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- Author or Editor: Mark Hemer x
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Abstract
The seasonal structure of the wind sea and swell is analyzed from the existing 29-yr surface gravity wave climatology produced using a coupled atmosphere–wave model. The swell energy fraction analysis shows that swell dominates most of the World Ocean basins for all four seasons, and the Southern Ocean swells dominate swell in the global ocean. The swells are loosely correlated with the surface wind in the midlatitude storm region in both hemispheres, while their energy distribution and propagation direction do not show any relation with local winds and vary significantly with season because of nonlinear interactions. The same coupled system is then used to investigate the projected future change in wind-sea and swell climate through a time-slice simulation. Forcing of the coupled model was obtained by perturbing the model sea surface temperatures and sea ice with anomalies generated by representative Working Group on Coupled Modelling (WGCM) phase 3 of the Coupled Model Intercomparison Project (CMIP3) coupled models that use the IPCC Fourth Assessment Report (AR4) A1B scenario late in the twenty-first century. Robust responses found in the wind seas are associated with modified climate indices. A dipole pattern in the North Atlantic during the boreal winter is associated with more frequent occurrence of the positive North Atlantic Oscillation (NAO) phases under global warming, and the wind-sea energy increase in the Southern Ocean is associated with the continuous shift of the southern annular mode (SAM) toward its positive phase. Swell responses are less robust because of nonlinearity. The only consistent response in swells is the strong energy increase in the western Pacific and Indian Ocean sector of the Southern Ocean during the austral winter and autumn.
Abstract
The seasonal structure of the wind sea and swell is analyzed from the existing 29-yr surface gravity wave climatology produced using a coupled atmosphere–wave model. The swell energy fraction analysis shows that swell dominates most of the World Ocean basins for all four seasons, and the Southern Ocean swells dominate swell in the global ocean. The swells are loosely correlated with the surface wind in the midlatitude storm region in both hemispheres, while their energy distribution and propagation direction do not show any relation with local winds and vary significantly with season because of nonlinear interactions. The same coupled system is then used to investigate the projected future change in wind-sea and swell climate through a time-slice simulation. Forcing of the coupled model was obtained by perturbing the model sea surface temperatures and sea ice with anomalies generated by representative Working Group on Coupled Modelling (WGCM) phase 3 of the Coupled Model Intercomparison Project (CMIP3) coupled models that use the IPCC Fourth Assessment Report (AR4) A1B scenario late in the twenty-first century. Robust responses found in the wind seas are associated with modified climate indices. A dipole pattern in the North Atlantic during the boreal winter is associated with more frequent occurrence of the positive North Atlantic Oscillation (NAO) phases under global warming, and the wind-sea energy increase in the Southern Ocean is associated with the continuous shift of the southern annular mode (SAM) toward its positive phase. Swell responses are less robust because of nonlinearity. The only consistent response in swells is the strong energy increase in the western Pacific and Indian Ocean sector of the Southern Ocean during the austral winter and autumn.
Abstract
We present four 140-yr wind-wave climate simulations (1961–2100) forced with surface wind speed and sea ice concentration from two CMIP6 GCMs under two different climate scenarios: SSP1–2.6 and SSP5–8.5. A global three-grid system is implemented in WAVEWATCH III to simulate the wave–ice interactions in the Arctic and Antarctic regions. The models perform well in comparison with global satellite altimeter and in situ buoys climatology. The comparison with traditional trend analyses demonstrates the present GCM-forced wave models’ ability to reproduce the main historical climate signals. The long-term datasets allow a comprehensive description of the twentieth- and twenty-first-century wave climate and yield statistically robust trends. Analysis of the latest IPCC ocean climatic regions highlights four regions where changes in wave climate are projected to be most significant: the Arctic, the North Pacific, the North Atlantic, and the Southern Ocean. The main driver of offshore wave climate change is the wind, except for the Arctic where the significant sea ice retreat causes a sharp increase in the projected wave heights. Distinct changes in the wave period and the wave direction are found in the Southern Hemisphere, where the poleward shift of the Southern Ocean westerlies causes an increase in the wave period of up to 5% and a counterclockwise change in wave direction of up to 5°. The new CMIP6 forced wave models improve in performance compared to previous CMIP5 forced wave models, and will ultimately contribute to a new CMIP6 wind-wave climate model ensemble, crucial for coastal adaptation strategies and the design of future marine offshore structures and operations.
Significance Statement
The purpose of this study is to advance the understanding of ocean wind-wave climate evolution over the twentieth and twenty-first centuries and to effectively communicate the long-term impacts of climate change in diverse wind-wave climatic regions across the globe. The 140-yr continuous model results produced in this work are crucial to studying changes in extreme sea states and investigating the relationship between interdecadal periodic oscillations and long-term climate trends. The dataset produced can be used to gain further insight into the substantial long-term changes of the polar wind-wave climate caused by the rapid decrease of sea ice coverage, and the evolution of the directional changes in the sea states triggered by climate change.
Abstract
We present four 140-yr wind-wave climate simulations (1961–2100) forced with surface wind speed and sea ice concentration from two CMIP6 GCMs under two different climate scenarios: SSP1–2.6 and SSP5–8.5. A global three-grid system is implemented in WAVEWATCH III to simulate the wave–ice interactions in the Arctic and Antarctic regions. The models perform well in comparison with global satellite altimeter and in situ buoys climatology. The comparison with traditional trend analyses demonstrates the present GCM-forced wave models’ ability to reproduce the main historical climate signals. The long-term datasets allow a comprehensive description of the twentieth- and twenty-first-century wave climate and yield statistically robust trends. Analysis of the latest IPCC ocean climatic regions highlights four regions where changes in wave climate are projected to be most significant: the Arctic, the North Pacific, the North Atlantic, and the Southern Ocean. The main driver of offshore wave climate change is the wind, except for the Arctic where the significant sea ice retreat causes a sharp increase in the projected wave heights. Distinct changes in the wave period and the wave direction are found in the Southern Hemisphere, where the poleward shift of the Southern Ocean westerlies causes an increase in the wave period of up to 5% and a counterclockwise change in wave direction of up to 5°. The new CMIP6 forced wave models improve in performance compared to previous CMIP5 forced wave models, and will ultimately contribute to a new CMIP6 wind-wave climate model ensemble, crucial for coastal adaptation strategies and the design of future marine offshore structures and operations.
Significance Statement
The purpose of this study is to advance the understanding of ocean wind-wave climate evolution over the twentieth and twenty-first centuries and to effectively communicate the long-term impacts of climate change in diverse wind-wave climatic regions across the globe. The 140-yr continuous model results produced in this work are crucial to studying changes in extreme sea states and investigating the relationship between interdecadal periodic oscillations and long-term climate trends. The dataset produced can be used to gain further insight into the substantial long-term changes of the polar wind-wave climate caused by the rapid decrease of sea ice coverage, and the evolution of the directional changes in the sea states triggered by climate change.
Abstract
The Australian marine research, industry, and stakeholder community has recently undertaken an extensive collaborative process to identify the highest national priorities for wind-waves research. This was undertaken under the auspices of the Forum for Operational Oceanography Surface Waves Working Group. The main steps in the process were first, soliciting possible research questions from the community via an online survey; second, reviewing the questions at a face-to-face workshop; and third, online ranking of the research questions by individuals. This process resulted in 15 identified priorities, covering research activities and the development of infrastructure. The top five priorities are 1) enhanced and updated nearshore and coastal bathymetry; 2) improved understanding of extreme sea states; 3) maintain and enhance the in situ buoy network; 4) improved data access and sharing; and 5) ensemble and probabilistic wave modeling and forecasting. In this paper, each of the 15 priorities is discussed in detail, providing insight into why each priority is important, and the current state of the art, both nationally and internationally, where relevant. While this process has been driven by Australian needs, it is likely that the results will be relevant to other marine-focused nations.
Abstract
The Australian marine research, industry, and stakeholder community has recently undertaken an extensive collaborative process to identify the highest national priorities for wind-waves research. This was undertaken under the auspices of the Forum for Operational Oceanography Surface Waves Working Group. The main steps in the process were first, soliciting possible research questions from the community via an online survey; second, reviewing the questions at a face-to-face workshop; and third, online ranking of the research questions by individuals. This process resulted in 15 identified priorities, covering research activities and the development of infrastructure. The top five priorities are 1) enhanced and updated nearshore and coastal bathymetry; 2) improved understanding of extreme sea states; 3) maintain and enhance the in situ buoy network; 4) improved data access and sharing; and 5) ensemble and probabilistic wave modeling and forecasting. In this paper, each of the 15 priorities is discussed in detail, providing insight into why each priority is important, and the current state of the art, both nationally and internationally, where relevant. While this process has been driven by Australian needs, it is likely that the results will be relevant to other marine-focused nations.
