| 1. |
- Arneborg, Lars, 1969, et al.
(author)
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Tidal Energy Loss, Internal Tide Radiation, and Local Dissipation for Two-Layer Tidal Flow over a Sill
- 2017
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In: Journal of Physical Oceanography. - : American Meteorological Society. - 0022-3670 .- 1520-0485. ; 47:7, s. 1521-1538
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Journal article (peer-reviewed)abstract
- A simple analytical model for tidal energy loss at fjord sills and its partitioning into local dissipation and radiated internal tides is presented. The analytical model builds on a two-layer assumption with quasi-steady nonlinear flow over the sill and wave radiation in the far field. When the interface is situated above sill level, upstream-and downstream-propagating internal waves are generated as the bottom-layer flow becomes partially blocked because of a hydraulic control over the sill. When this control sets in, energy is lost in the transition from supercritical flow over the sill to subcritical flow downstream of the sill. The analytical model is compared with observations at the Drobak sill in the Oslo Fjord and with idealized numerical simulations with a nonhydrostatic primitive equation model. The overall good agreement between observations, analytical model, and numerical model results indicates that the hydraulic control over the sill is a key player for both the generation of internal tides and the local energy loss. The tidal energy loss decreases with increasing height of the interface above the sill. At the same time, the fraction of energy dissipated locally increases from about 20% for the interface situated at sill level to > 50% when the upper-layer thickness is less than about 80% of the sill depth. These results correspond well with the observations in the Oslo Fjord where more energy is dissipated near the sill than is radiated away.
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| 2. |
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| 3. |
- Broström, Göran, et al.
(author)
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Social class and sex-specific adult mortality during 200 years in Sweden
- 2019
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Conference paper (peer-reviewed)abstract
- Recent regional studies on adult mortality and socio-economic status inSweden are merged and also completed with analyses from country-widecensuses in strategic time periods, with the purpose to find out whetherthe locally drawn conclusions about a changing social gradient in mortalitystill holds.The answer is firmly positive: While the upper classes have definiteadvantage in modern time (after, say, the 1960s), the reverse situationholds during the nineteenth and early twentieth century for men. Women, onthe other hand, seem to follow the expected pattern of a positive socialgradient through the last 200 years.
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| 4. |
- Broström, Göran
(author)
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The effect of socioeconomic status on marital fertility during the demographic transition, northern Sweden 1821--1950: Efficient data analysis with process point of view
- 2018
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Conference paper (peer-reviewed)abstract
- The impact of the family's socioeconomic status at marriage on later child births during the demographic transition (1821--1950) is studied. It is found that the fertility decline starts in the upper classes in the decades prior to 1900. The farmers are characterized by relatively high fertility in high ages even in the end of the study period. A stopping behavior seems to dominate a spacing one, especially along cohorts. The effect of declining infant mortality over time is minor. We show how efficient statistical modeling leads to easy and fast estimation of rather complicated data. The tools are statistical sufficiency and data reduction combined with models for fertility behavior, stopping and spacing.
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| 5. |
- Broström, Göran
(author)
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The effect of socioeconomic status on marital fertility during the demographic transition, northern Sweden 1821–1950
- 2016
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Conference paper (other academic/artistic)abstract
- The impact of the family’s socioeconomic status at marriage on later child births during thedemographic transition (1821–1950) is studied. It is found that the fertility decline starts inthe upper classes in the decades prior to 1900. The farmers are characterized by relativelyhigh fertility in high ages even in the end of the study period.A stopping behavior seems to dominate a spacing one, especially along cohorts. The effectof declining infant mortality over time is minor.
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| 6. |
- Broström, Göran
(author)
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The semi-supercentenarian mortality plateau in Sweden
- 2019
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Conference paper (peer-reviewed)abstract
- Two research questions are answered: (i) Is human life unlimited?, and (ii) Are there any differences in survival at extreme age between women and men, or between different socioeconomic groups? Mortality above the age of 105 years is studied. The answer to the first question is Yes, and to the second question the answer is No.
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| 7. |
- Broström, Linus, et al.
(author)
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Known unknowns and proto-second-personal address in photographic art
- 2015
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In: Against Boredom : 17 essays : on ignorance, values, creativity, metaphysics, decision-making, truth, preference, art, processes, Ramsey, ethics, rationality, validity, human ills, science and eternal life : to Nils-Eric Sahlin on the occasion of his 60th birthday - 17 essays : on ignorance, values, creativity, metaphysics, decision-making, truth, preference, art, processes, Ramsey, ethics, rationality, validity, human ills, science and eternal life : to Nils-Eric Sahlin on the occasion of his 60th birthday. - 9789187935374
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Book chapter (pop. science, debate, etc.)
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| 8. |
- Christensen, Kai Håkon, et al.
(author)
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On the variability in the onset of the Norwegian Coastal Current
- 2018
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In: Journal of Physical Oceanography. - 0022-3670 .- 1520-0485. ; 48, s. 723-738
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Journal article (peer-reviewed)abstract
- © 2018 American Meteorological Society. A high-resolution reanalysis of the circulation in the Kattegat and Skagerrak is used to investigate the mechanisms that control the variability in the onset of the Norwegian Coastal Current. In the reanalysis, the authors have used all available in situ and remote sensing observations of salinity and temperature and use surface current observations from two coastal high-frequency radars that were ideally placed to monitor the exchange between the two basins. This study finds a strong correlation between the variability in the wind forcing in the Skagerrak and the transport in the Norwegian Coastal Current through the Torungen-Hirtshals section. Two cases with winds into and out of the Skagerrak are studied in more detail, and the results suggest asymmetries in the forcing mechanisms. For winds out of the Skagerrak, strong outflows of Baltic Sea Water associated with a deflection of the Kattegat-Skagerrak Front may disrupt local processes in the Skagerrak, which is not accounted for in previously published conceptual models for the variability of the coastal currents in this region.
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| 9. |
- Edner, Anna, et al.
(author)
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Does a magnetic blanket induce changes in muscular blood flow, skin temperature and muscular tension in horses?
- 2015
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In: Equine Veterinary Journal. - : Wiley. - 0425-1644 .- 2042-3306. ; 47:3, s. 302-307
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Journal article (peer-reviewed)abstract
- Reasons for performing studyStatic magnetic blankets are often claimed to induce increases in blood flow, reduce muscle tension and tenderness, and be beneficial in both prevention and treatment of musculoskeletal injuries in horses. However, there are no studies that confirm alleged beneficial effects of magnets on muscles of the back in healthy horses. ObjectivesTo investigate whether static magnets sewn into a blanket affect back muscle blood flow, skin temperature, mechanical nociceptive threshold (MNT) and behaviour in healthy horses. Study designProspective, randomised, blinded, placebo-controlled crossover study. MethodsThe following outcome measurements of the back of 10 healthy horses were performed; blood flow by photoplethysmography, skin temperature by use of thermistors in conjunction with digital infrared thermography, and MNTs by algometry. The horses behaviour was filmed during the procedure and scored on an ethogram. Measurements were performed repeatedly for a 30min baseline period. Thereafter a blanket with active, static magnets (900 gauss) or placebo magnets was placed on the horse and measurements were performed for a 60min treatment period and a 30min post treatment period. The study procedure was repeated on the consecutive day, when the horse received the alternative treatment. ResultsBlood flow in muscle, skin temperatures, MNTs and behavioural traits did not differ between active and placebo magnetic blankets. Skin temperature increased similarly during both active and placebo blanket treatment. ConclusionsIn healthy horses, magnetic blankets did not induce additional significant effects on muscle blood flow, skin temperature, MNTs and behaviour when compared with nonmagnetic blankets.
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| 10. |
- Edvinsson, Sören, 1953-, et al.
(author)
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Life course and long-term perspectives of social inequality in mortality among elderly and adults in Northern Sweden 1801–2013
- 2017
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Conference paper (other academic/artistic)abstract
- We investigate the development of social inequality in Swedish mortality over the life course in the elderly and adult population during the mortality transition. The study focuses on two main questions, the first relate to the long-term change in social differences in mortality. The second question is whether socio-economic position have less impact on the elderly population compared to population in working age and if the age pattern of social inequalities has changed from the 19th century to the present. Furthermore, in this study we consider possible gender-specific patterns in this process. The development of mortality in different social classes is analysed according to both total mortality and major cause-of-death categories. For the later periods, we also compare the results from the class-based analysis with other measures of social position, in this case income and education. Focus is on mortality in the Skellefteå and Umeå regions in northern Sweden 1851-2013. The study is based on the historical population data from the Demographic Data Base, Umeå University and modern population register data from Statistics Sweden.
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| 11. |
- Fredriksson, Sam, 1966, et al.
(author)
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Large eddy simulation of the tidal power plant Deep Green using the actuator line method
- 2017
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In: IOP Conference Series: Materials Science and Engineering. - 1757-8981 .- 1757-899X. ; 276:1
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Conference paper (peer-reviewed)abstract
- Tidal energy has the potential to provide asubstantial part of the sustainable electric power generation. Thetidal power plant developed by Minesto, called Deep Green, is anovel technology using a ‘flying’ kite with an attached turbine,moving at a speed several times higher than the mean flow.Multiple Deep Green power plants will eventually form arrays,which requires knowledge of both flow interactions betweenindividual devices and how the array influences the surroundingenvironment. The present study uses large eddy simulations(LES) and an actuator line model (ALM) to analyze theoscillating turbulent boundary layer flow in tidal currentswithout and with a Deep Green power plant. We present themodeling technique and preliminary results so far.
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| 12. |
- Fredriksson, Sam, 1966, et al.
(author)
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MODEL TIDAL POWER IN A TURBULENT OCEAN
- 2018
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In: Oceanera-Net Final Conference, Edinburg, Scotland, 30-31 January 2018..
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Conference paper (other academic/artistic)
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| 13. |
- Fredriksson, Sam T, et al.
(author)
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Tidal power plant simulations using large eddy simulation (LES) and the actuator line method (ALM)
- 2018
-
Conference paper (other academic/artistic)abstract
- The share of the renewable energy in the gobal energy mix is to be increased according to the sustainable development goals of the UN. Tidal energy can here potentially play a substantial role for the electric power generation. The tidal power plant Deep Green developed by Minesto uses a novel technology with a “flying” kite that, with its attached turbine, sweeps the tidal stream with a velocity several times higher than he mean flow. Eventually these power plants will form arrays requiring knowledge of (1) the interaction between individual power plants as well as (2) how the power plants and the arrays will influence the surrounding environment. The tidally oscillating turbulent boundary layer flow is in the present study analyzed using Large Eddy Simulations (LES) utilizing two different modeling techniques (pseudo-spectral and finite volume method). The boundary layer flow is analyzed both undisturbed and with a sweeping tidal power plant. The power plant is modeled using the Actuator Line Method (ALM). This method has been reformulated in order to be able to take arbitrary pathways of the actuator line into account. The results for the undisturbed flow simulations show, e.g., variations of the turbulence intensity depending on pre- or post-tidal peak flow for equivalent volume mean flow. The results for the modeled power plant show, e.g., how the wake flow downstream of the power plant that can be related to the size of the pathway size.
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| 14. |
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| 15. |
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| 16. |
- Fredriksson, Sam, 1966, et al.
(author)
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Turbulence Characteristics in Tidal Flows Using LES and ALM to Model the Tidal Power Plant Deep Green
- 2018
-
In: 4th AWTEC, Taipei, Taiwan, 2018.
-
Conference paper (peer-reviewed)abstract
- The turbulence in tidal flows affects the design and operation of tidal plants, e.g., through control system and dynamical loads. Present work is focused on a specific site west of Holy Island along the north west cost of Wales and a specific tidal power plant, Deep Green. Although, specific and applied, the work is generally applicable regarding findings and modelling techniques for other sites and designs. Large Eddy Simulations (LES) are used to study first the undisturbed tidal flow and then the flow with a power plant in operation. The undisturbed tidal flow simulations show that the turbulence characteristics differ between the acceleration and deceleration phase of the tidal cycle. The turbulence statistics are also used to estimate dynamical loads on the tidal plant with respect to, e.g., fatigue. Secondly, a novel Actuator Line Method (ALM) tidal power plant model, that e.g., takes the arbitrary trajectories of the power plant wing into account, is used. It’s used to study how the power plants affect the environment, available power downstream, and turbulence characteristics affecting other power plants in possible power plant arrays. It is shown that the width of the trajectory can be used as a measure to estimate the wake extent.
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| 17. |
- Lachmann, Florina, 1989, et al.
(author)
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Marine Plastic Litter on Small Island Developing States (SIDS): Impacts and Measures
- 2017
-
Reports (other academic/artistic)abstract
- Plastic waste that ends up in the oceans as marine litter is a tangible and urgent environmental pressure reaching even the most remote parts of the global oceans. It impacts marine life from plankton to whales and turtles to albatrosses. Public awareness on how the modern lifestyle and the use of plastics in all sectors of society has influenced the marine ecosystems in the last decades is growing, and an emerging discourse about countermeasures of all types can be seen in policies enacted by authorities in national, regional, and international policy arenas. Different coastal areas have launched Regional Action Plans (RAP) on marine litter that provide structured measures that need to be taken and general advice adapted to the respective region. However, the scale of the problem is not only global in dimension, it also cuts across all sectors in society, and until the use of materials in society becomes sustainable, plastic waste will continues to flow into the seas. This report focuses on how marine plastic litter affects Small Island Developing States (SIDS) because these are considered to be more directly vulnerable to environmental changes, including marine litter, than other countries. This report was commissioned by the Swedish Agency for Marine and Water management and written by analysts at the Swedish Institute for the Marine Environment (affiliated with the University of Gothenburg, Lund University, and Chalmers University of Technology). In this report, it is documented how marine plastic litter reaches even the most remote parts of the oceans, such as some of the small island states, and how SIDS are especially vulnerable to environmental impacts such as climate change and marine litter. The origin and composition of marine plastic litter and its environmental and economic impacts are described. Finally, measures are discussed that can be launched to mitigate the problem, both from state agencies and private corporations. Here, measures from existing RAPs on marine litter are reviewed and examples of private initiatives are mentioned. Further, the corresponding legal framework is given and side effects of marine litter measures on the Sustainable Development Goals of the UN are debated.
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| 18. |
- Lachmann, Florina, et al.
(author)
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Marine plastic litter on Small Island Developing States (SIDS) : Impacts and measures
- 2017
-
Reports (other academic/artistic)abstract
- Plastic waste that ends up in the oceans as marine litter is a tangible and urgent environmental pressure reaching even the most remote parts of the global oceans. It impacts marine life from plankton to whales and turtles to albatrosses. Public awareness on how the modern lifestyle and the use of plastics in all sectors of society has influenced the marine ecosystems in the lastdecades is growing, and an emerging discourse about countermeasures of all types can be seen in policies enacted by authorities in national, regional, and international policy arenas. Different coastal areas have launched Regional Action Plans (RAP) on marine litter that provide structured measures that need to be taken and general advice adapted to the respective region.However, the scale of the problem is not only global in dimension, it also cuts across all sectors in society, and until the use of materials in society becomes sustainable, plastic waste will continues to flow into the seas. This report focuses on how marine plastic litter affects Small Island Developing States (SIDS) because these are considered to be more directly vulnerable to environmental changes, including marine litter, than other countries.
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| 19. |
- Lachmann, Florina, et al.
(author)
-
Marine plastic litter on Small Island Developing States (SIDS): Impacts and measures.
- 2017
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Reports (other academic/artistic)abstract
- This report was commissioned by the Swedish Agency for Marine and Water management and written by analysts at the Swedish Institute for the Marine Environment (affiliated with the University of Gothenburg, Lund University, and Chalmers University of Technology). This report documents how marine plastic litter reaches even the most remote parts of the oceans with small island states, and how SIDS are especially vulnerable to its impact. The origin and composition of marine plastic litter and its impacts are described. Measures are discussed, both from state agencies and private corporations. Measures from existing RAPs on marine litter are reviewed and examples of private initiatives are mentioned. Also, the corresponding legal framework is given and side effects of marine litter measures on the Sustainable Development Goals of the UN are debated. THE VULNERABILITY OF SIDS SIDS are a set of island nations in the Caribbean Sea, the Pacific Ocean, the Atlantic, Indian Ocean, and the South China Sea. SIDS are exposed to disproportionate concentrations of plastic litter due to their location near the ocean gyres where marine litter accumulates and to often sub-performing waste management systems. ORIGINS AND COMPOSITION OF MARINE PLASTIC LITTER Because plastic make up most marine debris, the focus here is on plastic litter. Marine plastic litter washed ashore on SIDS originates from both distant countries overseas and the SIDS themselves. Buoyant plastic litter is globally distributed by ocean currents and is washed ashore on beach lines around the globe where it negatively impacts ecological and human systems. Plastics end up in the marine environment through leaks from the global value chains that run from the oil industry through various other industries to local retailers and consumers. A smaller but significant stream of plastic litter follows from the difficulties of many SIDS to establish and maintain efficient waste management systems. IMPACT OF PLASTIC LITTER ON ECOLOGICAL, SOCIAL, AND ECONOMIC VALUES Marine litter impacts the environment and organisms therein in various ways, including entanglement, ingestion, transfer of chemicals, or by otherwise altering habitats. The extent of the social and economic impact that plastic on countries is not currently well known. However, the dependence of SIDS on their natural resources through tourism and fisheries, make them economically vulnerable to plastic litter. MITIGATION AND REMEDIATION STRATEGIES For plastic that reaches SIDS, both remediation and mitigation, especially through waste management and recycling, become necessary. LEGAL AND POLITICAL FRAMEWORKS The legal framework for preventing and managing marine litter is present on all levels of governance. A declaration particularly relevant to marine litter on SIDS is the SAMOA Pathway, a declaration from the 3rd International Conference on Small Island Developing States in 2014 calling for measures to manage waste, including marine plastic litter. Multilateral agreements require party states to take actions, but these requirements are often generally formulated, and their achievements depend on the choices and participation of all parties. POLICY MEASURES PROPOSED BY REGIONAL ACTION PLANS There are 18 Regional Seas programmes under the United Nations Environmental Program for the protection of the marine environment. Some Regional Seas programmes have written strategies to guide their actions, the RAPs, i.e. a political agenda for marine litter management agreed on by member governments of the region. The contents of different RAPs show strong similarities. The analyses conducted here show that most measures suggested by RAPs are aimed at downstream processes, while fewer address the problem upstream. Additional measures are needed to solve such a global problem. VOLUNTARY AND COMMERCIAL INITIATIVES Marine litter requires an array of actions from local to global level, and is thus a matter of governance. Most measures suggested in RAPs and other work against marine litter involve government managers as well as businesses, NGOs, and voluntary initiatives. RECOMMENDATION: FUTURE COOPERATION Competence and enthusiasm for the issue on SIDS and elsewhere is growing, but more is needed. Solutions require international cooperation. Four recommendations for cooperation are highlighted here: 1. Prevent litter from entering the ocean and thus reaching SIDS: Support cooperation in regional and international agreements 2. Plastic material reaching SIDS should not be released into the environment: Technical cooperation and support for local waste management 3. If waste reaches the environment, collect it where appropriate: Support beach clean-up campaigns and other remediation measures 4. When waste has been collected, ensure that is has a value: Develop recycling markets and opportunities
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| 20. |
- Norberg, Margareta, et al.
(author)
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Use of moist smokeless tobacco (snus) and the risk of development of alcohol dependence : a cohort study in a middle-aged population in Sweden.
- 2015
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In: Drug And Alcohol Dependence. - : Elsevier BV. - 0376-8716 .- 1879-0046. ; 149, s. 151-157
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Journal article (peer-reviewed)abstract
- BACKGROUND: Convincing evidence shows that smoking is associated with alcohol dependence (AD) and a positive correlation between snus and alcohol consumption was previously shown in cross-sectional studies. We performed a longitudinal evaluation of the risk of snus users to develop AD.METHODS: A cohort study in Västerbotten County, Sweden, linked individual data on socioeconomic situation and health survey data from 21,037 men and women (46.5% men). AD was defined by the CAGE questionnaire and evaluated at baseline 1991-1997 and again after 10 years. The risk of developing AD was assessed using logistic regression analysis and propensity score matching.RESULTS: 2370 men and 430 women used snus and were without AD at baseline. Over the 10-year period, 499 men and 257 women developed AD, among whom 191 and 26, respectively, were baseline snus users. The crude relative risks of AD for male and female snus users compared to non-users were 1.8 with 95% CI (1.5, 2.2) and 2.9 (2.0, 4.3), respectively. Adjusted logistic regression showed a positive dose-response relationship between snus use and risk of AD. Analyses involving propensity score matching revealed 33 and 17 new cases of AD in men and women, respectively, after 10 years given 1000 men and 1000 women without AD had been baseline snus users rather than non-users. Results for current, previous and never smokers were similar.CONCLUSIONS: The use of snus is prospectively associated with an increased risk of AD with a dose-response relationship that is independent of smoking status.
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| 21. |
- Rohrs, J., et al.
(author)
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Comparison of HF radar measurements with Eulerian and Lagrangian surface currents
- 2015
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In: Ocean Dynamics. - : Springer Science and Business Media LLC. - 1616-7341 .- 1616-7228. ; 65:5, s. 679-690
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Journal article (peer-reviewed)abstract
- High-frequency (HF) radar-derived ocean currents are compared with in situ measurements to conclude if the radar observations include effects of surface waves that are of second order in the wave amplitude. Eulerian current measurements from a high-resolution acoustic Doppler current profiler and Lagrangian measurements from surface drifters are used as references. Directional wave spectra are obtained from a combination of pressure sensor data and a wave model. Our analysis shows that the wave-induced Stokes drift is not included in the HF radar-derived currents, that is, HF radars measure the Eulerian current. A disputed nonlinear correction to the phase velocity of surface gravity waves, which may affect HF radar signals, has a magnitude of about half the Stokes drift at the surface. In our case, this contribution by nonlinear dispersion would be smaller than the accuracy of the HF radar currents, hence no conclusion can be made. Finally, the analysis confirms that the HF radar data represent an exponentially weighted vertical average where the decay scale is proportional to the wavelength of the transmitted signal.
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| 22. |
- Skoglund, Nils, et al.
(author)
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Combustion of seaweed - A fuel design strategy
- 2017
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In: Fuel Processing Technology. - : Elsevier BV. - 0378-3820 .- 1873-7188. ; 165, s. 155-161
-
Journal article (peer-reviewed)abstract
- The high ash content and varying ash composition in algal biomass is often mentioned as problematic if to be used for thermal energy conversion. This paper suggests an approach where detailed information on ash composition and predicted ash formation reactions are basis for successful remedies enabling the use of fuels considered to be difficult. The procedure is demonstrated on seaweed (Saccharina latissima) cultivated for biorefinery purposes. The ash composition of the seaweed was found suitable for co-combustion with Miscanthus x giganteus, an energy crop high in alkali and silicon. Fuel mixtures were combusted in a bubbling fluidized bed reactor and ash samples were analyzed by SEM-EDS and XRD. The results showed that Ca from the seaweed was very reactive and thus efficient in solving the silicate melting problems. The fuel design approach was proven successful and the potential for using otherwise difficult seaweed fuels in synergetic co-combustion was demonstrated. (C) 2017 Elsevier B.V. All rights reserved.
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| 23. |
- Staalstrom, A., et al.
(author)
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Observations of Turbulence Caused by a Combination of Tides and Mean Baroclinic Flow over a Fjord Sill
- 2015
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In: Journal of Physical Oceanography. - : American Meteorological Society. - 0022-3670 .- 1520-0485. ; 45:2, s. 355-368
-
Journal article (peer-reviewed)abstract
- This study investigates the dissipation rates and flow conditions at the Drobak Sill in the Oslofjord. The area was transected 13 times with a free-falling microstructure shear probe during 4 days in June 2011. At the same time, an ADCP was deployed inside the sill. During most tidal cycles, internal hydraulic jumps with high dissipation rates were found on the downstream side of the sill. However, the internal response varied strongly between different tidal cycles with similar barotropic forcing. In the beginning of the observational period, ebb tides had no hydraulic jumps, and in the end one of the flood tides did not have a hydraulic jump. During the same period, the mean baroclinic exchange flow changed from inflow to outflow in the bottom layer. The authors conclude that the conditions at the sill are on the edge of forming hydraulic jumps and that the mean baroclinic exchange may push the flow above or below the limit of a hydraulic jump depending on the situation. This conclusion is supported by two-layer hydraulic theory. The volume-integrated dissipation rates within 500m from the sill crest compare well with estimates of energy loss in the lower layer calculated from the Bernoulli drop under the assumption of no energy loss in the upper layer. Finally, the mean dissipation rate at the sill was compared with the radiation of internal tidal energy away from the sill, and it was found that about 60%-90% of the total energy loss was dissipated locally.
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| 24. |
- Sutherland, G., et al.
(author)
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Enhanced Turbulence Associated with the Diurnal Jet in the Ocean Surface Boundary Layer
- 2016
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In: Journal of Physical Oceanography. - : American Meteorological Society. - 0022-3670 .- 1520-0485. ; 46:10, s. 3051-3067
-
Journal article (peer-reviewed)abstract
- Detailed observations of the diurnal jet, a surface intensification of the wind-driven current associated with the diurnal cycle of sea surface temperature (SST), were obtained during August and September 2012 in the subtropical Atlantic. Adiurnal increase in SST of 0.2 degrees to 0.5 degrees C was observed, which corresponded to a diurnal jet of 0.15 m s(-1). The increase in near-surface stratification limits the vertical diffusion of the wind stress, which in turn increases the near-surface shear. While the stratification decreased the turbulent dissipation rate epsilon below the depth of the diurnal jet, there was an observed increase in epsilon within the diurnal jet. The diurnal jet was observed to increase the near-surface shear by a factor of 5, which coincided with enhanced values of epsilon. The diurnal evolution of the Richardson number, which is an indicator of shear instability, is less than 1, suggesting that shear instability may contribute to near-surface turbulence. While the increased stratification due to the diurnal heating limits the depth of the momentum flux due to the wind, shear instability provides an additional source of turbulence that interacts with the enhanced shear of the diurnal jet to increase epsilon within this shallow layer.
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| 25. |
- Weber, J. E. H., et al.
(author)
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Some aspects of the Coriolis-Stokes forcing in the oceanic momentum and energy budgets
- 2015
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In: Journal of Geophysical Research-Oceans. - : American Geophysical Union (AGU). - 2169-9275. ; 120:8, s. 5589-5596
-
Journal article (peer-reviewed)abstract
- The Coriolis-Stokes (CS) force is a wave-induced forcing of the Eulerian mean motion in a rotating ocean. For idealized conditions, it is demonstrated by comparison with Lagrangian results that the appropriate surface boundary condition for the Eulerian mean wave-induced flow is that of vanishing vertical shear. The Eulerian mean current derived by applying this condition plus the inviscid Stokes drift yield the Lagrangian wave-induced drift velocity, apart from a small boundary-layer correction. Appreciation of the importance of the CS force in the momentum balance has led to investigations of the role of the CS force in the energy budget. The present study shows that the CS force is not a source for the rate of change of the total average energy density in the fluid, when the vertical integration is performed to the moving material surface. However, results to fourth order in wave steepness confirm earlier findings that the CS force acts to change the vertically integrated Eulerian kinetic energy of the mean flow. A new interpretation relates this effect to the fact that the mean Eulerian Coriolis force performs work in acting along the motion of the Lagrangian wave-induced mass (caused by the divergence effect) at the surface.
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| 26. |
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