The New Zealand Defence Force (NZDF) has established a permanent wave observation station near Campbell Island, south of New Zealand (52 45.71 S, 169 02.54E). The site was chosen for logistical convenience and its unique location adjacent to the highly energetic Southern Ocean; allowing instrumentation typically deployed on the continental shelf to be used in this rarely observed southern environment. From February 2017, a Triaxys Directional Wave Buoy was moored in 147 m depth, some 17 km to the south of the island, with satellite telemetry of the 2D wave spectra at 3-hourly intervals. To date there have been three deployments on locations, yielding some 784 days of data. Validation of the measured significant wave height against co-located satellite altimeter observations suggests that the predominant wave directions are not attenuated by the island. The data provide a valuable record of the detailed wave spectral characteristics from one of the least-sampled parts of the Global Ocean.

Global wave hindcasts are developed using the third generation spectral wave model WAVEWATCH III with the observation-based source terms (ST6) and a hybrid rectilinear-curvilinear, irregular-regular-irregular grid system (approximately at 0.25 degrees x0.25 degrees). Three distinct global hindcasts are produced: (a) a long-term hindcast (1979-2019) forced by the ERA5 conventional winds U10 and (b) two short-term hindcasts (2011-2019) driven by the NCEP climate forecast system (CFS)v2 U10 and the ERA5 neutral winds U10,neu, respectively. The input field for ice is sourced from the Ocean and Sea Ice Satellite Application Facility (OSI SAF) sea-ice concentration climate data records. These wave simulations, together with the driving wind forcing, are validated against extensive in-situ observations and satellite altimeter records. The performance of the ST6 wave hindcasts shows promising results across multiple wave parameters, including the conventional wave characteristics (e.g., wave height Hs and wave period) and high-order spectral moments (e.g., the surface Stokes drift and mean square slope). The ERA5-based simulations generally present lower random errors, but the CFS-based run represents extreme sea states (e.g., Hs>10 m) considerably better. Novel wave parameters available in our hindcasts, namely the dominant wave breaking probability, wave-induced mixed layer depth, freak wave indexes and wave-spreading factor, are further described and briefly discussed. Inter-comparisons of Hs from the long-term (41 years) wave hindcast, buoy measurements and two different calibrated altimeter data sets highlight the inconsistency in these altimeter records arising from different calibration methodology. Significant errors in the low-frequency bins (period T>15 s) for both wave energy and directionality call for further model development.

Understanding the regional wave climate is essential for engineering applications. The last two decades have not been included in assessments of the wave climate of New Zealand’s Taranaki region, where the country exploits offshore oil and gas. To make up for this lack of assessment, we carried out a high-resolution long-term (1979–2018) wave hindcast and examined several aspects of the climate in the region. The hindcast data validation against buoy and satellite data showed good agreement and suitability for wave climate analysis. Seasonal wave distributions reveal a bi-modal pattern, composed of (1) more energetic and long period (13–15 s) westerly–southwesterly swells; and (2) shorter-period (∼8 s) southwesterly wind-seas. These signatures result from the region’s high exposure to swells generated by persistent strong winds blowing over long fetches in the Southern Ocean, and to local storm-associated wind-seas, respectively. The largest waves are found offshore, with mean Hs value reaching 2.83 m, 90th percentile 4.3 m, 99th percentile 6.1 m, and maximum 10.8 m. Storm wave monthly climatologies show that storm peaks are largest in the austral autumn, especially in May, while the number of events is the largest in July. Trends in Hs statistics reveal an increase over the past 40 years, with higher rates at higher percentiles. Storm peaks have also increased, by up to 8 cm/decade, whereas the number of storm events has decreased. In agreement with previous work, we found relationships between Hs and climate patterns. Waves get larger in Taranaki waters during El Nino events, as a result of stronger southwesterly winds, and during negative Antarctic Oscillation phases, as westerly winds displace northward.

Abstract Wind‐wave hindcast data have many applications including climatology assessments for renewable energy projects, maritime engineering design, event‐based impact assessments, generating boundary conditions for further downscaling, amongst others. Here, we present a global wave hindcast with nested high‐resolution grids for the Exclusive Economic Zones of Australia and south west Pacific Island Countries, that is extended in time monthly. The model employs strategic methods to incorporate the effects of subgrid sized features such as small islands and islets. Various bulk wave parameters are available hourly from January 1979 to present, along with the full wave spectra at a set of 3,683 predetermined points distributed globally.

The safety of vulnerable coastal and offshore infrastructures requires an in-depth understanding of wave variability and climate drivers. We investigate the association of significant wave height (Hs) and peak wave period (Tp) with the co-occurrence of El Niño–Southern Oscillation (ENSO) and the Madden–Julian Oscillation (MJO) at the global scale. We calculate composites of daily anomalies in modelled Hs, Tp, and surface wind for periods of ENSO–MJO phase combinations. Calculations spanned November–March seasons over the period 1979–2018. Wave anomalies are widespread across the world’s oceans, with remarkable strength during several ENSO–MJO phase combinations, demonstrating strong tropic–tropic and tropic-extratropic teleconnections. Positive Hs anomalies are strongest in the Pacific Ocean during El Niño–MJO phase 8, in the Atlantic Ocean during ENSO-neutral-MJO phase 3, and in the Indian Ocean during ENSO-neutral-MJO phase 4. Positive Tp anomalies are strongest in the Pacific Ocean during La Niña–MJO phase 8, in the Atlantic Ocean during El Niño–MJO phase 1, and in the Indian Ocean during El Niño–MJO phase 8. In the Southern Ocean, the strongest Hs anomalies occur during El Niño–MJO phase 8, whereas in the Maritime Continent, they appear during ENSO-neutral-MJO phases 5–6. Despite previous studies finding low correlations of ENSO indices with wave parameters in the North Atlantic, our results suggest that ENSO-related conditions play a significant role in the area when combined with certain MJO-related conditions. This study also reveals that the wave anomalies associated with ENSO–MJO phase combinations can be twice as strong as those found in previous work, related only to the MJO. Therefore, considering multiple concurrent climate patterns in the analysis of wave anomalies is essential to developing more reliable coastal management plans.

The generation and evolution of ocean waves by wind is one of the most complex phenomena in geophysics, and is of great practical significance. Predictive capabilities of respective wave models, however, are impaired by lack of field in situ observations, particularly in extreme Metocean conditions. The paper outlines and highlights important gaps in understanding the Metocean processes and suggests a major observational program in the Southern Ocean. This large, but poorly investigated part of the World Ocean is home to extreme weather around the year. The observational network would include distributed system of buoys (drifting and stationary) and autonomous surface vehicles (ASV), intended for measurements of waves and air-sea fluxes in the Southern Ocean. It would help to resolve the issues of limiting fetches, extreme Extra-Tropical cyclones, swell propagation and attenuation, wave-current interactions, and address the topics of wave-induced dispersal of floating objects, wave-ice interactions in the Marginal Ice Zone, Metocean climatology and its connection with the global climate.

This paper presents an assessment of the impact of the ocean circulation on modeled wave fields in the Southern Ocean, where a systematic positive bias of the modeled wave height against altimetry data has been reported. The inclusion of ocean currents in the wave model considerably reduces the positive bias of the simulated wave height for high southern latitudes. The decrease of wave energy in the presence of currents is almost exclusively related to the reduction of the relative wind, caused by an overall co-flowing current field associated with the Antarctic Circumpolar Current. Improvements of the model results are also found for the peak period and the mean period against a long-term moored buoy. At the mooring location, the effect of currents is greater for larger and longer waves, suggesting remotely generated swells are more influenced by the currents than local waves. However, an additional qualitative analysis using high-resolution currents in a finer grid nested to the global coarser grid shows that typical resolution of global hydrodynamic reanalysis is not sufficient to resolve mesoscale eddies, and as a consequence, the simulation of mesoscale wave patterns can be compromised. The results are also discussed in terms of the accuracy of forcing fields.

In February 2017, a wave buoy was deployed in the Southern Ocean, south of New Zealand at 52°45.71′S, 169°02.54′E. For 170 days, the moored buoy transmitted spectral and time domain observations, including measurements during a storm with a particularly large individual wave of 19.4-m crest-to-trough height. We present a detailed analysis of this storm and the measured and modelled spectra, also considering the probability of the occurrence of single large waves. After 170 days, the buoy broke free of its mooring and started drifting eastwards, still transmitting the essential data, thereby providing a unique opportunity to examine large wave events and their corresponding spectral conditions in the Southern Ocean on both moored and free-drifting platforms. The results are discussed quantitatively.

Australia is widely recognised as having an abundant wave energy resource which could contribute to the country's future energy mix. Prior assessments have provided general broad scale information on the resource magnitude, but detail needed to support next level site assessments has been deficient. Aiming to support all stakeholders in Australia's emerging wave energy industry, this study presents a revised assessment of Australia's national wave energy resource. The assessment is based on a state-of-the-art global wave hindcast, with higher resolution in the Australian region. Validation of the hindcast relative to in-situ wave buoy and satellite altimeter observations show better comparison than prior assessments. The total nationally available resource is similar in magnitude to earlier studies, but regional differences are evident. The total integrated energy flux across the 200 m contour is approximately 2730 TWh/yr, with estimates of resource along the north and eastern coasts being less than previously estimated. This revised pre-competitive resource information is delivered coincidently with marine management and alternative use (constraint layers), and energy infrastructure, spatial information via the open-access Australian Wave Energy Atlas (AWavEA), served through the Australian Renewable Energy Infrastructure (AREMI). The Atlas serves to reduce barriers to emergence of an Australian wave energy industry. (C) 2016 Elsevier Ltd. All rights reserved.

This is the first large-scale study of the influence of an offshore reef matrix on wave transmission. The focus was on the Great Barrier Reef (GBR), Australia, utilizing a 16 yr-record of wave height, from seven satellite altimeters. Within the GBR matrix, wave height is not strongly dependent on reef matrix submergence. This suggests that after initial wave breaking at the seaward edge of the reef matrix, waves that penetrate the matrix have little depth-modulation. There is no evidence to suggest that as reef matrix porosity (ratio of spaces between individual reefs to reef area) decreases, wave attenuation increases. This is because an individual reef casts a wave shadow much larger than the reef itself; thus a matrix of isolated reefs is remarkably effective at attenuating wave energy. This weak dependence of transmitted wave energy on depth of reef submergence, and reef matrix porosity, is also evident in the lee of the matrix. Here, wave conditions depend largely on local wind speed, rather than wave conditions either seaward, or within the matrix. This is because the GBR matrix is a very effective wave absorber, irrespective of water depth and reef matrix porosity.

We assess the impact of the tropical Madden Julian Oscillation (MJO) on global ocean wind waves using 30 years of wave data from a wave model hindcast that is forced with high resolution surface winds from the NCEP-CFSR reanalysis. We concentrate on the boreal winter season when the MJO has its greatest amplitude and is potentially a source of predictable wave impacts at intra-seasonal lead times. Statistically significant anomalies in significant wave height (H-s), peak wave period (T-p) and zonal wave energy flux (CgE) are found to covary with the intra-seasonal variation of surface zonal wind induced by the MJO as it traverses eastward from the western tropical Indian Ocean to the eastern tropical Pacific. T-p varies generally out of phase with Ifs over the life cycle of the MJO, indicating that these MJO-wave anomalies are locally wind generated rather than remotely generated by ocean swell.Pronounced H-s anomalies develop on the northwest shelf of Australia, where the MJO is known to influence sea level and surface temperatures, and in the western Caribbean Sea and Guatemalan-Panama Seas with enhanced wave anomalies apparent in the vicinity of the Tehuantepec and Papagayo gaps. Significant wave anomalies are also detected in the North Pacific and North Atlantic oceans in connection with the MJO teleconnection to the extratropics via atmospheric wave propagation. The impact in the north Atlantic stems from induction of the high phase of the North Atlantic Oscillation (NAO) about 1 week after MJO convection traverses the Indian Ocean, and the low phase of the NAO about one week after suppressed convection traverses the Indian Ocean. Strong positive H-s anomalies maximize on the Northern European coast in the positive NAO phase and vice versa for the negative NAO phase. The MJO also influences the occurrence of daily low (below the 5th percentile) and high (above the 95th percentile) wave conditions across the tropics and in the North Pacific and North Atlantic, emphasizing that the MJO may be a valuable source of intra-seasonal predictability of surface wave variability. (C) 2015 Elsevier Ltd. All rights reserved.

The Southern Ocean is an important component in the global wave climate. However, owing to a lack of observations, our understanding of waves is poor compared to other regions. The Southern Ocean Flux Station (SOFS) has been deployed to fill this gap and represents the first successful moored air-sea flux station at these southern hemisphere latitudes. In this paper, we present for the first time the results from the analysis of the wave measurements, focused on statistics and extremes of the main wave parameters. Furthermore, a spectral characterization is performed regarding the number of wave systems and predominance of swell/wind-sea. Our results indicate a high consistency in terms of wave parameters for all deployments. The maximum significant wave height obtained in the 705 days of observation was 13.41 m. The main spectra found represent unimodal swell dominated cases; however, the dimensionless energy plotted against dimensionless peak frequency for these spectra follows a well-known relation for wind-sea conditions. In addition, the Centre for Australian Weather and Climate Research wave hindcast is validated with the SOFS data.

Offshore reef systems consist of individual reefs, with spaces in between, which together constitute the reef matrix. This is the first comprehensive, large-scale study, of the influence of an offshore reef system on wave climate and wave transmission. The focus was on the Great Barrier Reef (GBR), Australia, utilizing a 16-yr record of wave height from seven satellite altimeters. Within the GBR matrix, the wave climate is not strongly dependent on reef matrix submergence. This suggests that after initial wave breaking at the seaward edge of the reef matrix, wave energy that penetrates the matrix has little depth modulation. There is no clear evidence to suggest that as reef matrix porosity (ratio of spaces between individual reefs to reef area) decreases, wave attenuation increases. This is because individual reefs cast a wave shadow much larger than the reef itself; thus, a matrix of isolated reefs is remarkably effective at attenuating wave energy. This weak dependence of transmitted wave energy on depth of reef submergence, and reef matrix porosity, is also evident in the lee of the GBR matrix. Here, wave conditions appear to be dependent largely on local wind speed, rather than wave conditions either seaward, or within the reef matrix. This is because the GBR matrix is a very effective wave absorber, irrespective of water depth and reef matrix porosity.

This study examines the application of three different variations of linear-regression corrections to the surface marine winds from the Australian Bureau of Meteorology's recently implemented operational atmospheric model. A simple correction over the entire domain is found to inadequately account for geographical variation in the wind bias. This is addressed by considering corrections that vary in space. Further, these spatially varying corrections are extended to vary in time. In an operational environment, the error characteristics of the wind forcing can be expected to change over time with the evolution of the atmospheric model. This in turn requires any applied correction to be monitored and maintained. Motivated by a desire to avoid this manual maintenance, a self-learning correction method is proposed whereby spatially and temporally varying corrections are calculated in real time from a moving window of historical comparisons between observations and preceding forecasts. This technique is shown to effectively remove both global and regionally varying wind speed biases.

The skill of modern wave models is such that the quality of their forecasts is, to a large degree, determined by errors in the forcing wind field. This work explores the extent to which large-scale systematic biases in modelled waves from a third generation wave model can be attributed to the forcing winds. Three different sets of winds with known global bias characteristics are used to force the WAVEWATCH III model. These winds are based on the Australian Bureau of Meteorology's ACCESS model output, with different statistical corrections applied. Wave forecasts are verified using satellite altimeter data. It is found that a negative bias in modelled Significant Wave Height (H-s) has its origins primarily in the forcing, however, the reduction of systematic wind biases does not result in universal improvement in modelled Hs. A positive bias is present in the Southern Hemisphere due primarily to an overestimation of high Hs values in the Southern Ocean storm tracks. A positive bias is also present in the east Pacific and East Indian Ocean. This is due both to the over-prediction of waves in the Southern Ocean and lack of swell attenuation in the wave model source terms used. Smaller scale features are apparent, such as a positive bias off the Cape of Good Hope, and a negative bias off Cape Horn. In some situations, internal wave model error has been compensated for by error in the forcing winds. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved.