| 1. |
- Semedo, Alvaro, 1966-, et al.
(författare)
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A Global View on the Wind Sea and Swell Climate and Variability from ERA-40
- 2011
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Ingår i: Journal of Climate. - 0894-8755 .- 1520-0442. ; 24:5, s. 1461-1479
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Tidskriftsartikel (refereegranskat)abstract
- In this paper a detailed global climatology of wind sea and swell parameters, based on the ERA-40 wave reanalysis, is presented. The spatial pattern of the swell dominance of the Earth’s Oceans, in terms of the wave field energy balance and wave field characteristics, is also investigated. Statistical analysis shows that the Global Ocean is strongly dominated by swell waves. The inter-annual variability of the wind sea and swell significant wave heights, and how they are related to the resultant significant wave height, is analyzed over the Pacific, Atlantic, and Indian Oceans. The leading modes of variability of wind sea and swell demonstrate noticeable differences, particularly in the Pacific and Atlantic Oceans. During the Northern Hemisphere winter a strong north-south swell propagation pattern is observed in the Atlantic Ocean. Statistically significant secular increases in the wind sea and swell significant wave heights are found in the North Pacific and North Atlantic Oceans.
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| 2. |
- Semedo, Alvaro, 1966-, et al.
(författare)
-
Global Distribution of the Wave Age Parameter
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In this paper a detailed global climatology of the wave age parameter, based on the ECMWF (European Centre for Medium-Range Weather Forecasts) ERA-40 reanalysis is presented. The global annual and seasonal mean climatological patterns of the wave age confirm, in line with previous studies, the global dominance of the World Ocean by swell waves. It is also shown, from a climatological perspective, that the state of equilibrium of the World Ocean is a relatively rare event. The leading modes of variability of the wave age demonstrate that the areas of higher explained variability (the centers of action) occur mostly along the equator, coinciding with the equatorial swell pools. Statistically significant secular changes of the annual wave age parameter are analyzed, revealing dominant upward trend in the equatorial and southeast Pacific Ocean, and partially in the extratropical storm tracks in the Southern Ocean, although in some areas, mainly in the Indian Ocean, some negative trends of the wave age are also observed.
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| 3. |
- Semedo, Alvaro, 1966-, et al.
(författare)
-
Global significant swell steepness
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Swell waves loose energy as they propagate. Part of this energy is lost into the ocean mixed layer, but most of it is transferred to the atmosphere as a wave-atmosphere feedback process. The swell loss of energy is related to its steepness. The swell modulation of the lower marine atmospheric boundary layer (MABL) dynamics has been shown to occur at high wave age regimes. In this paper we present an insight into the global significant swell steepness climate and long term variability. The areas of high probability of swell interaction with the MABL are also presented.
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| 4. |
- Semedo, Alvaro, 1966-, et al.
(författare)
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Wave induced wind in the marine boundary layer
- 2009
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Ingår i: Journal of the Atmospheric Sciences. - 0022-4928 .- 1520-0469. ; 66:8, s. 2256-2271
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Tidskriftsartikel (refereegranskat)abstract
- Recent field observations and large-eddy simulations have shown that the impact of fast swell on the marine atmospheric boundary layer (MABL) might be stronger than previously assumed. For low to moderate winds blowing in the same direction as the waves, swell propagates faster than the mean wind. The momentum flux above the sea surface will then have two major components: the turbulent shear stress, directed downward, and the swell-induced stress, directed upward. For sufficiently high wave age values, the wave-induced component becomes increasingly dominant, and the total momentum flux will be directed into the atmosphere. Recent field measurements have shown that this upward momentum transfer from the ocean into the atmosphere has a considerable impact on the surface layer flow dynamics and on the turbulence structure of the overall MABL. The vertical wind profile will no longer exhibit a logarithmic shape because an acceleration of the airflow near the surface will take place, generating a low-level wave-driven wind maximum (a wind jet). As waves propagate away from their generation area as swell, some of the wave momentum will be returned to the atmosphere in the form of wave-driven winds. A model that qualitatively reproduces the wave-following atmospheric flow and the wave-generated wind maximum, as seen from measurements, is proposed. The model assumes a stationary momentum and turbulent kinetic energy balance and uses the dampening of the waves at the surface to describe the momentum flux from the waves to the atmosphere. In this study, simultaneous observations of wind profiles, turbulent fluxes, and wave spectra during swell events are presented and compared with the model. In the absence of an established model for the linear damping ratio during swell conditions, the model is combined with observations to estimate the wave damping. For the cases in which the observations showed a pronounced swell signal and almost no wind waves, the agreement between observed and modeled wind profiles is remarkably good. The resulting attenuation length is found to be relatively short, which suggests that the estimated damping ratios are too large. The authors attribute this, at least partly, to processes not accounted for by the model, such as the existence of an atmospheric background wind. In the model, this extra momentum must be supplied by the waves in terms of a larger damping ratio.
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