| 1. |
- Ballarotta, Maxime, 1984-, et al.
(author)
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The residual circulation of the Southern Ocean : Which spatio-temporal scales are needed?
- 2013
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In: Ocean Modelling. - : Elsevier BV. - 1463-5003 .- 1463-5011. ; 64, s. 46-55
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Journal article (peer-reviewed)abstract
- The Southern Ocean circulation consists of a complicated mixture of processes and phenomena that arise at different time and spatial scales which need to be parametrized in the state-of-the-art climate models. The temporal and spatial scales that give rise to the present-day residual mean circulation are here inves- tigated by calculating the Meridional Overturning Circulation (MOC) in density coordinates from an eddy-permitting global model. The region sensitive to the temporal decomposition is located between 38°S and 63°S, associated with the eddy-induced transport. The ‘‘Bolus’’ component of the residual circu- lation corresponds to the eddy-induced transport. It is dominated by timescales between 1 month and 1 year. The temporal behavior of the transient eddies is examined in splitting the ‘‘Bolus’’ component into a ‘‘Seasonal’’, an ‘‘Eddy’’ and an ‘‘Inter-monthly’’ component, respectively representing the correlation between density and velocity fluctuations due to the average seasonal cycle, due to mesoscale eddies and due to large-scale motion on timescales longer than one month that is not due to the seasonal cycle. The ‘‘Seasonal’’ bolus cell is important at all latitudes near the surface. The ‘‘Eddy’’ bolus cell is dominant in the thermocline between 50°S and 35°S and over the whole ocean depth at the latitude of the Drake Passage. The ‘‘Inter-monthly’’ bolus cell is important in all density classes and is maximal in the Brazil– Malvinas Confluence and the Agulhas Return Current. The spatial decomposition indicates that a large part of the Eulerian mean circulation is recovered for spatial scales larger than 11.25°, implying that small-scale meanders in the Antarctic Circumpolar Current (ACC), near the Subantarctic and Polar Fronts, and near the Subtropical Front are important in the compensation of the Eulerian mean flow.
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| 2. |
- Brodeau, Laurent, et al.
(author)
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An ERA40-based atmospheric forcing for global ocean circulation models
- 2010
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In: Ocean Modelling. - : Elsevier BV. - 1463-5003 .- 1463-5011. ; 31:3-4, s. 88-104
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Journal article (peer-reviewed)abstract
- We develop, calibrate and test a dataset intended to drive global ocean hindcasts simulations of the last five decades. This dataset provides surface meteorological variables needed to estimate air-sea fluxes and is built from 6-hourly surface atmospheric state variables of ERA40. We first compare the raw fields of ERA40 to the CORE.v1 dataset of Large and Yeager (2004), used here as a reference, and discuss our choice to use daily radiative fluxes and monthly precipitation products extracted from satellite data rather than their ERA40 counterparts. Both datasets lead to excessively high global imbalances of heat and freshwater fluxes when tested with a prescribed climatological sea surface temperature. After identifying unrealistic time discontinuities (induced by changes in the nature of assimilated observations) and obvious global and regional biases in ERA40 fields (by comparison to high quality observations), we propose a set of corrections. Tropical surface air humidity is decreased from 1979 onward, representation of Arctic surface air temperature is improved using recent observations and the wind is globally increased. These corrections lead to a significant decrease of the excessive positive global imbalance of heat. Radiation and precipitation fields are then submitted to a small adjustment (in zonal mean) that yields a near-zero global imbalance of heat and freshwater. A set of 47-year-long simulations is carried out with the coarse-resolution (2° × 2°) version of the NEMO OGCM to assess the sensitivity of the model to the proposed corrections. Model results show that each of the proposed correction contributes to improve the representation of central features of the global ocean circulation.
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| 3. |
- de Lavergne, C., et al.
(author)
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Toward global maps of internal tide energy sinks
- 2019
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In: Ocean Modelling. - : Elsevier BV. - 1463-5003 .- 1463-5011. ; 137, s. 52-75
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Journal article (peer-reviewed)abstract
- Internal tides power much of the observed small-scale turbulence in the ocean interior. To represent mixing induced by this turbulence in ocean climate models, the cascade of internal tide energy to dissipation scales must be understood and mapped. Here, we present a framework for estimating the geography of internal tide energy sinks. The mapping relies on the following ingredients: (i) a global observational climatology of stratification; (ii) maps of the generation of M-2, S-2 and K-1 internal tides decomposed into vertical normal modes; (iii) simplified representations of the dissipation of low-mode internal tides due to wave-wave interactions, scattering by small-scale topography, interaction with critical slopes and shoaling; (iv) Lagrangian tracking of low-mode energy beams through observed stratification, including refraction and reflection. We thus obtain a global map of the column-integrated energy dissipation for each of the four considered dissipative processes, each of the three tidal constituents and each of the first five modes. Modes >= 6 are inferred to dissipate within the local water column at the employed half-degree horizontal resolution. Combining all processes, modes and constituents, we construct a map of the total internal tide energy dissipation, which compares well with observational inferences of internal wave energy dissipation. This result suggests that tides largely shape observed spatial contrasts of dissipation, and that the framework has potential in improving understanding and modelling of ocean mixing. However, sensitivity to poorly constrained parameters and simplifying assumptions entering the parameterized energy sinks calls for additional investigation. The attenuation of low-mode internal tides by wave-wave interactions needs particular attention.
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| 4. |
- Döös, Kristofer, et al.
(author)
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Dispersion of surface drifters and model-simulated trajectories
- 2011
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In: Ocean Modelling. - : Elsevier BV. - 1463-5003 .- 1463-5011. ; 39:3-4, s. 301-310
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Journal article (peer-reviewed)abstract
- From a data set encompassing the years 1990-2008 pairs of surface drifters with maximum initial separations of 5, 10 and 25 km have been identified. Model trajectories have been calculated using the same initial positions and times as the selected pairs of surface drifters. The model trajectories are based on the TRACMASS trajectory code and driven by the ocean general circulation model NEMO. The trajectories are calculated off-line, i.e. with the stored velocity fields from the circulation model. The sensitivity of the trajectory simulations to the frequency of the stored velocity fields was tested for periods of 3 and 6 h as well as 5 days. The relative dispersion of the surface-drifter and model trajectories has been compared, where the latter was found to be too low compared to the relative dispersion of the drifters. Two low-order trajectory sub-grid parameterisations were tested and successfully tuned so that the total amplitude of the relative dispersion of the model trajectories is similar to that associated with the drifter trajectories. These parameterisations are, however, too simple for a correct simulation of Lagrangian properties such as the correlation time scales and the variance of the eddy kinetic energy. The importance of model-grid resolution is quantified by comparing the relative dispersion from an eddy-permitting and a coarse-resolution model, respectively. The dispersion rate is halved with the coarse grid. The consequences of the two-dimensionality of the trajectories is evaluated by comparing the results obtained with the 2D and the Lagrangian 3D trajectories. This shows that the relative dispersion is 15% stronger when the trajectories are freely advected with the 3D velocity field.
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| 5. |
- Emmanuel, George Victor, et al.
(author)
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Role of source terms in parameterizing wave decay in the marginal ice zones
- 2022
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In: Ocean Modelling. - : Elsevier. - 1463-5003 .- 1463-5011. ; 180
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Journal article (peer-reviewed)abstract
- Wave decay in the marginal ice zones (MIZ) plays a crucial role in shaping the Arctic Ocean behaviours. Parameterizing wave decay in the MIZ is indispensable in climate models for better capturing the climate change in the Arctic. However, current wave decay parameterizations were developed without considering the influences of wave source terms. This study investigated the role and contributions of different source terms in shaping the MIZ wave decay based on sensitivity simulations. Simulation results show that the ice-induced damping term is the main contributor to MIZ wave decay. The wind input source term also plays an important role in the wave evolution in the MIZ. During high wind speeds (wind speed>10 m/s), wind input was found to increase the wave height by about 10% on average (relative to the wave height decayed by ice), irrespective of the sea ice concentration. Wind input contributes up to 30% in high wind speed areas with low sea ice concentration. Meanwhile, the contributions from wind input term to MIZ wave are more important when winds blow from the open water to MIZ. However, the angle between winds and waves is insignificant in shaping contributions from wind input. Low SIC and high wind speed conditions also favour the enhancement of wave spreading. In general, the contributions from nonlinear wave–wave interactions and dissipation source terms were found to play a minor role in shaping MIZ wave decay. However, the role of nonlinear wave–wave interactions can be important in shaping the wave spectrum. Thus, it is suggested to update the model wave decay parameterizations to accommodate the role played by wind input source term, in particular under high wind speed conditions.
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| 6. |
- Hieronymus, Magnus, 1982-, et al.
(author)
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The budgets of heat and salinity in NEMO
- 2013
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In: Ocean Modelling. - : Elsevier BV. - 1463-5003 .- 1463-5011. ; 67, s. 28-38
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Journal article (peer-reviewed)abstract
- The near steady state heat and salinity budgets under surfaces of constant depth are examined in the Nucleus for European Modelling of the Ocean (NEMO) model. It is seen that the heat fluxes in NEMO are difficult to reconcile with the idea of a deep ocean in advection-diffusion balance. Some reasons for this are that the resolved heat advection is downward above 2000 m, and that geothermal heating is, in fact, a major heat source in the deeper parts of the domain. It is also seen that isoneutral diffusion gives a very large contribution to the budgets and that the fluxes from isoneutral diffusion is in general upward. It is explained how the sign of these fluxes depends on the stratification. The heat budget for the upper 100 m of the ocean is seen to be dominated by penetrative shortwave radiation, which is so influential that we would have a mixed layer of considerable thickness even in the absence of other sources of turbulent mixing. Penetrative shortwave radiation is therefore a considerable source of potential energy.
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| 7. |
- Ibragimov, Ranis, et al.
(author)
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Effects of rotation on self-resonant internal gravity waves in the ocean
- 2010
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In: Ocean Modelling. - : Elsevier. - 1463-5003 .- 1463-5011. ; 31:3-4
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Journal article (peer-reviewed)abstract
- The Resonant Triad Model (RTM) developed in (Ibragimov, 2007), is used to study the Thorpe’s problem (Thorpe, 1997) on the existence of self-resonant internal waves, i.e., the waves for which a resonant interaction occurs at second order between the incident and reflected internal waves off slopes. The RTM represents the extension of the McComas and Bretherton’s three wave hydrostatic model (McComas and Bretherton, 1977) which ignores the effects of the earth’s rotation to the case of the non-hydrostatic analytical model involving arbitrarily large number of rotating internal waves with frequencies spanning the range of possible frequencies, i.e., between the maximum of the buoyancy frequency (vertical motion) and a minimum of the inertial frequency (horizontal motion). The present analysis is based on classification of resonant interactions into the sum, middle and difference interaction classes. It is shown in this paper that there exists a certain value of latitude, which is classified as the singular latitude, at which the coalescence of the middle and difference interaction classes occurs. Such coalescence, which apparently had passed unnoticed before, can be used to study the Thorpe’s problem on the existence of selfresonant waves. In particular, it is shown that the value of the bottom slope at which the second-order frequency and wave number components of the incident and reflected waves satisfy the internal wave dispersion relation can be approximated by two latitude-dependent parameters in the limiting case when latitude approaches its singular value. Since the existence of a such singular latitude is generic for resonant triad interactions, a question on application of the RTM to the modeling of enhanced mixing in the vicinity of ridges in the ocean arises.
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| 8. |
- Nordström, Jan, et al.
(author)
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A New Well-posed Vorticity Divergence Formulation of the Shallow Water Equations
- 2015
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In: Ocean Modelling. - : Elsevier. - 1463-5003 .- 1463-5011. ; 93, s. 1-6
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Journal article (peer-reviewed)abstract
- A new vorticity–divergence formulation of the two-dimensional shallow water equations including boundary conditions is derived. The new formulation is necessary since the conventional one does not lead to a well-posed initial boundary value problem for limited-area modelling.The new vorticity–divergence formulation includes four dependent variables instead of three and requires more equations and boundary conditions than the conventional formulation. On the other hand, it forms a hyperbolic set of equations with well-defined boundary conditions that leads to a well-posed problem with bounded energy.
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| 9. |
- Roquet, Fabien, et al.
(author)
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Accurate polynomial expressions for the density and specific volume of seawater using the TEOS-10 standard
- 2015
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In: Ocean Modelling. - : Elsevier BV. - 1463-5003 .- 1463-5011. ; 90, s. 29-43
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Journal article (peer-reviewed)abstract
- A new set of approximations to the standard TEOS-10 equation of state are presented. These follow a polynomial form, making it computationally efficient for use in numerical ocean models. Two versions are provided, the first being a fit of density for Boussinesq ocean models, and the second fitting specific volume which is more suitable for compressible models. Both versions are given as the sum of a vertical reference profile (6th-order polynomial) and an anomaly (52-term polynomial, cubic in pressure), with relative errors of similar to 0.1% on the thermal expansion coefficients. A 75-term polynomial expression is also presented for computing specific volume, with a better accuracy than the existing TEOS-10 48-term rational approximation, especially regarding the sound speed, and it is suggested that this expression represents a valuable approximation of the TEOS-10 equation of state for hydrographic data analysis. In the last section, practical aspects about the implementation of TEOS-10 in ocean models are discussed.
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| 10. |
- Tao, Y., et al.
(author)
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A simulation modeling approach to hydrothermal plumes and its comparison to analytical models
- 2013
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In: Ocean Modelling. - : Elsevier BV. - 1463-5003 .- 1463-5011. ; 61, s. 68-80
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Journal article (peer-reviewed)abstract
- We study the dynamics of hydrothermal plumes with the 3D time-dependent, Eulerian, adaptive mesh refinement code GERRIS, which solves the equations of viscous, incompressible hydrodynamics. We have implemented a new module into Gerris that treats buoyancy-driven turbulence by means of a subgrid mode. Our model is validated in numerical experiment and applied to the dynamics of a rising plume. First we simulate hydrothermal plumes in a static environment and compare our results to the widely used integral models (MTT or Briggs' model). The entrainment coefficient that we deduce from simulations falls into the range of the experimentally determined values. We also investigate the ratio between the level of the neutral-buoyancy layer and the maximum plume height. This ratio is frequently used to estimate plume heat flux via the measured level of neutral buoyancy. Although the ratio is only moderately (less than 10%) higher than the one predicted by the integral model, heat flux estimations can be substantially different. Finally, we explore the importance of background currents. We find that the simulated trajectories agree with integral models in the rising stage but the subsequent oscillations around the neutral-buoyancy layer are damped much more quickly and the level of the neutral buoyancy is also higher, same as the calm environment cases. By simulating the oscillation of a plume with suppressed transported turbulence and find a stronger oscillation than the original simulation, we suggest that a significant fraction of the difference between our model and the integral model can be explained by the absence of the turbulent transport of the latter.
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| 11. |
- van Sebille, Erik, et al.
(author)
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Lagrangian ocean analysis : Fundamentals and practices
- 2018
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In: Ocean Modelling. - : Elsevier BV. - 1463-5003 .- 1463-5011. ; 121, s. 49-75
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Research review (peer-reviewed)abstract
- Lagrangian analysis is a powerful way to analyse the output of ocean circulation models and other ocean velocity data such as from altimetry. In the Lagrangian approach, large sets of virtual particles are integrated within the three-dimensional, time-evolving velocity fields. Over several decades, a variety of tools and methods for this purpose have emerged. Here, we review the state of the art in the field of Lagrangian analysis of ocean velocity data, starting from a fundamental kinematic framework and with a focus on large-scale open ocean applications. Beyond the use of explicit velocity fields, we consider the influence of unresolved physics and dynamics on particle trajectories. We comprehensively list and discuss the tools currently available for tracking virtual particles. We then showcase some of the innovative applications of trajectory data, and conclude with some open questions and an outlook. The overall goal of this review paper is to reconcile some of the different techniques and methods in Lagrangian ocean analysis, while recognising the rich diversity of codes that have and continue to emerge, and the challenges of the coming age of petascale computing.
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| 12. |
- Wu, Lichuan, et al.
(author)
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A review of surface swell waves and their role in air-sea interactions
- 2024
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In: Ocean Modelling. - 1463-5003 .- 1463-5011.
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Journal article (peer-reviewed)abstract
- Swell waves, characterized by the long wavelength components generated by distant weather systems or storms, exert a significant influence on various air-sea interaction processes, thereby impacting weather and climate systems. Over recent decades, substantial progress has been achieved in comprehending the dynamics of swell waves and their implications for air-sea interactions. This paper presents a comprehensive review of advancements and key findings concerning surface swell waves and their interactions with the atmosphere. It encompasses a range of topics, including wave growth theory, the effects of swell waves on air-sea momentum, heat, and mass fluxes, as well as their influence on atmospheric turbulence and mixed layer processes. The most important characteristics of the swell impact (where it differs from wind sea conditions) are the wave-induced upward component of the surface stress leading to alteration of total surface stress, generation of a low-level wind maxima or changed wind profile and change of scale and behaviour of turbulence properties (turbulence kinetic energy and integral length scale). Furthermore, the paper explores the modelling of swell dissipation, the integration of swell influences in weather and climate models, and the broader climatic implications of surface swell waves. Despite notable advances in understanding swell processes, persistent knowledge gaps remain, underscoring the need for further research efforts, which are outlined in the paper.
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| 13. |
- Wu, Lichuan, et al.
(author)
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Wave effects on coastal upwelling and water level
- 2019
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In: Ocean Modelling. - : Elsevier BV. - 1463-5003 .- 1463-5011. ; 140
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Journal article (peer-reviewed)abstract
- Traditional atmosphere, ocean and wave models are run independently of each other. This means that the energy and momentum fluxes do not fully account for the impact of the oceanic wave field at the air-sea interface. In this study, the Stokes drift impact on mass and tracer advection, the Stokes-Coriolis forcing, and the sea-state-dependent momentum and energy fluxes are introduced into an ocean circulation model and tested for a domain covering the Baltic Sea and the North Sea. Sensitivity experiments are designed to investigate the influence on the simulation of storms and Baltic Sea upwelling. Inclusion of wave effects improves the model performance compared with the stand-alone circulation model in terms of sea level height, temperature and circulation. The direct sea-state-dependent momentum and turbulent kinetic energy fluxes prove to be of higher importance than the Stokes drift related effects investigated in this study (i.e., Stokes-Coriolis forcing and Stokes drift advection on tracers and on mass). The latter affects the mass and tracer advection but largely balances the influence of the Stokes-Coriolis forcing. The upwelling frequency changes by > 10% along the Swedish coast when wave effects are included. In general, the strong (weak) upwelling probability is reduced (increased) when adding the wave effects. From the results, we conclude that inclusion of wave effects can be important for regional, high-resolution ocean models even on short time scales, suggesting that they should be introduced in operational ocean circulation models. However, care should be taken when introducing the Stokes-Coriolis forcing as it should be balanced by the Stokes drift in mass and tracer advection.
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| 14. |
- Nycander, Jonas, et al.
(author)
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Open boundary conditions for nonlinear channel flow
- 2008
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In: Ocean Modelling. - : Elsevier BV. - 1463-5003. ; 24, s. 108-121
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Journal article (peer-reviewed)abstract
- Open boundary conditions are derived for the one-dimensional nonrotating two-layer shallow-water equations. The conditions are based on characteristics of the external and internal modes. It is possible to find exact nonlinear characteristic conditions for the external mode, as well as approximate nonlinear conditions for the internal mode. These conditions can also be linearised by Taylor expansion; the approximate linear conditions are similar to those used in several previous studies. Both of the nonlinear and linearised conditions perform well, indicating that either the nonlinear or linearised conditions may potentially be extended to the more general case of multi-layer flows.
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| 15. |
- Fall, Per-Arne, et al.
(author)
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ECT in Parkinson's disease-dopamine transporter visualised by [123I]-beta-CIT SPECT
- 2000
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In: Journal of Neural Transmission. - : Springer Science and Business Media LLC. - 0300-9564 .- 1435-1463. ; 107:8-9, s. 997-1008
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Journal article (peer-reviewed)abstract
- Parkinson's disease (PD) is characterised by a loss of dopaminergic neurones in the basal ganglia. These neurones may be visualised by single photon emission computed tomography (SPECT) with the cocaine analogue 2β-carboxymethyl-3-β-(4-iodophenyl)tropane ([123I]β-CIT), which labels the dopamine reuptake sites in the nerve terminals. In order to evaluate the possibility to predict the outcome of ECT a prospective study was per-formed with six PD patients in whom the [123I]β-CIT uptake was measured before and after an electroconvulsive therapy (ECT) series. The side-to-side difference in the radiotracer uptake was found to be significantly lower in striatum located contralaterally to the part of the body with the most pronounced symptomathology. No significant change in uptake of the radioligand was seen after ECT. Patients with best uptake and thus with less advanced PD improved most after ECT. The possibility to use the [123I]β-CIT uptake to predict the outcome of ECT treatment has to be further evaluated.
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| 16. |
- Fall, Per-Arne, et al.
(author)
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Maintenance ECT in Parkinson's disease
- 1999
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In: Journal of Neural Transmission. - : Springer Science and Business Media LLC. - 0300-9564 .- 1435-1463. ; 106:7-8, s. 737-741
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Journal article (peer-reviewed)abstract
- Electroconvulsive therapy (ECT) has an anti-Parkinsonian effect. In two cases repeated single ECT, i.e. maintenance ECT (MECT), caused different, hitherto unreported positive effects. One patient had either severe mental side effects from higher L-dopa doses or intolerable parkinsonian symptoms on lower doses. MECT entailed a marked improvement in parkinsonian symptoms without mental side effects. Another patient with depression as well as Parkinson's disease who showed a slight improvement of motor symptoms after a series of ECT presented further anti-parkinsonian effects on MECT.
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| 17. |
- Eberhardson, Michael, et al.
(author)
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Tumour necrosis factor inhibitors in Crohn's disease and the effect on surgery rates
- 2022
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In: Colorectal Disease. - : Wiley. - 1462-8910 .- 1463-1318. ; 24:4, s. 470-483
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Journal article (peer-reviewed)abstract
- Aim: Surgery is an important therapeutic option for Crohn's disease. The need for first bowel surgery seems to have decreased with the introduction of tumour necrosis factor inhibitors (TNFi; adalimumab or infliximab). However, the impact of TNFi on the need for intestinal surgery in Crohn's disease patients irrespective of prior bowel resection is not known. The aim of this work is to compare the incidence of bowel surgery in Crohn's disease patients who remain on TNFi treatment versus those who discontinue it. Method: We performed a nationwide register-based observational cohort study in Sweden of all incident and prevalent cases of Crohn's disease who started first-line TNFi treatment between 2006 and 2017. Patients were categorized according to TNFi treatment retention less than or beyond 1 year. The study cohort was evaluated with regard to incidence of bowel surgery from 12 months after the first ever TNFi dispensation. Results: We identified 5003 Crohn's disease patients with TNFi exposure: 3748 surgery naïve and 1255 with bowel surgery prior to TNFi initiation. Of these patients, 7% (n = 353) were subjected to abdominal surgery during the first 12 months after the start of TNFi and were subsequently excluded from the main analysis. A majority (62%) continued TNFi for 12 months or more. Treatment with TNFi for less than 12 months was associated with a significantly higher surgery rate compared with patients who continued on TNFi for 12 months or more (hazard ratio 1.26, 95% CI 1.09–1.46; p = 0.002). Conclusion: Treatment with TNFi for less than 12 months was associated with a higher risk of bowel surgery in Crohn's disease patients compared with those who continued TNFi for 12 months or more.
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