storm

A mathematical model has been developed to forecast or hindcast wind, waves, and longshore currents during the passage of a coastal storm. Storm intensity is a function of the barometric pressure gradient which is modeled by rotating an inverted normal curve around the center of an ellipse. The length and orientation of the major and minor axes of the ellipse control the size and shape of the storm. The path of the storm is determined by a sequence of storm positions for the hindcast mode, and by interpolated positions assuming constant speed and direction for the forecast mode. The site location, shoreline orientation, and nearshore bottom slope provide input data for the shore position. The geostrophic wind speed and direction at the shore site are computed from the latitude and barometric pressure gradient. The geostrophic wind is converted into surface wind speed and direction by applying corrections for frictional effects over land and sea. The surface wind speed and direction, effective fetch, and wind duration are used to compute wave period, breaker height, and breaker angle at the shore site. The longshore current velocity is computed as a function of wave period, breaker height and angle, and nearshore slope. The model was tested by comparing observed data for several coastal locations with predicted values for wind speed, wave period and height, and longshore current velocity. Forecasts were made for actual storms and for hypothetical circular and elliptical storms.