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"Sea states"
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Satellite Remote Sensing of Surface Winds, Waves, and Currents: Where are we Now?
This review paper reports on the state-of-the-art concerning observations of surface winds, waves, and currents from space and their use for scientific research and subsequent applications. The development of observations of sea state parameters from space dates back to the 1970s, with a significant increase in the number and diversity of space missions since the 1990s. Sensors used to monitor the sea-state parameters from space are mainly based on microwave techniques. They are either specifically designed to monitor surface parameters or are used for their abilities to provide opportunistic measurements complementary to their primary purpose. The principles on which is based on the estimation of the sea surface parameters are first described, including the performance and limitations of each method. Numerous examples and references on the use of these observations for scientific and operational applications are then given. The richness and diversity of these applications are linked to the importance of knowledge of the sea state in many fields. Firstly, surface wind, waves, and currents are significant factors influencing exchanges at the air/sea interface, impacting oceanic and atmospheric boundary layers, contributing to sea level rise at the coasts, and interacting with the sea-ice formation or destruction in the polar zones. Secondly, ocean surface currents combined with wind- and wave- induced drift contribute to the transport of heat, salt, and pollutants. Waves and surface currents also impact sediment transport and erosion in coastal areas. For operational applications, observations of surface parameters are necessary on the one hand to constrain the numerical solutions of predictive models (numerical wave, oceanic, or atmospheric models), and on the other hand to validate their results. In turn, these predictive models are used to guarantee safe, efficient, and successful offshore operations, including the commercial shipping and energy sector, as well as tourism and coastal activities. Long-time series of global sea-state observations are also becoming increasingly important to analyze the impact of climate change on our environment. All these aspects are recalled in the article, relating to both historical and contemporary activities in these fields.
Journal Article
140 Years of Global Ocean Wind-Wave Climate Derived from CMIP6 ACCESS-CM2 and EC-Earth3 GCMs
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.
Journal Article
Asymmetry of Cyclonic Sea Surface Wind and Wave Observed by SAR
CyclObs‐derived wind and SWH field are extracted from over 600 dual‐polarized Sentinel‐1 (S‐1) images of around 300 tropical cyclones (TCs) over the past eight years to investigate asymmetry of wind and wave fields during TCs. Fetch analysis and machine learning technique, eXtreme Gradient Boosting (XGBoost), is used to establish a relationship between TC wind speed and significant wave height (SWH). It was found that TC wind and SWH radii become asymmetric as sea states intensify. Notably, wind radii correlations (CORs) increase on the left‐right and left‐back quadrants for wind speeds larger than 20 m/s, while SWH radii exhibit the opposite trend. XGBoost is employed to obtain the improved relationship between wind fetch and SWH (COR < 0.17). Validation against buoys and Haiyang‐2 (HY‐2) observations of 20 TCs indicates that the root mean squared error in SWH predictions is reduced by up to 1.1 m using XGBoost instead of empirical model. The new TC wave model by XGBoost is particularly robust under high‐wind conditions, therefore vital for warning and mitigation of extreme storms and improved parameterizations of air‐sea interaction.
Journal Article
Field Measurements of Rogue Water Waves
This paper concerns the collation, quality control, and analysis of single-point field measurements from fixed sensors mounted on offshore platforms. In total, the quality-controlled database contains 122 million individual waves, of which 3649 are rogue waves. Geographically, the majority of the field measurements were recorded in the North Sea, with supplementary data from the Gulf of Mexico, the South China Sea, and the North West shelf of Australia. The significant wave height ranged from 0.12 to 15.4 m, the peak period ranged from 1 to 24.7 s, the maximum crest height was 18.5 m, and the maximum recorded wave height was 25.5 m. This paper will describe the offshore installations, instrumentation, and the strict quality control procedure employed to ensure a reliable dataset. An examination of sea state parameters, environmental conditions, and local characteristics is performed to gain an insight into the behavior of rogue waves. Evidence is provided to demonstrate that rogue waves are not governed by sea state parameters. Rather, the results are consistent with rogue waves being merely extraordinary and rare events of the normal population caused by dispersive focusing.
Journal Article
Militarism in a global age : naval ambitions in Germany and the United States before World War I
At the turn of the twentieth century, the United States and Germany emerged as the two most rapidly developing industrial nation-states of the Atlantic world. The elites and intelligentsias of both countries staked out claims to dominance in the twentieth century. In Militarism in a Global Age, Dirk Bönker explores the far-reaching ambitions of naval officers before World War I as they advanced navalism, a particular brand of modern militarism that stressed the paramount importance of sea power as a historical determinant. Aspiring to make their own countries into self-reliant world powers in an age of global empire and commerce, officers viewed the causes of the industrial nation, global influence, elite rule, and naval power as inseparable. Characterized by both transnational exchanges and national competition, the new maritime militarism was technocratic in its impulses; its makers cast themselves as members of a professional elite that served the nation with its expert knowledge of maritime and global affairs.
American and German navalist projects differed less in their principal features than in their eventual trajectories. Over time, the pursuits of these projects channeled the two naval elites in different directions as they developed contrasting outlooks on their bids for world power and maritime force. Combining comparative history with transnational and global history, Militarism in a Global Age challenges traditional, exceptionalist assumptions about militarism and national identity in Germany and the United States in its exploration of empire and geopolitics, warfare and military-operational imaginations, state formation and national governance, and expertise and professionalism.
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