| 1. |
- Gutiérrez Loza, Lucia, et al.
(författare)
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Measurement of air-sea methane fluxes in the Baltic Sea using the eddy covariance method
- 2019
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Ingår i: Frontiers in Earth Science. - : Frontiers Media SA. - 2296-6463. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Methane (CH4) is the second-most important greenhouse gas in the atmosphere having a significant effect on global climate. The ocean-particularly the coastal regions-have been recognized to be a net source of CH4, however, the constraints on temporal and spatial resolution of CH4 measurements have been the limiting factor to estimate the total oceanic contributions. In this study, the viability of micrometeorological methods for the analysis of CH4 fluxes in the marine environment was evaluated. We present 1 year of semi-continuous eddy covariance measurements of CH4 atmospheric dry mole fractions and air-sea CH4 flux densities at the Ostergarnsholm station at the east coast of the Gotland Island in the central Baltic Sea. The mean annual CH4 flux density was positive, indicating that the region off Gotland is a net source of CH4 to the atmosphere with monthly mean flux densities ranging between -0.1 and 36 nmol m(-2)s(-1). Both the air-water concentration gradient and the wind speed were found to be crucial parameters controlling the flux. The results were in good agreement with other measurements in the Baltic Sea reported in the MEMENTO database. Our results suggest that the eddy covariance technique is a useful tool for studying CH4 fluxes and improving the understanding of air-sea gas exchange processes with high-temporal resolution. Potentially, the high resolution of micrometeorological data can increase the understanding of the temporal variability and forcing processes of CH4 flux.
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| 2. |
- Högström, Ulf, et al.
(författare)
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The Transition from Downward to Upward Air–Sea Momentum Flux in Swell-Dominated Light Wind Conditions
- 2018
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Ingår i: Journal of the Atmospheric Sciences. - 0022-4928 .- 1520-0469. ; 75:8, s. 2579-2588
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Tidskriftsartikel (refereegranskat)abstract
- Fifteen hours of consecutive swell data from the experiment Flux, État de la Mer, et Télédétection en Condition de Fetch Variable (FETCH) in the Mediterranean show a distinct upward momentum flux. The characteristics are shown to vary systematically with wind speed. A hysteresis effect is found for wave energy of the wind-sea waves when represented as a function of wind speed, displaying higher energy during decaying winds compared to increasing winds. For the FETCH measurements, the upward momentum transfer regime is found to begin for wind speeds lower than about U 5 4ms21 . For the lowest observed wind speeds U , 2.4 m s21 , the water surface appears to be close to dynamically smooth. In this range almost all the upward momentum flux is accomplished by the peak in the cospectrum between the vertical and horizontal components of the wind velocity. It is demonstrated that this contribution in turn is linearly related to the swell significant wave height Hsd in the range 0.6 , Hsd , 1.4 m. For Hsd , 0.6 m, the contribution is zero in the present dataset but may depend on the swell magnitude in other situations. It is speculated that the observed upward momentum flux in the smooth regime, which is so strongly related to the cospectral peak at the dominant swell frequency, might be caused by the recirculation mechanism found by Wen and Mobbs in their numerical simulation of laminar flow of a nonlinear progressive wave at low wind speed
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| 3. |
- Nilsson, Erik O., 1983-, et al.
(författare)
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Characterization of Wave Energy Potential for the Baltic Sea with Focus on the Swedish Exclusive Economic Zone
- 2019
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 12:5
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Tidskriftsartikel (refereegranskat)abstract
- In this study, a third-generation wave model is used to examine the wave power resource for the Baltic Sea region at an unprecedented one-kilometer-scale resolution for the years 1998 to 2013. Special focus is given to the evaluation and description of wave field characteristics for the Swedish Exclusive Economic Zone (SEEZ). It is carried out to provide a more detailed assessment of the potential of waves as a renewable energy resource for the region. The wave energy potential is largely controlled by the distance from the coast and the fetch associated with the prevailing dominant wave direction. The ice cover is also shown to significantly influence the wave power resource, especially in the most northern basins of the SEEZ. For the areas in focus here, the potential annual average wave energy flux reaches 45 MWh/m/year in the two sub-basins with the highest wave energies, but local variations are up to 65 MWh/m/year. The assessment provides the basis for a further detailed identification of potential sites for wave energy converters. An outlook is given for additional aspects studied within a broad multi-disciplinary project to assess the conditions for offshore wave energy conversion within the SEEZ.
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