Experimental characterization of the marine atmospheric boundary layer in the Havsul area, Norway

Offshore wind energy applications depend strongly on an improved knowledge of the physical processes taking place in marine atmospheric boundary layer (MABL). In particular the better understanding of the complex interactions between wind shear, atmospheric stability and turbulence and the effects of wind-wave interactions on offshore vertical wind profiles are essential for the development of offshore wind projects. This paper presents an analysis of the relation between turbulence parameters, such as horizontal and vertical turbulence intensity, and turbulence kinetic energy and average vertical wind profiles and wind shear. The investigations are based on 4 years of wind lidar measurements on the small island of Storholmen in the Havsul area about 8 km off the coast of the Norwegian mainland. The results show systematic dep endencies between the investigated turbulence parameters, both with respect to average wind speeds and average wind shear. The results indicate that in particular the horizontal turbulence intensity has the potential to act as a proxy for atmospheric stability in cases where corresponding temperature profiles are not available.publishedVersio

In situ coastal observations of wave homogeneity and coherence

A better understanding of wave homogeneity, i.e. the spatial variations of the wave characteristics, and wave coherence in coastal areas and fjords is essential for the design and analysis of sea-crossing infrastructures, such as floating bridge concepts. The wave conditions in fjords that are exposed to the open sea are complex and often characterized by a mixed swell–wind sea state. This study investigates the spatial coherence and homogeneity of ocean waves using two years of unique buoy observations from Sulafjorden – a fjord partly exposed to the open sea. We analyze both long term statistics and four selected cases with different sea states. The most exposed locations are dominated by long waves (swell), while the energy of the wind sea is comparable to the swell energy in the more sheltered locations. Despite the study area being relatively small (ca. 2 km ×1 km), the differences in wave conditions are significant because the complex fjord geometry blocks the incoming offshore waves, and changes in fetch and wind conditions affects the local wave growth. For swell waves we measured an along-crest spatial coherence (ca. 0.6) over a 1–2 km distance. The coherence between consecutive crests for swell was weaker (up to 0.3–0.4) for distances between 0.6 km and 1.3 km (up to about 5 wavelengths). Wind sea (both along crest and between crests) showed no coherence over these distances.publishedVersio

Characterization of Wind-Sea- and Swell-Induced Wave Energy along the Norwegian Coast

The necessity to reduce CO2 emissions in combination with the rising energy demand worldwide makes the extensive use of renewable energy sources increasingly important. To that end, countries with long coastlines, such as Norway, can exploit ocean wave energy to produce large amounts of power. In order to facilitate these efforts as well as to provide quantitative data on the wave energy potential of a specific area, it is essential to analyze the weather and climatic conditions detecting any variabilities. The complex physical processes and the atmosphere-wave synergetic effects make the investigation of temporal variability of wave energy a challenging issue. This work aims to shed new light on potential wave energy mapping, presenting a spatio-temporal assessment of swell- and wind-sea-induced energy flux in the Nordic Seas with a focus on the Norwegian coastline using the NORA10 hindcast for the period 1958–2017 (59 years). The results indicate high spatial and seasonal variability of the wave energy flux along the coast. The maximum wave energy flux is observed during winter, while the minimum is observed during summer. The highest coastal wave energy flux is observed in the Norwegian Sea. The majority of areas with dominant swell conditions (i.e., in the Norwegian Sea) are characterized by the highest coastal wave energy flux. The maximum values of wave energy flux in the North Sea are denoted in its northern parts in the intersection with the Norwegian Sea. In contrast to the Norwegian Sea, areas located in the North Sea and the Barents Sea show that wind sea is contributing more than swell to the total wave energy flux.publishedVersio

The importance of wind forcing in fjord wave modelling

Accurate predictions of surface ocean waves in coastal areas are important for a number of marine activities. In complex coastlines with islands and fjords, the quality of wind forcing significantly affects the results. We investigate the role of wind forcing on wave conditions in a fjord system partly exposed to open sea. For this reason, we implemented the wave model SWAN at the west coast of Norway using four different wind forcing. Wind and wave estimates were compared with observations from five measurement sites. The best results in terms of significant wave height are found at the sites exposed to offshore conditions using a wind input that is biased slightly high compared with the buoy observations. Positively biased wind input, on the other hand, leads to significant overestimation of significant wave height in more sheltered locations. The model also shows a poorer performance for mean wave period in these locations. Statistical results are supported by two case studies which also illustrate the effect of high spatial resolution in wind forcing. Detailed wind forcing is necessary in order to obtain a realistic wind field in complex fjord terrain, but wind channelling and lee effects may have unpredictable effects on the wave simulations. Pure wave propagation (no wind forcing) is not able to reproduce the highest significant wave height in any of the locations.publishedVersio

Nora3: A nonhydrostatic high-resolution hindcast of the North sea, the Norwegian sea, and the Barents sea

The 3-km Norwegian Reanalysis (NORA3) is a 15-yr mesoscale-permitting atmospheric hindcast of the North Sea, the Norwegian Sea, and the Barents Sea. With a horizontal resolution of 3 km, the nonhydrostatic numerical weather prediction model HARMONIE–AROME runs explicitly resolved deep convection and yields hindcast fields that realistically downscale the ERA5 reanalysis. The wind field is much improved relative to its host analysis, in particular in mountainous areas and along the improved grid-resolving coastlines. NORA3 also performs much better than the earlier hydrostatic 10-km Norwegian Hindcast Archive (NORA10) in complex terrain. NORA3 recreates the detailed structures of mesoscale cyclones with sharp gradients in wind and with clear frontal structures, which are particularly important when modeling polar lows. In extratropical windstorms, NORA3 exhibits significantly higher maximum wind speeds and compares much better to observed maximum wind than do NORA10 and ERA5. The activity of the model is much more realistic than that of NORA10 and ERA5, both over the ocean and in complex terrain.publishedVersio

Meteorological observations in tall masts for the mapping of atmospheric flow in Norwegian fjords

Since 2014, 11 tall meteorological masts have been erected in coastal areas of mid-Norway in order to provide observational data for a detailed description of the wind conditions at several potential fjord crossing sites. The planned fjord crossings are part of the Norwegian Public Roads Administration (NPRA) Coastal Highway E39 project. The meteorological masts are 50–100 m high and located in complex terrain near the shoreline in Halsafjorden, Julsundet and Storfjorden in the Møre og Romsdal county of Norway. Observations of the three-dimensional wind vector are made at 2–4 levels of each mast with a temporal frequency of 10 Hz. The dataset is corroborated with observed profiles of temperature at two masts, as well as observations of precipitation, atmospheric pressure, relative humidity and dew point at one site. The first masts were erected in 2014, and the measurement campaign will continue until at least 2024. The current paper describes the observational setup, and observations of key atmospheric parameters are presented and put in context with observations and climatological data from a nearby reference weather station. The 10 min and 10 Hz wind data, as well as other meteorological parameters, are publicly available through the Arctic Data Centre (https://doi.org/10.21343/z9n1-qw63; Furevik et al., 2019).publishedVersio

Achieving Reliable Estimates of the Spatial Distribution of Kelp Biomass

Kelp forests are highly productive systems that are important ecologically and commercially as well as in a blue carbon perspective. Given their importance, there is an urgent need to achieve reliable estimates of the spatial distribution of their biomass. Species distribution modelling is a powerful tool for producing such estimates, but it requires a solid framework, including important environmental covariates that have a direct effect on their biomass, a proper sampling strategy, and an independent evaluation dataset. Using Laminaria hyperborea as a model species, we developed a modelling framework considering these requirements and necessary steps to produce reliable predictions. Our modelling framework included proportion of hard substrate and bottom wave exposure, both crucial covariates that have a direct effect on the biomass of L. hyperborea, but rarely included in modelling studies. Furthermore, we devised a sampling strategy with field observations covering the whole environmental covariate space present in the study area. Subsequently, we fitted GAMs relating the field observations of the biomass of L. hyperborea to relevant environmental covariates. The best model containing the predictors bottom wave exposure, depth, and proportion hard substrate explained most of the variance in the dataset (83.1% deviance explained). This model was then used to predict the spatial distribution of biomass across the whole study area. To assess the reliability of the biomass predictions, we used an independent dataset of L. hyperborea biomass observations from the same area. This independent dataset correlated very well with spatial predictions of biomass based on our best model (R = 0.85). In total, we predicted a biomass of 457,000 tonnes in a 1,150 km2 study area on the West coast of Norway. Our modelling framework provides the means for developing a biomass model on a broader geographical scale. Such a model will be invaluable in improving kelp management regimes as well as for estimating the contribution of kelp forests to ecosystem services such as carbon sequestration and climate budgets.publishedVersio

On Common Research Needs for the Next Generation of Floating Support Structures

The world is facing several industrial and societal challenges, such as providing enough renewable energy and enough safe and healthy food as formulated in the United Nations sustainable development goals. Using floating stationary structures, the ocean can contribute to solving several of the challenges. New applications need new types of structures, with which we have limited experience. These support structures will be diverse, but also have essential research needs in common. Design of novel floating structures need reliable descriptions of the marine environment. This is particularly challenging for semi-sheltered coastal regions, with complex topography and bathymetry. Novel structures are likely to be compliant, modular and/or multi-body, requiring increased understanding and rational models for wave-structure interaction. Structures with sustainable, safe, and cost-efficient use of materials, including untraditional ones, must be developed. Smart, affordable, and reliable mooring systems and anchors for novel applications are necessary for station keeping. Digital solutions connecting the various stages of design and operation, as well as various design disciplines, researchers, and innovators, will be necessary. Sustainability will be an integral part of any new design. To unlock the potential of novel floating structures, we need to understand the requirements of the applications, as well as the associated technology gaps and knowledge and research needs. This paper highlights research needs for innovation within floating offshore wind, floating solar power plants, novel aquaculture structures, and coastal infrastructure.acceptedVersio