Southern Ocean Wave Atlas presentation at NZ Antarctic Science Conference

MetOcean Solutions, commissioned by the New Zealand Defence Force, produced a state of the art wave atlas of the Southern Ocean (SO). Next week our key findings will be presented at New Zealand Antarctic Science Conference in Christchurch.

The Southern Ocean Wave Atlas includes a collaborative measurement campaign between MetOcean Solutions and Defence Technology Agency (DTA), and a large modelling effort. A critical analysis of wave model performance against these and other available observations was conducted, as well as the production of a long term hindcast in the SO.

The detailed understanding of the characteristics of wave climate is required to test and inform future designs of vessels that will be tasked with operating in the highly energetic SO. The gathered data help reduce known deficiencies in the model physics for this region and improve model guidance, which are used ultimately to make informed operational decisions.

 
Mean Significant wave height for 1993-2017 presented as layers in files suitable for viewing in Google Earth (www.google.com/earth/)

Mean Significant wave height for 1993-2017 presented as layers in files suitable for viewing in Google Earth (www.google.com/earth/)

 

As part of the measurement campaign, MetOcean Solutions has deployed instruments to collect wave data using moored and drifting buoys. All data is freely available to the scientific community and can be viewed in real time. For further information and data access see www.metocean.co.nz/southern-ocean/.

Running from 17 to 19 June, the NZ Antarctic Science Conference is hosted by Antarctica New Zealand, the government agency charged with carrying out New Zealand's activities in Antarctica, supporting world leading science and environmental protection. This year the conference theme is ‘Our Future in Focus’, showcasing the latest findings from NZ’s Antarctic research programme, discussing research and policy imperatives, and providing an opportunity for researchers, iwi, policy-makers and educators to foster collaborations that will collectively influence our future.

MetOcean Solutions is a division of New Zealand’s National Meteorological Service.

The full abstract is provided below.


Southern Ocean Wave Atlas

Tom Durrant1, Jorge Perez2, Henrique Rapizo2, Rafael Guedes1, Sally Garrett3, Peter McComb1

While the Southern Ocean is the least observed or understood of any major ocean, the combination of persistent westerly winds and the large expanse of sea produces higher wave heights for longer periods than any other body of water. The New Zealand Navy has patrol and search and rescue responsibilities over large areas of this ocean, and are planning the next generation of vessels to safely operate in these waters. However, the spectral wave characteristics have not been adequately characterised for the Southern Ocean, meaning the critical design factors were unavailable.

To meet those needs, a campaign of measurement and modelling was undertaken. Observations included buoy deployments at 52.7S, the southernmost directional wave mooring to date, where phenomenal conditions were observed including the highest measured wave in the Southern Hemisphere (24.8 m). Additionally, five drifting buoys were deployed in a trial of a new technology in energetic open ocean states.

The wave modelling, conducted with WAVEWATCH III, included a comprehensive analysis of available forcings including wind and ice from the CFSR and ERA5 reanalyses. The relative importance of large scale ocean currents was also examined, with currents from CFSR, HYCOM and Glorys considered. ERA5 winds were found to be superior to CFSR, and Glorys provided the best results for currents, significantly reducing the positive wave height bias in the Southern Ocean. This configuration was used to produce a 25 year hindcast, from which an atlas of the relevant physical surface ocean variables was been produced.

The atlas is a freely available gridded dataset of derived statistics that includes monthly and annual directional values for the surface current speed, wavelength, wave period, significant wave height, return period significant wave height, Douglas sea states, and dangerous seas indices.

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  1. Oceanum Ltd, New Plymouth, New Zealand
  2. Meteorological Service New Zealand, Raglan, 3225, New Zealand
  3. New Zealand Defence Force, Devonport, New Zealand