Tidal Kinetic Energy Research Articles

Nonlinear Internal Tides in a Realistically Forced Global Ocean Simulation

AbstractThe decay of the low‐mode internal tide due to the superharmonic energy cascade is investigated in a realistically forced global Hybrid Coordinate Ocean Model simulation with 1/25° (4 km) horizontal grid spacing. Time‐mean and depth‐integrated supertidal kinetic energy is found to be largest near low‐latitude internal tide generation sites, such as the Bay of Bengal, Amazon Shelf, and Mascarene Ridge. The supertidal kinetic energy can make up to 50% of the total internal tide kinetic energy several hundred kilometers from the generation sites. As opposed to the tidal flux divergence, the supertidal flux divergence does not correlate with the barotropic to baroclinic energy conversion. Instead, the time‐mean and depth‐integrated supertidal flux divergence correlates with the nonlinear kinetic energy transfers from (sub)tidal to supertidal frequency bands as estimated with a novel coarse‐graining approach. The regular spaced banding patterns of the surface‐intensified nonlinear energy transfers are attributed to semidiurnal mode 1 and mode 2 internal waves that interfere constructively at the surface. This causes patches where both surface tidal kinetic energy and nonlinear energy transfers are elevated. The simulated internal tide off the Amazon Shelf steepens significantly near these patches, generating solitary‐like waves in good agreement with Synthetic Aperture Radar imagery. Globally, we find that regions of high supertidal energy flux also show a high correlation with observed instances of internal solitary waves.

Numerical modeling of internal tides and submesoscale turbulence in the US Caribbean regional ocean

The US Caribbean ocean circulation is governed by an influx of Atlantic water through the passages between Puerto Rico, Hispaniola and the Virgin Islands, and an interplay of the Caribbean Sea water with the local topography of the region. We present an analysis of the US Caribbean ocean flow simulated by the USCROMS; which is the ROMS AGRIF model configured for the US Caribbean regional ocean at a horizontal resolution of 2 km. Outputs from the USCROMS show a seasonal variability in the strength of submesoscale turbulence within a mixed layer whose depth varies from −70 to −20 m from winter to summer, and internal tides originating from the passages between the islands. Energy spectra of the simulated baroclinic velocity show diurnal and semi-diurnal maxima and several higher-order harmonic frequency maxima associated with non-linear internal waves forming over steep slopes with super-critical topography in the continental shelf. The strongest conversion rates of the depth-averaged barotropic to baroclinic tidal energy occur at localized regions in the continental shelf with super-critical topography. These regions also exhibit enhanced transport and dissipation of the depth-averaged barotropic and baroclinic tidal kinetic energy. The dissipation in these regions is nearly 3 orders of magnitude stronger than the open ocean dissipation. The energy transport terms show a seasonal pattern characterized by stronger variance during summer and reduced variance during the winter. At the benthic regions, the dissipation levels depend on the topographic depth and the tidal steepness parameter. If the benthic region lies within the upper-ocean mixed-layer, the benthic dissipation is enhanced by surface-forced processes like wind forcing, convective mixing, submesoscale turbulence and bottom friction. If the benthic region lies below the mixed-layer, the benthic dissipation is enhanced by the friction between the super-critical topographic slopes and the periodically oscillating baroclinic tidal currents. Due to bottom friction, the tidal oscillation in the lateral currents adjacent to the sloping topography generates cyclonic and anti-cyclonic vortices with O(1) Rossby number depending on the orientation of the flow. While the cyclonic vortices form positive potential vorticity (q) leading to barotropic shear instability, anti-cyclonic vortices form negative q which leads to periodically occurring inertial instability. The lateral and inertial instabilities caused by the baroclinic tidal oscillations act as routes to submesoscale turbulence at the benthic depths of −100 m to −400 m near the super-critical topography of the continental shelf, forming O(10 km) long streaks of turbulent water with dissipation levels that are 3 orders of magnitude stronger than the dissipation in the open ocean at the same depth. The magnitudes of the dissipation and q at the benthic regions over super-critical continental-shelf topography are also modulated by the spring-neap tidal signals.

Observed Tidal Currents in Prydz Bay and Their Contribution to the Amery Ice Shelf Basal Melting

Tides play a key role in regulating the circulation and water properties around Antarctica, yet tidal currents and the corresponding influences in Prydz Bay have not been quantified with observational datasets. This study focuses on the observed characteristics of tidal currents and quantifies the tidal contribution to the basal melting of the Amery Ice Shelf (AIS). Long-term hydrography observations are provided by 10 moorings over the continental shelf and 6 borehole sites drilled through the AIS. Based on the mooring observations, we analyze the observed tidal currents, and evident seasonality in the mixed diurnal–semidiurnal tidal currents is identified. Barotropic tides dominate the tidal currents at the AIS front, except at the western corner where the seabed is abruptly deeper. The spatially and temporally averaged magnitude of tidal currents for all the current meter records is only ~3 cm s −1 . However, an observed maximum tidal velocity of ~11 cm s −1 occurs at the AIS front, and the maximal time-averaged tidal kinetic energy reaches ~31% of the total kinetic energy over the outer continental shelf. Based on the borehole observations, tide-like pulsing is identified in the ocean layer adjacent to the AIS basal surface. The maximal tidal contribution of the AIS basal melting is estimated at 69% based on a simple model. Due to the paucity of long-term velocity observations in the sub-ice-shelf cavity, the uncertainties of the estimated tide-induced melting in this study could be attributed to the simulated velocity.

Dispatchability, Energy Security, and Reduced Capital Cost in Tidal-Wind and Tidal-Solar Energy Farms

The global tidal energy resource for electricity generation is small, and converting tidal kinetic energy to electricity is expensive compared to solar-photovoltaic or land-based wind turbine generators. However, as the renewable energy content in electricity supplies grows, the need to stabilise these supplies increases. This paper describes tidal energy’s potential to reduce intermittency and variability in electricity supplied from solar and wind power farms while lowering the capital expenditure needed to improve dispatchability. The paper provides a model and hypothetical case studies to demonstrate how sharing energy storage between tidal stream power generators and wind or solar power generators can mitigate the level, frequency, and duration of power loss from wind or solar PV farms. The improvements in dispatchability use tidal energy’s innate regularity and take account of tidal asymmetry and extended duration low-velocity neap tides. The case studies are based on a national assessment of Australian tidal energy resources carried out from 2018 to 2021.

Arctic tidal current atlas

Tidal and wind-driven near-inertial currents play a vital role in the changing Arctic climate and the marine ecosystems. We compiled 429 available moored current observations taken over the last two decades throughout the Arctic to assemble a pan-Arctic atlas of tidal band currents. The atlas contains different tidal current products designed for the analysis of tidal parameters from monthly to inter-annual time scales. On shorter time scales, wind-driven inertial currents cannot be analytically separated from semidiurnal tidal constituents. Thus, we include 10–30 h band-pass filtered currents, which include all semidiurnal and diurnal tidal constituents as well as wind-driven inertial currents for the analysis of high-frequency variability of ocean dynamics. This allows for a wide range of possible uses, including local case studies of baroclinic tidal currents, assessment of long-term trends in tidal band kinetic energy and Arctic-wide validation of ocean circulation models. This atlas may also be a valuable tool for resource management and industrial applications such as fisheries, navigation and offshore construction.

Baroclinic Residual Circulation and Mass Transport Due to Internal Tides

AbstractBaroclinic (BC) tidal residual circulation due to internal tides is investigated around islands over a shallow ridge using a numerical ocean model. Internal tides enhance vertical mixing over shallow slopes, leading to horizontal density gradients that drive BC residual circulation along the main thermocline. For a strongly stratified summer case, the vertical diffusivity estimated by the Mellor and Yamada turbulence closure model exceeds 1 × 10−2 m2 s−1, and the velocity of BC residual circulations reaches 0.2 m s−1. The magnitude of BC residual circulation is larger than that of barotropic residual tidal circulation, implying that BC residual circulation due to internal tides plays an important role in coastal ocean circulation. Furthermore, BC residual flow accounts for an equal percentage (5%) of the total tidal kinetic energy as the barotropic residual flow under summer stratification conditions. Results from a coupled sediment resuspension and transport model show the growth of intermediate nepheloid layers formed by strong bottom shear stress and BC residual flow. The residual component contributes largely (23% of the total in summer) to the total suspended sediment flux. Seasonal variability is explored, with weaker winter stratification leading to reduced mixing, and thus weaker BC residual circulation and sediment flux. The magnitude of the BC residual circulation is also shown to be proportional to the square of the tidal amplitude.

Tide-current-eddy interaction: A seasonal study using high frequency radar observations along the western Bay of Bengal near 16°N

The seasonally reversing boundary currents along the western Bay of Bengal (BoB) provide a background for studying the rich and complex relationship between tidally-driven currents, mean current structure and mesoscale eddies. A year-long high-resolution surface current data set from high-frequency radars (HFR) during 2015 along the Andhra Pradesh coast (near 82°E, 16°N) has been utilized to investigate the interaction of tidal currents with bathymetry and eddies during three seasons: January, March–April and November–December. The seasonal variability shows the reversibility of boundary currents with speeds of ~1.58 (1.24) m s−1 during poleward (equatorward) flow associated with an offshore anticyclonic (inshore cyclonic) eddy in this region. The amplitudes of the tidal constituents from the HFR currents are highly correlated (R > 0.80) with those from the sea level observations from a nearby tide gauge. Among the semi-diurnal and diurnal tidal constituents, M2 (5.25–6.51 cm s−1) and K1 (2.36–4.32 cm s−1) are the dominant two respectively, in all three seasons. The tidal variance of 40–70% is observed throughout the domain, with highest contribution from the M2 tidal currents. The M2 tidal ellipse patterns match well with the mean circulation pattern, i.e., cyclonic (anticyclonic) during November–December (March–April). In the nearshore regions, the tidal currents amplify mainly through shallow-water tidal constituents (M4 and MS4) interacting with bathymetry; whereas in the offshore regions, they are dominated by M2, which co-vary with the mean seasonal circulation pattern. The highest amplitude of M2 tidal currents during November–December is predominantly due to high stratification along the western BoB. In the presence of stratification, the loss of tidal kinetic energy into turbulent processes is reduced, resulting in the amplification of M2 tidal currents. The shallow water constituents are also observed with significant amplitudes of 0.50–3.50 cm s−1 in the nearshore region. The amplitudes of overtides (M3, M4 and S4) associated with an offshore anti-cyclonic eddy are higher during March–April, whereas those for the compound tides (MK3, SK3, MS4, 2SK5, 2MN6 and 2SM6) are associated with an inshore cyclonic eddy dominate during November–December.

Turbulent mixing above the Atlantic Water around the Chukchi Borderland in 2014

This study presents an analysis of the CTD data and the turbulent microstructure data collected in 2014, the turbulent mixing environment above the Atlantic Water (AW) around the Chukchi Borderland region is studied. Surface wind becomes more efficient in driving the upper ocean movement along with the rapid decline of sea ice, thus results in a more restless interior of the Arctic Ocean. The turbulent dissipation rate is in the range of 4.60×10–10–3.31×10–9 W/kg with a mean value of 1.33×10–9 W/kg, while the diapycnal diffusivity is in the range of 1.45×10–6–1.46×10–5 m2/s with a mean value of 4.84×10–6 m2/s in 200–300 m (above the AW). After investigating on the traditional factors (i.e., wind, topography and tides) that may contribute to the turbulent dissipation rate, the results show that the tidal kinetic energy plays a dominating role in the vertical mixing above the AW. Besides, the swing of the Beaufort Gyre (BG) has an impact on the vertical shear of the geostrophic current and may contribute to the regional difference of turbulent mixing. The parameterized method for the double-diffusive convection flux above the AW is validated by the direct turbulent microstructure results.

Tidal Turbines’ Layout in a Stream with Asymmetry and Misalignment

A refined assessment of tidal currents variability is a prerequisite for successful turbine deployment in the marine environment. However, the numerical evaluation of the tidal kinetic energy resource relies, most of the time, on integrated parameters, such as the averaged or maximum stream powers. Predictions from a high resolution three-dimensional model are exploited here to characterize the asymmetry and misalignment between the flood and ebb tidal currents in the “Raz de Sein”, a strait off western Brittany (France) with strong potential for array development. A series of parameters is considered to assess resource variability and refine the cartography of local potential tidal stream energy sites. The strait is characterized by strong tidal flow divergence with currents’ asymmetry liable to vary output power by 60% over a tidal cycle. Pronounced misalignments over 20 ∘ are furthermore identified in a great part of energetic locations, and this may account for a deficit of the monthly averaged extractable energy by more than 12%. As sea space is limited for turbines, it is finally suggested to aggregate flood and ebb-dominant stream powers on both parts of the strait to output energy with reduced asymmetry.

The influence of waves on the tidal kinetic energy resource at a tidal stream energy site

Successful deployment of tidal energy converters relies on access to accurate and high resolution numerical assessments of available tidal stream power. However, since suitable tidal stream sites are located in relatively shallow waters of the continental shelf where tidal currents are enhanced, tidal energy converters may experience effects of wind-generated surface-gravity waves. Waves may thus influence tidal currents, and associated kinetic energy, through two non-linear processes: the interaction of wave and current bottom boundary layers, and the generation of wave-induced currents. Here, we develop a three-dimensional tidal circulation model coupled with a phase-averaged wave model to quantify the impact of the waves on the tidal kinetic energy resource of the Fromveur Strait (western Brittany) - a region that has been identified with strong potential for tidal array development. Numerical results are compared with in situ observations of wave parameters (significant wave height, peak period and mean wave direction) and current amplitude and direction 10m above the seabed (the assumed technology hub height for this region). The introduction of waves is found to improve predictions of tidal stream power at 10m above the seabed at the measurement site in the Strait, reducing kinetic energy by up to 9% during storm conditions. Synoptic effects of wave radiation stresses and enhanced bottom friction are more specifically identified at the scale of the Strait. Waves contribute to a slight increase in the spatial gradient of available mean tidal stream potential between the north-western area and the south-eastern part of the Strait. At the scale of the region within the Strait that has been identified for tidal stream array development, the available mean spring tidal stream potential is furthermore reduced by 12% during extreme waves conditions. Isolated effects of wave radiation stresses and enhanced bottom friction lead to a reduction in spring tidal potential of 7.8% and 5.3%, respectively. It is therefore suggested that models used for tidal resource assessment consider the effect of waves in appropriately wave-exposed regions.

Turbulent mixing in the upper ocean of the northwestern Weddell Sea, Antarctica

Turbulent mixing in the upper ocean (30–200 m) of the northwestern Weddell Sea is investigated based on profiles of temperature, salinity and microstructure data obtained during February 2014. Vertical thermohaline structures are distinct due to geographic features and sea ice distribution, resulting in that turbulent dissipation rates (e) and turbulent diffusivity (K) are vertically and spatially non-uniform. On the shelf north of Antarctic Peninsula and Philip Ridge, with a relatively homogeneous vertical structure of temperature and salinity through the entire water column in the upper 200 m, both e and K show significantly enhanced values in the order of O(10–7)–O(10–6) W/kg and O(10–3)–O(10–2) m2/s respectively, about two or three orders of magnitude higher than those in the open ocean. Mixing intensities tend to be mild due to strong stratification in the Powell Basin and South Orkney Plateau, where e decreases with depth from O(10–8) to O(10–9) W/kg, while K changes vertically in an inverse direction relative to e from O(10–6) to O(10–5) m2/s. In the marginal ice zone, K is vertically stable with the order of 10–4 m2/s although both intense dissipation and strong stratification occur at depth of 50–100 m below a cold freshened mixed layer. Though previous studies indentify wind work and tides as the primary energy sources for turbulent mixing in coastal regions, our results indicate weak relationship between K and wind stress or tidal kinetic energy. Instead, intensified mixing occurs with large bottom roughness, demonstrating that only when internal waves generated by wind and tide impinge on steep topography can the energy dissipate to support mixing. In addition, geostrophic current flowing out of the Weddell Sea through the gap west of Philip Passage is another energy source contributing to the local intense mixing.

Seasonal characteristics of internal tides and their responses to background currents in the Luzon Strait

The spatial-temporal characteristics of internal tides (ITs) in the southwest Luzon Strait are examined, based on 9-month mooring current records from autumn 2008 to summer 2009. The results of spectral analysis show that the ITs in diurnal and semidiurnal frequencies are prominent at the mooring site, especially for the clockwise rotary component. The diurnal ITs are mostly dominated by the first mode except for that in spring when the second mode is relatively predominant. The semidiurnal ITs display a variable multimodal structure. Moreover, an apparent difference is detected in the kinetic energy of diurnal ITs. The energy is strongest in winter, and followed by that in summer, whereas the value is smallest in spring and autumn. It is suggested that the incoherent motions are responsible for the significant seasonal variations of diurnal ITs, reflecting interaction between diurnal ITs and the varying background conditions. However, the semidiurnal ITs are independent of seasonal change, whose energy is smaller and only one-third of the diurnal energy in winter. Nevertheless, the abnormal variations of semidiurnal ITs are also related to the variable background conditions. The incoherent semidiurnal constituent accounts for about 37% of the total semidiurnal tidal kinetic energy, but the diurnal tidal motions contain fewer incoherent component (22.2%).

Scaling laws to understand tidal dissipation in fluid planetary regions and stars I. Rotation, stratification and thermal diffusivity

Tidal dissipation in planets and stars is one of the key physical mechanisms driving the evolution of star-planet and planet-moon systems. Several signatures of its action are observed in planetary systems thanks to their orbital architecture and the rotational state of their components. Tidal dissipation inside the fluid layers of celestial bodies are intrinsically linked to the dynamics and the physical properties of the latter. This complex dependence must be characterized. We compute the tidal kinetic energy dissipated by viscous friction and thermal diffusion in a rotating local fluid Cartesian section of a star/planet/moon submitted to a periodic tidal forcing. The properties of tidal gravito-inertial waves excited by the perturbation are derived analytically as explicit functions of the tidal frequency and local fluid parameters (i.e. the rotation, the buoyancy frequency characterizing the entropy stratification, viscous and thermal diffusivities) for periodic normal modes. The sensitivity of the resulting possibly highly resonant dissipation frequency-spectra to a control parameter of the system is either important or negligible depending on the position in the regime diagram relevant for planetary and stellar interiors. For corresponding asymptotic behaviors of tidal gravito-inertial waves dissipated by viscous friction and thermal diffusion, scaling laws for the frequencies, number, width, height and contrast with the non-resonant background of resonances are derived to quantify these variations. We characterize the strong impact of the internal physics and dynamics of fluid planetary layers and stars on the dissipation of tidal kinetic energy in their bulk. We point out the key control parameters that really play a role and demonstrate how it is now necessary to develop ab-initio modeling for tidal dissipation in celestial bodies.

Feasibility study on tidal and wave energy conversion in Iranian seas

This research aims to evaluate the best locations for tidal and wave energy conversion in Iranian seas. First, relevant technologies were reviewed. Then the application of these technologies in Iranian seas was studied focusing on the most important parameters of wave heights, wave period, tidal velocity, water depth, and shore condition. The results show that power of 15.8MW can be extracted by constructing a tidal dam with a tidal level of 3.75m in Khowr-e Doragh. In the case of tidal kinetic energy, the Qeshm Channel with an average tidal current velocity of 1.5m/s and a power flux of 13MW at its narrowest point is suitable for extracting tidal current energy in Iran. For wave energy absorption, three different sites were investigated: Amirabad in the Caspian Sea, Asaluyeh port, and Faroor Island in the Persian Gulf. The results revealed that a heaving-buoy array was most compatible with the wave condition of these sites for energy extraction. However, a U-oscillating water column (OWC) wave converter was appropriate for wave energy extraction at the Faroor site, due to its shoreline and more extreme wave climate.

Skill testing a three‐dimensional global tide model to historical current meter records

We apply several skill tests to assess tidal currents within a three‐dimensional, eddy resolving, global ocean circulation model compared to over 5000 observational velocity records spanning 40 years. We examine the skill of the HYbrid Coordinate Ocean Model (HYCOM) on a regional, basin, and global scale and in deep versus shallow water. On a global scale, we examine the model tidal kinetic energy (KE) compared to the tidal KE estimated from the observational velocity records. We examine the vertical structure of the model tidal KE by averaging over predetermined depth bins. We also investigate the ability of the model to satisfy the 95% confidence intervals of the individual tidal ellipse parameters. On a basin scale, we determine if any bias exists in model performance with regards to a particular part of the global ocean and further investigate if any variability of model skill exists within the ocean basins by testing the model against smaller subsets of the observations. Our results show that the skill of the nondata assimilative HYCOM is comparable to the skill of the altimetric‐constrained model TPXO7.2. HYCOM is shown to have up to 20% higher skill in resolving the Greenwich phase of the tides on a global basis and demonstrates moderate skill in replicating the vertical structure of the tidal currents as represented by the current meters. HYCOM demonstrates up to 20% higher skill than TPXO7.2 for some ocean basins and some ocean regions but exhibits up to 20% weaker skill in the Southern Ocean.

The Impact of Tidal Stream Turbines on Circulation and Sediment Transport in Muskeget Channel, MA

AbstractThe Finite-Volume Community Ocean Model (FVCOM) is configured to evaluate the potential impact of the proposed Muskeget Tidal Energy Project on circulation and sediment transport in the surrounding region. The extraction of tidal kinetic energy from the water column is modeled by augmenting the momentum equations with additional drag terms parameterized using local flow velocities and parameters specific to the installed turbine farm. Model-computed power output compares well with estimates based on velocities derived from a shipboard acoustic Doppler current profiler (ADCP). Total extracted power from the proposed installations during a spring ebb tide represents roughly 9% of the natural power in the deep section of the channel and 30% of the natural tidal dissipation in the turbine installation region. Due to this low level of extraction, turbine installations at the proposed transects result in relatively minor differences in the tidal current magnitude (2.5%), water level (0.8%), sediment flux (0.6%), and bed level (9%). Computations also indicate that the proposed installation generates minimal impacts to the tidal harmonics (3.3% change in amplitude and 1-min delay in phase) and tide-induced depth-averaged residual currents (2.8%). Model-computed extraction at increased levels is associated with greater perturbations to the natural conditions.

A nonhydrostatic version of FVCOM: 2. Mechanistic study of tidally generated nonlinear internal waves in Massachusetts Bay

The generation, propagation, and dissipation processes of large‐amplitude nonlinear internal waves in Massachusetts Bay during the stratified season were examined using the nonhydrostatic Finite‐Volume Coastal Ocean Model (FVCOM‐NH). The model reproduced well the characteristics of the high‐frequency internal waves observed in Massachusetts Bay in August 1998. The model experiments suggested that internal waves over Stellwagen Bank are generated by the interaction of tidal currents with steep bottom topography through a process of forming a large‐density front on the western slope of the bank by the release of an initial density perturbation near ebb‐flood transition, nonlinear steepening of the density front into a deep density depression, and disintegrating of the density depression into a wave train. Earth's rotation tends to transfer the cross‐bank tidal kinetic energy into the along‐bank direction and thus reduces the intensity of the density perturbation at ebb‐flood transition and density depression in the flood period. The internal wave packet propagates as a leading edge feature of the internal tidal wave, and the faster propagation speed of the high‐frequency internal waves in Massachusetts Bay is caused by Earth's rotation. The model experiments suggested that bottom friction can significantly influence the cross‐bank scale of the density perturbation and thus the density depression during wave generation and the dissipation during the wave's shoaling. Inclusion of vertical mixing using the Mellor‐Yamada level 2.5 turbulence closure model had only a marginal effect on wave evolution. The model results support the internal wave theory proposed by Lee and Beardsley (1974) but are in disagreement with the lee‐wave mechanism proposed by Maxworthy (1979).

Energetics of the Beamed Zombie Turbulence Maser Action Mechanism for Remote Detection of Submerged Oceanic Turbulence

Sea surface brightness spectral anomalies from a Honolulu municipal outfall have been detected from space satellites in 200 km areas extending 20 km from the wastewater diffuser (Leung and Gibson 2004, Bondur 2005, Keeler et al. 2005, Gibson et al. 2006). Dropsonde and towed body microstructure measurements show greatly enhanced viscous and temperature dissipation rates above the outfall trapping-layer. Fossil-turbulencewaves (FTWs) and secondary zombie-turbulence-waves (ZTWs) break as they propagate near-vertically and then break again near the surface to produce wind-ripple smoothing with narrow-wavelength λ patterns from the soliton-like internal waves that supply turbulence energy to advected outfall fossils and to the ZTWs they radiate. The λ = 30-250 m solitons reflect an efficient maser-action conversion of horizontal tidal and current kinetic energy by bottom boundary layer turbulence events to near-vertical FTWs with λ the Ozmidov scale of the events at fossilization. Secondary (zombie) turbulence amplifies, channels in chimneys, and near-vertically beams ambient internal wave energy at scales λ just as energized metastable molecules amplify and beam quantum wavelengths in astrophysical lasers and masers around stars. Kilowatts of buoyancy power from the treatment plant produce fossil turbulence patches trapped below the thermocline. Beamed zombie turbulence maser action (BZTMA) in mixing chimneys amplifies these kilowatts into the megawatts of surface turbulence dissipation required to affect brightness on wide sea surface areas. The BZTMA vertical mixing mechanism appears critical to vertical oceanic transport of information, heat, mass and momentum, and to the conversion of barotropic tides to baroclinic tides.

Tidal dissipation in binary systems

To first approximation, a binary system conserves its angular momentum while it evolves to its state of minimum kinetic energy: circular orbit, all spins aligned, and components rotating in synchronism with the orbital motion. The pace at which this final state is achieved depends on the physical processes that are responsible for the dissipation of the tidal kinetic energy. For stars (or planets) with an outer convection zone, the dominant mechanism identified so far is the viscous dissipation acting on the equilibrium tide. For stars with an outer radiation zone, it is the radiative damping operating on the dynamical tide. After a brief presentation of the tides, I shall review these physical processes; I shall discuss the uncertainties of their present treatment, describe the latest developments, and compare the theoretical predictions with the observed properties concerning the orbital circularization of close binaries.

The structure of tides in the Western Iberian region

A s-coordinate three-dimensional model, regional ocean modeling system (ROMS), was implemented in the Western Iberian region ranging from the coast to 11°W aiming high-resolution tidal simulations for an homogeneous ocean. The features for tidal heights and ellipses for the principal constituents, M 2, S 2, N 2, K 2, K 1, O 1, P 1 and Q 1, were imposed at the boundaries of the model. A tidal analysis for heights and tidal currents was done allowing to calculate two-dimensional distribution of amplitudes and three-dimensional structure of tidal currents. The amplitudes and phases for heights agree with previous results and observations, showing a good precision on the tidal propagation in the interior of the domain. Tidal kinetic energy is dominated by the semi-diurnal components, mainly M 2, and increases on the shelf. Over the Lisbon Promontory the diurnal component K 1 is however the second more energetic harmonic. Vertical variation of tidal ellipse parameters evidences the different structure of semi-diurnal and diurnal tidal components, as well as differences between the open sea and shelf tidal circulation.