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1
Koutitas, Christopher, et Maria Gousidou-Koutita. « A comparative study of three mathematical models for wind-generated circulation in coastal areas ». Coastal Engineering 10, no 2 (juillet 1986) : 127–38. http://dx.doi.org/10.1016/0378-3839(86)90013-x.
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Lucas, Carine, Madalina Petcu et Antoine Rousseau. « Quasi-hydrostatic primitive equations for ocean global circulation models ». Chinese Annals of Mathematics, Series B 31, no 6 (22 octobre 2010) : 939–52. http://dx.doi.org/10.1007/s11401-010-0611-6.
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Qiao, Fangli, Yeli Yuan, Jia Deng, Dejun Dai et Zhenya Song. « Wave–turbulence interaction-induced vertical mixing and its effects in ocean and climate models ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 374, no 2065 (13 avril 2016) : 20150201. http://dx.doi.org/10.1098/rsta.2015.0201.
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Heated from above, the oceans are stably stratified. Therefore, the performance of general ocean circulation models and climate studies through coupled atmosphere–ocean models depends critically on vertical mixing of energy and momentum in the water column. Many of the traditional general circulation models are based on total kinetic energy (TKE), in which the roles of waves are averaged out. Although theoretical calculations suggest that waves could greatly enhance coexisting turbulence, no field measurements on turbulence have ever validated this mechanism directly. To address this problem, a specially designed field experiment has been conducted. The experimental results indicate that the wave–turbulence interaction-induced enhancement of the background turbulence is indeed the predominant mechanism for turbulence generation and enhancement. Based on this understanding, we propose a new parametrization for vertical mixing as an additive part to the traditional TKE approach. This new result reconfirmed the past theoretical model that had been tested and validated in numerical model experiments and field observations. It firmly establishes the critical role of wave–turbulence interaction effects in both general ocean circulation models and atmosphere–ocean coupled models, which could greatly improve the understanding of the sea surface temperature and water column properties distributions, and hence model-based climate forecasting capability.
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Belyaev, K. P., A. A. Kuleshov, I. N. Smirnov et C. A. S. Tanajura. « Comparison of Data Assimilation Methods in Hydrodynamics Ocean Circulation Models ». Mathematical Models and Computer Simulations 11, no 4 (juillet 2019) : 564–74. http://dx.doi.org/10.1134/s2070048219040045.
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Zanna, Laure, et Eli Tziperman. « Optimal Surface Excitation of the Thermohaline Circulation ». Journal of Physical Oceanography 38, no 8 (1 août 2008) : 1820–30. http://dx.doi.org/10.1175/2008jpo3752.1.
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Abstract The amplification of thermohaline circulation (THC) anomalies resulting from heat and freshwater forcing at the ocean surface is investigated in a zonally averaged coupled ocean–atmosphere model. Optimal initial conditions of surface temperature and salinity leading to the largest THC growth are computed, and so are the structures of stochastic surface temperature and salinity forcing that excite maximum THC variance (stochastic optimals). When the THC amplitude is defined as its sum of squares (equivalent to using the standard L2 norm), the nonnormal linearized dynamics lead to an amplification with a time scale on the order of 100 yr. The optimal initial conditions have a vanishing THC anomaly, and the complex amplification mechanism involves the advection of both temperature and salinity anomalies by the mean flow and of the mean temperature and salinity by the anomaly flow. The L2 characterization of THC anomalies leads to physically interesting results, yet to a mathematically singular problem. A novel alternative characterizing the THC amplitude by its maximum value, as often done in general circulation model studies, is therefore introduced. This complementary method is shown to be equivalent to using the L-infinity norm, and the needed mathematical approach is developed and applied to the THC problem. Under this norm, an amplification occurs within 10 yr explained by the classic salinity advective feedback mechanism. The analysis of the stochastic optimals shows that the character of the THC variability may be very sensitive to the spatial pattern of the surface forcing. In particular, a maximum THC variance and long-time-scale variability are excited by a basin-scale surface forcing pattern, while a significantly higher frequency and to some extent a weaker variability are induced by a smooth and large-scale, yet mostly concentrated in polar areas, surface forcing pattern. Overall, the results suggest that a large THC variability can be efficiently excited by atmospheric surface forcing, and the simple model used here makes several predictions that would be interesting to test using more complex models.
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Janecki, Maciej, Dawid Dybowski, Jaromir Jakacki, Artur Nowicki et Lidia Dzierzbicka-Glowacka. « The Use of Satellite Data to Determine the Changes of Hydrodynamic Parameters in the Gulf of Gdańsk via EcoFish Model ». Remote Sensing 13, no 18 (8 septembre 2021) : 3572. http://dx.doi.org/10.3390/rs13183572.
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Using mathematical models alone to describe the changes in the parameters characterizing the analyzed reservoir may be insufficient due to the complexity of ocean circulation. One of the ways to improve the accuracy of models is to use data assimilation based on remote sensing methods. In this study, we tested the EcoFish numerical model that was developed for the Gulf of Gdańsk area, under the FindFish Knowledge Transfer Platform. In order to improve the model results and map local phenomena occurring in the studied water, which would be difficult to simulate using only mathematical equations, EcoFish was extended with a satellite data assimilation module that assimilates the sea surface temperature data from a medium-resolution imaging spectroradiometer and an advanced ultrahigh-resolution radiometer. EcoFish was then statistically validated, which resulted in high correlations for water temperature and salinity as well as low errors in comparison with in situ experimental data.
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Saenz, Juan A., Qingshan Chen et Todd Ringler. « Prognostic Residual Mean Flow in an Ocean General Circulation Model and its Relation to Prognostic Eulerian Mean Flow ». Journal of Physical Oceanography 45, no 9 (septembre 2015) : 2247–60. http://dx.doi.org/10.1175/jpo-d-15-0024.1.
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AbstractRecent work has shown that taking the thickness-weighted average (TWA) of the Boussinesq equations in buoyancy coordinates results in exact equations governing the prognostic residual mean flow where eddy–mean flow interactions appear in the horizontal momentum equations as the divergence of the Eliassen–Palm flux tensor (EPFT). It has been proposed that, given the mathematical tractability of the TWA equations, the physical interpretation of the EPFT, and its relation to potential vorticity fluxes, the TWA is an appropriate framework for modeling ocean circulation with parameterized eddies. The authors test the feasibility of this proposition and investigate the connections between the TWA framework and the conventional framework used in models, where Eulerian mean flow prognostic variables are solved for. Using the TWA framework as a starting point, this study explores the well-known connections between vertical transfer of horizontal momentum by eddy form drag and eddy overturning by the bolus velocity, used by Greatbatch and Lamb and Gent and McWilliams to parameterize eddies. After implementing the TWA framework in an ocean general circulation model, the analysis is verified by comparing the flows in an idealized Southern Ocean configuration simulated using the TWA and conventional frameworks with the same mesoscale eddy parameterization.
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Thompson, Andrew F. « The atmospheric ocean : eddies and jets in the Antarctic Circumpolar Current ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 366, no 1885 (25 septembre 2008) : 4529–41. http://dx.doi.org/10.1098/rsta.2008.0196.
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Although the Antarctic Circumpolar Current (ACC) is the longest and the strongest oceanic current on the Earth and is the primary means of inter-basin exchange, it remains one of the most poorly represented components of global climate models. Accurately describing the circulation of the ACC is made difficult owing to the prominent role that mesoscale eddies and jets, oceanic equivalents of atmospheric storms and storm tracks, have in setting the density structure and transport properties of the current. The successes and limitations of different representations of eddy processes in models of the ACC are considered, with particular attention given to how the circulation responds to changes in wind forcing. The dynamics of energetic eddies and topographically steered jets may both temper and enhance the sensitivity of different aspects of the ACC's circulation to changes in climate.
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Belyaev, Konstantin P., et Clemente A. S. Tanajura. « On the correction of perturbations due to data assimilation in ocean circulation models ». Applied Mathematical Modelling 29, no 7 (juillet 2005) : 690–709. http://dx.doi.org/10.1016/j.apm.2004.10.001.
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Hogg, Andrew McC, et David R. Munday. « Does the sensitivity of Southern Ocean circulation depend upon bathymetric details ? » Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 372, no 2019 (13 juillet 2014) : 20130050. http://dx.doi.org/10.1098/rsta.2013.0050.
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The response of the major ocean currents to changes in wind stress forcing is investigated with a series of idealized, but eddy-permitting, model simulations. Previously, ostensibly similar models have shown considerable variation in the oceanic response to changing wind stress forcing. Here, it is shown that a major reason for these differences in model sensitivity is subtle modification of the idealized bathymetry. The key bathymetric parameter is the extent to which the strong eddy field generated in the circumpolar current can interact with the bottom water formation process. The addition of an embayment, which insulates bottom water formation from meridional eddy fluxes, acts to stabilize the deep ocean density and enhances the sensitivity of the circumpolar current. The degree of interaction between Southern Ocean eddies and Antarctic shelf processes may thereby control the sensitivity of the Southern Ocean to change.
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Bryden, Harry L., Carol Robinson et Gwyn Griffiths. « Changing currents : a strategy for understanding and predicting the changing ocean circulation ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 370, no 1980 (13 décembre 2012) : 5461–79. http://dx.doi.org/10.1098/rsta.2012.0397.
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Within the context of UK marine science, we project a strategy for ocean circulation research over the next 20 years. We recommend a focus on three types of research: (i) sustained observations of the varying and evolving ocean circulation, (ii) careful analysis and interpretation of the observed climate changes for comparison with climate model projections, and (iii) the design and execution of focused field experiments to understand ocean processes that are not resolved in coupled climate models so as to be able to embed these processes realistically in the models. Within UK-sustained observations, we emphasize smart, cost-effective design of the observational network to extract maximum information from limited field resources. We encourage the incorporation of new sensors and new energy sources within the operational environment of UK-sustained observational programmes to bridge the gap that normally separates laboratory prototype from operational instrument. For interpreting the climate-change records obtained through a variety of national and international sustained observational programmes, creative and dedicated UK scientists should lead efforts to extract the meaningful signals and patterns of climate change and to interpret them so as to project future changes. For the process studies, individual scientists will need to work together in team environments to combine observational and process modelling results into effective improvements in the coupled climate models that will lead to more accurate climate predictions.
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Dyke, P. P. G. « Water circulation in the Firth of Forth, Scotland ». Proceedings of the Royal Society of Edinburgh. Section B. Biological Sciences 93, no 3-4 (1987) : 273–84. http://dx.doi.org/10.1017/s0269727000006734.
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SynopsisThe Firth of Forth, in terms of physical oceanography, is part of the North Sea. The general circulation pattern in the firth must be regarded as largely speculative. There have been insufficient measurements of insufficient quality, and what evidence exists leads to the view that what circulation there is, is sluggish and varies from season to season and from year to year.A description is given of the three principal mechanisms that contribute to circulation. Tides, due initially to astronomical forces, manifest themselves in the Firth of Forth through the rise and fall of the adjacent open sea. This rise and fall, periodic in mid ocean, is no longer strictly so in the firth and neither are the tidal currents. The wind-driven currents in the sea are influenced by the earth's rotation. In the Firth of Forth, some of this influence is retained. Naturally, wind-driven currents are larger near the surface. Finally, when water of different densities meets, overturning causes convection currents. All of these effects are present to some extent in the Firth of Forth. In addition, specific account has to be taken of complicated coastal and bottom topography and river outflow. Some attempt to bring together these effects and available measurements is made in this paper. Lastly, several theoretical models are proposed which account for the magnitudes and directions of the observed steady circulation. Mathematical details are given in appendices.
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Meijers, A. J. S. « The Southern Ocean in the Coupled Model Intercomparison Project phase 5 ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 372, no 2019 (13 juillet 2014) : 20130296. http://dx.doi.org/10.1098/rsta.2013.0296.
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The Southern Ocean is an important part of the global climate system, but its complex coupled nature makes both its present state and its response to projected future climate forcing difficult to model. Clear trends in wind, sea-ice extent and ocean properties emerged from multi-model intercomparison in the Coupled Model Intercomparison Project phase 3 (CMIP3). Here, we review recent analyses of the historical and projected wind, sea ice, circulation and bulk properties of the Southern Ocean in the updated Coupled Model Intercomparison Project phase 5 (CMIP5) ensemble. Improvements to the models include higher resolutions, more complex and better-tuned parametrizations of ocean mixing, and improved biogeochemical cycles and atmospheric chemistry. CMIP5 largely reproduces the findings of CMIP3, but with smaller inter-model spreads and biases. By the end of the twenty-first century, mid-latitude wind stresses increase and shift polewards. All water masses warm, and intermediate waters freshen, while bottom waters increase in salinity. Surface mixed layers shallow, warm and freshen, whereas sea ice decreases. The upper overturning circulation intensifies, whereas bottom water formation is reduced. Significant disagreement exists between models for the response of the Antarctic Circumpolar Current strength, for reasons that are as yet unclear.
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Premakumari, Ramapura N., Chandrali Baishya, Pundikala Veeresha et Lanre Akinyemi. « A Fractional Atmospheric Circulation System under the Influence of a Sliding Mode Controller ». Symmetry 14, no 12 (10 décembre 2022) : 2618. http://dx.doi.org/10.3390/sym14122618.
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The earth’s surface is heated by the large-scale movement of air known as atmospheric circulation, which works in conjunction with ocean circulation. More than 105 variables are involved in the complexity of the weather system. In this work, we analyze the dynamical behavior and chaos control of an atmospheric circulation model known as the Hadley circulation model, in the frame of Caputo and Caputo–Fabrizio fractional derivatives. The fundamental novelty of this paper is the application of the Caputo derivative with equal dimensionality to models that includes memory. A sliding mode controller (SMC) is developed to control chaos in this fractional-order atmospheric circulation system with uncertain dynamics. The proposed controller is applied to both commensurate and non-commensurate fractional-order systems. To demonstrate the intricacy of the models, we plot some graphs of various fractional orders with appropriate parameter values. We have observed the influence of thermal forcing on the dynamics of the system. The outcome of the analytical exercises is validated using numerical simulations.
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Dunstone, Nick J. « A perspective on sustained marine observations for climate modelling and prediction ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 372, no 2025 (28 septembre 2014) : 20130340. http://dx.doi.org/10.1098/rsta.2013.0340.
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Here, I examine some of the many varied ways in which sustained global ocean observations are used in numerical modelling activities. In particular, I focus on the use of ocean observations to initialize predictions in ocean and climate models. Examples are also shown of how models can be used to assess the impact of both current ocean observations and to simulate that of potential new ocean observing platforms. The ocean has never been better observed than it is today and similarly ocean models have never been as capable at representing the real ocean as they are now. However, there remain important unanswered questions that can likely only be addressed via future improvements in ocean observations. In particular, ocean observing systems need to respond to the needs of the burgeoning field of near-term climate predictions. Although new ocean observing platforms promise exciting new discoveries, there is a delicate balance to be made between their funding and that of the current ocean observing system. Here, I identify the need to secure long-term funding for ocean observing platforms as they mature, from a mainly research exercise to an operational system for sustained observation over climate change time scales. At the same time, considerable progress continues to be made via ship-based observing campaigns and I highlight some that are dedicated to addressing uncertainties in key ocean model parametrizations. The use of ocean observations to understand the prominent long time scale changes observed in the North Atlantic is another focus of this paper. The exciting first decade of monitoring of the Atlantic meridional overturning circulation by the RAPID-MOCHA array is highlighted. The use of ocean and climate models as tools to further probe the drivers of variability seen in such time series is another exciting development. I also discuss the need for a concerted combined effort from climate models and ocean observations in order to understand the current slow-down in surface global warming.
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Moore, P., Q. Zhang et A. Alothman. « Recent results on modelling the spatial and temporal structure of the Earth's gravity field ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 364, no 1841 (22 février 2006) : 1009–26. http://dx.doi.org/10.1098/rsta.2006.1751.
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The Earth's gravity field plays a central role in sea-level change. In the simplest application a precise gravity field will enable oceanographers to capitalize fully on the altimetric datasets collected over the past decade or more by providing a geoid from which absolute sea-level topography can be recovered. However, the concept of a static gravity field is now redundant as we can observe temporal variability in the geoid due to mass redistribution in or on the total Earth system. Temporal variability, associated with interactions between the land, oceans and atmosphere, can be investigated through mass redistributions with, for example, flow of water from the land being balanced by an increase in ocean mass. Furthermore, as ocean transport is an important contributor to the mass redistribution the time varying gravity field can also be used to validate Global Ocean Circulation models. This paper will review the recent history of static and temporal gravity field recovery, from the 1980s to the present day. In particular, mention will be made of the role of satellite laser ranging and other space tracking techniques, satellite altimetry and in situ gravity which formed the basis of gravity field determination until the last few years. With the launch of Challenging Microsatellite Payload and Gravity and Circulation Experiment (GRACE) our knowledge of the spatial distribution of the Earth's gravity field is taking a leap forward. Furthermore, GRACE is now providing insight into temporal variability through ‘monthly’ gravity field solutions. Prior to this data we relied on satellite tracking, Global Positioning System and geophysical models to give us insight into the temporal variability. We will consider results from these methodologies and compare them to preliminary results from the GRACE mission.
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Gianchandani, Kaushal, Hezi Gildor et Nathan Paldor. « On the role of domain aspect ratio in the westward intensification of wind-driven surface ocean circulation ». Ocean Science 17, no 1 (18 février 2021) : 351–63. http://dx.doi.org/10.5194/os-17-351-2021.
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Abstract. The two seminal studies on westward intensification, carried out by Stommel and Munk over 70 years ago, are revisited to elucidate the role of the domain aspect ratio (i.e., meridional to zonal extents of the basin) in determining the transport of the western boundary current (WBC). We examine the general mathematical properties of the two models by transforming them to differential problems that contain only two parameters – the domain aspect ratio and the non-dimensional damping (viscous) coefficient. Explicit analytical expressions are obtained from solutions of the non-dimensional vorticity equations and verified by long-term numerical simulations of the corresponding time-dependent equations. The analytical expressions as well as the simulations imply that in Stommel's model both the domain aspect ratio and the damping parameter contribute to the non-dimensional transport of the WBC. However, the transport increases as a cubic power of the aspect ratio and decreases linearly with the damping coefficient. On the other hand, in Munk's model the WBC's transport increases linearly with the domain aspect ratio, while the damping coefficient plays a minor role only. This finding is employed to explain the weak WBC in the South Pacific. The decrease in transport of the WBC for small-domain aspect ratio results from the decrease in Sverdrup transport in the basin's interior because the meridional shear of the zonal velocity cannot be neglected as an additional vorticity term.
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Soldatenko, Sergei. « On the Effects of Mixed and Deep Ocean Layers on Climate Change and Variability ». Journal of Marine Science and Engineering 10, no 9 (31 août 2022) : 1216. http://dx.doi.org/10.3390/jmse10091216.
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The ocean, one of the five major components of the Earth’s climate system, plays a key role in climate-forming processes, affecting its change and variability. The ocean influences climate over a wide range of time–space scales. To explore the climate, its components, interactions between them and, in particular, the effect of the ocean on weather and climate, researchers commonly use extremely complex mathematical models of the climate system that describe the atmospheric and ocean general circulations. However, this class of climate models requires enormous human and computing resources to simulate the climate system itself and to analyze the output results. For simple climate models, such as energy balance and similar models, the computational cost is insignificant, which is why these models represent a test tool to mimic a complex climate system and obtaining preliminary estimates of the influence of various internal and external factors on climate, its change and variability. The global mean surface temperature (GMST) and its fluctuations in time serve as critical indicators of changes in the climate system state. We apply a simple two-box ocean model to explore the effect of mixed and deep ocean layers on climate-forming processes and especially on climate change and variability. The effect of mixed and deep ocean layers on GMST is parameterized via the layers’ effective heat capacities and heat exchange between layers. For the listed parameters, the sensitivity functions were derived numerically and analytically, allowing one to obtain an idea of how the mixed and deep ocean layers affect climate change and variability. To study climate change, a deterministic version of the model was used with radiative forcing parameterized by both stepwise and linear functions. In climate variability experiments, a stochastic version of the model was applied in which the radiative forcing is considered as a delta-correlated random process.
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Worster, M. Grae, et David W. Rees Jones. « Sea-ice thermodynamics and brine drainage ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 373, no 2045 (13 juillet 2015) : 20140166. http://dx.doi.org/10.1098/rsta.2014.0166.
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Significant changes in the state of the Arctic ice cover are occurring. As the summertime extent of sea ice diminishes, the Arctic is increasingly characterized by first-year rather than multi-year ice. It is during the early stages of ice growth that most brine is injected into the oceans, contributing to the buoyancy flux that mediates the thermo-haline circulation. Current operational sea-ice components of climate models often treat brine rejection between sea ice and the ocean similarly to a thermodynamic segregation process, assigning a fixed salinity to the sea ice, typical of multi-year ice. However, brine rejection is a dynamical, buoyancy-driven process and the salinity of sea ice varies significantly during the first growth season. As a result, current operational models may over predict the early brine fluxes from newly formed sea ice, which may have consequences for coupled simulations of the polar oceans. Improvements both in computational power and our understanding of the processes involved have led to the emergence of a new class of sea-ice models that treat brine rejection dynamically and should enhance predictions of the buoyancy forcing of the oceans.
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Stott, Peter A., et Chris E. Forest. « Ensemble climate predictions using climate models and observational constraints ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 365, no 1857 (14 juin 2007) : 2029–52. http://dx.doi.org/10.1098/rsta.2007.2075.
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Two different approaches are described for constraining climate predictions based on observations of past climate change. The first uses large ensembles of simulations from computationally efficient models and the second uses small ensembles from state-of-the-art coupled ocean–atmosphere general circulation models. Each approach is described and the advantages of each are discussed. When compared, the two approaches are shown to give consistent ranges for future temperature changes. The consistency of these results, when obtained using independent techniques, demonstrates that past observed climate changes provide robust constraints on probable future climate changes. Such probabilistic predictions are useful for communities seeking to adapt to future change as well as providing important information for devising strategies for mitigating climate change.
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Frame, D. J., T. Aina, C. M. Christensen, N. E. Faull, S. H. E. Knight, C. Piani, S. M. Rosier, K. Yamazaki, Y. Yamazaki et M. R. Allen. « The climate prediction .net BBC climate change experiment : design of the coupled model ensemble ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 367, no 1890 (16 décembre 2008) : 855–70. http://dx.doi.org/10.1098/rsta.2008.0240.
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Perturbed physics experiments are among the most comprehensive ways to address uncertainty in climate change forecasts. In these experiments, parameters and parametrizations in atmosphere–ocean general circulation models are perturbed across ranges of uncertainty, and results are compared with observations. In this paper, we describe the largest perturbed physics climate experiment conducted to date, the British Broadcasting Corporation (BBC) climate change experiment, in which the physics of the atmosphere and ocean are changed, and run in conjunction with a forcing ensemble designed to represent uncertainty in past and future forcings, under the A1B Special Report on Emissions Scenarios (SRES) climate change scenario.
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Shepherd, John G., Peter G. Brewer, Andreas Oschlies et Andrew J. Watson. « Ocean ventilation and deoxygenation in a warming world : introduction and overview ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 375, no 2102 (7 août 2017) : 20170240. http://dx.doi.org/10.1098/rsta.2017.0240.
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Changes of ocean ventilation rates and deoxygenation are two of the less obvious but important indirect impacts expected as a result of climate change on the oceans. They are expected to occur because of (i) the effects of increased stratification on ocean circulation and hence its ventilation, due to reduced upwelling, deep-water formation and turbulent mixing, (ii) reduced oxygenation through decreased oxygen solubility at higher surface temperature, and (iii) the effects of warming on biological production, respiration and remineralization. The potential socio-economic consequences of reduced oxygen levels on fisheries and ecosystems may be far-reaching and significant. At a Royal Society Discussion Meeting convened to discuss these matters, 12 oral presentations and 23 posters were presented, covering a wide range of the physical, chemical and biological aspects of the issue. Overall, it appears that there are still considerable discrepancies between the observations and model simulations of the relevant processes. Our current understanding of both the causes and consequences of reduced oxygen in the ocean, and our ability to represent them in models are therefore inadequate, and the reasons for this remain unclear. It is too early to say whether or not the socio-economic consequences are likely to be serious. However, the consequences are ecologically, biogeochemically and climatically potentially very significant, and further research on these indirect impacts of climate change via reduced ventilation and oxygenation of the oceans should be accorded a high priority. This article is part of the themed issue ‘Ocean ventilation and deoxygenation in a warming world’.
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Alkhayuon, Hassan, Peter Ashwin, Laura C. Jackson, Courtney Quinn et Richard A. Wood. « Basin bifurcations, oscillatory instability and rate-induced thresholds for Atlantic meridional overturning circulation in a global oceanic box model ». Proceedings of the Royal Society A : Mathematical, Physical and Engineering Sciences 475, no 2225 (mai 2019) : 20190051. http://dx.doi.org/10.1098/rspa.2019.0051.
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The Atlantic meridional overturning circulation (AMOC) transports substantial amounts of heat into the North Atlantic sector, and hence is of very high importance in regional climate projections. The AMOC has been observed to show multi-stability across a range of models of different complexity. The simplest models find a bifurcation associated with the AMOC ‘on’ state losing stability that is a saddle node. Here, we study a physically derived global oceanic model of Wood et al. with five boxes, that is calibrated to runs of the FAMOUS coupled atmosphere-ocean general circulation model. We find the loss of stability of the ‘on’ state is due to a subcritical Hopf for parameters from both pre-industrial and doubled CO 2 atmospheres. This loss of stability via subcritical Hopf bifurcation has important consequences for the behaviour of the basin of attraction close to bifurcation. We consider various time-dependent profiles of freshwater forcing to the system, and find that rate-induced thresholds for tipping can appear, even for perturbations that do not cross the bifurcation. Understanding how such state transitions occur is important in determining allowable safe climate change mitigation pathways to avoid collapse of the AMOC.
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Shindell, Drew. « Estimating the potential for twenty-first century sudden climate change ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 365, no 1860 (30 juillet 2007) : 2675–94. http://dx.doi.org/10.1098/rsta.2007.2088.
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I investigate the potential for sudden climate change during the current century. This investigation takes into account evidence from the Earth's history, from climate models and our understanding of the physical processes governing climate shifts. Sudden alterations to climate forcing seem to be improbable, with sudden changes instead most likely to arise from climate feedbacks. Based on projections from models validated against historical events, dramatic changes in ocean circulation appear unlikely. Ecosystem–climate feedbacks clearly have the potential to induce sudden change, but are relatively poorly understood at present. More probable sudden changes are large increases in the frequency of summer heatwaves and changes resulting from feedbacks involving hydrology. These include ice sheet decay, which may be set in motion this century. The most devastating consequences are likely to occur further in the future, however. Reductions in subtropical precipitation are likely to be the most severe hydrologic effects this century, with rapid changes due to the feedbacks of relatively well-understood large-scale circulation patterns. Water stress may become particularly acute in the Southwest US and Mexico, and in the Mediterranean and Middle East, where rainfall decreases of 10–25% (regionally) and up to 40% (locally) are projected.
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van den Bremer, T. S., et Ø. Breivik. « Stokes drift ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 376, no 2111 (11 décembre 2017) : 20170104. http://dx.doi.org/10.1098/rsta.2017.0104.
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During its periodic motion, a particle floating at the free surface of a water wave experiences a net drift velocity in the direction of wave propagation, known as the Stokes drift (Stokes 1847 Trans. Camb. Philos. Soc. 8 , 441–455). More generally, the Stokes drift velocity is the difference between the average Lagrangian flow velocity of a fluid parcel and the average Eulerian flow velocity of the fluid. This paper reviews progress in fundamental and applied research on the induced mean flow associated with surface gravity waves since the first description of the Stokes drift, now 170 years ago. After briefly reviewing the fundamental physical processes, most of which have been established for decades, the review addresses progress in laboratory and field observations of the Stokes drift. Despite more than a century of experimental studies, laboratory studies of the mean circulation set up by waves in a laboratory flume remain somewhat contentious. In the field, rapid advances are expected due to increasingly small and cheap sensors and transmitters, making widespread use of small surface-following drifters possible. We also discuss remote sensing of the Stokes drift from high-frequency radar. Finally, the paper discusses the three main areas of application of the Stokes drift: in the coastal zone, in Eulerian models of the upper ocean layer and in the modelling of tracer transport, such as oil and plastic pollution. Future climate models will probably involve full coupling of ocean and atmosphere systems, in which the wave model provides consistent forcing on the ocean surface boundary layer. Together with the advent of new space-borne instruments that can measure surface Stokes drift, such models hold the promise of quantifying the impact of wave effects on the global atmosphere–ocean system and hopefully contribute to improved climate projections. This article is part of the theme issue ‘Nonlinear water waves’.
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John, Eleanor H., Paul N. Pearson, Helen K. Coxall, Heather Birch, Bridget S. Wade et Gavin L. Foster. « Warm ocean processes and carbon cycling in the Eocene ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 371, no 2001 (28 octobre 2013) : 20130099. http://dx.doi.org/10.1098/rsta.2013.0099.
Texte intégralRésumé :
Sea surface and subsurface temperatures over large parts of the ocean during the Eocene epoch (55.5–33.7 Ma) exceeded modern values by several degrees, which must have affected a number of oceanic processes. Here, we focus on the effect of elevated water column temperatures on the efficiency of the biological pump, particularly in relation to carbon and nutrient cycling. We use stable isotope values from exceptionally well-preserved planktonic foraminiferal calcite from Tanzania and Mexico to reconstruct vertical carbon isotope gradients in the upper water column, exploiting the fact that individual species lived and calcified at different depths. The oxygen isotope ratios of different species' tests are used to estimate the temperature of calcification, which we converted to absolute depths using Eocene temperature profiles generated by general circulation models. This approach, along with potential pitfalls, is illustrated using data from modern core-top assemblages from the same area. Our results indicate that, during the Early and Middle Eocene, carbon isotope gradients were steeper (and larger) through the upper thermocline than in the modern ocean. This is consistent with a shallower average depth of organic matter remineralization and supports previously proposed hypotheses that invoke high metabolic rates in a warm Eocene ocean, leading to more efficient recycling of organic matter and reduced burial rates of organic carbon.
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Tailleux, Rémi. « Generalized Patched Potential Density and Thermodynamic Neutral Density : Two New Physically Based Quasi-Neutral Density Variables for Ocean Water Masses Analyses and Circulation Studies ». Journal of Physical Oceanography 46, no 12 (décembre 2016) : 3571–84. http://dx.doi.org/10.1175/jpo-d-16-0072.1.
Texte intégralRésumé :
AbstractIn this paper, two new quasi-neutral density variables—generalized patched potential density (GPPD) and thermodynamic neutral density γT—are introduced, which are showed to approximate Jackett and McDougall empirical neutral density γn significantly better than the quasi-material rational polynomial approximation γa previously introduced by McDougall and Jackett. In contrast to γn, γT is easily and efficiently computed for arbitrary climatologies of temperature and salinity (both realistic and idealized), has a clear physical basis rooted in the theory of available potential energy, and does not suffer from nonmaterial effects that make γn so difficult to use in water masses analysis. In addition, γT is also significantly more neutral than all known quasi-material density variables, such as σ2, while remaining less neutral than γn. Because unlike γn, γT is mathematically explicit, it can be used for theoretical as well as observational studies, as well as a generalized vertical coordinate in isopycnal models of the ocean circulation. On the downside, γT exhibits inversions and degraded neutrality in the polar regions, where the Lorenz reference state is the furthest away from the actual state. Therefore, while γT represents progress over previous approaches, further work is still needed to determine whether its polar deficiencies can be corrected, an essential requirement for γT to be useful in Southern Ocean studies, for instance.
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Oschlies, Andreas, Olaf Duteil, Julia Getzlaff, Wolfgang Koeve, Angela Landolfi et Sunke Schmidtko. « Patterns of deoxygenation : sensitivity to natural and anthropogenic drivers ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 375, no 2102 (7 août 2017) : 20160325. http://dx.doi.org/10.1098/rsta.2016.0325.
Texte intégralRésumé :
Observational estimates and numerical models both indicate a significant overall decline in marine oxygen levels over the past few decades. Spatial patterns of oxygen change, however, differ considerably between observed and modelled estimates. Particularly in the tropical thermocline that hosts open-ocean oxygen minimum zones, observations indicate a general oxygen decline, whereas most of the state-of-the-art models simulate increasing oxygen levels. Possible reasons for the apparent model-data discrepancies are examined. In order to attribute observed historical variations in oxygen levels, we here study mechanisms of changes in oxygen supply and consumption with sensitivity model simulations. Specifically, the role of equatorial jets, of lateral and diapycnal mixing processes, of changes in the wind-driven circulation and atmospheric nutrient supply, and of some poorly constrained biogeochemical processes are investigated. Predominantly wind-driven changes in the low-latitude oceanic ventilation are identified as a possible factor contributing to observed oxygen changes in the low-latitude thermocline during the past decades, while the potential role of biogeochemical processes remains difficult to constrain. We discuss implications for the attribution of observed oxygen changes to anthropogenic impacts and research priorities that may help to improve our mechanistic understanding of oxygen changes and the quality of projections into a changing future. This article is part of the themed issue ‘Ocean ventilation and deoxygenation in a warming world’.
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Dunkley Jones, T., A. Ridgwell, D. J. Lunt, M. A. Maslin, D. N. Schmidt et P. J. Valdes. « A Palaeogene perspective on climate sensitivity and methane hydrate instability ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 368, no 1919 (28 mai 2010) : 2395–415. http://dx.doi.org/10.1098/rsta.2010.0053.
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The Palaeocene–Eocene thermal maximum (PETM), a rapid global warming event and carbon-cycle perturbation of the early Palaeogene, provides a unique test of climate and carbon-cycle models as well as our understanding of sedimentary methane hydrate stability, albeit under conditions very different from the modern. The principal expression of the PETM in the geological record is a large and rapid negative excursion in the carbon isotopic composition of carbonates and organic matter from both marine and terrestrial environments. Palaeotemperature proxy data from across the PETM indicate a coincident increase in global surface temperatures of approximately 5–6°C. Reliable estimates of atmospheric CO 2 changes and global warming through past transient climate events can provide an important test of the climate sensitivities reproduced by state-of-the-art atmosphere–ocean general circulation models. Here, we synthesize the available carbon-cycle model estimates of the magnitude of the carbon input to the ocean–atmosphere–biosphere system, and the consequent atmospheric p CO 2 perturbation, through the PETM. We also review the theoretical mass balance arguments and available sedimentary evidence for the role of massive methane hydrate dissociation in this event. The plausible range of carbon mass input, approximately 4000–7000 PgC, strongly suggests a major alternative source of carbon in addition to any contribution from methane hydrates. We find that the potential range of PETM atmospheric p CO 2 increase, combined with proxy estimates of the PETM temperature anomaly, does not necessarily imply climate sensitivities beyond the range of state-of-the-art climate models.
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Romeshkani, Mohsen, Mohammad A. Sharifi et Dimitrios Tsoulis. « Estimation of gravitational curvature through a deterministic approach and spectral combination of space-borne second-order gravitational potential derivatives ». Geophysical Journal International 224, no 2 (26 septembre 2020) : 825–42. http://dx.doi.org/10.1093/gji/ggaa466.
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SUMMARY Second- and third-order gravitational potential derivatives can be employed for the determination of the medium- and high-frequency parts of the Earth's gravity field. Due to the Gravity field and steady-state Ocean Circulation Explorer mission, second-order derivatives (SOD) in particular, express currently observed functionals of high accuracy and global coverage. Third-order derivatives (TOD), or gravitational curvature data, provide significant gravity field information when applied regionally. The absence of directly observed TOD data underlines the importance of investigating the relationship between SOD and TOD. This paper discusses the combination of simulated SOD in order to obtain TOD at satellite altitude by applying the spectral combination method. For the determination of TOD integral equations are developed that utilize SOD data at satellite altitude, thus extending the well-known Meissl spectral scheme. The performance of the derived mathematical models is investigated numerically for the test area of Himalayas and the Tibet region. Two different TOD computational strategies are examined. First, we define a deterministic approach that recovers TOD data from noise-free simulated SOD data. Results show that retrieved TOD data at satellite level reach an agreement of the level of 1 × 10−17 m−1s−2 when compared with the true TOD data. Secondly, we propose a new mathematical model based on the spectral combination of integral relations and noisy SOD data with Gaussian noise for recovering TOD. Integral estimators of biased and unbiased types are examined in the cases of SOD data at satellite altitude. The used vertical SOD components show differences between the recovered and true vertical TOD components in the order of 1 × 10−17 m−1s−2 in magnitude, proving the vertical–vertical component of SOD as the best for validating purposes.
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Kennedy, A. T., A. Farnsworth, D. J. Lunt, C. H. Lear et P. J. Markwick. « Atmospheric and oceanic impacts of Antarctic glaciation across the Eocene–Oligocene transition ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 373, no 2054 (13 novembre 2015) : 20140419. http://dx.doi.org/10.1098/rsta.2014.0419.
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The glaciation of Antarctica at the Eocene–Oligocene transition (approx. 34 million years ago) was a major shift in the Earth’s climate system, but the mechanisms that caused the glaciation, and its effects, remain highly debated. A number of recent studies have used coupled atmosphere–ocean climate models to assess the climatic effects of Antarctic glacial inception, with often contrasting results. Here, using the HadCM3L model, we show that the global atmosphere and ocean response to growth of the Antarctic ice sheet is sensitive to subtle variations in palaeogeography, using two reconstructions representing Eocene and Oligocene geological stages. The earlier stage (Eocene; Priabonian), which has a relatively constricted Tasman Seaway, shows a major increase in sea surface temperature over the Pacific sector of the Southern Ocean in response to the ice sheet. This response does not occur for the later stage (Oligocene; Rupelian), which has a more open Tasman Seaway. This difference in temperature response is attributed to reorganization of ocean currents between the stages. Following ice sheet expansion in the earlier stage, the large Ross Sea gyre circulation decreases in size. Stronger zonal flow through the Tasman Seaway allows salinities to increase in the Ross Sea, deep-water formation initiates and multiple feedbacks then occur amplifying the temperature response. This is potentially a model-dependent result, but it highlights the sensitive nature of model simulations to subtle variations in palaeogeography, and highlights the need for coupled ice sheet–climate simulations to properly represent and investigate feedback processes acting on these time scales.
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MacMartin, Douglas G., et Eli Tziperman. « Using transfer functions to quantify El Niño Southern Oscillation dynamics in data and models ». Proceedings of the Royal Society A : Mathematical, Physical and Engineering Sciences 470, no 2169 (8 septembre 2014) : 20140272. http://dx.doi.org/10.1098/rspa.2014.0272.
Texte intégralRésumé :
Transfer function tools commonly used in engineering control analysis can be used to better understand the dynamics of El Niño Southern Oscillation (ENSO), compare data with models and identify systematic model errors. The transfer function describes the frequency-dependent input–output relationship between any pair of causally related variables, and can be estimated from time series. This can be used first to assess whether the underlying relationship is or is not frequency dependent, and if so, to diagnose the underlying differential equations that relate the variables, and hence describe the dynamics of individual subsystem processes relevant to ENSO. Estimating process parameters allows the identification of compensating model errors that may lead to a seemingly realistic simulation in spite of incorrect model physics. This tool is applied here to the TAO array ocean data, the GFDL-CM2.1 and CCSM4 general circulation models, and to the Cane–Zebiak ENSO model. The delayed oscillator description is used to motivate a few relevant processes involved in the dynamics, although any other ENSO mechanism could be used instead. We identify several differences in the processes between the models and data that may be useful for model improvement. The transfer function methodology is also useful in understanding the dynamics and evaluating models of other climate processes.
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Moffat, C., et M. Meredith. « Shelf–ocean exchange and hydrography west of the Antarctic Peninsula : a review ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 376, no 2122 (14 mai 2018) : 20170164. http://dx.doi.org/10.1098/rsta.2017.0164.
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The West Antarctic Peninsula (WAP) is a highly productive marine ecosystem where extended periods of change have been observed in the form of glacier retreat, reduction of sea-ice cover and shifts in marine populations, among others. The physical environment on the shelf is known to be strongly influenced by the Antarctic Circumpolar Current flowing along the shelf slope and carrying warm, nutrient-rich water, by cold waters flooding into the northern Bransfield Strait from the Weddell Sea, by an extensive network of glaciers and ice shelves, and by strong seasonal to inter-annual variability in sea-ice formation and air–sea interactions, with significant modulation by climate modes like El Niño–Southern Oscillation and the Southern Annular Mode. However, significant gaps have remained in understanding the exchange processes between the open ocean and the shelf, the pathways and fate of oceanic water intrusions, the shelf heat and salt budgets, and the long-term evolution of the shelf properties and circulation. Here, we review how recent advances in long-term monitoring programmes, process studies and newly developed numerical models have helped bridge these gaps and set future research challenges for the WAP system. This article is part of the theme issue ‘The marine system of the West Antarctic Peninsula: status and strategy for progress in a region of rapid change’.
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Weisheimer, Antje, Susanna Corti, Tim Palmer et Frederic Vitart. « Addressing model error through atmospheric stochastic physical parametrizations : impact on the coupled ECMWF seasonal forecasting system ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 372, no 2018 (28 juin 2014) : 20130290. http://dx.doi.org/10.1098/rsta.2013.0290.
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The finite resolution of general circulation models of the coupled atmosphere–ocean system and the effects of sub-grid-scale variability present a major source of uncertainty in model simulations on all time scales. The European Centre for Medium-Range Weather Forecasts has been at the forefront of developing new approaches to account for these uncertainties. In particular, the stochastically perturbed physical tendency scheme and the stochastically perturbed backscatter algorithm for the atmosphere are now used routinely for global numerical weather prediction. The European Centre also performs long-range predictions of the coupled atmosphere–ocean climate system in operational forecast mode, and the latest seasonal forecasting system—System 4—has the stochastically perturbed tendency and backscatter schemes implemented in a similar way to that for the medium-range weather forecasts. Here, we present results of the impact of these schemes in System 4 by contrasting the operational performance on seasonal time scales during the retrospective forecast period 1981–2010 with comparable simulations that do not account for the representation of model uncertainty. We find that the stochastic tendency perturbation schemes helped to reduce excessively strong convective activity especially over the Maritime Continent and the tropical Western Pacific, leading to reduced biases of the outgoing longwave radiation (OLR), cloud cover, precipitation and near-surface winds. Positive impact was also found for the statistics of the Madden–Julian oscillation (MJO), showing an increase in the frequencies and amplitudes of MJO events. Further, the errors of El Niño southern oscillation forecasts become smaller, whereas increases in ensemble spread lead to a better calibrated system if the stochastic tendency is activated. The backscatter scheme has overall neutral impact. Finally, evidence for noise-activated regime transitions has been found in a cluster analysis of mid-latitude circulation regimes over the Pacific–North America region.
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Sagoo, Navjit, Paul Valdes, Rachel Flecker et Lauren J. Gregoire. « The Early Eocene equable climate problem : can perturbations of climate model parameters identify possible solutions ? » Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 371, no 2001 (28 octobre 2013) : 20130123. http://dx.doi.org/10.1098/rsta.2013.0123.
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Geological data for the Early Eocene (56–47.8 Ma) indicate extensive global warming, with very warm temperatures at both poles. However, despite numerous attempts to simulate this warmth, there are remarkable data–model differences in the prediction of these polar surface temperatures, resulting in the so-called ‘equable climate problem’. In this paper, for the first time an ensemble with a perturbed climate-sensitive model parameters approach has been applied to modelling the Early Eocene climate. We performed more than 100 simulations with perturbed physics parameters, and identified two simulations that have an optimal fit with the proxy data. We have simulated the warmth of the Early Eocene at 560 ppmv CO 2 , which is a much lower CO 2 level than many other models. We investigate the changes in atmospheric circulation, cloud properties and ocean circulation that are common to these simulations and how they differ from the remaining simulations in order to understand what mechanisms contribute to the polar warming. The parameter set from one of the optimal Early Eocene simulations also produces a favourable fit for the last glacial maximum boundary climate and outperforms the control parameter set for the present day. Although this does not ‘prove’ that this model is correct, it is very encouraging that there is a parameter set that creates a climate model able to simulate well very different palaeoclimates and the present-day climate. Interestingly, to achieve the great warmth of the Early Eocene this version of the model does not have a strong future climate change Charney climate sensitivity. It produces a Charney climate sensitivity of 2.7 ° C, whereas the mean value of the 18 models in the IPCC Fourth Assessment Report (AR4) is 3.26 ° C±0.69 ° C. Thus, this value is within the range and below the mean of the models included in the AR4.
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Gregory, J. M., et P. Huybrechts. « Ice-sheet contributions to future sea-level change ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 364, no 1844 (25 mai 2006) : 1709–32. http://dx.doi.org/10.1098/rsta.2006.1796.
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Accurate simulation of ice-sheet surface mass balance requires higher spatial resolution than is afforded by typical atmosphere–ocean general circulation models (AOGCMs), owing, in particular, to the need to resolve the narrow and steep margins where the majority of precipitation and ablation occurs. We have developed a method for calculating mass-balance changes by combining ice-sheet average time-series from AOGCM projections for future centuries, both with information from high-resolution climate models run for short periods and with a 20 km ice-sheet mass-balance model. Antarctica contributes negatively to sea level on account of increased accumulation, while Greenland contributes positively because ablation increases more rapidly. The uncertainty in the results is about 20% for Antarctica and 35% for Greenland. Changes in ice-sheet topography and dynamics are not included, but we discuss their possible effects. For an annual- and area-average warming exceeding in Greenland and in the global average, the net surface mass balance of the Greenland ice sheet becomes negative, in which case it is likely that the ice sheet would eventually be eliminated, raising global-average sea level by 7 m.
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Bunyard, P., M. Hodnett, G. Poveda, J. D. Burgos Salcedo et C. Peña. « Experimental evidence of condensation-driven airflow ». Hydrology and Earth System Sciences Discussions 12, no 10 (27 octobre 2015) : 10921–74. http://dx.doi.org/10.5194/hessd-12-10921-2015.
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Abstract. The dominant "convection" model of atmospheric circulation is based on the premise that hot air expands and rises, to be replaced by colder air, thereby creating horizontal surface winds. A recent theory put forward by Makarieva and Gorshkov (2007, 2013) maintains that the primary motive force of atmospheric circulation derives from the intense condensation and sharp pressure reduction that is associated with regions where a high rate of evapotranspiration from natural closed-canopy forests provides the "fuel" for cloud formation. The net result of the "biotic pump" theory is that moist air flows from ocean to land, drawn in by the pressure changes associated with a high rate of condensation. To test the physics underpinning the biotic pump theory, namely that condensation of water vapour, at a sufficiently high rate, results in an uni-directional airflow, a 5 m tall experimental apparatus was designed and built, in which a 20 m3 body of atmospheric air is enclosed inside an annular 14 m long space (a "square donut") around which it can circulate freely, allowing for rotary air flows. One vertical side of the apparatus contains some 17 m of copper refrigeration coils, which cause condensation. The apparatus contains a series of sensors measuring temperature, humidity and barometric pressure every five seconds, and air flow every second. The laws of Newtonian physics are used in calculating the rate of condensation inside the apparatus. The results of more than one hundred experiments show a highly significant correlation, with r2 > 0.9, of airflow and the rate of condensation. The rotary air flows created appear to be consistent both in direction and velocity with the biotic pump hypothesis, the critical factor being the rate change in the partial pressure of water vapour in the enclosed body of atmospheric air. Air density changes, in terms of kinetic energy, are found to be orders of magnitude smaller than the kinetic energy of partial pressure change. The consistency of the laboratory experiments, in confirming the physics of the biotic pump, has profound implications for current mathematical climate models, not just in terms of predicting the consequences of widespread deforestation, but also for better understanding the atmospheric processes which lead to air mass convection.
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Haines, Keith, Leon Hermanson, Chunlei Liu, Debbie Putt, Rowan Sutton, Alan Iwi et Doug Smith. « Decadal climate prediction (project GCEP) ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 367, no 1890 (16 décembre 2008) : 925–37. http://dx.doi.org/10.1098/rsta.2008.0178.
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Decadal prediction uses climate models forced by changing greenhouse gases, as in the International Panel for Climate Change, but unlike longer range predictions they also require initialization with observations of the current climate. In particular, the upper-ocean heat content and circulation have a critical influence. Decadal prediction is still in its infancy and there is an urgent need to understand the important processes that determine predictability on these timescales. We have taken the first Hadley Centre Decadal Prediction System (DePreSys) and implemented it on several NERC institute compute clusters in order to study a wider range of initial condition impacts on decadal forecasting, eventually including the state of the land and cryosphere. The eScience methods are used to manage submission and output from the many ensemble model runs required to assess predictive skill. Early results suggest initial condition skill may extend for several years, even over land areas, but this depends sensitively on the definition used to measure skill, and alternatives are presented. The Grid for Coupled Ensemble Prediction (GCEP) system will allow the UK academic community to contribute to international experiments being planned to explore decadal climate predictability.
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Lenton, Timothy M., Richard J. Myerscough, Robert Marsh, Valerie N. Livina, Andrew R. Price et Simon J. Cox. « Using GENIE to study a tipping point in the climate system ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 367, no 1890 (16 décembre 2008) : 871–84. http://dx.doi.org/10.1098/rsta.2008.0171.
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We have used the Grid ENabled Integrated Earth system modelling framework to study the archetypal example of a tipping point in the climate system; a threshold for the collapse of the Atlantic thermohaline circulation (THC). eScience has been invaluable in this work and we explain how we have made it work for us. Two stable states of the THC have been found to coexist, under the same boundary conditions, in a hierarchy of models. The climate forcing required to collapse the THC and the reversibility or irreversibility of such a collapse depends on uncertain model parameters. Automated methods have been used to assimilate observational data to constrain the pertinent parameters. Anthropogenic climate forcing leads to a robust weakening of the THC and increases the probability of crossing a THC tipping point, but some ensemble members collapse readily, whereas others are extremely resistant. Hence, we test general methods that have been developed to directly diagnose, from time-series data, the proximity of a ‘tipping element’, such as the THC to a bifurcation point. In a three-dimensional ocean–atmosphere model exhibiting THC hysteresis, despite high variability in the THC driven by the dynamical atmosphere, some early warning of an approaching tipping point appears possible.
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Willebrand, Jurgen, et Carl Wunsch. « Inversion of ocean circulation models ». Eos, Transactions American Geophysical Union 71, no 1 (1990) : 2. http://dx.doi.org/10.1029/90eo00006.
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Aryal, Abhiru, Albira Acharya et Ajay Kalra. « Assessing the Implication of Climate Change to Forecast Future Flood Using CMIP6 Climate Projections and HEC-RAS Modeling ». Forecasting 4, no 3 (29 juin 2022) : 582–603. http://dx.doi.org/10.3390/forecast4030032.
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Climate change has caused uncertainty in the hydrological pattern including weather change, precipitation fluctuations, and extreme temperature, thus triggering unforeseen natural tragedies such as hurricanes, flash flooding, heatwave and more. Because of these unanticipated events occurring all around the globe, the study of the influence of climate change on the alteration of flooding patterns has gained a lot of attention. This research study intends to provide an insight into how the future projected streamflow will affect the flooding-inundation extent by comparing the change in floodplain using both historical and future simulated scenarios. For the future projected data, the climate model Atmosphere/Ocean General Circulation Model (AOGCM) developed by Coupled Model Intercomparison Project Phase 6 (CMIP6) is used, which illustrates that the flood is increasing in considering climate models. Furthermore, a comparison of the existing flood inundation map by the Federal Emergency Management Agency (FEMA) study with the map generated by future projected streamflow data presents the entire inundation area in flood maps, implying the expansion area compared to FEMA needs to be considered in making emergency response plans. The effect of flooding in the inundation area from historical to future flow values, presented mathematically by a calculation of inundation extent percentage, infers that the considered watershed of Rock River is a flood-prone area. The goal is to provide insights on the importance of using the forecasted data for flood analysis and to offer the necessary background needed to strategize an emergency response plan for flood management.
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Gent, Peter R., et James C. Mcwilliams. « Isopycnal Mixing in Ocean Circulation Models ». Journal of Physical Oceanography 20, no 1 (janvier 1990) : 150–55. http://dx.doi.org/10.1175/1520-0485(1990)020<0150:imiocm>2.0.co;2.
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Higdon, Robert L. « Numerical modelling of ocean circulation ». Acta Numerica 15 (mai 2006) : 385–470. http://dx.doi.org/10.1017/s0962492906250013.
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Computational simulations of ocean circulation rely on the numerical solution of partial differential equations of fluid dynamics, as applied to a relatively thin layer of stratified fluid on a rotating globe. This paper describes some of the physical and mathematical properties of the solutions being sought, some of the issues that are encountered when the governing equations are solved numerically, and some of the numerical methods that are being used in this area.
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Zelazowski, Przemyslaw, Yadvinder Malhi, Chris Huntingford, Stephen Sitch et Joshua B. Fisher. « Changes in the potential distribution of humid tropical forests on a warmer planet ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 369, no 1934 (13 janvier 2011) : 137–60. http://dx.doi.org/10.1098/rsta.2010.0238.
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The future of tropical forests has become one of the iconic issues in climate-change science. A number of studies that have explored this subject have tended to focus on the output from one or a few climate models, which work at low spatial resolution, whereas society and conservation-relevant assessment of potential impacts requires a finer scale. This study focuses on the role of climate on the current and future distribution of humid tropical forests (HTFs). We first characterize their contemporary climatological niche using annual rainfall and maximum climatological water stress, which also adequately describe the current distribution of other biomes within the tropics. As a first-order approximation of the potential extent of HTFs in future climate regimes defined by global warming of 2 ° C and 4 ° C, we investigate changes in the niche through a combination of climate-change anomaly patterns and higher resolution (5 km) maps of current climatology. The climate anomalies are derived using data from 17 coupled Atmosphere–Ocean General Circulation Models (AOGCMs) used in the Fourth Assessment of the Intergovernmental Panel for Climate Change. Our results confirm some risk of forest retreat, especially in eastern Amazonia, Central America and parts of Africa, but also indicate a potential for expansion in other regions, for example around the Congo Basin. The finer spatial scale enabled the depiction of potential resilient and vulnerable zones with practically useful detail. We further refine these estimates by considering the impact of new environmental regimes on plant water demand using the UK Met Office land-surface scheme (of the HadCM3 AOGCM). The CO 2 -related reduction in plant water demand lowers the risk of die-back and can lead to possible niche expansion in many regions. The analysis presented here focuses primarily on hydrological determinants of HTF extent. We conclude by discussing the role of other factors, notably the physiological effects of higher temperature.
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Rhein, Monika, Reiner Steinfeldt, Dagmar Kieke, Ilaria Stendardo et Igor Yashayaev. « Ventilation variability of Labrador Sea Water and its impact on oxygen and anthropogenic carbon : a review ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 375, no 2102 (7 août 2017) : 20160321. http://dx.doi.org/10.1098/rsta.2016.0321.
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Ventilation of Labrador Sea Water (LSW) receives ample attention because of its potential relation to the strength of the Atlantic Meridional Overturning Circulation (AMOC). Here, we provide an overview of the changes of LSW from observations in the Labrador Sea and from the southern boundary of the subpolar gyre at 47° N. A strong winter-time atmospheric cooling over the Labrador Sea led to intense and deep convection, producing a thick and dense LSW layer as, for instance, in the early to mid-1990s. The weaker convection in the following years mostly ventilated less dense LSW vintages and also reduced the supply of oxygen. As a further consequence, the rate of uptake of anthropogenic carbon by LSW decreased between the two time periods 1996–1999 and 2007–2010 in the western subpolar North Atlantic. In the eastern basins, the rate of increase in anthropogenic carbon became greater due to the delayed advection of LSW that was ventilated in previous years. Starting in winter 2013/2014 and prevailing at least into winter 2015/2016, production of denser and more voluminous LSW resumed. Increasing oxygen signals have already been found in the western boundary current at 47° N. On decadal and shorter time scales, anomalous cold atmospheric conditions over the Labrador Sea lead to an intensification of convection. On multi-decadal time scales, the ‘cold blob’ in the subpolar North Atlantic projected by climate models in the next 100 years is linked to a weaker AMOC and weaker convection (and thus deoxygenation) in the Labrador Sea. This article is part of the themed issue ‘Ocean ventilation and deoxygenation in a warming world’.
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Halpern, David. « Data assimilation and ocean general circulation models ». Eos, Transactions American Geophysical Union 68, no 35 (1987) : 731. http://dx.doi.org/10.1029/eo068i035p00731-02.
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Salmon, Rick. « Generalized two-layer models of ocean circulation ». Journal of Marine Research 52, no 5 (1 septembre 1994) : 865–908. http://dx.doi.org/10.1357/0022240943076939.
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Gaither, K., R. Moorhead, S. Nations et D. Fox. « Visualizing ocean circulation models through virtual environments ». IEEE Computer Graphics and Applications 17, no 1 (1997) : 16–19. http://dx.doi.org/10.1109/38.576851.
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Eden, Carsten, Lars Czeschel et Dirk Olbers. « Toward Energetically Consistent Ocean Models ». Journal of Physical Oceanography 44, no 12 (26 novembre 2014) : 3160–84. http://dx.doi.org/10.1175/jpo-d-13-0260.1.
Texte intégralRésumé :
Abstract Possibilities to construct a realistic quasi-global ocean model in Boussinesq approximation with a closed energy cycle are explored in this study. In such a model, the energy related to the mean variables would interact with all parameterized forms of energy without any spurious energy sources or sinks. This means that the energy available for interior mixing in the ocean would be only controlled by external energy input from the atmosphere and the tidal system and by internal exchanges. In the current implementation of such a consistent model, however, numerical biases and sources due to the nonlinear equation of state violate energy conservation, resulting in an overall residual up to several percent. In three (approximately) consistent model versions with different scenarios of mesoscale eddy dissipation, the parameterized internal wave field provides between 2 and 3 TW for interior mixing from the total external energy input of about 4 TW, such that a transfer between 0.3 and 0.4 TW into mean potential energy contributes to drive the large-scale circulation in the model. In contrast, the wind work on the mean circulation contributes by about 1.8 TW to the large-scale circulation in all model versions. It is shown that the consistent model versions are more energetic than standard and inconsistent model versions and in better agreement with hydrographic observations.
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Meccia, Virna L., Doroteaciro Iovino et Alessio Bellucci. « North Atlantic gyre circulation in PRIMAVERA models ». Climate Dynamics 56, no 11-12 (14 février 2021) : 4075–90. http://dx.doi.org/10.1007/s00382-021-05686-z.
Texte intégralRésumé :
AbstractWe study the impact of horizontal resolution in setting the North Atlantic gyre circulation and representing the ocean–atmosphere interactions that modulate the low-frequency variability in the region. Simulations from five state-of-the-art climate models performed at standard and high-resolution as part of the High-Resolution Model Inter-comparison Project (HighResMIP) were analysed. In some models, the resolution is enhanced in the atmospheric and oceanic components whereas, in some other models, the resolution is increased only in the atmosphere. Enhancing the horizontal resolution from non-eddy to eddy-permitting ocean produces stronger barotropic mass transports inside the subpolar and subtropical gyres. The first mode of inter-annual variability is associated with the North Atlantic Oscillation (NAO) in all the cases. The rapid ocean response to it consists of a shift in the position of the inter-gyre zone and it is better captured by the non-eddy models. The delayed ocean response consists of an intensification of the subpolar gyre (SPG) after around 3 years of a positive phase of NAO and it is better represented by the eddy-permitting oceans. A lagged relationship between the intensity of the SPG and the Atlantic Meridional Overturning Circulation (AMOC) is stronger in the cases of the non-eddy ocean. Then, the SPG is more tightly coupled to the AMOC in low-resolution models.