Science.gov

Sample records for ocean circulation models

  1. Modeling ocean circulation

    SciTech Connect

    Semtner, A.J.

    1995-09-08

    Ocean numerical models have become quite realistic over the past several years as a result of improved methods, faster computers, and global data sets. Models now treat basin-scale to global domains while retaining the fine spatial scales that are important for modeling the transport of heat, salt, and other properties over vast distances. Simulations are reproducing observed satellite results on the energetics of strong currents and are properly showing diverse aspects of thermodynamic and dynamic ocean responses ranging from deep-water production of El Nino. Now models can represent not only currents but also the consequences for climate, biology, and geo-chemistry over time spans for months to decades. However, much remains to be understood from models about ocean circulation on longer time scales, including the evolution of the dominant water masses, the predictability of climate, and the ocean`s influence on global change. 34 refs., 6 figs.

  2. Ocean General Circulation Models

    SciTech Connect

    Yoon, Jin-Ho; Ma, Po-Lun

    2012-09-30

    1. Definition of Subject The purpose of this text is to provide an introduction to aspects of oceanic general circulation models (OGCMs), an important component of Climate System or Earth System Model (ESM). The role of the ocean in ESMs is described in Chapter XX (EDITOR: PLEASE FIND THE COUPLED CLIMATE or EARTH SYSTEM MODELING CHAPTERS). The emerging need for understanding the Earth’s climate system and especially projecting its future evolution has encouraged scientists to explore the dynamical, physical, and biogeochemical processes in the ocean. Understanding the role of these processes in the climate system is an interesting and challenging scientific subject. For example, a research question how much extra heat or CO2 generated by anthropogenic activities can be stored in the deep ocean is not only scientifically interesting but also important in projecting future climate of the earth. Thus, OGCMs have been developed and applied to investigate the various oceanic processes and their role in the climate system.

  3. LLNL Ocean General Circulation Model

    Energy Science and Technology Software Center (ESTSC)

    2005-12-29

    The LLNL OGCM is a numerical ocean modeling tool for use in studying ocean circulation over a wide range of space and time scales, with primary applications to climate change and carbon cycle science.

  4. Numerical Modeling of Ocean Circulation

    NASA Astrophysics Data System (ADS)

    Miller, Robert N.

    2007-01-01

    The modelling of ocean circulation is important not only for its own sake, but also in terms of the prediction of weather patterns and the effects of climate change. This book introduces the basic computational techniques necessary for all models of the ocean and atmosphere, and the conditions they must satisfy. It describes the workings of ocean models, the problems that must be solved in their construction, and how to evaluate computational results. Major emphasis is placed on examining ocean models critically, and determining what they do well and what they do poorly. Numerical analysis is introduced as needed, and exercises are included to illustrate major points. Developed from notes for a course taught in physical oceanography at the College of Oceanic and Atmospheric Sciences at Oregon State University, this book is ideal for graduate students of oceanography, geophysics, climatology and atmospheric science, and researchers in oceanography and atmospheric science. Features examples and critical examination of ocean modelling and results Demonstrates the strengths and weaknesses of different approaches Includes exercises to illustrate major points and supplement mathematical and physical details

  5. Warm World Ocean Thermohaline Circulation Model

    NASA Astrophysics Data System (ADS)

    Zimov, N.; Zimov, S. A.

    2014-12-01

    Modern day ocean circulation is dominated by thermal convection with cold waters subsiding in the Northern Atlantic, filling the ocean interior with cold and heavy water. However, ocean circulation diminished during the last glaciation and consequently the downwelling of the cold. Therefore interior ocean water temperatures must have been affected by other mechanisms which are negligible in the current state. We propose that the submergence of highly saline water from warm seas with high rates of evaporation (like the Red or Mediterranean Sea) was a major factor controlling ocean circulation during the last glaciation. Even today, waters in these poorly connected seas are the heaviest waters in the World ocean (1.029 g/cm3). The second mechanism affecting ocean temperature is the geothermal heat flux. With no heat exchange between the atmosphere and the ocean, geothermal heat flux through the ocean floor is capable of increasing ocean temperature by tens of degrees C over a 100 thousand year glacial cycle. To support these hypotheses we present an ocean box model that describes thermohaline circulation in the World Ocean. According to the model parameters, all water circulation is driven by the water density gradient. Boxes include high-latitude seas, high salinity seas, surface ocean, glaciers, and rift and lateral zones of the ocean interior. External heat sources are radiative forcing, affected by Milankovich cycles, and geothermal heat flux. Additionally this model accounts for the heat produced by organic rain decay. Taking all input parameters close to currently observed values, the model manages to recreate the glacial-interglacial cycles. During the glacial periods only haline circulation takes place, the ocean is strongly stratified, and the interior ocean accumulates heat while high-latitudes accumulate ice. 112,000 years after glaciation starts, water density on the ocean bottom becomes equal to the density of water in high-latitude seas, strong thermal

  6. Ocean general circulation models for parallel architectures

    SciTech Connect

    Smith, R.D.

    1993-05-01

    The authors report continuing work in developing ocean general circulation models for parallel architectures. In earlier work, they began with the widely-used Bryan-Cox ocean model, but reformulated the barotropic equations (which describe the vertically integrated flow) to solve for the surface-pressure field rather than the volume-transport streamfunction as in the original model. This had the advantage of being more easily parallelized and allowed for a more realistic representation of coastal and bottom topography. Both streamfunction and surface-pressure formulations use a rigid-lid approximation to eliminate fast surface waves. They have now replaced the rigid-lid with a free surface, and solve the barotropic equations implicitly to overcome the timestep restriction associated with the fast waves. This method has several advantages, including: (1) a better physical representation of the barotropic mode, and (2) a better-conditioned operator matrix, which leads to much faster convergence in the conjugate-gradient solver. They have also extended the model to allow use of arbitrary orthogonal curvilinear coordinates for the horizontal grid. The original model uses a standard polar grid that has a singularity at each pole, making it difficult to include the Arctic basin, which plays an important role in global ocean circulation. They can now include the Arctic (while still using an explicit time-integration scheme without high-latitude filtering) by using a distorted grid with a displaced pole for the North Atlantic - Arctic region of the ocean. The computer code, written in Fortran 90 and developed on the Connection Machine, has been substantially restructured so that all communication occurs in low-level stencil routines. The idea is that the stencil routines may be rewritten to optimize communication costs on a particular architecture, while the remainder of the code is for the most part machine-independent, involving only the simplest Fortran 90 constructs.

  7. Ocean circulation modeling by use of radar altimeter data

    NASA Technical Reports Server (NTRS)

    Olbers, Dirk; Alpers, W.; Hasselmann, K.; Maier-Reimer, E.; Kase, R.; Krauss, W.; Siedler, G.; Willebrand, J.; Zahel, W.

    1991-01-01

    The project will investigate the use of radar altimetry (RA) data in the determination of the ocean circulation models. RA data will be used to verify prognostic experiments of the steady state and seasonal cycle of large-scale circulation models and the statistical steady state of eddy-resolving models. The data will serve as initial and update conditions in data assimilation experiments and as constraints in inverse calculations. The aim of the project is a better understanding of ocean physics, the determination and mapping of ocean currents, and a contribution to the establishment of ocean circulation models for climate studies. The goal of the project is to use satellite radar altimetry data for improving our knowledge of ocean circulation both in a descriptive sense and through the physics that govern the circulation state. The basic tool is a series of ocean circulation models. Depending on the model, different techniques will be applied to incorporate the RA data.

  8. Ocean circulation

    NASA Astrophysics Data System (ADS)

    Thompson, Andrew F.; Rahmstorf, Stefan

    The ocean moderates the Earth's climate due to its vast capacity to store and transport heat; the influence of the large-scale ocean circulation on changes in climate is considered in this chapter. The ocean experiences both buoyancy forcing (through heating/cooling and evaporation/precipitation) and wind forcing. Almost all ocean forcing occurs at the surface, but these changes are communicated throughout the entire depth of the ocean through the meridional overturning circulation (MOC). In a few localized regions, water become sufficiently dense to penetrate thousands of meters deep, where it spreads, providing a continuous source of deep dense water to the entire ocean. Dense water returns to the surface and thus closes the MOC, either through density modification due to diapycnal mixing or by upwelling along sloping isopycnals across the Southern Ocean. Determination of the relative contributions of these two processes in the MOC remains an active area of research. Observations obtained primarily from isotopic compositions in ocean sediments provide substantial evidence that the structure of the MOC has changed significantly in the past. Indeed, large and abrupt changes to the Earth's climate during the past 120,000 years can be linked to either a reorganization or a complete collapse of the MOC. Two of the more dramatic instances of abrupt change include Dansgaard-Oeschger events, abrupt warmings that could exceed 10°C over a period as short as a few decades, and Heinrich events, which are associated with massive freshwater fluxes due to rapid iceberg discharges into the North Atlantic. Numerical models of varying complexity that have captured these abrupt transitions all underscore that the MOC is a highly nonlinear system with feedback loops, multiple equilibria, and hysteresis effects. Prediction of future abrupt shifts in the MOC or "tipping points" remains uncertain. However, the inferred behavior of the MOC during glacial climates suggests that

  9. Adaptation of a general circulation model to ocean dynamics

    NASA Technical Reports Server (NTRS)

    Turner, R. E.; Rees, T. H.; Woodbury, G. E.

    1976-01-01

    A primitive-variable general circulation model of the ocean was formulated in which fast external gravity waves are suppressed with rigid-lid surface constraint pressires which also provide a means for simulating the effects of large-scale free-surface topography. The surface pressure method is simpler to apply than the conventional stream function models, and the resulting model can be applied to both global ocean and limited region situations. Strengths and weaknesses of the model are also presented.

  10. A fully-implicit model of the global ocean circulation

    NASA Astrophysics Data System (ADS)

    Weijer, Wilbert; Dijkstra, Henk A.; Öksüzoğlu, Hakan; Wubs, Fred W.; de Niet, Arie C.

    2003-12-01

    With the recent developments in the solution methods for large-dimensional nonlinear algebraic systems, fully-implicit ocean circulation models are now becoming feasible. In this paper, the formulation of such a three-dimensional global ocean model is presented. With this implicit model, the sensitivity of steady states to parameters can be investigated efficiently using continuation methods. In addition, the implicit formulation allows for much larger time steps than can be used with explicit models. To demonstrate current capabilities of the implicit global ocean model, we use a relatively low-resolution (4° horizontally and 12 levels vertically) version. For this configuration, we present: (i) an explicit calculation of the bifurcation diagram associated with hysteresis behavior of the ocean circulation and (ii) the scaling behavior of the Atlantic meridional overturning versus the magnitude of the vertical mixing coefficient of heat and salt.

  11. 14C-age tracers in global ocean circulation models

    NASA Astrophysics Data System (ADS)

    Koeve, W.; Wagner, H.; Kähler, P.; Oschlies, A.

    2015-07-01

    The natural abundance of 14C in total CO2 dissolved in seawater (DIC) is a property applied to evaluate the water age structure and circulation in the ocean and in ocean models. In this study we use three different representations of the global ocean circulation augmented with a suite of idealised tracers to study the potential and limitations of using natural 14C to determine water age, which is the time elapsed since a body of water has been in contact with the atmosphere. We find that, globally, bulk 14C-age is dominated by two equally important components, one associated with ageing, i.e. the time component of circulation, and one associated with a "preformed 14C-age". The latter quantity exists because of the slow and incomplete atmosphere-ocean equilibration of 14C particularly in high latitudes where many water masses form. In the ocean's interior, preformed 14C-age behaves like a passive tracer. The relative contribution of the preformed component to bulk 14C-age varies regionally within a given model, but also between models. Regional variability in the Atlantic Ocean is associated with the mixing of waters with very different end members of preformed 14C-age. Here, variations in the preformed component over space and time mask the circulation component to an extent that its patterns are not detectable from bulk 14C-age. Between models, the variability of preformed 14C-age can also be considerable (factor of 2), related to the combination of physical model parameters, which influence circulation dynamics or gas exchange. The preformed component was found to be very sensitive to gas exchange and moderately sensitive to ice cover. In our model evaluation, the choice of the gas-exchange constant from within the currently accepted range of uncertainty had such a strong influence on preformed and bulk 14C-age that if model evaluation would be based on bulk 14C-age, it could easily impair the evaluation and tuning of a model's circulation on global and regional

  12. 14C-age tracers in global ocean circulation models

    NASA Astrophysics Data System (ADS)

    Koeve, W.; Wagner, H.; Kähler, P.; Oschlies, A.

    2014-10-01

    The natural abundance of 14C in total CO2 dissolved in seawater is a property applied to evaluate the water age structure and circulation in the ocean and in ocean models. In this study we use three different representations of the global ocean circulation augmented with a suite of idealised tracers to study the potential and limitations of using natural 14C to determine water age, the time elapsed since a body of water had contact with the atmosphere. We find that, globally, bulk 14C-age is dominated by two equally important components, one associated with aging, i.e. the time component of circulation and one associated with a "preformed 14C-age". This latter quantity exists because of the slow and incomplete atmosphere/ocean equilibration of 14C in particular in high latitudes where many water masses form. The relative contribution of the preformed component to bulk 14C-age varies regionally within a given model, but also between models. Regional variability, e.g. in the Atlantic Ocean is associated with the mixing of waters with very different end members of preformed 14C-age. In the Atlantic, variations in the preformed component over space and time mask the circulation component to an extent that its patterns are not detectable from bulk 14C-age alone. Between models the variability of age can also be considerable (factor of 2), related to the combinations of physical model parameters, which influence circulation dynamics, and gas exchange in the models. The preformed component was found to be very sensitive to gas exchange and moderately sensitive to ice cover. In our model evaluation exercise, the choice of the gas exchange constant from within the current range of uncertainty had such a strong influence on preformed and bulk 14C-age that if model evaluation would be based on bulk 14C-age it could easily impair the evaluation and tuning of a models circulation on global and regional scales. Based on the results of this study, we propose that considering

  13. Strong coupling among Antarctic ice shelves, ocean circulation and sea ice in a global sea-ice - ocean circulation model

    NASA Astrophysics Data System (ADS)

    Sergienko, Olga

    2016-04-01

    The thermodynamic effects of Antarctic ice shelf interaction with ocean circulation are investigated using a global, high-resolution, isopycnal ocean-circulation model coupled to a sea-ice model. The model uses NASA MERRA Reanalysis from 1992 to 2011 as atmospheric forcing. The simulated long-period variability of ice-shelf melting/freezing rates differ across geographic locations. The ice shelves in Antarctic Peninsula, Amundsen and Bellingshausen sea embayments and the Amery Ice Shelf experience an increase in melting starting from 2005. This increase in melting is due to an increase in the subsurface (100-500 m) ocean heat content in the embayments of these ice shelves, which is caused by an increase in sea-ice concentration after 2005, and consequent reduction of the heat loss to the atmosphere. Our simulations provide a strong evidence for a coupling between ocean circulation, sea ice and ice shelves.

  14. Evaluating the deep-ocean circulation of a global ocean model using carbon isotopic ratios

    NASA Astrophysics Data System (ADS)

    Paul, André; Dutkiewicz, Stephanie; Gebbie, Jake; Losch, Martin; Marchal, Olivier

    2016-04-01

    We study the sensitivity of a global three-dimensional biotic ocean carbon-cycle model to the parameterizations of gas exchange and biological productivity as well as to deep-ocean circulation strength, and we employ the carbon isotopic ratios δ13C and Δ14C of dissolved inorganic carbon for a systematic evaluation against observations. Radiocarbon (Δ14C) in particular offers the means to assess the model skill on a time scale of 100 to 1000 years relevant to the deep-ocean circulation. The carbon isotope ratios are included as tracers in the MIT general circulation model (MITgcm). The implementation involves the fractionation processes during photosynthesis and air-sea gas exchange. We present the results of sixteen simulations combining two different parameterizations of the piston velocity, two different parameterizations of biological productivity (including the effect of iron fertilization) and four different overturning rates. These simulations were first spun up to equilibrium (more than 10,000 years of model simulation) and then continued from AD 1765 to AD 2002. For the model evaluation, we followed the OCMIP-2 (Ocean Carbon-Cycle Model Intercomparision Project phase two) protocol, comparing the results to GEOSECS (Geochemical Ocean Sections Survey) and WOCE (World Ocean Circulation Experiment) δ13C and natural Δ14C data in the world ocean. The range of deep natural Δ14C (below 1000 m) for our single model (MITgcm) was smaller than for the group of different OCMIP-2 models. Furthermore, differences between different model parameterizations were smaller than for different overturning rates. We conclude that carbon isotope ratios are a useful tool to evaluate the deep-ocean circulation. Since they are also available from deep-sea sediment records, we postulate that the simulation of carbon isotope ratios in a global ocean model will aid in estimating the deep-ocean circulation and climate during present and past.

  15. (CO sub 2 uptake in an Ocean Circulation Model)

    SciTech Connect

    Siegenthaler, U.C.

    1990-11-06

    The traveler collaborated with Drs. J. L. Sarmiento and J. C. Orr of the Program in Atmospheric Sciences at Princeton University to finish the article A Perturbation Simulation of CO{sub 2} Uptake in an Ocean Circulation Model,'' which has been submitted to the Journal of Geophysical Research for publication. With F. Joos, a graduate student from the University of Bern, the traveler started writing a journal article describing a box model of the global carbon cycle that is an extension of the one-dimensional box-diffusion model. The traveler further collaborated with F. Joos and Dr. J. L. Sarmiento on modeling the potential enhancement of oceanic CO{sub 2} uptake by fertilizing the southern ocean with iron. A letter describing the results is currently being written for the journal Nature.

  16. Barotropic-baroclinic time splitting for ocean circulation modeling

    SciTech Connect

    Higdon, R.L.; Szoeke, R.A. de

    1997-07-15

    This paper discusses the following topics on oceanic circulation modeling: time splitting in context of the nonlinear primitive equations; analysis of the stability of this splitting when applied to a linearized flow in two-layer fluid with one horizontal dimensions and a flat lower boundary; analysis of this splitting for horizontal dimensions in a rotating reference frame with constant coriolis parameters; and then numerical tests of the new splitting are discussed.

  17. Testing Components of New Community Isopycnal Ocean Circulation Model

    SciTech Connect

    Bryan, Kirk

    2008-05-09

    The ocean and atmosphere are both governed by the same physical laws and models of the two media have many similarities. However, there are critical differences that call for special methods to provide the best simulation. One of the most important difference is that the ocean is nearly opaque to radiation in the visible and infra-red part of the spectrum. For this reason water mass properties in the ocean are conserved along trajectories for long distances and for long periods of time. For this reason isopycnal coordinate models would seem to have a distinct advantage in simulating ocean circulation. In such a model the coordinate surfaces are aligned with the natural paths of near adiabatic, density conserving flow in the main thermocline. The difficulty with this approach is at the upper and lower boundaries of the ocean, which in general do not coincide with density surfaces. For this reason hybrid coordinate models were proposed by Bleck and Boudra (1981) in which Cartesian coordinates were used near the ocean surface and isopycnal coordinates were used in the main thermocline. This feature is now part of the HICOM model (Bleck, 2002).

  18. Stochastic Ocean Eddy Perturbations in a Coupled General Circulation Model.

    NASA Astrophysics Data System (ADS)

    Howe, N.; Williams, P. D.; Gregory, J. M.; Smith, R. S.

    2014-12-01

    High-resolution ocean models, which are eddy permitting and resolving, require large computing resources to produce centuries worth of data. Also, some previous studies have suggested that increasing resolution does not necessarily solve the problem of unresolved scales, because it simply introduces a new set of unresolved scales. Applying stochastic parameterisations to ocean models is one solution that is expected to improve the representation of small-scale (eddy) effects without increasing run-time. Stochastic parameterisation has been shown to have an impact in atmosphere-only models and idealised ocean models, but has not previously been studied in ocean general circulation models. Here we apply simple stochastic perturbations to the ocean temperature and salinity tendencies in the low-resolution coupled climate model, FAMOUS. The stochastic perturbations are implemented according to T(t) = T(t-1) + (∆T(t) + ξ(t)), where T is temperature or salinity, ΔT is the corresponding deterministic increment in one time step, and ξ(t) is Gaussian noise. We use high-resolution HiGEM data coarse-grained to the FAMOUS grid to provide information about the magnitude and spatio-temporal correlation structure of the noise to be added to the lower resolution model. Here we present results of adding white and red noise, showing the impacts of an additive stochastic perturbation on mean climate state and variability in an AOGCM.

  19. A parallel coupled oceanic-atmospheric general circulation model

    SciTech Connect

    Wehner, M.F.; Bourgeois, A.J.; Eltgroth, P.G.; Duffy, P.B.; Dannevik, W.P.

    1994-12-01

    The Climate Systems Modeling group at LLNL has developed a portable coupled oceanic-atmospheric general circulation model suitable for use on a variety of massively parallel (MPP) computers of the multiple instruction, multiple data (MIMD) class. The model is composed of parallel versions of the UCLA atmospheric general circulation model, the GFDL modular ocean model (MOM) and a dynamic sea ice model based on the Hiber formulation extracted from the OPYC ocean model. The strategy to achieve parallelism is twofold. One level of parallelism is accomplished by applying two dimensional domain decomposition techniques to each of the three constituent submodels. A second level of parallelism is attained by a concurrent execution of AGCM and OGCM/sea ice components on separate sets of processors. For this functional decomposition scheme, a flux coupling module has been written to calculate the heat, moisture and momentum fluxes independent of either the AGCM or the OGCM modules. The flux coupler`s other roles are to facilitate the transfer of data between subsystem components and processors via message passing techniques and to interpolate and aggregate between the possibly incommensurate meshes.

  20. An integrated modeling study of ocean circulation, the ocean carbon cycle, marine ecosystems, and climate change

    NASA Astrophysics Data System (ADS)

    Cao, Long

    The unifying theme of this study is to conduct an extensive exploration of various interactions between ocean circulation, the carbon cycle, marine ecosystems, and climate change using an earth system model of intermediate complexity, ISAM-2.5D (Integrated Science Assessment Model). First, through the simulation of radiocarbon (in terms of Delta14C) it is demonstrated that the inclusion of isopycnal diffusion and a parameterization of eddy-induced circulation in the ISAM-2.5D model yields the most realistic representation of ocean mixing and circulation. Secondly, I demonstrate the value of the simulation of multiple tracers, combined with a variety of observational data, in constraining the ISAM-2.5D model that has been constrained by the simulation of Delta14C. Through the simulation of ocean biogeochemical cycles and CFC-11 and the use of the updated observational data of bomb radiocarbon, I improve the Delta14C-constrained ISAM-2.5D model's performance in simulating ocean circulation and air-sea gas exchange, as well as its credibility in predicting oceanic carbon uptake. Third, I use the ISAM-2.5D model to assess the efficiency of direct carbon injection into the deep ocean with the influence of climate change. It is shown that the consideration of climate change enhances the retention time of injected carbon into the Atlantic Ocean as a result of weakened North Atlantic overturning circulation in a warming climate. However, the climatic effect is insignificant on the efficiency of carbon injection into the Pacific and Indian Oceans. Finally, I quantify that increased atmospheric CO2 concentrations would be mainly responsible for future ocean acidification, including lowering in ocean pH and sea water saturation state with respect to carbonate minerals. The consideration of climate change produces a second-order modification to projected ocean acidification. Therefore, in addition to its radiative effects on climate change, increased atmospheric CO2

  1. Anisotropic Mesoscale Eddy Transport in Ocean General Circulation Models

    NASA Astrophysics Data System (ADS)

    Reckinger, S. J.; Fox-Kemper, B.; Bachman, S.; Bryan, F.; Dennis, J.; Danabasoglu, G.

    2014-12-01

    Modern climate models are limited to coarse-resolution representations of large-scale ocean circulation that rely on parameterizations for mesoscale eddies. The effects of eddies are typically introduced by relating subgrid eddy fluxes to the resolved gradients of buoyancy or other tracers, where the proportionality is, in general, governed by an eddy transport tensor. The symmetric part of the tensor, which represents the diffusive effects of mesoscale eddies, is universally treated isotropically in general circulation models. Thus, only a single parameter, namely the eddy diffusivity, is used at each spatial and temporal location to impart the influence of mesoscale eddies on the resolved flow. However, the diffusive processes that the parameterization approximates, such as shear dispersion, potential vorticity barriers, oceanic turbulence, and instabilities, typically have strongly anisotropic characteristics. Generalizing the eddy diffusivity tensor for anisotropy extends the number of parameters to three: a major diffusivity, a minor diffusivity, and the principal axis of alignment. The Community Earth System Model (CESM) with the anisotropic eddy parameterization is used to test various choices for the newly introduced parameters, which are motivated by observations and the eddy transport tensor diagnosed from high resolution simulations. Simply setting the ratio of major to minor diffusivities to a value of five globally, while aligning the major axis along the flow direction, improves biogeochemical tracer ventilation and reduces global temperature and salinity biases. These effects can be improved even further by parameterizing the anisotropic transport mechanisms in the ocean.

  2. A Pacific Ocean general circulation model for satellite data assimilation

    NASA Technical Reports Server (NTRS)

    Chao, Y.; Halpern, D.; Mechoso, C. R.

    1991-01-01

    A tropical Pacific Ocean General Circulation Model (OGCM) to be used in satellite data assimilation studies is described. The transfer of the OGCM from a CYBER-205 at NOAA's Geophysical Fluid Dynamics Laboratory to a CRAY-2 at NASA's Ames Research Center is documented. Two 3-year model integrations from identical initial conditions but performed on those two computers are compared. The model simulations are very similar to each other, as expected, but the simulations performed with the higher-precision CRAY-2 is smoother than that with the lower-precision CYBER-205. The CYBER-205 and CRAY-2 use 32 and 64-bit mantissa arithmetic, respectively. The major features of the oceanic circulation in the tropical Pacific, namely the North Equatorial Current, the North Equatorial Countercurrent, the South Equatorial Current, and the Equatorial Undercurrent, are realistically produced and their seasonal cycles are described. The OGCM provides a powerful tool for study of tropical oceans and for the assimilation of satellite altimetry data.

  3. Modeling the impact of polar mesocyclones on ocean circulation

    NASA Astrophysics Data System (ADS)

    Condron, Alan; Bigg, Grant R.; Renfrew, Ian A.

    2008-10-01

    Subsynoptic polar mesoscale cyclones (or mesocyclones) are underrepresented in atmospheric reanalysis data sets and are subgrid scale processes in most models used for seasonal or climate forecasting. This lack of representation, particularly over the Nordic Seas, has a significant impact on modeled ocean circulation due to a consequent underestimation of atmospheric forcing at the air-sea boundary. Using Rankine vortices and a statistically significant linear relationship between mesocyclone diameter and maximum wind speed, a novel parameterization is developed that allows the bogusing in of missing or underrepresented vortices by exploiting a satellite-derived mesocyclone database. From October 1993 to September 1995, more than 2500 cyclones known to be missing from reanalysis data over the northeast Atlantic are parameterized into the forcing fields for a global ocean-only numerical modeling experiment. A comparison of this perturbed forcing simulation to a control simulation shows enhanced surface latent and sensible heat fluxes and a dramatic increase in the cyclonic rotation of the Nordic Seas gyre by four times the average interannual variability. In response to these changes, Greenland Sea Deep Water (GSDW) formation generally increases by up to 20% in 1 month, indicating more active open ocean convection. However such enhancements are smaller than the considerable monthly variability in GSDW production. An accompanying increase in the volume transport of intermediate and deep water overflowing the Denmark Strait highlights an important coupling between short-lived, intense atmospheric activity and deep ocean circulation. The parameterization scheme has the potential to be adapted for use in coupled climate models.

  4. World Ocean Circulation Experiment

    NASA Technical Reports Server (NTRS)

    Clarke, R. Allyn

    1992-01-01

    The oceans are an equal partner with the atmosphere in the global climate system. The World Ocean Circulation Experiment is presently being implemented to improve ocean models that are useful for climate prediction both by encouraging more model development but more importantly by providing quality data sets that can be used to force or to validate such models. WOCE is the first oceanographic experiment that plans to generate and to use multiparameter global ocean data sets. In order for WOCE to succeed, oceanographers must establish and learn to use more effective methods of assembling, quality controlling, manipulating and distributing oceanographic data.

  5. Horizontal density compensation in ocean general circulation models

    NASA Astrophysics Data System (ADS)

    Koch, Andrey O.; Helber, Robert W.; Richman, James G.; Barron, Charlie N.

    2013-04-01

    Density compensation is the condition where temperature (T) and salinity (S) gradients counteract in their effect on density. Open ocean observations with SeaSoar tows and recent glider observations in the Gulf of Mexico reported in the scientific literature suggest that horizontal gradients in the surface mixed layer tend to be strongly density compensated over a range of spatial scales while in seasonal thermocline and deeper layers T,S-fronts are only partially compensated or uncompensated. We assess the capability of ocean general circulation models (OGCM) to develop horizontal density compensation as observed in the upper ocean. The physics required to evolve the initial density compensated mixed layer toward the partially compensated conditions of the thermocline is tested. Idealistic scenarios with horizontal, partially compensated density fronts in the mixed layer are examined in submesoscale-resolved run-down simulations on Hybrid Coordinate Ocean Model (HYCOM). Simulations with no atmospheric forcing show that initial Density compensation does not change substantially experiencing only minor decrease with time simultaneously with the restratification of the mixed layer by submesoscale eddies. Submesoscale fronts tend to be more compensated than mesoscale fronts. A sensitivity analysis shows that the density compensation of submesoscale fronts is particularly sensitive to the horizontal diffusion rate. Simulations with wind forcing exhibit destruction of initial density compensation due to ageostrophic frontogenesis which is confirmed by recent glider observations in the Gulf of Mexico. The lack of the model skill to develop and maintain compensated thermohaline variability is attributed to the T, S horizontal diffusion parameterization used in HYCOM and generally in modern OGCMs: it is decoupled from vertical diffusion and T and S diffusion is horizontally identical. Our findings suggest that OGCM's skill to develop compensated thermohaline variability

  6. Ocean circulation using altimetry

    NASA Technical Reports Server (NTRS)

    Minster, Jean-Francois; Brossier, C.; Gennero, M. C.; Mazzega, P.; Remy, F.; Letraon, P. Y.; Blanc, F.

    1991-01-01

    Our group has been very actively involved in promoting satellite altimetry as a unique tool for observing ocean circulation and its variability. TOPEX/POSEIDON is particularly interesting as it is optimized for this purpose. It will probably be the first instrument really capable of observing the seasonal and interannual variability of subtropical and polar gyres and the first to eventually document the corresponding variability of their heat flux transport. The studies of these phenomena require data of the best quality, unbiased extraction of the signal, mixing of these satellite data with in situ measurements, and assimilation of the whole set into a dynamic description of ocean circulation. Our group intends to develop responses to all these requirements. We will concentrate mostly on the circulation of the South Atlantic and Indian Oceans: This will be done in close connection with other groups involved in the study of circulation of the tropical Atlantic Ocean, in the altimetry measurements (in particular, those of the tidal issue), and in the techniques of data assimilation in ocean circulation models.

  7. Volume, heat, and freshwater transports of the global ocean circulation 1993-2000, estimated from a general circulation model constrained by World Ocean Circulation Experiment (WOCE) data

    NASA Astrophysics Data System (ADS)

    Stammer, D.; Wunsch, C.; Giering, R.; Eckert, C.; Heimbach, P.; Marotzke, J.; Adcroft, A.; Hill, C. N.; Marshall, J.

    2003-01-01

    An analysis of ocean volume, heat, and freshwater transports from a fully constrained general circulation model (GCM) is described. Output from a data synthesis, or state estimation, method is used by which the model was forced to large-scale, time-varying global ocean data sets over 1993 through 2000. Time-mean horizontal transports, estimated from this fully time-dependent circulation, have converged with independent time-independent estimates from box inversions over most parts of the world ocean but especially in the southern hemisphere. However, heat transport estimates differ substantially in the North Atlantic where our estimates result in only 1/2 previous results. The models drift over the estimation period is consistent with observations from TOPEX/Poseidon in their spatial pattern, but smaller in their amplitudes by about a factor of 2. Associated temperature and salinity changes are complex, and both point toward air-sea interaction over water mass formation regions as the primary source for changes in the deep ocean. The estimated mean circulation around Australia involves a net volume transport of 11 Sv through the Indonesian Throughflow and the Mozambique Channel. In addition, we show that this flow regime exists on all timescales above 1 month, rendering the variability in the South Pacific strongly coupled to the Indian Ocean. Moreover, the dynamically consistent variations in the model show temporal variability of oceanic heat transports, heat storage, and atmospheric exchanges that are complex and with a strong dependence upon location, depth, and timescale. Our results demonstrate the great potential of an ocean state estimation system to provide a dynamical description of the time-dependent observed heat transport and heat content changes and their relation to air-sea interactions.

  8. Assimilation of GRACE-derived oceanic mass distributions with a global ocean circulation model

    NASA Astrophysics Data System (ADS)

    Saynisch, J.; Bergmann-Wolf, I.; Thomas, M.

    2015-02-01

    To study the sub-seasonal distribution and generation of ocean mass anomalies, Gravity Recovery and Climate Experiment (GRACE) observations of daily and monthly resolution are assimilated into a global ocean circulation model with an ensemble-based Kalman-Filter technique. The satellite gravimetry observations are processed to become time-variable fields of ocean mass distribution. Error budgets for the observations and the ocean model's initial state are estimated which contain the full covariance information. The consistency of the presented approach is demonstrated by increased agreement between GRACE observations and the ocean model. Furthermore, the simulations are compared with independent observations from 54 bottom pressure recorders. The assimilation improves the agreement to high-latitude recorders by up to 2 hPa. The improvements are caused by assimilation-induced changes in the atmospheric wind forcing, i.e., quantities not directly observed by GRACE. Finally, the use of the developed Kalman-Filter approach as a destriping filter to remove artificial noise contaminating the GRACE observations is presented.

  9. A Coupled Ocean General Circulation, Biogeochemical, and Radiative Model of the Global Oceans: Seasonal Distributions of Ocean Chlorophyll and Nutrients

    NASA Technical Reports Server (NTRS)

    Gregg, Watson W.; Busalacchi, Antonio (Technical Monitor)

    2000-01-01

    A coupled ocean general circulation, biogeochemical, and radiative model was constructed to evaluate and understand the nature of seasonal variability of chlorophyll and nutrients in the global oceans. Biogeochemical processes in the model are determined from the influences of circulation and turbulence dynamics, irradiance availability. and the interactions among three functional phytoplankton groups (diatoms. chlorophytes, and picoplankton) and three nutrients (nitrate, ammonium, and silicate). Basin scale (greater than 1000 km) model chlorophyll results are in overall agreement with CZCS pigments in many global regions. Seasonal variability observed in the CZCS is also represented in the model. Synoptic scale (100-1000 km) comparisons of imagery are generally in conformance although occasional departures are apparent. Model nitrate distributions agree with in situ data, including seasonal dynamics, except for the equatorial Atlantic. The overall agreement of the model with satellite and in situ data sources indicates that the model dynamics offer a reasonably realistic simulation of phytoplankton and nutrient dynamics on synoptic scales. This is especially true given that initial conditions are homogenous chlorophyll fields. The success of the model in producing a reasonable representation of chlorophyll and nutrient distributions and seasonal variability in the global oceans is attributed to the application of a generalized, processes-driven approach as opposed to regional parameterization and the existence of multiple phytoplankton groups with different physiological and physical properties. These factors enable the model to simultaneously represent many aspects of the great diversity of physical, biological, chemical, and radiative environments encountered in the global oceans.

  10. General circulation of the ocean

    SciTech Connect

    Abarbanel, H.D.I.; Young, W.R.

    1986-01-01

    This book is an analysis of the geophysics of ocean circulation and its interaction with the atmosphere. It reviews the new concepts and models which have emerged in the last five years, as well as classical theories and observations. The contributions cover topics such as: the observational basis for large-scale circulation, including surface and deep circulation and subtropical gyres; thermocline theories; inverse methods for ocean circulation; baroclinic theories of the wind-driven circulation; and single layer models. This volume sets the current research literature in context, and suggests promising avenues for future study.

  11. Calibrating the ECCO ocean general circulation model using Green's functions

    NASA Technical Reports Server (NTRS)

    Menemenlis, D.; Fu, L. L.; Lee, T.; Fukumori, I.

    2002-01-01

    Green's functions provide a simple, yet effective, method to test and calibrate General-Circulation-Model(GCM) parameterizations, to study and quantify model and data errors, to correct model biases and trends, and to blend estimates from different solutions and data products.

  12. Benchmarking ocean circulation models on massively parallel computers

    SciTech Connect

    Poling, D.A.

    1997-08-01

    General circulation models are becoming the premier theoretical tools for studying the complex structure of the global climate. GEONET was envisioned as exercising the resources developed for the nuclear weapons program to address environmental problems. The similarity of circulation models to weapons codes made them an attractive field for them to develop expertise. The author hoped to become an active player in mainline climate research through computer simulation. This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The intention of this research was to establish the Laboratory in mainstream climate research in conjunction with the GEONET project.

  13. Adaptive Error Estimation in Linearized Ocean General Circulation Models

    NASA Technical Reports Server (NTRS)

    Chechelnitsky, Michael Y.

    1999-01-01

    Data assimilation methods are routinely used in oceanography. The statistics of the model and measurement errors need to be specified a priori. This study addresses the problem of estimating model and measurement error statistics from observations. We start by testing innovation based methods of adaptive error estimation with low-dimensional models in the North Pacific (5-60 deg N, 132-252 deg E) to TOPEX/POSEIDON (TIP) sea level anomaly data, acoustic tomography data from the ATOC project, and the MIT General Circulation Model (GCM). A reduced state linear model that describes large scale internal (baroclinic) error dynamics is used. The methods are shown to be sensitive to the initial guess for the error statistics and the type of observations. A new off-line approach is developed, the covariance matching approach (CMA), where covariance matrices of model-data residuals are "matched" to their theoretical expectations using familiar least squares methods. This method uses observations directly instead of the innovations sequence and is shown to be related to the MT method and the method of Fu et al. (1993). Twin experiments using the same linearized MIT GCM suggest that altimetric data are ill-suited to the estimation of internal GCM errors, but that such estimates can in theory be obtained using acoustic data. The CMA is then applied to T/P sea level anomaly data and a linearization of a global GFDL GCM which uses two vertical modes. We show that the CMA method can be used with a global model and a global data set, and that the estimates of the error statistics are robust. We show that the fraction of the GCM-T/P residual variance explained by the model error is larger than that derived in Fukumori et al.(1999) with the method of Fu et al.(1993). Most of the model error is explained by the barotropic mode. However, we find that impact of the change in the error statistics on the data assimilation estimates is very small. This is explained by the large

  14. Relaxation oscillations in an idealized ocean circulation model

    NASA Astrophysics Data System (ADS)

    Roberts, Andrew; Saha, Raj

    2016-06-01

    This work is motivated by a desire to understand transitions between stable equilibria observed in Stommel's 1961 thermohaline circulation model. We adapt the model, including a forcing parameter as a dynamic slow variable. The resulting model is a piecewise-smooth, three time-scale system. The model is analyzed using geometric singular perturbation theory to demonstrate the existence of attracting periodic orbits. The system is capable of producing classical relaxation oscillations as expected, but there is also a parameter regime in which the model exhibits small amplitude oscillations known as canard cycles. Forcing the model with obliquity variations from the last 100,000 years produces oscillations that are modulated in amplitude and frequency. The output shows similarities with important features of the climate proxy data of the same period.

  15. Improvement in Geoid Models for Ocean Circulation Studies

    NASA Technical Reports Server (NTRS)

    Tapley, Byron D.; Chambers, Don P.; Poole, Steve; Ries, John c.

    2003-01-01

    At wavelengths of 500 km and longer, the GRACE GGM01 Model produces a significantly better marine geoid than any previous model. This conclusion follows from evaluating the geostrophic currents determined by combining the model with a mean sea surface from altimetry. The agreement with currents computed from a traditional hydrographic map is very close, which suggests that one of the primary missions of the TOPEX/POSEIDON mission, to determine the absolute dynamic ocean topography, may soon be met. This solution has been made available to the public at http://www.csr.utexs.edu/grace/gravity. The results reported in this paper have been presented at the 2003 EGS-AGU-EUG Joint Assembly. Two articles are currently being prepared for Geophysical Research Letters to summarize these results.

  16. Anisotropic mesoscale eddy transport in ocean general circulation models

    NASA Astrophysics Data System (ADS)

    Reckinger, Scott; Fox-Kemper, Baylor; Bachman, Scott; Bryan, Frank; Dennis, John; Danabasoglu, Gokhan

    2014-11-01

    In modern climate models, the effects of oceanic mesoscale eddies are introduced by relating subgrid eddy fluxes to the resolved gradients of buoyancy or other tracers, where the proportionality is, in general, governed by an eddy transport tensor. The symmetric part of the tensor, which represents the diffusive effects of mesoscale eddies, is universally treated isotropically. However, the diffusive processes that the parameterization approximates, such as shear dispersion and potential vorticity barriers, typically have strongly anisotropic characteristics. Generalizing the eddy diffusivity tensor for anisotropy extends the number of parameters from one to three: major diffusivity, minor diffusivity, and alignment. The Community Earth System Model (CESM) with the anisotropic eddy parameterization is used to test various choices for the parameters, which are motivated by observations and the eddy transport tensor diagnosed from high resolution simulations. Simply setting the ratio of major to minor diffusivities to a value of five globally, while aligning the major axis along the flow direction, improves biogeochemical tracer ventilation and reduces temperature and salinity biases. These effects can be improved by parameterizing the oceanic anisotropic transport mechanisms.

  17. The response of an ocean general circulation model to surface wind stress produced by an atmospheric general circulation model

    SciTech Connect

    Huang, B.; Schneider, E.K.

    1995-10-01

    Two surface wind stress datasets for 1979-91, one based on observations and the other from an investigation of the COLA atmospheric general circulation model (AGCM) with prescribed SST, are used to drive the GFDL ocean general circulation model. These two runs are referred to as the control and COLA experiments, respectively. Simulated SST and upper-ocean heat contents (HC) in the tropical Pacific Ocean are compared with observations and between experiments. Both simulation reproduced the observed mean SST and HC fields as well as their annual cycles realistically. Major errors common to both runs are colder than observed SST in the eastern equatorial ocean and HC in the western Pacific south of the equator, with errors generally larger in the COLA experiment. New errors arising from the AGCM wind forcing include higher SST near the South American coast throughout the year and weaker HC gradients along the equator in boreal spring. The former is associated with suppressed coastal upwelling by weak along shore AGCM winds, and the latter is caused by weaker equatorial easterlies in boreal spring. The low-frequency ENSO fluctuations are also realistic for both runs. Correlations between the observed and simulated SST anomalies from the COLA simulation are as high as those from the control run in the central equatorial Pacific. A major problem in the COLA simulation is the appearance of unrealistic tropical cold anomalies during the boreal spring of mature El Nino years. These anomalies propagate along the equator from the western Pacific to the eastern coast in about three months, and temporarily eliminate the warm SST and HC anomalies in the eastern Pacific. This erroneous oceanic response in the COLA simulation is caused by a reversal of the westerly wind anomalies on the equator, associated with an unrealistic southward shift of the ITCZ in boreal spring during El Nino events. 66 refs., 16 figs.

  18. Modeling of submarine melting of Greenland tidewater glaciers using an ocean general circulation model

    NASA Astrophysics Data System (ADS)

    Xu, Y.; Rignot, E. J.; Menemenlis, D.; Koppes, M.

    2010-12-01

    The acceleration of Greenland tidewater glaciers has increased the mass loss from the Greenland Ice Sheet. Submarine melting is one of the possible drivers for glacier acceleration. Enhanced submarine melting could result from ocean warming, changes in ocean current, and increase in sub-glacial runoff. We use a combination of numerical modeling and field data to understand the mechanism of submarine melting in Greenland. Specifically, oceanographic data (temperature, salinity, and current velocity) were collected in August 2008 and 2010 near the calving fronts of the Lille Gletscher, Store Gletscher, Eqip Sermia, Kangilerngata Sermia, Sermeq Kujatdleq and Sermeq Avangnardleq glaciers in central West Greenland. These data are compared to high-resolution regional ocean simulations carried out using the Massachusetts Institute of Technology general circulation model (MITgcm). MITgcm includes submarine melting at the base of an ice shelf and we have added a new module to simulate the melting process along the vertical calving face of Greenland tidewater glaciers. We integrate the MITgcm with JRA25 atmospheric and ECCO2 oceanic boundary conditions and compare the simulation results with the West Greenland data. We also conduct model sensitivity studies for ocean temperature, sub-glacial runoff, and fjord. The preliminary results show a quadratic increase in submarine melting with warmer ocean temperature and a role of sub-glacial runoff in changing ocean circulation. This study could help us evaluate the impact of ocean warming and enhanced runoff on submarine melting and in turn on glacier mass balance. This work is performed at UCI under a contact with NASA Cryosphere Science Program.

  19. Miocene ocean circulation inferred from marine carbon cycle modeling combined with benthic isotope records

    NASA Astrophysics Data System (ADS)

    Butzin, Martin; Lohmann, Gerrit; Bickert, Torsten

    2011-02-01

    In a modeling sensitivity study we investigate the evolution of the ocean circulation and of marine carbon isotope (δ13C) records during the Miocene (about 23-5 million years ago). For this purpose we ran an ocean-circulation carbon cycle model of intermediate complexity (Large Scale Geostrophic- Hamburg Ocean Carbon Cycle Model, version 2s) exploring various seaway configurations. Our investigations confirm that the Central American Seaway played a decisive role in the history of the Miocene ocean circulation. In simulations with a deep Central American Seaway (depth range 1-3 km), typical for the early to middle Miocene, deep water production in the North Atlantic is absent or weak, while the meridional overturning circulation is dominated by water mass formation in the Southern Ocean. Deep water formation in the North Atlantic begins when the Central American Seaway shoals to a few hundreds of meters, which is typical for the late Miocene. Our results do not support ideas that the mid-Miocene closing of the Eastern Tethys contributed to Antarctic glaciation. On the other hand, we find some water exchange between the Indian Ocean and the Atlantic via the Eastern Tethys during the early Miocene. Our model results for the Atlantic meridional overturning circulation and for Atlantic δ13C during the late Miocene are largely independent from depth variations of the Greenland-Scotland Ridge. To a large extent, the evolution of Miocene deep-sea δ13C records can be explained with large-scale ocean circulation changes. Our model-data comparison for the middle and early Miocene suggests that during the early Neogene the seaway effect on benthic δ13C may have been superimposed by further factors such as climate regime shifts and/or terrestrial carbon cycle changes.

  20. Assimilation of TOPEX/POSEIDON Altimeter Data into a Global Ocean Circulation Model: Are the Results Any Good?

    NASA Technical Reports Server (NTRS)

    Fukumori, I.; Fu, L. L.; Chao, Y.

    1998-01-01

    The feasibility of assimilating satellite altimetry data into a global ocean general ocean general circulation model is studied. Three years of TOPEX/POSEIDON data is analyzed using a global, three-dimensional, nonlinear primitive equation model.

  1. Variability of the thermohaline circulation in a simple coupled atmosphere-ocean model

    NASA Astrophysics Data System (ADS)

    Taboada, J. J.; Lorenzo, M. N.

    2003-04-01

    The behavior of the Atlantic thermohaline circulation (THC) is essential to a better understanding of climate change. Paleoclimatic studies suggest that this circulation has experimented repeated changes throughout the history of the Earth associated to climate changes [1]. The coupled 3-dimensional climate models are useful in quantitatively assessing the details of the thermohaline circulation and for comparison with observations. However, the currently available computing capacity reduces the possibility of carry out exhaustive parametric studies of the THC. Models of reduced complexity can help overcome this difficulty and make valuable contributions to a better understanding of parameter space. Moreover, these models are most useful as exploratory tools for hypothesis building. Here we study a low-order coupled atmosphere-ocean general circulation model in order to understand the behavior of the thermohaline circulation through different changes on the interaction between atmosphere-ocean [1,2]. The atmosphere is represented by a low-order atmospheric "general circulation" model introduced by Lorenz in 1984 [3] and the ocean model considered here is a 3-box model which simulates the North Atlantic thermohaline circulation [2]. [1] Broecker W.S. (1997) Thermohaline circulation, the Achilles Heel of our climate system: will man-made CO_2 upset the current balance?. Science, 278, 1582-1588. [2] Roebber, P.J. (1995) Climate variability in a low-order coupled atmosphere-ocean model. Tellus, 47A, 473-494. [3] Lorenz, E.N. (1984) Irregularity. A fundamental property of the atmosphere. Tellus, 36A, 98-110.

  2. Ocean circulation studies

    NASA Technical Reports Server (NTRS)

    Koblinsky, C. J.

    1984-01-01

    Remotely sensed signatures of ocean surface characteristics from active and passive satellite-borne radiometers in conjunction with in situ data were utilized to examine the large scale, low frequency circulation of the world's oceans. Studies of the California Current, the Gulf of California, and the Kuroshio Extension Current in the western North Pacific were reviewed briefly. The importance of satellite oceanographic tools was emphasized.

  3. Characterizing the circulation off the Kenyan-Tanzanian coast using an ocean model

    NASA Astrophysics Data System (ADS)

    Gabriela Mayorga-Adame, C.; Ted Strub, P.; Batchelder, Harold P.; Spitz, Yvette H.

    2016-02-01

    The Kenyan-Tanzanian coastal region in the western Indian Ocean faces several environmental challenges including coral reef conservation, fisheries management, coastal erosion, and nearshore pollution. The region lacks hydrodynamic records and oceanographic studies at adequate spatial and temporal scales to provide information relevant to the local environmental issues. We have developed a 4 km horizontal resolution ocean circulation model of the region: the Kenyan-Tanzanian Coastal Model (KTCM) that provides coastal circulation and hydrography with higher resolution than previous models and observational studies of this region. Comparisons to temperature profiles, satellite-derived sea surface temperature and sea surface height anomaly fields, indicate that the model reproduces the main features of the regional circulation, while greatly increasing the details of the nearshore circulation. We describe the seasonal ocean circulation and hydrography of the Kenyan-Tanzanian coastal region based on a climatology of 8 years (2000-2007) of the KTCM simulations. The regional monsoon seasonality produces two distinct coastal circulation regimes: (1) during December-March, there are relatively sluggish shelf flows and (2) during April-November, there are strong northward transports. Simulations from the model will be useful for examining dispersal of pollutants and spatial connectivity of coral reef species.

  4. Cloud-radiative effects on implied oceanic energy transports as simulated by atmospheric general circulation models

    SciTech Connect

    Gleckler, P.J.; Randall, D.A.; Boer, G.

    1994-03-01

    This paper reports on energy fluxes across the surface of the ocean as simulated by fifteen atmospheric general circulation models in which ocean surface temperatures and sea-ice boundaries are prescribed. The oceanic meridional energy transport that would be required to balance these surface fluxes is computed, and is shown to be critically sensitive to the radiative effects of clouds, to the extent that even the sign of the Southern Hemisphere ocean energy transport can be affected by the errors in simulated cloud-radiation interactions.

  5. Cloud-radiative effects on implied oceanic energy transport as simulated by atmospheric general circulation models

    NASA Technical Reports Server (NTRS)

    Gleckler, P. J.; Randall, D. A.; Boer, G.; Colman, R.; Dix, M.; Galin, V.; Helfand, M.; Kiehl, J.; Kitoh, A.; Lau, W.

    1995-01-01

    This paper summarizes the ocean surface net energy flux simulated by fifteen atmospheric general circulation models constrained by realistically-varying sea surface temperatures and sea ice as part of the Atmospheric Model Intercomparison Project. In general, the simulated energy fluxes are within the very large observational uncertainties. However, the annual mean oceanic meridional heat transport that would be required to balance the simulated surface fluxes is shown to be critically sensitive to the radiative effects of clouds, to the extent that even the sign of the Southern Hemisphere ocean heat transport can be affected by the errors in simulated cloud-radiation interactions. It is suggested that improved treatment of cloud radiative effects should help in the development of coupled atmosphere-ocean general circulation models.

  6. Simulation of seasonal anomalies of atmospheric circulation using coupled atmosphere-ocean model

    NASA Astrophysics Data System (ADS)

    Tolstykh, M. A.; Diansky, N. A.; Gusev, A. V.; Kiktev, D. B.

    2014-03-01

    A coupled atmosphere-ocean model intended for the simulation of coupled circulation at time scales up to a season is developed. The semi-Lagrangian atmospheric general circulation model of the Hydrometeorological Centre of Russia, SLAV, is coupled with the sigma model of ocean general circulation developed at the Institute of Numerical Mathematics, Russian Academy of Sciences (INM RAS), INMOM. Using this coupled model, numerical experiments on ensemble modeling of the atmosphere and ocean circulation for up to 4 months are carried out using real initial data for all seasons of an annual cycle in 1989-2010. Results of these experiments are compared to the results of the SLAV model with the simple evolution of the sea surface temperature. A comparative analysis of seasonally averaged anomalies of atmospheric circulation shows prospects in applying the coupled model for forecasts. It is shown with the example of the El Niño phenomenon of 1997-1998 that the coupled model forecasts the seasonally averaged anomalies for the period of the nonstationary El Niño phase significantly better.

  7. Idealised modelling of ocean circulation driven by geothermal and hydrothermal fluxes at the seabed

    NASA Astrophysics Data System (ADS)

    Barnes, Jowan; Morales Maqueda, Miguel; Polton, Jeff

    2016-04-01

    There are two distinct processes by which heat is transferred from the solid Earth into the abyssal ocean. The first is conductive geothermal heating and the second is hydrothermal heating, involving advection of heated water from within the Earth's crust. Here, the noticeably different impacts of these two physical systems on ocean circulation are investigated. Previous modelling studies have applied geothermal heat fluxes at the seabed and shown discrepancies in circulation compared to cases which neglected heat from the Earth in their boundary conditions. The true heat flux in the ocean, however, is not entirely geothermal. From areas where the crust is younger a significant proportion of the heat input from the Earth could be in the form of fluid flow from hydrothermal vents, introducing forcing to the circulation which has previously been unaccounted for. In this study a set of idealised modelling experiments are run in order to investigate the effects of changing the balance of the total heat flux from purely geothermal to purely hydrothermal, via intermediate states in which the two boundary conditions are combined in different ratios. By performing such experiments it will be shown which of the two processes is dominant in its effects on circulation driven by heating at the seabed, and whether neglecting the hydrothermal advection in favour of a fully conductive geothermal boundary condition is justifiable. The results will inform the construction of boundary conditions for future circulation models involving ocean floor heat fluxes, specifically a regional study of geothermal and hydrothermal contributions within the Panama Basin.

  8. Modeling of the circulation in the Northwestern Mediterranean Sea with the Princeton Ocean Model

    NASA Astrophysics Data System (ADS)

    Ahumada, M. A.; Cruzado, A.

    2007-02-01

    The Princeton Ocean Model - POM (Blumberg and Mellor, 1987) has been implemented in the Northwestern Mediterranean nested (in one-way off-line mode) to a general circulation model of the Mediterranean Sea - OGCM (Pinardi and Masetti, 2000; Demirov and Pinardi, 2002) in order to investigate if this model configuration is capable of reproducing the major features of the circulation as known from observations and to improve what has been made by previous numerical modeling works. According to the model results, the large-scale cyclonic circulation in the northern part of the Northwestern Mediterranean is, at least in the upper layers, less coherent in winter and spring than in summer and autumn. Furthermore, there is evidence that the mesoscale structure (eddies and meanders) is, during all year, a significant dynamic characteristic in this region of the Mediterranean Sea. Finally, concerning the circulation in the lower layers, the model results have confirmed that Levantine Intermediate Water (LIW) and Western Mediterranean Deep Water (WMDW) follow essentially a cyclonic path during all year.

  9. Effects of Southern Hemisphere Wind Changes on the Meridional Overturning Circulation in Ocean Models.

    PubMed

    Gent, Peter R

    2016-01-01

    Observations show that the Southern Hemisphere zonal wind stress maximum has increased significantly over the past 30 years. Eddy-resolving ocean models show that the resulting increase in the Southern Ocean mean flow meridional overturning circulation (MOC) is partially compensated by an increase in the eddy MOC. This effect can be reproduced in the non-eddy-resolving ocean component of a climate model, providing the eddy parameterization coefficient is variable and not a constant. If the coefficient is a constant, then the Southern Ocean mean MOC change is balanced by an unrealistically large change in the Atlantic Ocean MOC. Southern Ocean eddy compensation means that Southern Hemisphere winds cannot be the dominant mechanism driving midlatitude North Atlantic MOC variability. PMID:26163010

  10. A parallel Atmosphere-Ocean Global Circulation Model of intermediate complexity for Earth system climate research

    NASA Astrophysics Data System (ADS)

    Silva, T. A.; Schmittner, A.

    2007-12-01

    We present the evolution of an Earth System model of intermediate complexity featuring an ocean global circulation model to include a fully coupled 3D primitive equations atmospheric model. The original Earth System climate model, UVic ESCM (Weaver et al. 2001), uses an ocean global circulation model coupled to a one layer atmospheric energy-moisture balance model. It also comprises a viscous-plastic rheology sea ice model, a mechanical land ice model, land surface, oceanic and terrestrial carbon models and a simple 3D marine ecosystem model (Schmittner et al. 2005). A spectral atmospheric, model, PUMA (Fraedrich et al. 2005), was coupled to the UVic ESCM to provide an atmosphere with nonlinear dynamics in target resolutions of T21, T31 and T42, as required. The coupling with the atmosphere, which involves data transfer, preprocessing and interpolation, is done through the OASIS3 coupler. During a run there are 2 + 2N parallel processes: the UVic ESCM, the Oasis3 coupler and the PUMA model with its domain split across 2N processes. The choice of N allows to balance more or less complex configurations of UVic model (e.g. higher level marine ecosystem model or number of biogeochemical tracers) with the atmospheric model at different resolutions, in order to maintain computational efficiency. The relatively simple parameterizations make this new atmosphere-ocean global circulation model much faster than a state-of-the-art Atmosphere-Ocean Global Circulation Model, and so optimally geared for decadal to millennial scale integrations. The latter require special care with the conservation of fluxes during coupling. A second order conservative interpolation method was applied (Jones 1999) and this is compared with the use of typical non-conservative methods.

  11. Barbi: a simplified general circulation model for a baroclinic ocean with topography

    NASA Astrophysics Data System (ADS)

    Eden, C.; Olbers, D.

    2003-04-01

    A new type of ocean general circulation model with simplified physics is described and tested for various simple wind--driven circulation problems.The model consists of the vorticity balance of the depth-averaged flow and a hierarchy of equations for ``vertical moments'' of density and baroclinic velocity. The first vertical density moment is the (vertically integrated) potential energy, which is used to describe the predominant link between the barotropic and the baroclinic oceanic flow in the presence of sloping topography. Tendency equations for the vertical moments of density and baroclinic velocity and an appropriate truncation of the coupled hierarchy of moments are derived which, together with the barotropic vorticity balance, yield a closed set of equations describing the BARotropic-Baroclinic-Interaction (BARBI) model of the oceanic circulation. Idealized companion experiments with a numerical implementation of the BARBI model and a primitive equation model indicate that wave propagation properties and baroclinic adjustments are correctly represented in BARBI in mid latitudes as well as in equatorial latitudes. Furthermore, a set of experiments with a realistic application to the Atlantic/Southern Ocean system reproduces important aspects which have been previously reported by studies of gyre circulations and circumpolar currents using full primitive equation models.

  12. Modelling of the circulation in the Northwestern Mediterranean Sea with the Princeton Ocean Model

    NASA Astrophysics Data System (ADS)

    Ahumada, M. A.; Cruzado, A.

    2006-08-01

    The Princeton Ocean Model - POM (Blumberg and Mellor, 1987) has been implemented in the Northwestern Mediterranean nested (in one-way off-line mode) to a general circulation model of the Mediterranean Sea - OGCM (Pinardi and Masetti, 2000; Demirov and Pinardi, 2002) in order to investigate if this model configuration is capable of reproducing the major features of the circulation as known from observations and to improve what has been made by previous numerical modeling works. According to the model results, the large-scale cyclonic circulation in the northern part of the Northwestern Mediterranean is, at least in the upper layers, less coherent in winter and spring than in summer and autumn. Furthermore, there is evidence that the mesoscale structure (eddies and meanders) is, during all year, a significant dynamic characteristic in this region of the Mediterranean Sea. Finally, concerning the circulation in the lower layers has been confirmed that the Levantine Intermediate Water and the Western Mediterranean Deep Water follow essentially a cyclonic path during all year.

  13. Ocean circulation and climate change

    NASA Astrophysics Data System (ADS)

    Hasselmann, Klaus

    1991-09-01

    Recent numerical simulations using global ocean circulation models are reviewed together with model experiments involving further important climate sub-systems with which the ocean interacts: the atmosphere, the air-sea interface and the global carbon cycle. A common feature of all ocean circulation experiments considered is the strong sensitivity of the circulation to relatively minor changes in surface forcing, particularly to the buoyancy fluxes in regions of deep water formation in high latitudes. This may explain some of the well-known deficiencies of past global ocean circulation simulations. The strong sensitivity may also have been the cause of rapid climate changes observed in paleoclimatic records and can lead further to significant natural climate variability on the time scales of a few hundred years through the stochastic forcing of the ocean by atmospheric weather variability. Gobal warming computations using two different coupled ocean-atmosphere models for the "business-as-usual" scenario of the Intergovernmental Panel on Climate Change yield a significantly stronger warming delay due to the heat uptake by the oceans in the Southern Ocean than estimated on the basis of box-diffusion models. Recent advances in surface wave modelling, illustrated by a comparison of wave height fields derived from the WAM model and the GEOSAT altimeter, hold promise for the development of an improved representation of ocean-atmosphere coupling based on an explicit description of the dynamical processes at the air-sea interface. Global carbon cycle simulations with a three dimensional carbon cycle model tuned to reproduce past variations of carbon cycle indices show a significant impact of variations in the ocean circulation on the CO2 concentration in the atmosphere and thereby on climate. The series of experiments suggest that for the study of climate in the time scale range from 10-Ocean circulation and climate change

    NASA Astrophysics Data System (ADS)

    Hasselmann, Klaus

    1991-08-01

    Recent numerical simulations using global ocean circulation models are reviewed together with model experiments involving further important climate sub-systems with which the ocean interacts: the atmosphere, the air-sea interface and the global carbon cycle. A common feature of all ocean circulation experiments considered is the strong sensitivity of the circulation to relatively minor changes in surface forcing, particularly to the buoyancy fluxes in regions of deep water formation in high latitudes. This may explain some of the well-known deficiencies of past global ocean circulation simulations. The strong sensitivity may also have been the cause of rapid climate changes observed in paleoclimatic records and can lead further to significant natural climate variability on the time scales of a few hundred years through the stochastic forcing of the ocean by atmospheric weather variability. Gobal warming computations using two different coupled ocean-atmosphere models for the "business-as-usual" scenario of the Intergovernmental Panel on Climate Change yield a significantly stronger warming delay due to the heat uptake by the oceans in the Southern Ocean than estimated on the basis of box-diffusion models. Recent advances in surface wave modelling, illustrated by a comparison of wave height fields derived from the WAM model and the GEOSAT altimeter, hold promise for the development of an improved representation of ocean-atmosphere coupling based on an explicit description of the dynamical processes at the air-sea interface. Global carbon cycle simulations with a three dimensional carbon cycle model tuned to reproduce past variations of carbon cycle indices show a significant impact of variations in the ocean circulation on the CO2 concentration in the atmosphere and thereby on climate. The series of experiments suggest that for the study of climate in the time scale range from 10-A Nd Isotopic Composition Modeling Approach of the Oceanic Thermohaline Circulation Change During LGM

    NASA Astrophysics Data System (ADS)

    Arsouze, T.; Dutay, J.; Lacan, F.; Jeandel, C.; Alkama, R.; Kageyama, M.; Piotrowski, A.

    2006-12-01

    The role of thermohaline circulation in climate change has been a matter of debate for a long time. Proxies of past ocean circulation such as δ13C or 231Pa/230Th suggest a relationship between North Atlantic Deep Water (NADW) strength and rapid climate change. Neodymium isotopic composition (Nd IC) is a quasi conservative geochemical tracer of water masses in the ocean interior and thus can be used as a proxy for NADW. Seawater Nd IC being recorded in marine sediments, this proxy is used to infer paleo-circulations on various time scales. Recent studies of Nd IC records, in the ferromanganese oxide components of a South Atlantic core, confirm the close relation between thermohaline circulation and North Atlantic climate changes through the last deglaciation (Piotrowski et al., 2004). Our purpose here is to model the Nd IC during the LGM and the Holocene with the Ocean Global Circulation Model NEMO, in the ORCA2 (2°) configuration. The explicit simulation of this proxy in the model allows to investigate and quantify the circulation change that corresponds to the Nd isotopic composition variation recorded in the sediments. We consider that the main source of Nd into the ocean is the interaction between water masses and continental margins (Boundary Exchange process; (Lacan and Jeandel, 2005). Boundary exchange is parameterized using a relaxing term (Arsouze et al., 2006). Simulated Nd IC distributions are evaluated by comparison with available records for the LGM and Holocene. References: Arsouze, T., Dutay, J.-C., Lacan, F. and Jeandel, C., 2006. Modeling the neodymium isotopic composition with a global ocean circulation model Chemical Geology, in press. Lacan, F. and Jeandel, C., 2005. Neodymium isotopes as a new tool for quantifying exchange fluxes at the continent - ocean interface. Earth and Planetary Science Letters, 232(3-4): 245-257. Piotrowski, A.M., Goldstein, S.L., Hemming, S.R. and Fairbanks, R.G., 2004. Intensification and variability of ocean

  14. Global coupled ocean-atmosphere general circulation models in LASG/IAP

    NASA Astrophysics Data System (ADS)

    Yongqiang, Yu; Xuehong, Zhang; Yufu, Guo

    2004-06-01

    Coupled ocean-atmospheric general circulation models are the only tools to quantitatively simulate the climate system. Since the end of the 1980s, a group of scientists in the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences (CAS), have been working to develop a global OGCM and a global coupled ocean-atmosphere general circulation model (CGCM). From the original flux anomaly-coupling model developed in the beginning of the 1990s to the latest directly-coupling model, LASG scientists have developed four global coupled GCMs. This study summarizes the development history of these models and describes the third and fourth coupled GCMs and selected applications. Strengths and weaknesses of these models are highlighted.

  15. Zonal momentum budget along the equator in the Indian Ocean from a high-resolution ocean general circulation model

    NASA Astrophysics Data System (ADS)

    Nagura, Motoki; McPhaden, Michael J.

    2014-07-01

    This study examines the zonal momentum budget along the equator in the Indian Ocean in a high-resolution ocean general circulation model. Wyrtki Jets, wind-driven eastward flows in the upper 100 m that appear typically twice per year in boreal spring and fall, are a prominent feature of the ocean circulation in this region. Our results indicate that nonlinearity associated with these jets is an important element of the zonal momentum budget, with wind driven eastward momentum advected downward into the thermocline. This advection results in annually averaged zonal currents that flow against the zonal pressure gradient in the upper 200 m, such that there is no mean subsurface undercurrent in the Indian Ocean as there is in the Pacific and Atlantic Oceans. Zonal momentum is further distributed along the equator by zonal advection, with eastward flow substantially enhanced in the eastern basin relative to the western basin. Meridional advection, though generally weak, tends to decelerate surface eastward flow along the equator. These results contrast with those from previous idealized wind-forced model experiments that primarily emphasized the importance of vertical momentum advection. Also, beyond semiannual period fluctuations, significant momentum advection results from a broad range of interacting processes, spanning intraseasonal to interannual time scales. We conclude that proper simulation of zonal flows along the equator in the Indian Ocean, including their climatically relevant impacts on the mass and heat balance, requires accurate representation of nonlinearities that derive from a broad range of time and space scales.

  16. Development of a high-resolution coastal circulation model for the ocean observatory in lunenburg bay

    NASA Astrophysics Data System (ADS)

    Wang, Liang; Sheng, Jinyu

    2005-10-01

    An advanced ocean observatory has been established in Lunenburg Bay of Nova Scotia, Canada as part of an interdisciplinary research project of marine environmental prediction. The development of a high-resolution coastal circulation model is one of important components of the observatory. The model horizontal resolution is 60 m and the vertical resolution is about lm. The coastal circulation model is used to simulate the semi-diurnal tidal circulation and associated nonlinear dynamics with the M2 forcing specified at the model open boundaries. The model is also used to simulate the storm-induced circulation in the bay during Hurricane Juan in September 2003, with the model forcing to be the combination of tides and remotely generated waves specified at the model open boundaries and wind stress applied at the sea surface. The model results demonstrate strong interactions between the local wind stress, tidal forcing, and remotely generated waves during this period. Comparison of model results with the surface elevation and current observations demonstrates that the coastal circulation model has reasonable skills in simulating the tidal and storm-induced circulation in the bay.

  17. Impact of variable seawater conductivity on motional induction simulated with an ocean general circulation model

    NASA Astrophysics Data System (ADS)

    Irrgang, C.; Saynisch, J.; Thomas, M.

    2016-01-01

    Carrying high concentrations of dissolved salt, ocean water is a good electrical conductor. As seawater flows through the Earth's ambient geomagnetic field, electric fields are generated, which in turn induce secondary magnetic fields. In current models for ocean-induced magnetic fields, a realistic consideration of seawater conductivity is often neglected and the effect on the variability of the ocean-induced magnetic field unknown. To model magnetic fields that are induced by non-tidal global ocean currents, an electromagnetic induction model is implemented into the Ocean Model for Circulation and Tides (OMCT). This provides the opportunity to not only model ocean-induced magnetic signals but also to assess the impact of oceanographic phenomena on the induction process. In this paper, the sensitivity of the induction process due to spatial and temporal variations in seawater conductivity is investigated. It is shown that assuming an ocean-wide uniform conductivity is insufficient to accurately capture the temporal variability of the magnetic signal. Using instead a realistic global seawater conductivity distribution increases the temporal variability of the magnetic field up to 45 %. Especially vertical gradients in seawater conductivity prove to be a key factor for the variability of the ocean-induced magnetic field. However, temporal variations of seawater conductivity only marginally affect the magnetic signal.

  18. An implementation of a barotropic quasigeostrophic model of ocean circulation on the MPP

    NASA Technical Reports Server (NTRS)

    Grosch, C. E.; Fatoohi, R.

    1987-01-01

    The implementation on the Massively Parallel Processor (MPP) of a barotropic quasigeostrophic model of ocean circulation is discussed. The mathematical model, including scalings and boundary conditions is discussed. The numerical scheme, which uses compact differencing is also discussed. The implementation of this model on the MPP is then presented. Finally, some performance results are given and compared to results obtained using the VPS-32 and one processor of a CRAY-2.

  1. Oceanic circulation models help to predict global biogeography of pelagic yellow-bellied sea snake.

    PubMed

    Brischoux, François; Cotté, Cédric; Lillywhite, Harvey B; Bailleul, Frédéric; Lalire, Maxime; Gaspar, Philippe

    2016-08-01

    It is well recognized that most marine vertebrates, and especially tetrapods, precisely orient and actively move in apparently homogeneous oceanic environments. Here, we investigate the presumptive role of oceanic currents in biogeographic patterns observed in a secondarily marine tetrapod, the yellow-bellied sea snake (Hydrophis [Pelamis] platurus). State-of-the-art world ocean circulation models show how H. platurus, the only pelagic species of sea snake, can potentially exploit oceanic currents to disperse and maintain population mixing between localities that spread over two-thirds of the Earth's circumference. The very close association of these snakes with surface currents seems to provide a highly efficient dispersal mechanism that allowed this species to range extensively and relatively quickly well beyond the central Indo-Pacific area, the centre of origin, abundance and diversity of sea snakes. Our results further suggest that the pan-oceanic population of this species must be extraordinarily large. PMID:27555651

  2. Emulation of a couple atmosphere-ocean general circulation model with a simple climate model

    NASA Astrophysics Data System (ADS)

    Ishizaki, Y.; Emori, S.; Oki, T.; Shiogama, H.; Yokohata, T.; Yoshimori, M.

    2013-12-01

    Simple climate models have been used to investigate uncertainty of future projections under a very wide range of emission scenarios because the use of Atmosphere-ocean general circulation models (AOGCMs) requires very huge computer resources to project future climate changes under many different socio-economic scenarios. We developed a simple climate model, and investigated the ability of the simple climate model to emulate global mean surface air temperature (SAT) changes of an AOGCM (MIROC5) in a representative concentration pathway (RCP8.5). Some previous research indicated that climate sensitivity, ocean vertical diffusion and anthropogenic aerosol forcing (direct and indirect effects of sulfate aerosol, black carbon and organic carbon) are essentially important factors to emulate of global mean SAT changes of AOGCMs. We, therefore, estimate these important factors in the simple climate model using a Metropolis-Hastings Markov chain Monte Carlo (MCMC) approach, and compared the results of the emulation of the simple climate model with those of AIM/impact[policy] simple climate model. Although root mean square error (RMSE) in decadal means of global mean SAT changes during the period of 2001-2100 in the AIM/impact[policy] simple climate model are large (0.6), the RMSE in our new simple climate model are dramatically improved (0.02). Thus, the estimation of these important factors by a MCMC is very useful for emulation of AOGCMs by the use of simple climate models.

  3. Global warming and changes in ocean circulation

    SciTech Connect

    Duffy, P.B.; Caldeira, K.C.

    1998-02-01

    This final report provides an overview of the goals and accomplishments of this project. Modeling and observational work has raised the possibility that global warming may cause changes in the circulation of the ocean. If such changes would occur they could have important climatic consequences. The first technical goal of this project was to investigate some of these possible changes in ocean circulation in a quantitative way, using a state-of -the-art numerical model of the ocean. Another goal was to develop our ocean model, a detailed three-dimensional numerical model of the ocean circulation and ocean carbon cycles. A major non-technical goal was to establish LLNL as a center of excellence in modelling the ocean circulation and carbon cycle.

  4. A multi-level adaptation model of circulation for the western Indian Ocean

    NASA Astrophysics Data System (ADS)

    Shaji, C.; Bahulayan, N.; Dube, S. K.; Rao, A. D.

    1999-12-01

    A three-dimensional, fully non-linear semi-diagnostic (adaptation) model is described. This model is used to compute the climatological mean circulation and to understand the role of local, steady forcing of the wind and thermohaline forcing on the observed circulation in the western tropical Indian Ocean. The model consists of equations of motion and continuity, sea surface topography, equations of state and temperature, and salinity diffusion equations. While the sea surface topography equation is solved by a successive overrelaxation technique, the other model equations are solved by a leap-frog numerical scheme. Two versions of the model, having 18 and 33 levels in the vertical direction, were prepared to study climatological mean circulation in the western tropical Indian Ocean. The first numerical experiment is carried out with the 18-level adaptation model to study the sensitivity of the solution to different values of eddy coefficients. The main scientific rationale behind these numerical experiments was to obtain the most appropriate values of the eddy coefficients for the realistic computation of climatological circulation in the western tropical Indian Ocean. Three numerical experiments were conducted for the month of February to understand the sensitivity of the model solution to different eddy coefficients. The model reproduced the circulation features during February, even with low values of horizontal and vertical eddy coefficients. In the second experiment, the adaptation model, with 33 levels in the vertical direction, is applied to study the seasonal mean climatological circulation at selected depths during Spring in the western tropical Indian Ocean. Adapted (steady state) results of currents, sea surface topography, temperature and salinity anomaly fields are presented. Reasonable agreement is obtained between the model results on currents and the observational data. The computed anomaly fields for temperature and salinity at selected depths

  5. Ross ice shelf cavity circulation, residence time, and melting: Results from a model of oceanic chlorofluorocarbons

    NASA Astrophysics Data System (ADS)

    Reddy, Tasha E.; Holland, David M.; Arrigo, Kevin R.

    2010-04-01

    Despite their harmful effects in the upper atmosphere, anthropogenic chlorofluorocarbons dissolved in seawater are extremely useful for studying ocean circulation and ventilation, particularly in remote locations. Because they behave as a passive tracer in seawater, and their atmospheric concentrations are well-mixed, well-known, and have changed over time, they are ideal for gaining insight into the oceanographic characteristics of the isolated cavities found under Antarctic ice shelves, where direct observations are difficult to obtain. Here we present results from a modeling study of air-sea chlorofluorocarbon exchange and ocean circulation in the Ross Sea, Antarctica. We compare our model estimates of oceanic CFC-12 concentrations along an ice shelf edge transect to field data collected during three cruises spanning 16 yr. Our model produces chlorofluorocarbon concentrations that are quite similar to those measured in the field, both in magnitude and distribution, showing high values near the surface, decreasing with depth, and increasing over time. After validating modeled circulation and air-sea gas exchange through comparison of modeled temperature, salinity, and chlorofluorocarbons with field data, we estimate that the residence time of water in the Ross Ice Shelf cavity is approximately 2.2 yr and that basal melt rates for the ice shelf average 10 cm yr -1. The model predicts a seasonal signature to basal melting, with highest melt rates in the spring and also the fall.

  6. The seasonal variability of the circulation in the South Indian Ocean: Model and observations

    NASA Astrophysics Data System (ADS)

    Matano, R. P.; Beier, E. J.; Strub, P. T.

    2008-11-01

    This article compares the seasonal variability patterns of the South Indian Ocean circulation derived from a global, eddy-permitting, numerical model and altimeter observations. The seasonal variability of the Indian Ocean circulation is driven by the inflow from the Indonesian Passages and by the local wind forcing. Our analysis indicates that the influence of the Indonesian throughflow is confined to the easternmost portion of the basin, while the influence of the wind stress forcing is important everywhere. Model and observations indicate that, between ~ 105°E and 75°E, the seasonal variability is characterized by the southwestward propagation of an annual wave over a period of ~ 4 months. Preliminary calculations using Pathfinder data also indicate that, in the western region, there are seasonal perturbations that originate in the tropics and propagate poleward through the Mozambique Channel. Our calculations, however, did not find the connections between the tropical and the Agulhas Current variability suggested by earlier modeling studies.

  7. Two regimes of the Arctic's circulation from ocean models with ice and contaminants.

    PubMed

    Proshutinsky, A Y; Johnson, M

    2001-01-01

    A two-dimensional barotropic, coupled, ocean-ice model with a space resolution of 55.5 km and driven by atmospheric forces, river run-off, and sea-level slope between the Pacific and the Arctic Oceans, has been used to simulate the vertically averaged currents and ice drift in the Arctic Ocean. Results from 43 years of numerical simulations of water and ice motions demonstrate that two wind-driven circulation regimes are possible in the Arctic, a cyclonic and an anti-cyclonic circulation. These two regimes appear to alternate at 5-7 year intervals with the 10-15 year period. It is important to pollution studies to understand which circulation regime prevails at any time. It is anticipated that 1995 is a year with a cyclonic regime, and during this cyclonic phase and possibly during past cyclonic regimes as well, pollutants may reach the Alaskan shelf. The regime shifts demonstrated in this paper are fundamentally important to understanding the Arctic's general circulation and particularly important for estimating pollution transport. PMID:11601534

  8. Simulating the three-dimensional circulation and hydrography of Halifax Harbour using a multi-nested coastal ocean circulation model

    NASA Astrophysics Data System (ADS)

    Shan, Shiliang; Sheng, Jinyu; Thompson, Keith Richard; Greenberg, David Alexander

    2011-07-01

    Halifax Harbour is located on the Atlantic coast of Nova Scotia, Canada. It is one of the world's largest, ice-free natural harbours and of great economic importance to the region. A good understanding of the physical processes controlling tides, flooding, transport and dispersion, and hydrographic variability is required for pollution control and sustainable development of the Harbour. For the first time, a multi-nested, finite difference coastal ocean circulation model is used to reconstruct the three-dimensional circulation and hydrography of the Harbour and its variability on timescales of hours to months for 2006. The model is driven by tides, wind and sea level pressure, air-sea fluxes of heat, and terrestrial buoyancy fluxes associated with river and sewage discharge. The predictive skill of the model is assessed by comparing the model simulations with independent observations of sea level from coastal tide gauges and currents from moored instruments. The simulated hydrography is also compared against a new monthly climatology created from all available temperature and salinity observations made in the Harbour over the last century. It is shown that the model can reproduce accurately the main features of the observed tides and storm surge, seasonal mean circulation and hydrography, and wind driven variations. The model is next used to examine the main physical processes controlling the circulation and hydrography of the Harbour. It is shown that non-linear interaction between tidal currents and complex topography occurs over the Narrows. The overall circulation can be characterized as a two-layer estuarine circulation with seaward flow in the thin upper layer and landward flow in the broad lower layer. An important component of this estuarine circulation is a relatively strong, vertically sheared jet situated over a narrow sill connecting the inner Harbour to the deep and relatively quiescent Bedford Basin. Local wind driven variability is strongest in

  9. Interdecadal variations of the thermohaline circulation in a coupled ocean-atmosphere model

    SciTech Connect

    Delworth, T.; Manabe, S.; Stouffer, R.J. )

    1993-11-01

    A fully coupled ocean-atmosphere model is shown to have irregular oscillations of the thermohaline circulation in the NOrth Atlantic Ocean with a time scale of approximately 50 years. The irregular oscillation appears to be driven by density anomalies in the sinking region of the thermohaline circulation (approximately 52[degrees]N to 72[degrees]N) combined with much smaller density anomalies of opposite sign in the broad, rising region. The spatial pattern of sea surface temperature anomalies associated with this irregular oscillation bears an encouraging resemblance to a pattern of observed interdecadal variability in the North Atlantic. The anomalies of sea surface temperature induce model surface air temperature anomalies over the northern North Atlantic, Arctic, and northwestern Europe. 21 refs., 28 figs.

  10. Dynamics of the Atlantic meridional overturning circulation and Southern Ocean in an ocean model of intermediate complexity

    NASA Astrophysics Data System (ADS)

    McCreary, Julian P.; Furue, Ryo; Schloesser, Fabian; Burkhardt, Theodore W.; Nonaka, Masami

    2016-04-01

    A steady-state, variable-density, 2-layer, ocean model (VLOM) is used to investigate basic dynamics of the Atlantic meridional overturning circulation and Southern Ocean. The domain consists of idealized (rectangular) representations of the Atlantic, Southern, and Pacific Oceans. The model equations represent the depth-averaged, layer-1 response (except for one solution in which they represent the depth-integrated flow over both layers). To allow for overturning, water can cross the bottom of layer 1 at the velocity we =wd +wm +wn , the three parts representing: interior diffusion wd that increases the layer-1 thickness h throughout the basin, mixed-layer entrainment wm that ensures h is never less than a minimum value hm , and diapycnal (cooling) processes external to the basin wn that adjust h to hn . For most solutions, horizontal mixing has the form of Rayleigh damping with coefficient ν , which we interpret to result from baroclinic instability through the closure, V∗ = - (ν /f2) ∇P , where ∇P = ∇(1/2 g‧h2) is the depth-integrated pressure gradient, g‧ is the reduced-gravity coefficient, and ν is a mixing coefficient; with this interpretation, the layer-1 flow corresponds to the sum of the Eulerian-mean and eddy-mean (V∗) transport/widths, that is, the "residual" circulation. Finally, layer-1 temperature cools polewards in response to a surface heat flux Q, and the cooling can be strong enough in the Southern Ocean for g‧ = 0 south of a latitude y0 , in which case layer 1 vanishes and the model reduces to a single layer 2. Solutions are obtained both numerically and analytically. The analytic approach splits fields into interior and boundary-layer parts, from which a coupled set of integral constraints can be derived. The set allows properties of the circulation (upwelling-driven transport out of the Southern Ocean M , downwelling transport in the North Atlantic, transport of the Antarctic Circumpolar Current) and stratification (Atlantic

  11. Geochemical constraints on ocean general circulation models. Final report, May 1, 1995--April 30, 1997

    SciTech Connect

    Broecker, W.S.

    1998-05-17

    A better understanding of the manner in which the ocean operates is essential to the preparation for the consequences of the generation of CO{sub 2} by fossil fuel burning. Examples are as follows: (1) the ocean will ultimately take up a major fraction of the CO{sub 2} produced, but this uptake is retarded by the slow mixing rates, in order to predict the uptake, researchers must develop and validate general circulation models for the ocean; (2) during glacial time large global climate changes occurred. The changes were abrupt happening in a few decades. The trigger for these changes appears to have been reorganizations of the large-scale thermohaline circulation of the ocean. Models suggest that if the CO{sub 2} content of the atmosphere rises to more than 700 ppm, then a possibility exists that another such reorganization might occur. Hence, researchers must learn more about the factors influencing deep-water formation both in the northern Atlantic and in the Souther Ocean. The thrust of this research was to develop constraints based on the distributions of chemicals and tracers in the sea. The accomplishments are outlined in this report.

  12. Mean circulation in the coastal ocean off northeastern North America from a regional-scale ocean model

    NASA Astrophysics Data System (ADS)

    Chen, K.; He, R.

    2015-07-01

    A regional-scale ocean model was used to hindcast the coastal circulation over the Middle Atlantic Bight (MAB) and Gulf of Maine (GOM) from 2004 to 2013. The model was nested inside a data assimilative global ocean model that provided initial and open boundary conditions. Realistic atmospheric forcing, tides and observed river runoff were also used to drive the model. Hindcast solutions were compared against observations, which included coastal sea levels, satellite altimetry sea surface height, in situ temperature and salinity measurements in the GOM, and observed mean depth-averaged velocities. Good agreements with observations suggest that the hindcast model is capable of capturing the major circulation variability in the MAB and GOM. Time- and space-continuous hindcast fields were used to depict the mean circulation, along- and cross-shelf transport and the associated momentum balances. The hindcast confirms the presence of the equatorward mean shelf circulation, which varies from 2.33 Sv over the Scotian Shelf to 0.22 Sv near Cape Hatteras. Using the 200 m isobath as the shelf/slope boundary, the mean cross-shelf transport calculations indicate that the shelfbreak segments off the Gulf of Maine (including the southern flank of Georges Bank and the Northeast Channel) and Cape Hatteras are the major sites for shelf water export. The momentum analysis reveals that the along-shelf sea level difference from Nova Scotia to Cape Hatteras is about 0.36 m. The nonlinear advection, stress, and horizontal viscosity terms all contribute to the ageostrophic circulation in the along-isobath direction, whereas the nonlinear advection plays a dominant role in determining the ageostrophic current in the cross-isobath direction.

  13. Mean circulation in the coastal ocean off northeastern North America from a regional-scale ocean model

    NASA Astrophysics Data System (ADS)

    Chen, K.; He, R.

    2014-12-01

    A regional-scale ocean model was used to hindcast the coastal circulation over the Middle Atlantic Bight (MAB) and Gulf of Maine (GOM) from 2004 to 2013. The model was nested inside a data assimilative global ocean model that provided initial and open boundary conditions. Realistic atmospheric forcing, tides and observed river runoff were also used to drive the model. Hindcast solutions were compared against observations, which included coastal sea levels, satellite altimetry sea surface height, temperature and salinity time series in the GOM, glider transects in the MAB, and observed mean depth-averaged velocities by Lentz (2008a). Good agreements with observations suggest that the hindcast model is capable of capturing the major circulation variability in the MAB and GOM. Time- and space-continuous hindcast fields were used to depict the mean circulation, along- and cross-shelf transport and the associated momentum balances. The hindcast confirms the presence of the equatorward mean shelf circulation, which varies from 2.33 Sv at Scotian Shelf to 0.22 Sv near Cape Hatteras. Using the 200 m isobath as the shelf/slope boundary, the mean cross-shelf transport calculations indicate that the shelfbreak segments off the Gulf of Maine (including the southern flank of Georges Bank and the Northeast Channel) and Cape Hatteras are the major sites for shelf water export. The momentum analysis reveals that the along-shelf sea level difference from Nova Scotia to Cape Hatteras is about 0.36 m. The nonlinear advection, stress, and horizontal viscosity terms all contribute to the ageostrophic circulation in the along-isobath direction, whereas the nonlinear advection plays a dominant role in determining the ageostrophic current in the cross-isobath direction.

  14. Century-scale variability in a randomly forced, two-dimensional thermohaline ocean circulation model

    SciTech Connect

    Mysak, L.A.; Stocker, T.F.; Huang, F.

    1993-01-01

    The response of a two-dimensional thermohaline ocean circulation model to a random freshwater flux superimposed on the usual mixed boundary conditions for temperature and salinity is considered. It is shown that for a wide range of vertical and horizontal diffusivities and a box geometry that approximates the Atlantic Ocean, 200-300 yr period oscillations exist in the basic-state, interhemispheric meridional overturning circulation with deep convection in the north. These fluctuations can also be described in terms of propagating salinity anomalies which travel in the direction of the thermohaline flow. For large horizontal (K{sub h} = 15 x 10{sup 3} m{sup 2}/s) and small vertical (K{sub v}=0.5 x 10{sup -4}m{sup 2}/s) diffusivities, the random forcing also excites deca-millennial oscillations in the basic structure of the thermohaline circulation. In this case, the meridional circulation pattern slowly oscillates between three different stages: a large positive cell, with deep convection in the North Atlantic and upwelling in the south; a symmetric two-cell circulation, with deep convection in both polar regions and upwelling near the equator; and a large negative cell, with deep convection in the South Atlantic and upwelling in the north. Each state can persist for 0 (10 kyr).

  15. Use of Ocean Remote Sensing Data to Enhance Predictions with a Coupled General Circulation Model

    NASA Technical Reports Server (NTRS)

    Rienecker, Michele M.

    1999-01-01

    Surface height, sea surface temperature and surface wind observations from satellites have given a detailed time sequence of the initiation and evolution of the 1997/98 El Nino. The data have beet complementary to the subsurface TAO moored data in their spatial resolution and extent. The impact of satellite observations on seasonal prediction in the tropical Pacific using a coupled ocean-atmosphere general circulation model will be presented.

  16. Longitudinal biases in the Seychelles Dome simulated by 35 ocean-atmosphere coupled general circulation models

    NASA Astrophysics Data System (ADS)

    Nagura, Motoki; Sasaki, Wataru; Tozuka, Tomoki; Luo, Jing-Jia; Behera, Swadhin K.; Yamagata, Toshio

    2013-02-01

    Seychelles Dome refers to the shallow climatological thermocline in the southwestern Indian Ocean, where ocean wave dynamics efficiently affect sea surface temperature, allowing sea surface temperature anomalies to be predicted up to 1-2 years in advance. Accurate reproduction of the dome by ocean-atmosphere coupled general circulation models (CGCMs) is essential for successful seasonal predictions in the Indian Ocean. This study examines the Seychelles Dome as simulated by 35 CGCMs, including models used in phase five of the Coupled Model Intercomparison Project (CMIP5). Among the 35 CGCMs, 14 models erroneously produce an upwelling dome in the eastern half of the basin whereas the observed Seychelles Dome is located in the southwestern tropical Indian Ocean. The annual mean Ekman pumping velocity in these models is found to be almost zero in the southern off-equatorial region. This result is inconsistent with observations, in which Ekman upwelling acts as the main cause of the Seychelles Dome. In the models reproducing an eastward-displaced dome, easterly biases are prominent along the equator in boreal summer and fall, which result in shallow thermocline biases along the Java and Sumatra coasts via Kelvin wave dynamics and a spurious upwelling dome in the region. Compared to the CMIP3 models, the CMIP5 models are even worse in simulating the dome longitudes.

  17. Vertical heat flux in the ocean: Estimates from observations and from a coupled general circulation model

    NASA Astrophysics Data System (ADS)

    Cummins, Patrick F.; Masson, Diane; Saenko, Oleg A.

    2016-06-01

    The net heat uptake by the ocean in a changing climate involves small imbalances between the advective and diffusive processes that transport heat vertically. Generally, it is necessary to rely on global climate models to study these processes in detail. In the present study, it is shown that a key component of the vertical heat flux, namely that associated with the large-scale mean vertical circulation, can be diagnosed over extra-tropical regions from global observational data sets. This component is estimated based on the vertical velocity obtained from the geostrophic vorticity balance, combined with estimates of absolute geostrophic flow. Results are compared with the output of a non-eddy resolving, coupled atmosphere-ocean general circulation model. Reasonable agreement is found in the latitudinal distribution of the vertical heat flux, as well as in the area-integrated flux below about 250 m depth. The correspondence with the coupled model deteriorates sharply at depths shallower than 250 m due to the omission of equatorial regions from the calculation. The vertical heat flux due to the mean circulation is found to be dominated globally by the downward contribution from the Southern Hemisphere, in particular the Southern Ocean. This is driven by the Ekman vertical velocity which induces an upward transport of seawater that is cold relative to the horizontal average at a given depth. The results indicate that the dominant characteristics of the vertical transport of heat due to the mean circulation can be inferred from simple linear vorticity dynamics over much of the ocean.

  18. Seasonal Distributions of Global Ocean Chlorophyll and Nutrients: Analysis with a Coupled Ocean General Circulation Biogeochemical, and Radiative Model

    NASA Technical Reports Server (NTRS)

    Gregg, Watson W.

    1999-01-01

    A coupled general ocean circulation, biogeochemical, and radiative model was constructed to evaluate and understand the nature of seasonal variability of chlorophyll and nutrients in the global oceans. The model is driven by climatological meteorological conditions, cloud cover, and sea surface temperature. Biogeochemical processes in the model are determined from the influences of circulation and turbulence dynamics, irradiance availability, and the interactions among three functional phytoplankton groups (diatoms, chorophytes, and picoplankton) and three nutrient groups (nitrate, ammonium, and silicate). Phytoplankton groups are initialized as homogeneous fields horizontally and vertically, and allowed to distribute themselves according to the prevailing conditions. Basin-scale model chlorophyll results are in very good agreement with CZCS pigments in virtually every global region. Seasonal variability observed in the CZCS is also well represented in the model. Synoptic scale (100-1000 km) comparisons of imagery are also in good conformance, although occasional departures are apparent. Agreement of nitrate distributions with in situ data is even better, including seasonal dynamics, except for the equatorial Atlantic. The good agreement of the model with satellite and in situ data sources indicates that the model dynamics realistically simulate phytoplankton and nutrient dynamics on synoptic scales. This is especially true given that initial conditions are homogenous chlorophyll fields. The success of the model in producing a reasonable representation of chlorophyll and nutrient distributions and seasonal variability in the global oceans is attributed to the application of a generalized, processes-driven approach as opposed to regional parameterization, and the existence of multiple phytoplankton groups with different physiological and physical properties. These factors enable the model to simultaneously represent the great diversity of physical, biological

  19. Transport of 137Cs to the Southern Hemisphere in an ocean general circulation model

    NASA Astrophysics Data System (ADS)

    Tsumune, Daisuke; Aoyama, Michio; Hirose, Katsumi; Bryan, Frank O.; Lindsay, Keith; Danabasoglu, Gokhan

    2011-04-01

    137Cs originating from global fallout is transported into the ocean interior by advection and diffusion, and the 137Cs concentration is reduced by radioactive decay. 137Cs concentrations in the global ocean can be simulated by global integration of the coarse-resolution Parallel Ocean Program to understand the mechanism of material transport in the ocean. We investigated the transport mechanism of 137Cs to the Southern Hemisphere using an ocean general circulation model (OGCM) and compared the simulated results with observations of 137Cs concentrations in the Southern Hemisphere. 137Cs was deposited on the ocean surface mainly as global fallout originating from atmospheric nuclear weapons testing since 1945, and the global distribution of cumulative 137Cs deposition has been reconstructed from global measurements of 137Cs in rain, seawater, and soil. We estimated the global distribution of 137Cs deposition from 1945 to 2003 using these distribution data, 137Cs deposition data observed at the Meteorological Research Institute, Tsukuba, Japan, from 1958 to 2003, and 137Cs deposition data for 1945-1957 estimated from ice-core data. We compared the simulated results with 137Cs sections from the South Pacific, Indian, and South Atlantic Oceans obtained during the BEAGLE2003 cruise in 2003. The simulated 137Cs sections were in good agreement with the observations, except for the effects of mesoscale eddies, which not be simulated by the model because of its coarse resolution. OGCMs can simulate the general pattern of 137Cs distribution in the world’s oceans and improve our understanding of the transport mechanism leading to those 137Cs distributions on a time scale of several decades. The model simulation results suggest that the 137Cs deposited in the North Pacific advected to the South Pacific and Indian Ocean, and then to the South Atlantic over about four decades. The North Pacific is thus an important source area of 137Cs to the Southern Hemisphere.

  20. Primary reasoning behind the double ITCZ phenomenon in a coupled ocean-atmosphere general circulation model

    NASA Astrophysics Data System (ADS)

    Li, Jianglong; Zhang, Xuehong; Yu, Yongqiang; Dai, Fushan

    2004-12-01

    This paper investigates the processes behind the double ITCZ phenomenon, a common problem in Coupled ocean-atmosphere General Circulation Models (CGCMs), using a CGCM—FGCM-0 (Flexible General Circulation Model, version 0). The double ITCZ mode develops rapidly during the first two years of the integration and becomes a perennial phenomenon afterwards in the model. By way of Singular Value Decomposition (SVD) for SST, sea surface pressure, and sea surface wind, some air-sea interactions are analyzed. These interactions prompt the anomalous signals that appear at the beginning of the coupling to develop rapidly. There are two possible reasons, proved by sensitivity experiments: (1) the overestimated east-west gradient of SST in the equatorial Pacific in the ocean spin-up process, and (2) the underestimated amount of low-level stratus over the Peruvian coast in CCM3 (the Community Climate Model, Version Three). The overestimated east-west gradient of SST brings the anomalous equatorial easterly. The anomalous easterly, affected by the Coriolis force in the Southern Hemisphere, turns into an anomalous westerly in a broad area south of the equator and is enhanced by atmospheric anomalous circulation due to the underestimated amount of low-level stratus over the Peruvian coast simulated by CCM3. The anomalous westerly leads to anomalous warm advection that makes the SST warm in the southeast Pacific. The double ITCZ phenomenon in the CGCM is a result of a series of nonlocal and nonlinear adjustment processes in the coupled system, which can be traced to the uncoupled models, oceanic component, and atmospheric component. The zonal gradient of the equatorial SST is too large in the ocean component and the amount of low-level stratus over the Peruvian coast is too low in the atmosphere component.

  1. Upper-Ocean Heat Balance Processes and the Walker Circulation in CMIP5 Model Projections

    NASA Technical Reports Server (NTRS)

    Robertson, F. R.; Roberts, J. B.; Funk, C.; Lyon, B.; Ricciardulli, L.

    2012-01-01

    Considerable uncertainty remains as to the importance of mechanisms governing decadal and longer variability of the Walker Circulation, its connection to the tropical climate system, and prospects for tropical climate change in the face of anthropogenic forcing. Most contemporary climate models suggest that in response to elevated CO2 and a warmer but more stratified atmosphere, the required upward mass flux in tropical convection will diminish along with the Walker component of the tropical mean circulation as well. Alternatively, there is also evidence to suggest that the shoaling and increased vertical stratification of the thermocline in the eastern Pacific will enable a muted SST increase there-- preserving or even enhancing some of the dynamical forcing for the Walker cell flow. Over the past decade there have been observational indications of an acceleration in near-surface easterlies, a strengthened Pacific zonal SST gradient, and globally-teleconnected dislocations in precipitation. But is this evidence in support of an ocean dynamical thermostat process posited to accompany anthropogenic forcing, or just residual decadal fluctuations associated with variations in warm and cold ENSO events and other stochastic forcing? From a modeling perspective we try to make headway on this question by examining zonal variations in surface energy fluxes and dynamics governing tropical upper ocean heat content evolution in the WCRP CMIP5 model projections. There is some diversity among model simulations; for example, the CCSM4 indicates net ocean warming over the IndoPacific region while the CSIRO model concentrates separate warming responses over the central Pacific and Indian Ocean regions. The models, as with observations, demonstrate strong local coupling between variations in column water vapor, downward surface longwave radiation and SST; but the spatial patterns of changes in the sign of this relationship differ among models and, for models as a whole, with

  2. The sensitivity of latent heat flux to the air humidity approximations used in ocean circulation models

    NASA Technical Reports Server (NTRS)

    Liu, W. Timothy; Niiler, Pearn P.

    1990-01-01

    In deriving the surface latent heat flux with the bulk formula for the thermal forcing of some ocean circulation models, two approximations are commonly made to bypass the use of atmospheric humidity in the formula. The first assumes a constant relative humidity, and the second supposes that the sea-air humidity difference varies linearly with the saturation humidity at sea surface temperature. Using climatological fields derived from the Marine Deck and long time series from ocean weather stations, the errors introduced by these two assumptions are examined. It is shown that the errors reach above 100 W/sq m over western boundary currents and 50 W/sq m over the tropical ocean. The two approximations also introduce erroneous seasonal and spatial variabilities with magnitudes over 50 percent of the observed variabilities.

  3. Modeling tidal circulation and stratification in Skagit River estuary using an unstructured grid ocean model

    NASA Astrophysics Data System (ADS)

    Yang, Zhaoqing; Khangaonkar, Tarang

    Tidal circulation and river plume dynamics in shallow-water estuarine systems with large intertidal zones are complex. Strong asymmetries in tidal currents and stratification often occur in the intertidal zones and subtidal channels over a tidal cycle. The Skagit River is the largest estuary with respect to the discharge of a significant amount of freshwater and sediment into Puget Sound, Washington. It consists of a large intertidal zone with multiple tidal channels near the mouth of the estuary. To simulate the tidal circulation and salinity stratification accurately in the intertidal region, an unstructured grid numerical model with wetting-drying capability and the capability to accurately represent the bathymetry of tidal flats and the geometry of shallow distributary channels is necessary. In this paper, a modeling study for the Skagit River estuary using a three-dimensional unstructured grid, finite-volume coastal ocean model (FVCOM) supported by high-resolution LIDAR data is presented. The hydrodynamic model was validated with observed water surface elevation, velocity, and salinity data over spring and neap tidal cycles under low-river-flow and high-river-flow conditions. Wetting and drying processes in the intertidal zone and strong stratification in the estuary were simulated successfully by the model. Model results indicate that the Skagit River estuary is a highly stratified estuary, but destratification can occur during flood tide. Tides and baroclinic motion are the dominant forcing in the Skagit River estuary, but strong wind events can affect the currents in the intertidal zone significantly. Preliminary analysis also indicated that the salinity intrusion length scale is proportional to the river flow to the -¼ power.

  4. Carbon dioxide induced ocean climatic change and tracer experiment with an atmosphere-ocean general circulation model

    SciTech Connect

    Jiang, Xingjian.

    1991-01-01

    The principal objective of this study is to determine whether or not the penetration of a passive tracer is analogous to the penetration of a greenhouse-gas-induced heating. The Atmosphere Ocean General Circulation Model (A-O GCM) has been used to study CO2-induced climate change and the penetration of passive tracers into the world ocean. The present climate and a 2 x CO2 climate have been simulated. The passive tracers tritium, CFC-11, CFC-12 and a 'passive CO2- induced heating' are simulated. The CO2-induced active and passive warmings are larger in the subtropics and high latitudes than in the tropics. The largest difference between the active and passive CO2-induced heatings occur in the North Atlantic deep ocean, with maximum cooling about -1.5C for the active case in layer four of the ocean (1150m). There is no hemispherically asymmetric warming as that found by Manabe et al. (1990) and Stouffer et al. (1990). The convective overturning and large-scale sinking motion are responsible for the large penetration of CO2-induced warming in high latitudes. The CO2-induced circulation changes show that the North Atlantic thermohaline circulation is significantly weakened due to the penetration of CO2-induced heating. Associated with this change, the strength of North Atlantic conveyor belt is reduced, which results in a large warming in the upper ocean and cooling in the deep layers. The characteristic response time ranges from 40-50 years for the active CO2-induced climate change, and 70-160 years for passive CO2-induced climate change. The physical processes controlling the geochemical tracer penetration are very similar to those for the CO2-induced heating. There is not a single tracer which penetrates into the ocean exactly like the active CO2-induced heating in terms of distribution, transport or physical process. CFC's may be the best candidate as a surrogate for the CO2-induced oceanic climate study.

  5. Ocean circulation model predicts high genetic structure observed in a long-lived pelagic developer.

    PubMed

    Sunday, J M; Popovic, I; Palen, W J; Foreman, M G G; Hart, M W

    2014-10-01

    Understanding the movement of genes and individuals across marine seascapes is a long-standing challenge in marine ecology and can inform our understanding of local adaptation, the persistence and movement of populations, and the spatial scale of effective management. Patterns of gene flow in the ocean are often inferred based on population genetic analyses coupled with knowledge of species' dispersive life histories. However, genetic structure is the result of time-integrated processes and may not capture present-day connectivity between populations. Here, we use a high-resolution oceanographic circulation model to predict larval dispersal along the complex coastline of western Canada that includes the transition between two well-studied zoogeographic provinces. We simulate dispersal in a benthic sea star with a 6-10 week pelagic larval phase and test predictions of this model against previously observed genetic structure including a strong phylogeographic break within the zoogeographical transition zone. We also test predictions with new genetic sampling in a site within the phylogeographic break. We find that the coupled genetic and circulation model predicts the high degree of genetic structure observed in this species, despite its long pelagic duration. High genetic structure on this complex coastline can thus be explained through ocean circulation patterns, which tend to retain passive larvae within 20-50 km of their parents, suggesting a necessity for close-knit design of Marine Protected Area networks. PMID:25231198

  6. El Nino-southern oscillation simulated in an MRI atmosphere-ocean coupled general circulation model

    SciTech Connect

    Nagai, T.; Tokioka, T.; Endoh, M.; Kitamura, Y. )

    1992-11-01

    A coupled atmosphere-ocean general circulation model (GCM) was time integrated for 30 years to study interannual variability in the tropics. The atmospheric component is a global GCM with 5 levels in the vertical and 4[degrees]latitude X 5[degrees] longitude grids in the horizontal including standard physical processes (e.g., interactive clouds). The oceanic component is a GCM for the Pacific with 19 levels in the vertical and 1[degrees]x 2.5[degrees] grids in the horizontal including seasonal varying solar radiation as forcing. The model succeeded in reproducing interannual variations that resemble the El Nino-Southern Oscillation (ENSO) with realistic seasonal variations in the atmospheric and oceanic fields. The model ENSO cycle has a time scale of approximately 5 years and the model El Nino (warm) events are locked roughly in phase to the seasonal cycle. The cold events, however, are less evident in comparison with the El Nino events. The time scale of the model ENSO cycle is determined by propagation time of signals from the central-eastern Pacific to the western Pacific and back to the eastern Pacific. Seasonal timing is also important in the ENSO time scale: wind anomalies in the central-eastern Pacific occur in summer and the atmosphere ocean coupling in the western Pacific operates efficiently in the first half of the year.

  7. Regional eddy vorticity transport and the equilibrium vorticity budgets of a numerical model ocean circulation

    NASA Technical Reports Server (NTRS)

    Harrison, D. E.; Holland, W. R.

    1981-01-01

    A mean vorticity budget analysis is presented of Holland's (1978) numerical ocean general circulation experiment. The stable budgets are compared with classical circulation theory to emphasize the ways in which the mesoscale motions of the model alter (or leave unaltered) classical vorticity balances. The basinwide meridional transports of vorticity by the mean flow and by the mesoscale flow in the mean are evaluated to establish the role(s) of the mesoscale in the larger scale equilibrium vorticity transports. The vorticity equation for this model fluid system is presented and the budget analysis method is described. Vorticity budgets over the selected regions and on a larger scale are given, and a summary of budget results is provided along with remarks about the utility of this type of analysis.

  8. An eddy-permitting oceanic general circulation model and its preliminary evaluation

    NASA Astrophysics Data System (ADS)

    Liu, Hailong; Zhang, Xuehong; Li, Wei; Yu, Yongqiang; Yu, Rucong

    2004-10-01

    An eddy-permitting, quasi-global oceanic general circulation model, LICOM (LASG/IAP (State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics) Climate System Ocean Model), with a uniform grid of 0.5° × 0.5° is established. Forced by wind stresses from Hellerman and Rosenstain (1983), a 40-yr integration is conducted with sea surface temperature and salinity being restored to the Levitus 94 datasets. The evaluation of the annual mean climatology of the LICOM control run shows that the large-scale circulation can be well reproduced. A comparison between the LICOM control run and a parallel integration of L30T63, which has the same framework but a coarse resolution, is also made to confirm the impact of resolution on the model performance. On account of the reduction of horizontal viscosity with the enhancement of the horizontal resolution, LICOM improves the simulation with respect to not only the intensity of the large scale circulations, but also the magnitude and structure of the Equatorial Undercurrent and South Equatorial Current. Taking advantage of the fine grid size, the pathway of the Indonesian Throughflow (ITF) is better represented in LICOM than in L30T63. The transport of ITF in LICOM is more convergent in the upper layer. As a consequence, the Indian Ocean tends to get warmer in LICOM. The poleward heat transports for both the global and individual basins are also significantly improved in LICOM. A decomposed analysis indicates that the transport due to the barotropic gyre, which primarily stands for the barotropic effect of the western boundary currents, plays a crucial role in making the difference.

  9. Using Green's Functions to initialize and adjust a global, eddying ocean biogeochemistry general circulation model

    NASA Astrophysics Data System (ADS)

    Brix, H.; Menemenlis, D.; Hill, C.; Dutkiewicz, S.; Jahn, O.; Wang, D.; Bowman, K.; Zhang, H.

    2015-11-01

    The NASA Carbon Monitoring System (CMS) Flux Project aims to attribute changes in the atmospheric accumulation of carbon dioxide to spatially resolved fluxes by utilizing the full suite of NASA data, models, and assimilation capabilities. For the oceanic part of this project, we introduce ECCO2-Darwin, a new ocean biogeochemistry general circulation model based on combining the following pre-existing components: (i) a full-depth, eddying, global-ocean configuration of the Massachusetts Institute of Technology general circulation model (MITgcm), (ii) an adjoint-method-based estimate of ocean circulation from the Estimating the Circulation and Climate of the Ocean, Phase II (ECCO2) project, (iii) the MIT ecosystem model "Darwin", and (iv) a marine carbon chemistry model. Air-sea gas exchange coefficients and initial conditions of dissolved inorganic carbon, alkalinity, and oxygen are adjusted using a Green's Functions approach in order to optimize modeled air-sea CO2 fluxes. Data constraints include observations of carbon dioxide partial pressure (pCO2) for 2009-2010, global air-sea CO2 flux estimates, and the seasonal cycle of the Takahashi et al. (2009) Atlas. The model sensitivity experiments (or Green's Functions) include simulations that start from different initial conditions as well as experiments that perturb air-sea gas exchange parameters and the ratio of particulate inorganic to organic carbon. The Green's Functions approach yields a linear combination of these sensitivity experiments that minimizes model-data differences. The resulting initial conditions and gas exchange coefficients are then used to integrate the ECCO2-Darwin model forward. Despite the small number (six) of control parameters, the adjusted simulation is significantly closer to the data constraints (37% cost function reduction, i.e., reduction in the model-data difference, relative to the baseline simulation) and to independent observations (e.g., alkalinity). The adjusted air-sea gas

  10. Ocean Circulation Modeling for Aquatic Dispersion of Liquid Radioactive Effluents from Nuclear Power Plants

    SciTech Connect

    Chung, Y.G.; Lee, G.B.; Bang, S.Y.; Choi, S.B.; Lee, S.U.; Yoon, J.H.; Nam, S.Y.; Lee, H.R.

    2006-07-01

    Recently, three-dimensional models have been used for aquatic dispersion of radioactive effluents in relation to nuclear power plant siting based on the Notice No. 2003-12 'Guideline for investigating and assessing hydrological and aquatic characteristics of nuclear facility site' of the Ministry of Science and Technology (MOST) in Korea. Several nuclear power plants have been under construction or planed, which are Shin-Kori Unit 1 and 2, Shin-Wolsong Unit 1 and 2, and Shin-Ulchin Unit 1 and 2. For assessing the aquatic dispersion of radionuclides released from the above nuclear power plants, it is necessary to know the coastal currents around sites which are affected by circulation of East Sea. In this study, a three dimensional hydrodynamic model for the circulation of the East Sea of Korea has been developed as the first phase, which is based on the RIAMOM (Research Institute of Applied Mechanics' Ocean Model, Kyushu University, Japan). The model uses the primitive equation with hydrostatic approximation, and uses Arakawa-B grid system horizontally and Z coordinate vertically. Model domain is 126.5 deg. E to 142.5 deg. E of east longitude and 33 deg. N and 52 deg. N of the north latitude. The space of the horizontal grid was 1/12 deg. to longitude and latitude direction and vertical level was divided to 20. This model uses Generalized Arakawa Scheme, Slant Advection, and Mode-Splitting Method. The input data were from JODC (Japan Oceanographic Data Center), KNFRDI (Korea National Fisheries Research and Development Institute), and ECMWF (European Center for Medium-Range Weather Forecasts). The modeling results are in fairly good agreement with schematic patterns of the surface circulation in the East Sea/Japan Sea. The local current model and aquatic dispersion model of the coastal region will be developed as the second phase. The oceanic dispersion experiments will be also carried out by using ARGO Drifter around a nuclear power plant site. (authors)

  11. A zonally averaged, three-basin ocean circulation model for climate studies

    SciTech Connect

    Hovine, S.; Fichefet, T.

    1994-09-01

    A two-dimensional, three-basin ocean model suitable for long-term climate studies is developed. The model is based on the zonally averaged form of the primitive equations written in spherical coordinates. The east-west density difference which arises upon averaging the momentum equations is taken to be proportional to the meridional density gradient. Lateral exchanges of heat and salt between the basins are explicitly resolved. Moreover, the model includes bottom topography and has representations of the Arctic Ocean and of the Weddell and Ross seas. Under realistic restoring boundary conditions, the model reproduces the global conveyor belt: deep water is formed in the Atlantic between 60 and 70{degree}N at a rate of about 17 Sv (1 Sv=10{sup 6} m{sup 3}S{sup {minus}1}) and in the vicinity of the Antarctic continent, while the Indian and Pacific basins show broad upwelling. Superimposed on this thermohaline circulation are vigorous wind-driven cells in the upper thermocline. The simulated temperature and salinity fields and the computed meridional heat transport compare reasonably well with the observational estimates. When mixed boundary conditions i.e., a restoring condition no sea-surface temperature and flux condition on sea-surface salinity are applied, the model exhibits an irregular behavior before reaching a steady state characterized by self-sustained oscillations of 8.5-y period. The conveyor-belt circulation always results at this stage. A series of perturbation experiments illustrates the ability of the model to reproduce different steady-state circulations under mixed boundary conditions. Finally, the model sensitivity to various factors is examined. This sensitivity study reveals that the bottom topography and the presence of a submarine meridional ridge in the zone of the Drake passage play a crucial role in determining the properties of the model bottom-water masses. The importance of the seasonality of the surface forcing is also stressed.

  12. A Tailored Computation of the Mean Dynamic Topography for a Consistent Integration into Ocean Circulation Models

    NASA Astrophysics Data System (ADS)

    Becker, S.; Losch, M.; Brockmann, J. M.; Freiwald, G.; Schuh, W.-D.

    2014-11-01

    Geostrophic surface velocities can be derived from the gradients of the mean dynamic topography—the difference between the mean sea surface and the geoid. Therefore, independently observed mean dynamic topography data are valuable input parameters and constraints for ocean circulation models. For a successful fit to observational dynamic topography data, not only the mean dynamic topography on the particular ocean model grid is required, but also information about its inverse covariance matrix. The calculation of the mean dynamic topography from satellite-based gravity field models and altimetric sea surface height measurements, however, is not straightforward. For this purpose, we previously developed an integrated approach to combining these two different observation groups in a consistent way without using the common filter approaches (Becker et al. in J Geodyn 59(60):99-110, 2012; Becker in Konsistente Kombination von Schwerefeld, Altimetrie und hydrographischen Daten zur Modellierung der dynamischen Ozeantopographie 2012). Within this combination method, the full spectral range of the observations is considered. Further, it allows the direct determination of the normal equations (i.e., the inverse of the error covariance matrix) of the mean dynamic topography on arbitrary grids, which is one of the requirements for ocean data assimilation. In this paper, we report progress through selection and improved processing of altimetric data sets. We focus on the preprocessing steps of along-track altimetry data from Jason-1 and Envisat to obtain a mean sea surface profile. During this procedure, a rigorous variance propagation is accomplished, so that, for the first time, the full covariance matrix of the mean sea surface is available. The combination of the mean profile and a combined GRACE/GOCE gravity field model yields a mean dynamic topography model for the North Atlantic Ocean that is characterized by a defined set of assumptions. We show that including the

  13. Variational data assimilation system with nesting model for high resolution ocean circulation

    NASA Astrophysics Data System (ADS)

    Ishikawa, Yoichi; In, Teiji; Nakada, Satoshi; Nishina, Kei; Igarashi, Hiromichi; Hiyoshi, Yoshimasa; Sasaki, Yuji; Wakamatsu, Tsuyoshi; Awaji, Toshiyuki

    2015-10-01

    To obtain the high-resolution analysis fields for ocean circulation, a new incremental approach is developed using a four-dimensional variational data assimilation system with nesting models. The results show that there are substantial biases when using a classical method combined with data assimilation and downscaling, caused by different dynamics resulting from the different resolutions of the models used within the nesting models. However, a remarkable reduction in biases of the low-resolution model relative to the high-resolution model was observed using our new approach in narrow strait regions, such as the Tsushima and Tsugaru straits, where the difference in the dynamics represented by the high- and low-resolution models is substantial. In addition, error reductions are demonstrated in the downstream region of these narrow channels associated with the propagation of information through the model dynamics.

  14. Behavior of 137Cs concentrations in the North Pacific in an ocean general circulation model

    NASA Astrophysics Data System (ADS)

    Tsumune, Daisuke; Aoyama, Michio; Hirose, Katsumi

    2003-08-01

    We have carried out a first simulation of the spatial distributions and the temporal variations of 137Cs concentrations in the North Pacific in off line calculations by using archived output of an ocean general circulation model (OGCM) developed by the National Center of Atmospheric Research (NCAR). Artificial radionuclides including 137Cs are introduced into ocean surface due to global fallout originating from the large-scale atmospheric nuclear weapons tests in 1961-1962. The distribution of radioactive deposition used as forcing for this simulation is estimated from global precipitation data and observed values of annual deposition of radionuclides at the Meteorological Research Institute (MRI) in Japan. 137Cs originating from global fallout have been transported into the ocean interior by advection and diffusion, and the 137Cs concentrations reduced by radioactive decay. We assess the skill of the model calculations by comparing simulated values of 137Cs in seawater with the observed values included in the database compiled by MRI because 137Cs is one of the most useful tracers regarding water motion in the ocean. The vertical and horizontal distributions of the calculated 137Cs concentrations were in good agreement with those of the observed 137Cs concentrations, except in the deep layer.

  15. Heinrich events induced by oceanic circulation changes

    NASA Astrophysics Data System (ADS)

    Alvarez-Solas, Jorge; Robinson, Alexander; Montoya, Marisa; Banderas, Rubén; Ritz, Catherine

    2014-05-01

    Proxy data reveal the existence of episodes of increased deposition of ice-rafted debris in the North Atlantic Ocean during the last glacial period. These are interpreted as massive iceberg discharges mainly from the Laurentide Ice Sheet. Although these have long been attributed to self-sustained ice sheet oscillations, growing evidence points to an active role of the oceanic circulation. Here, we present simulations of the last glacial period carried out with a hybrid ice sheet-ice shelf model forced by an oceanic warming index derived from proxy data that accounts for the impact of past ocean circulation changes on ocean temperatures. The model generates a time series of iceberg calving that closely agrees with ice-rafted debris records over the past 80 ka. Our results indicate that oceanic circulation variations were responsible for the enigmatic ice purges of the last ice age through the control that ice shelves exert on the dynamics of the inland ice sheet

  16. Assimilation of temperature into an isopycnal ocean general circulation model using a parallel ensemble Kalman filter

    NASA Astrophysics Data System (ADS)

    Keppenne, Christian L.; Rienecker, Michele M.

    2003-04-01

    Temperature data from the Tropical Atmosphere and Ocean (TAO) array are assimilated into the Pacific basin configuration of the Poseidon quasi-isopycnal ocean general circulation model (OGCM) using a multivariate ensemble Kalman filter (EnKF) implemented on a massively parallel computer architecture. An assimilation algorithm whereby each processing element (PE) solves a localized analysis problem is used. The algorithm relies on a locally supported error-covariance model to avoid the introduction of spurious long-range covariances associated with small ensemble sizes and to facilitate its efficient parallel implementation on a computing platform with distributed memory. Each time data are assimilated, multivariate background-error statistics estimated from the phase-space distribution of an ensemble of model states are used to calculate the Kalman gain matrix and the analysis increments. The resulting cross-field covariances are used to compute temperature, salinity and current increments. The layer thicknesses are left unchanged by the analysis. Instead, they are dynamically adjusted by the model between successive analyses. Independent acoustic Doppler current profiler data are used to assess the performance of the temperature data assimilation. The temperature analyses are also compared to analyses obtained with a univariate optimal interpolation (UOI) algorithm and to a control run without temperature assimilation. The results demonstrate that the multivariate EnKF is both practical and effective for assimilating in situ and remotely sensed observations into a high resolution ocean model in a quasi-operational framework.

  17. Modeling of the World Ocean circulation with the four-dimensional assimilation of temperature and salinity fields

    NASA Astrophysics Data System (ADS)

    Marchuk, G. I.; Zalesny, V. B.

    2012-02-01

    The problem of modeling the World Ocean circulation with the four-dimensional assimilation of temperature and salinity fields is considered. A mathematical model of the ocean general circulation and a numerical algorithm for its solution are formulated. The model equations are written in a σ coordinate system on the sphere with the North Pole shifted to the point of the continent (60° E, 60.5° N). The model has a flexible numerical structure and consists of two parts: the forward prognostic model and its adjoint analog. The numerical algorithm for solving the forward and adjoint problems is based on the method of multicomponent splitting. This method includes splitting with respect to physical processes and geometric coordinates. Three series of numerical experiments are performed: (1) a test solution to the problem of the four-dimensional variational assimilation, (2) modeling of the World Ocean circulation with the variational assimilation of climatic temperature and salinity fields, and (3) modeling of the World Ocean circulation with the variational assimilation of climatic temperature and salinity fields and the data of Argo buoys. The results of calculations demonstrate the expediency of using the model of World Ocean circulation with the procedure of assimilating observational data for a description of the general structure of thermohaline fields.

  18. Mechanical power input from buoyancy and wind to the circulation in an ocean model

    NASA Astrophysics Data System (ADS)

    Saenz, J. A.; Hogg, A. M.; Hughes, G. O.; Griffiths, R. W.

    2012-07-01

    We make a systematic quantitative comparison of the effects that surface buoyancy forcing and wind stress have on the energy balance of an idealized, rotating, pole-to-pole ocean model with a zonally re-entrant channel in the south, forced by realistic heat (buoyancy) fluxes and wind stresses representative of global climatology. Surface buoyancy fluxes and wind stress forcing are varied independently; both have significant effects on the reservoirs of various forms of energy and the rates of transfer between them. Importantly, we show for the first time that in the ocean, each power input has a positive feedback on the other. Changes in the rate of generation of available potential energy by buoyancy fluxes at the surface lead to similar changes in the rate of conversion of potential energy to kinetic energy by buoyancy forces (sinking) in the interior, and to changes in the rate of generation of kinetic energy by wind stress. Conversely, changes in the rate of generation of kinetic energy by wind stress lead to changes in the rate of generation of available potential energy by buoyancy forcing. We discuss how this feedback is mediated by the circumpolar current, and processes involving buoyancy, mixing and geostrophic balances. Our results support the notion that surface buoyancy forcing, along with wind and tidal forcing, plays an active role in the energy balance of the oceans. The overturning circulation in the oceans is not the result of a single driving force. Rather, it is a manifestation of a complex and subtle balance.

  19. Carbon dioxide, climate and the deep ocean circulation: Carbon chemistry model. Final report

    SciTech Connect

    Menawat, A.S.

    1992-09-21

    The objective of this study was to investigate the role of oceanic carbon chemistry in modulating the atmospheric levels of CO{sub 2}. It is well known that the oceans are the primary sink of the excess carbon pumped into the atmosphere since the beginning of the industrial period. The suspended particulate and the dissolved organic matters in the deep ocean play important roles as carriers of carbon and other elements critical to the fate of CO{sub 2}. In addition, the suspended particulate matter provides sites for oxidation-reduction reactions and microbial activities. The problem is of an intricate system with complex chemical, physical and biological processes. This report describes a methodology to describe the interconversions of different forms of the organic and inorganic nutrients, that may be incorporated in the ocean circulation models. Our approach includes the driving force behind the transfers in addition to balancing the elements. Such thermodynamic considerations of describing the imbalance in the chemical potentials is a new and unique feature of our approach.

  20. Carbon dioxide, climate and the deep ocean circulation: Carbon chemistry model

    SciTech Connect

    Menawat, A.S.

    1992-09-21

    The objective of this study was to investigate the role of oceanic carbon chemistry in modulating the atmospheric levels of CO[sub 2]. It is well known that the oceans are the primary sink of the excess carbon pumped into the atmosphere since the beginning of the industrial period. The suspended particulate and the dissolved organic matters in the deep ocean play important roles as carriers of carbon and other elements critical to the fate of CO[sub 2]. In addition, the suspended particulate matter provides sites for oxidation-reduction reactions and microbial activities. The problem is of an intricate system with complex chemical, physical and biological processes. This report describes a methodology to describe the interconversions of different forms of the organic and inorganic nutrients, that may be incorporated in the ocean circulation models. Our approach includes the driving force behind the transfers in addition to balancing the elements. Such thermodynamic considerations of describing the imbalance in the chemical potentials is a new and unique feature of our approach.

  1. Local and Global Views of Systematic Errors of Atmosphere-Ocean General Circulation Models

    NASA Astrophysics Data System (ADS)

    Mechoso, C. Roberto; Wang, Chunzai; Lee, Sang-Ki; Zhang, Liping; Wu, Lixin

    2014-05-01

    Coupled Atmosphere-Ocean General Circulation Models (CGCMs) have serious systematic errors that challenge the reliability of climate predictions. One major reason for such biases is the misrepresentations of physical processes, which can be amplified by feedbacks among climate components especially in the tropics. Much effort, therefore, is dedicated to the better representation of physical processes in coordination with intense process studies. The present paper starts with a presentation of these systematic CGCM errors with an emphasis on the sea surface temperature (SST) in simulations by 22 participants in the Coupled Model Intercomparison Project phase 5 (CMIP5). Different regions are considered for discussion of model errors, including the one around the equator, the one covered by the stratocumulus decks off Peru and Namibia, and the confluence between the Angola and Benguela currents. Hypotheses on the reasons for the errors are reviewed, with particular attention on the parameterization of low-level marine clouds, model difficulties in the simulation of the ocean heat budget under the stratocumulus decks, and location of strong SST gradients. Next the presentation turns to a global perspective of the errors and their causes. It is shown that a simulated weak Atlantic Meridional Overturning Circulation (AMOC) tends to be associated with cold biases in the entire Northern Hemisphere with an atmospheric pattern that resembles the Northern Hemisphere annular mode. The AMOC weakening is also associated with a strengthening of Antarctic bottom water formation and warm SST biases in the Southern Ocean. It is also shown that cold biases in the tropical North Atlantic and West African/Indian monsoon regions during the warm season in the Northern Hemisphere have interhemispheric links with warm SST biases in the tropical southeastern Pacific and Atlantic, respectively. The results suggest that improving the simulation of regional processes may not suffice for a more

  2. Subaqueous melting in Zachariae Isstrom, Northeast Greenland combining observations and an ocean general circulation model

    NASA Astrophysics Data System (ADS)

    Cai, C.; Rignot, E. J.; Menemenlis, D.

    2015-12-01

    Zachariae Isstrom, a major ice stream in northeast Greenland, has lost its entire ice shelf in the past decade. Here, we study the evolution of subaqueous melting of its floating section during the transition. Observations show that the rate of ice shelf melting has doubled during 1999-2010 and is twice higher than that maintaining the ice shelf in a state of mass equilibrium. The ice shelf melt rate depends on the thermal forcing from warm, salty, subsurface ocean water of Atlantic origin (AW), and - in contrast with Antarctic ice shelves - on the mixing of AW with fresh buoyant subglacial discharge. Subglacial discharge has increased as result of enhanced ice sheet runoff driven by warmer air temperature; ocean thermal forcing has increased due enhanced advection of AW. Here, we employ the Massassuchetts Institute of Technology general circulation model (MITgcm) at a high spatial resolution (1 m horizontal and 1 m vertical spacing near the grounding line) to simulate the melting process in 3-D. The model is constrained by ice thickness from mass conservation, oceanic bathymetry from NASA Operation IceBridge gravity data, in-situ ocean temperature/salinity data, ocean tide height and current from the Arctic Ocean Tidal Inverse Model (AOTIM-5) and subglacial discharge from output products of the Regional Atmospheric Climate Model (RACMO). We compare the results in winter (no runoff) with summer (maximum runoff) at two different stages with (prior to 2012) and without the ice shelf (after 2012) to subaqueous melt rates deduced from remote sensing observations. We show that ice melting by the ocean has increased by one order of magnitude as a result of the transition from ice shelf terminating to near-vertical calving front terminating. We also find that subglacial discharge has a significant impact on the ice shelf melt rates in Greenland. We conclude on the impact of ocean warming and air temperature warming on the melting regime of the ice margin of Zachariae

  3. Validation of a Three-Dimensional Model of the Ocean Circulation

    NASA Astrophysics Data System (ADS)

    Monier, L.; Brossier, F.; Razafimahery, F.

    2008-10-01

    This paper is devoted to a numerical model of the oceanic circulation. In order to obtain the variability of the currents with respect to time and depth, we have to use 3D Navier-Stokes equations. The horizontal gradient of pressure appears as an unknown term in these equations. It is directly related to the gradient of the sea surface topography and obtained by solving a 2D model governed by shallow water equations. Numerical experiments are carried out in a parallelepiped canal located in the south hemisphere. First experiment proves coherence between the 2D and 3D models. Then, we test the influence of the Coriolis stress on a southward flow. Finally, we compute different vertical profiles of velocity depending on virtual viscosity used in order to model turbulence.

  4. An Improved Heat Budget Estimation Including Bottom Effects for General Ocean Circulation Models

    NASA Technical Reports Server (NTRS)

    Carder, Kendall; Warrior, Hari; Otis, Daniel; Chen, R. F.

    2001-01-01

    This paper studies the effects of the underwater light field on heat-budget calculations of general ocean circulation models for shallow waters. The presence of a bottom significantly alters the estimated heat budget in shallow waters, which affects the corresponding thermal stratification and hence modifies the circulation. Based on the data collected during the COBOP field experiment near the Bahamas, we have used a one-dimensional turbulence closure model to show the influence of the bottom reflection and absorption on the sea surface temperature field. The water depth has an almost one-to-one correlation with the temperature rise. Effects of varying the bottom albedo by replacing the sea grass bed with a coral sand bottom, also has an appreciable effect on the heat budget of the shallow regions. We believe that the differences in the heat budget for the shallow areas will have an influence on the local circulation processes and especially on the evaporative and long-wave heat losses for these areas. The ultimate effects on humidity and cloudiness of the region are expected to be significant as well.

  5. Finding the 'lost years' in green turtles: insights from ocean circulation models and genetic analysis.

    PubMed

    Putman, Nathan F; Naro-Maciel, Eugenia

    2013-10-01

    Organismal movement is an essential component of ecological processes and connectivity among ecosystems. However, estimating connectivity and identifying corridors of movement are challenging in oceanic organisms such as young turtles that disperse into the open sea and remain largely unobserved during a period known as 'the lost years'. Using predictions of transport within an ocean circulation model and data from published genetic analysis, we present to our knowledge, the first basin-scale hypothesis of distribution and connectivity among major rookeries and foraging grounds (FGs) of green turtles (Chelonia mydas) during their 'lost years'. Simulations indicate that transatlantic dispersal is likely to be common and that recurrent connectivity between the southwestern Indian Ocean and the South Atlantic is possible. The predicted distribution of pelagic juvenile turtles suggests that many 'lost years hotspots' are presently unstudied and located outside protected areas. These models, therefore, provide new information on possible dispersal pathways that link nesting beaches with FGs. These pathways may be of exceptional conservation concern owing to their importance for sea turtles during a critical developmental period. PMID:23945687

  6. Secular Trends and Climate Drift in Coupled Ocean-Atmosphere General Circulation Models

    SciTech Connect

    Covey, C C; Gleckler, P J; Phillips, T J; Bader, D C

    2004-11-23

    Coupled ocean-atmosphere general circulation models (coupled GCMs) with interactive sea ice are the primary tool for investigating possible future global warming and numerous other issues in climate science. A long-standing problem with such models is that when different components of the physical climate system are linked together, the simulated climate can drift away from observations unless constrained by ad hoc adjustments to interface fluxes. However, eleven modern coupled GCMs--including three that do not employ flux adjustments--behave much better in this respect than the older generation of models. Surface temperature trends in control run simulations (with external climate forcing such as solar brightness and atmospheric carbon dioxide held constant) are small compared with observed trends, which include 20th century climate change due to both anthropogenic and natural factors. Sea ice changes in the models are dominated by interannual variations. Deep ocean temperature and salinity trends are small enough for model control runs to extend over 1000 simulated years or more, but trends in some regions, most notably the Arctic, are inconsistent among the models and may be problematic.

  7. Sedimentary response to ocean gateway circulation changes

    NASA Astrophysics Data System (ADS)

    Heinze, Christoph; Crowley, Thomas J.

    1997-12-01

    Previous modeling studies suggested that changes in ocean gateways may have exerted a dramatic influence on the ocean circulation. In this pilot study we extend those results to examining the potential ramifications of circulation changes on the sedimentary record. A version of the Hamburg carbon cycle/sediment model is used in these sensitivity experiments. Results indicate that internal reorganization of the ocean circulation can potentially cause very large regional changes in lysocline depth (1500-3000 m) and opal deposition. These shifts are sometimes comparable in magnitude to those imposed by changes in external forcing (e.g., climate, sea level, and weathering). Comparisons of the model response with the geologic record indicate some significant levels of first-order agreement. This exercise suggests that opportunities now exist for physically based modeling of past sediment responses to circulation and climate changes.

  8. How stationary are the internal tides in a high-resolution global ocean circulation model?

    NASA Astrophysics Data System (ADS)

    Shriver, Jay F.; Richman, James G.; Arbic, Brian K.

    2014-05-01

    The stationarity of the internal tides generated in a global eddy-resolving ocean circulation model forced by realistic atmospheric fluxes and the luni-solar gravitational potential is explored. The root mean square (RMS) variability in the M2 internal tidal amplitude is approximately 2 mm or less over most of the ocean and exceeds 2 mm in regions with larger internal tidal amplitude. The M2 RMS variability approaches the mean amplitude in weaker tidal areas such as the tropical Pacific and eastern Indian Ocean, but is smaller than the mean amplitude near generation regions. Approximately 60% of the variance in the complex M2 tidal amplitude is due to amplitude-weighted phase variations. Using the RMS tidal amplitude variations normalized by the mean tidal amplitude (normalized RMS variability (NRMS)) as a metric for stationarity, low-mode M2 internal tides with NRMS < 0.5 are stationary over 25% of the deep ocean, particularly near the generation regions. The M2 RMS variability tends to increase with increasing mean amplitude. However, the M2 NRMS variability tends to decrease with increasing mean amplitude, and regions with strong low-mode internal tides are more stationary. The internal tide beams radiating away from generation regions become less stationary with distance. Similar results are obtained for other tidal constituents with the overall stationarity of the constituent decreasing as the energy in the constituent decreases. Seasonal variations dominate the RMS variability in the Arabian Sea and near-equatorial oceans. Regions of high eddy kinetic energy are regions of higher internal tide nonstationarity.

  9. Global ocean circulation by altimetry

    NASA Technical Reports Server (NTRS)

    Wunsch, Carl; Haidvogel, D.

    1991-01-01

    The overall objectives of this project are to determine the general circulation of the oceans and many of its climate and biochemical consequences through the optimum use of altimetry data from TOPEX/POSEIDON and related missions. Emphasis is on the global-scale circulation, as opposed to the regional scale, but some more local studies will be carried out. Because of funding limitations, the primary initial focus will be on the time-dependent global-scale circulation rather than the mean; eventually, the mean circulation must be dealt with as well.

  10. Sensitivity of an oceanic general circulation model forced by satellite wind stress fields

    NASA Astrophysics Data System (ADS)

    Grima, Nicolas; Bentamy, Abderrahim; Katsaros, Kristina; Quilfen, Yves; Delecluse, Pascale; Levy, Claire

    1999-04-01

    Satellite wind and wind stress fields at the sea surface, derived from the scatterometers on European Remote Sensing satellites 1 and 2 (ERS-1 and ERS-2) are used to drive the ocean general circulation model (OGCM) "OPA" in the tropical oceans. The results of the impact of ERS winds are discussed in terms of the resulting thermocline, current structures, and sea level anomalies. Their adequacy is evaluated on the one hand by comparison with simulations forced by the Arpege-Climat model and on the other hand by comparison with measurements of the Tropical Atmosphere-Ocean (TAO) buoy network and of the TOPEX/Poseidon altimeter. Regarding annual mean values, the thermal and current responses of the OGCM forced by ERS winds are in good agreement with the TAO buoy observations, especially in the central and eastern Pacific Ocean. In these regions the South Equatorial Current, the Equatorial Undercurrent, and the thermocline features simulated by the OGCM forced by scatterometer wind fields are described. The impact of the ERS-1 winds is particularly significant to the description of the main oceanic variability. Compared to the TAO buoy observations, the high-frequency (a few weeks) and the low-frequency of the thermocline and zonal current variations are described. The correlation coefficients between the time series of the thermocline simulated by ERS winds and that observed by the TAO buoy network are highly significant; their mean value is 0.73, over the whole basin width, while it is 0.58 between Arpege model simulation and buoy observations. At the equator the time series of the zonal current simulated by the ERS winds, at three locations (110°W, 140°W, and 165°E) and at two depths, are compared to the TAO current meter and acoustic Doppler current profiler (ADCP) measurements. The mean value of the significant correlation coefficients computed with the in situ measurements is 0.72 for ERS, while it is 0.51 for the Arpege-Climat model. Thus ERS wind fields

  11. Interaction between surface wind and ocean circulation in the Carolina Capes in a coupled low-order model

    SciTech Connect

    Xie, L.; Pietrafesa, L.J.; Raman, S.

    1997-03-18

    Interactions between surface winds and ocean currents over an east-coast continental shelf are studied using a simple mathematical model. The model physics include cross-shelf advection of sea surface temperature (SST) by Ekman drift, upwelling due to Ekman transport divergence, differential heating of the low-level atmosphere by a cross-shelf SST gradient, and the Coriolis effect. Additionally, the effects of diabatic cooling of surface waters due to air-sea heat exchange and of the vertical density stratification on the thickness of the upper ocean Ekman layer are considered. The model results are qualitatively consistent with observed wind-driven coastal ocean circulation and surface wind signatures induced by SST. This simple model also demonstrates that two-way air-sea interaction plays a significant role in the subtidal frequency variability of coastal ocean circulation and mesoscale variability of surface wind fields over coastal waters.

  12. Tracers of Past Ocean Circulation

    NASA Astrophysics Data System (ADS)

    Lynch-Stieglitz, J.

    2003-12-01

    Information about how the ocean circulated during the past is useful in understanding changes in ocean and atmospheric chemistry, changes in the fluxes of heat and freshwater between the ocean and atmosphere, and changes in global wind patterns. The circulation of surface waters in the ocean leaves an imprint on sea surface temperature, and is also inextricably linked to the patterns of oceanic productivity. Much valuable information about past ocean circulation has been inferred from reconstructions of surface ocean temperature and productivity, which are covered in separate chapters. Here the focus is on the geochemical tracers that are used to infer the flow patterns and mixing of subsurface water masses.Several decades ago it was realized that chemistry of the shells of benthic foraminifera (carbon isotope and Cd/Ca ratios) carried an imprint of the nutrient content of deep-water masses (Shackleton, 1977; Broecker, 1982; Boyle, 1981). This led rapidly to the recognition that the water masses in the Atlantic Ocean were arrayed differently during the last glacial maximum than they are today, and the hypothesis that the glacial arrangement reflected a diminished contribution of low-nutrient North Atlantic deep water (NADW) ( Curry and Lohmann, 1982; Boyle and Keigwin, 1982). More detailed spatial reconstructions indicated a shallow nutrient-depleted water mass overlying a more nutrient-rich water mass in the glacial Atlantic. These findings spurred advances not only in geochemistry but in oceanography and climatology, as workers in these fields attempted to simulate the inferred glacial circulation patterns and assess the vulnerability of the modern ocean circulation to changes such as observed for the last ice age.While the nutrient distributions in the glacial Atlantic Ocean were consistent with a diminished flow of NADW, they also could have reflected an increase in inflow from the South Atlantic and/or a shallower yet undiminished deep-water mass. Clearly

  13. Eddy properties in the Mozambique Channel: A comparison between observations and two numerical ocean circulation models

    NASA Astrophysics Data System (ADS)

    Halo, I.; Backeberg, B.; Penven, P.; Ansorge, I.; Reason, C.; Ullgren, J. E.

    2014-02-01

    Analysis of satellite altimetry observations, transports estimates from a mooring array, as well as output from two different numerical ocean circulation models (ROMS and HYCOM), have been used to investigate the mesoscale eddy properties and transport variability in the Mozambique Channel. The power spectral density of model transports at 17°S indicates the models ability to represent the transport variability at mesoscale frequencies (range between 3 yr-1 and 10 yr-1). The models have shown an exaggerated representation of the lower frequencies (~ <3 yr-1), while underestimating the higher frequency signals (~ >10 yr-1). The overestimation of the seasonal cycle appears in our case not to be related to a misrepresentation of the mesoscale variability. The eddies were identified using an automatic eddy tracking scheme. Both anticyclonic and cyclonic eddies appeared to have a preferred site of formation within the channel. The density distribution showed that the anticyclones exhibited a bi-modal distribution: the first mode was associated with the typical scale for the oceanic mesoscale turbulence, while the second mode was related to the passage of large rings at a frequency of about 4-7 per year. On the other hand, cyclonic eddies had a single mode distribution that follows the first baroclinic Rossby radius of deformation, which is a typical scale for the oceanic mesoscale surface eddy variability, suggesting that their formation is associated with baroclinic instability. Eddy mean amplitudes per class of radius (<100 km), increase linearly with increasing radius, while no linear relationship exists for the rings. Different from the rings, the increase in the amplitude of the eddies was consistent with the increase of their life expectancy and travelling distances.

  14. High resolution modeling of the monsoon circulation in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Diansky, N. A.; Zalesny, V. B.; Moshonkin, S. N.; Rusakov, A. S.

    2006-10-01

    The goal of this paper is to present some results on the monsoon circulation in the Indian Ocean simulated with a σ-coordinate ocean model developed at the Institute of Numerical Mathematics, RAS. The model has a horizontal resolution of (1/8)° × (1/12)° and contains 21 σ-layers of uneven thickness. Realistic bottom topography and land geometry are used. The numerical experiments were carried out for 15 years starting from the Levitus climatology for January and monthly mean climatic atmospheric forcing from the NCEP reanalysis data. The annual cycle of the surface and subsurface currents and temperature and salinity fields were analyzed. The model reproduces well the Summer Monsoon and the Winter Monsoon currents and their time evolution and spatial structures. The Somali Current is adequately modeled. During the Summer Monsoon, the velocities of the current exceed 2 m/s, while the total mass transport is approximately 70 Sv. The model results show that a reversal of the Somali Current from the northern direction in the summer to the southern direction in the winter is accompanied by the generation of anticyclonic eddies, which drift westward owing to the β-effect and dissipate either near the Somali shore or in the Gulf of Aden. The monsoon variability of the equatorial surface current and equatorial subsurface countercurrent system are analyzed. It is shown that these currents are generated predominantly by the zonal component of wind stress, in which the half-year harmonic dominates. This leads to the fact that the equatorial surface current also changes its direction with a half-year periodicity almost in phase with the wind. The oppositely directed subsurface compensational countercurrent changes its direction with a time lag of approximately one month. Gradient currents, which appear in the Bay of Bengal due to the riverine runoff, make an important contribution to the circulation. This effect manifests itself especially strongly in the summer during

  15. Spaceborne studies of ocean circulation

    NASA Technical Reports Server (NTRS)

    Patzert, W. C.

    1984-01-01

    The history and near-term future of ocean remote sensing to study ocean circulation are examined. Seasat provided the first-ever global data sets of sea surface topography (altimeter) and marine winds (scatterometer) and laid the foundation for the next generation of satellite missions planned for the late 1980s. The future missions are the next generation of altimeter and scatterometer to be flown aboard TOPEX (TOPography EXperiment) and NROSS (Navy Remote Sensing System), respectively. The data from these satellites will be coordinated with measurements made at sea to determine the driving forces of ocean circulation and to study the oceans' role in climate variability. The significance of such studies to such matters as climatic changes, fisheries, commerce, waste disposal, and national defense is noted.

  16. Lessons from Multi-Millenium Runs of Coupled Atmospheric-Ocean General Circulation Models

    NASA Astrophysics Data System (ADS)

    Liang, M.; Lin, L.; Tung, K.; Yung, Y. L.; Sun, S.

    2012-12-01

    Coupled atmosphere-ocean general circulation models (AOGCM) are used for climate prediction on the degree of warming due to increases in greenhouse gases, and for policy recommendations on emission curbs. We first demonstrate that the currently adopted protocol for obtaining such a prediction does not yield a robust solution and therefore cannot be relied upon for policy recommendations. The range of uncertainty in such predictions may have been underreported when models participating in Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) were run with their oceans at various stages of flux adjustment with their atmosphere, and could change significantly simply by running them longer. This is shown by comparing multi-millennium long runs of the Goddard Institute for Space Studies coupled model (GISS-EH) and the Community Climate System Model (CCSM4) with what were reported to AR4. For common predictions from preindustrial condition to 2030-2100, the previously predicted warming and spatial patterns vary even in ensemble average. The commonly adopted remedy of subtracting the "climate drift" is ineffective and often leads to a wrong solution. The long model runs here also reveal the range of variability (~30%) in the Transient Climate Response (TCR) within the same model with the same Equilibrium Climate Sensitivity (ECS). Fortunately, for simulations with multi-decadal to century long time horizon, robust solutions can be obtained off thousand-year-long control runs that reach "quasi-equilibrium" using a new protocol. The problem of different quasi-equilibrium states in long runs and the memory of the solution on these states are also addressed.

  17. Seasonal mixed-layer dynamics in an eddy-resolving ocean circulation model

    NASA Astrophysics Data System (ADS)

    Schiller, Andreas; Ridgway, Ken R.

    2013-07-01

    Mean and seasonal mixed-layer depths (MLDs) derived from an eddy-resolving ocean general circulation model with a horizontal resolution of (1/10)° are validated with climatological observations. Associated heat budgets on seasonal timescales are analyzed for six boundary current regions with high eddy kinetic energy (Somali Current, Agulhas Current region, Kuroshio, East Australian Current, Gulf Stream, and Brazil-Malvinas/Falkland Confluence). In all of these regions and on seasonal timescales, (a) horizontal advection significantly contributes to the mixed-layer heat budget (MLHB) on eddy scales and locally exceeds ±5°C/month; (b) lateral mixing (calculated as a residual term) is similar in size to surface net heat flux, horizontal advection, and vertical entrainment in defining the mixed-layer temperature; (c) seasonal vertical entrainment has a cooling effect on mixed-layer temperature throughout the year in the regions investigated; and (d) a phase lag between MLD and changes in mixed-layer heat content exists such that local cooling (warming) in the mixed layer precedes maxima (minima) in MLD by 1-3 months. A rather complex picture emerges where the MLHB in ocean boundary currents on larger spatial scales is determined by net surface heat fluxes and entrainment, whereas local, eddy-related advection and stirring modulate the large-scale signals.

  18. The Development of a Degree 360 Expansion of the Dynamic Ocean Topography of the POCM_4B Global Circulation Model

    NASA Technical Reports Server (NTRS)

    Rapp, Richard H.

    1998-01-01

    This paper documents the development of a degree 360 expansion of the dynamic ocean topography (DOT) of the POCM_4B ocean circulation model. The principles and software used that led to the final model are described. A key principle was the development of interpolated DOT values into land areas to avoid discontinuities at or near the land/ocean interface. The power spectrum of the POCM_4B is also presented with comparisons made between orthonormal (ON) and spherical harmonic magnitudes to degree 24. A merged file of ON and SH computed degree variances is proposed for applications where the DOT power spectrum from low to high (360) degrees is needed.

  19. A semi-implicit ocean circulation model using a generalized topography-following coordinate system

    SciTech Connect

    Song, Yuhe; Haidvogel, D.

    1994-11-01

    We introduce a new ocean circulation model featuring an improved vertical coordinate representation. This new coordinate is a generalized {sigma}coordinate; however, it is capable of simultaneously maintaining high resolution in the surface layer as well as dealing with steep and/or tall topography. The model equations are the tree-dimensional, free surface, primitive equations with orthogonal curvilinear coordinates in the horizontal and the new general coordinate in the vertical. Vertical mixing is treated implicitly by the generalized Crank-Nicolson method based on a Galerkin finite element formulation. Two alternate parameterizations of surface mixing are incorporated, based respectively on the approaches of Price, Weller, and Pinkel and Mellor and Yamada. Finally, a quadrature formula of Lagrange interpolation is employed to produce a more accurate calculation of pressure and vertical velocity. Three tests are used to demonstrate the accuracy, stability, and applicability of the model: the diurnal cycling of the surface mixed layer, flow around a tall seamount, and a regional simulation of the California current system.

  20. The North Atlantic subpolar circulation in an eddy-resolving global ocean model

    NASA Astrophysics Data System (ADS)

    Marzocchi, Alice; Hirschi, Joël J.-M.; Holliday, N. Penny; Cunningham, Stuart A.; Blaker, Adam T.; Coward, Andrew C.

    2015-02-01

    The subpolar North Atlantic represents a key region for global climate, but most numerical models still have well-described limitations in correctly simulating the local circulation patterns. Here, we present the analysis of a 30-year run with a global eddy-resolving (1/12°) version of the NEMO ocean model. Compared to the 1° and 1/4° equivalent versions, this simulation more realistically represents the shape of the Subpolar Gyre, the position of the North Atlantic Current, and the Gulf Stream separation. Other key improvements are found in the representation of boundary currents, multi-year variability of temperature and depth of winter mixing in the Labrador Sea, and the transport of overflows at the Greenland-Scotland Ridge. However, the salinity, stratification and mean depth of winter mixing in the Labrador Sea, and the density and depth of overflow water south of the sill, still present challenges to the model. This simulation also provides further insight into the spatio-temporal development of the warming event observed in the Subpolar Gyre in the mid 1990s, which appears to coincide with a phase of increased eddy activity in the southernmost part of the gyre. This may have provided a gateway through which heat would have propagated into the gyre's interior.

  1. An Empirical Model of Global Climate: Reduced Impact of Volcanoes upon Consideration of Ocean Circulation

    NASA Astrophysics Data System (ADS)

    Canty, T. P.; Mascioli, N. R.; Smarte, M.; Salawitch, R. J.

    2012-12-01

    Observed reductions in Earth's surface temperature following explosive volcanic eruptions are often used as a proxy for geo-engineering of climate by enhancement of stratospheric sulfate. We use a multiple linear regression model applied to the global surface temperature record to suggest that exchange of heat between the atmosphere and ocean, driven by variations in the strength of the Atlantic Meridional Overturning Circulation (AMOC), has been an important factor in the decline of temperature following the four major volcanic eruptions since 1900. The veracity of this suggestion depends on whether the Atlantic Multidecadal Oscillation (AMO) truly represents a proxy for the strength of the AMOC and quantification of volcanic cooling depends on how the AMO is detrended. If the AMO is detrended using anthropogenic radiative forcing of climate, surface cooling attributed to Mount Pinatubo, using the Hadley surface temperature record, maximizes at 0.15°C globally and 0.35°C over land. These values are about a factor of 2 lower than found when the AMO is neglected. We show that the satellite record of atmospheric temperature is also consistent with our suggestion that volcanic cooling may have been over estimated by about a factor of 2. The AMO had begun to decrease prior to the four major eruptions, suggesting that exchange of heat between the atmosphere and ocean due to variations in the strength of the AMOC drives the climate system, rather than responds to volcanic perturbations. We will discuss implications of our study for the Geoengineering Model Intercomparison Project (GeoMIP).

  2. Construction of the adjoint MIT ocean general circulation model and application to Atlantic heat transport sensitivity

    NASA Astrophysics Data System (ADS)

    Marotzke, Jochem; Giering, Ralf; Zhang, Kate Q.; Stammer, Detlef; Hill, Chris; Lee, Tong

    1999-12-01

    We first describe the principles and practical considerations behind the computer generation of the adjoint to the Massachusetts Institute of Technology ocean general circulation model (GCM) using R. Giering's software tool Tangent-Linear and Adjoint Model Compiler (TAMC). The TAMC's recipe for (FORTRAN-) line-by-line generation of adjoint code is explained by interpreting an adjoint model strictly as the operator that gives the sensitivity of the output of a model to its input. Then, the sensitivity of 1993 annual mean heat transport across 29°N in the Atlantic, to the hydrography on January 1, 1993, is calculated from a global solution of the GCM. The "kinematic sensitivity" to initial temperature variations is isolated, showing how the latter would influence heat transport if they did not affect the density and hence the flow. Over 1 year the heat transport at 29°N is influenced kinematically from regions up to 20° upstream in the western boundary current and up to 5° upstream in the interior. In contrast, the dynamical influences of initial temperature (and salinity) perturbations spread from as far as the rim of the Labrador Sea to the 29°N section along the western boundary. The sensitivities calculated with the adjoint compare excellently to those from a perturbation calculation with the dynamical model. Perturbations in initial interior salinity influence meridional overturning and heat transport when they have propagated to the western boundary and can thus influence the integrated east-west density difference. Our results support the notion that boundary monitoring of meridional mass and heat transports is feasible.

  3. Atmospheric Torques on the Solid Earth and Oceans Based on the GEOS-1 General Circulation Model

    NASA Technical Reports Server (NTRS)

    Sanchez, Braulio V.; Au, Andrew Y.

    1998-01-01

    The GEOS-1 general circulation model has been used to compute atmospheric torques on the oceans and solid Earth for the period 1980-1995. The time series for the various torque components have been analyzed by means of Fourier transform techniques. It was determined that the wind stress torque over land is more powerful than the wind stress torque over water by 55%, 42%, and 80% for the x, y, and z components respectively. This is mainly the result of power in the high frequency range. The pressure torques due to polar flattening, equatorial ellipticity, marine geoid, and continental orography were computed. The orographic or "mountain torque" components are more powerful than their wind stress counterparts (land plus ocean) by 231% (x), 191% (y), and 77% (z). The marine pressure torques due to geoidal undulations are much smaller than the orographic ones, as expected. They are only 3% (x), 4% (y), and 5% (z) of the corresponding mountain torques. The geoidal pressure torques are approximately equal in magnitude to those produced by the equatorial ellipticity of the Earth. The pressure torque due to polar flattening makes the largest contributions to the atmospheric torque budget. It has no zonal component, only equatorial ones. Most of the power of the latter, between 68% and 69%, is found in modes with periods under 15 days. The single most powerful mode has a period of 361 days. The gravitational torque ranks second in power only to the polar flattening pressure torque. Unlike the former, it does produce a zonal component, albeit much smaller (1%) than the equatorial ones. The gravitational and pressure torques have opposite signs, therefore, the gravitational torque nullifies 42% of the total pressure torque. Zonally, however, the gravitational torque amounts to only 6% of the total pressure torque. The power budget for the total atmospheric torque yields 7595 and 7120 Hadleys for the equatorial components and 966 Hadleys for the zonal. The x-component exhibits

  4. Atmospheric Torques on the Solid Earth and Oceans Based on the GEOS-1 General Circulation Model

    NASA Technical Reports Server (NTRS)

    Sanchez, Braulio

    1999-01-01

    The GEOS-1 general circulation model has been used to compute atmospheric torques on the oceans and solid Earth for the period 1980-1995. The time series for the various torque components have been analyzed by means of Fourier transform techniques. It was determined that the wind stress torque over land is more powerful than the wind stress torque over water by 55\\%, 42\\%, and 80\\t for the x, y, and z components respectively. This is mainly the result of power in the high frequency range. The pressure torques due to polar flattening, equatorial ellipticity, marine geoid, and continental orography were computed. The orographic or "mountain torque" components are more powerful than their wind stress counterparts (land plus ocean) by 231\\% (x), 191\\% (y), and 77\\% (z). The marine pressure torques due to geoidal undulations are much smaller than the orographic ones, as expected. They are only 3\\% (x), 4\\% (y), and 5\\% (z) of the corresponding mountain torques. The geoidal pressure torques are approximately equal in magnitude to those produced by the equatorial ellipticity of the Earth. The pressure torque due to polar flattening makes the largest contributions to the atmospheric'torque budget. It has no zonal component, only equatorial ones. Most of the power of the latter, between 68\\% and 69 %, is found in modes with periods under 15 days. The single most powerful mode has a period of 361 days. The gravitational torque ranks second in power only to the polar flattening pressure torque. Unlike the former, it does produce a zonal component, albeit much smaller (1\\ ) than the equatorial ones. The gravitational and pressure torques have opposite signs, therefore, the gravitational torque nullifies 42\\% of the total pressure torque. Zonally, however, the gravitational torque amounts to only 6\\% of the total pressure torque. The power budget for the total atmospheric torque yields 7595 and 7120 Hadleys for the equatorial components and 966 Hadleys for the

  5. Effect of improved subgrid scale transport of tracers on uptake of bomb radiocarbon in ghe GFDL ocean general circulation model

    SciTech Connect

    Duffy, P.B.; Elgroth, P.; Caldeira, K.

    1995-05-01

    The authors show that the Gent-McWilliams tracer transport parameterization greatly improves the ability of the GFDL ocean general circulation model to simulate vertical profiles of both temperature and bomb radiocarbon with a single set of model parameter values. This parameterization, which includes new advection terms as well as isopycnal mixing, has previously been shown to greatly improve simulated temperature fields. Here, the authors show that it does not markedly affect the already good simulation of oceanic absorption of bomb radiocarbon, and discuss the reasons for this result. 19 refs., 3 figs., 2 tabs.

  6. Satellite Altimetry, Ocean Circulation, and Data Assimilation

    NASA Technical Reports Server (NTRS)

    Fu, Lee-Lueng

    1999-01-01

    Ocean circulation is a critical factor in determining the Earth's climate. Satellite altimetry has been proven a powerful technique for measuring the height of the sea surface for the study of global ocean circulation dynamics. A major objective of my research is to investigate the utility of altimeter data for ocean circulation studies. The 6 years' data record of TOPEX/POSEIDON have been analyzed to study the spatial and temporal characteristics of large-scale ocean variability. A major result obtained in 1998 is the discovery of large-scale oscillations in sea level with a period of 25 days in the Argentine Basin of the South Atlantic Ocean (see diagram). They exhibit a dipole pattern with counterclockwise rotational propagation around the Zapiola Rise (centered at 45S and 317E), a small seamount in the abyssal plain of the basin. The peak-to-trough amplitude is about 10 cm over a distance of 500-1000 km. The amplitude of these oscillations has large seasonal-to-interannual variations. The period and rotational characteristics of these oscillations are remarkably similar to the observations made by two current meters deployed near the ocean bottom in the region. What TOPEX/POSEIDON has detected apparently are manifestations of the movement of the entire water column (barotropic motion). The resultant transport variation is estimated to be about 50 x 10(exp 6) cubic M/S, which is about 50% of the total water transport in the region. Preliminary calculations suggest that these oscillations are topographically trapped waves. A numerical model of the South Atlantic is used to investigate the nature of and causes for these waves. A very important property of sea surface height is that it is directly related to the surface geostrophic velocity, which is related to deep ocean circulation through the density field. Therefore altimetry observations are not only useful for determining the surface circulation but also for revealing information about the deep ocean. Another

  7. Numerical simulation of the world ocean circulation

    NASA Technical Reports Server (NTRS)

    Takano, K.; Mintz, Y.; Han, Y. J.

    1973-01-01

    A multi-level model, based on the primitive equations, is developed for simulating the temperature and velocity fields produced in the world ocean by differential heating and surface wind stress. The model ocean has constant depth, free slip at the lower boundary, and neglects momentum advection; so that there is no energy exchange between the barotropic and baroclinic components of the motion, although the former influences the latter through temperature advection. The ocean model was designed to be coupled to the UCLA atmospheric general circulation model, for the study of the dynamics of climate and climate changes. But here, the model is tested by prescribing the observed seasonally varying surface wind stress and the incident solar radiation, the surface air temperature and humidity, cloudiness and the surface wind speed, which, together with the predicted ocean surface temperature, determine the surface flux of radiant energy, sensible heat and latent heat.

  8. Ice sheet collapse affects ocean circulation

    NASA Astrophysics Data System (ADS)

    Tretkoff, Ernie

    2011-06-01

    As Earth's climate warms and ice melts, freshwater input to oceans could weaken the large-scale Atlantic meridional overturning circulation, which acts as an important conveyor of heat and has significant effects on climate. Green et al. used an intermediate complexity climate model to study how freshwater input to oceans can affect the meridional overturning circulation. They applied their model to the collapse of the Barents ice sheet about 140,000 years ago—the first study of this kind for the time period—which resulted in a huge influx of freshwater to the North Atlantic Ocean as large icebergs calved off of the ice sheet. (Paleoceanography, doi:10.1029/ 2010PA002088, 2011)

  9. ENSO Bred Vectors in Coupled Ocean-Atmosphere General Circulation Models

    NASA Technical Reports Server (NTRS)

    Yang, S. C.; Cai, Ming; Kalnay, E.; Rienecker, M.; Yuan, G.; Toth, ZA.

    2004-01-01

    The breeding method has been implemented in the NASA Seasonal-to-Interannual Prediction Project (NSIPP) Coupled General Circulation Model (CGCM) with the goal of improving operational seasonal to interannual climate predictions through ensemble forecasting and data assimilation. The coupled instability as cap'tured by the breeding method is the first attempt to isolate the evolving ENSO instability and its corresponding global atmospheric response in a fully coupled ocean-atmosphere GCM. Our results show that the growth rate of the coupled bred vectors (BV) peaks at about 3 months before a background ENSO event. The dominant growing BV modes are reminiscent of the background ENSO anomalies and show a strong tropical response with wind/SST/thermocline interrelated in a manner similar to the background ENSO mode. They exhibit larger amplitudes in the eastern tropical Pacific, reflecting the natural dynamical sensitivity associated with the presence of the shallow thermocline. Moreover, the extratropical perturbations associated with these coupled BV modes reveal the variations related to the atmospheric teleconnection patterns associated with background ENSO variability, e.g. over the North Pacific and North America. A similar experiment was carried out with the NCEP/CFS03 CGCM. Comparisons between bred vectors from the NSIPP CGCM and NCEP/CFS03 CGCM demonstrate the robustness of the results. Our results strongly suggest that the breeding method can serve as a natural filter to identify the slowly varying, coupled instabilities in a coupled GCM, which can be used to construct ensemble perturbations for ensemble forecasts and to estimate the coupled background error covariance for coupled data assimilation.

  10. Coupling of wave and circulation models in coastal-ocean predicting systems: a case study for the German Bight

    NASA Astrophysics Data System (ADS)

    Staneva, J.; Wahle, K.; Günther, H.; Stanev, E.

    2015-12-01

    This study addresses the impact of coupling between wind wave and circulation models on the quality of coastal ocean predicting systems. This is exemplified for the German Bight and its coastal area known as the Wadden Sea. The latter is the area between the barrier islands and the coast. This topic reflects the increased interest in operational oceanography to reduce prediction errors of state estimates at coastal scales, which in many cases are due to unresolved nonlinear feedback between strong tidal currents and wind-waves. In this study we present analysis of wave and hydrographic observations, as well as results of numerical simulations. A nested-grid modelling system is used to producing reliable nowcasts and short-term forecasts of ocean state variables, including wind waves and hydrodynamics. The data base includes ADCP observations and continuous measurements from data stations. The individual and collective role of wind, waves and tidal forcing are quantified. The performance of the forecast system is illustrated for the cases of several extreme events. Effects of ocean waves on coastal circulation and sea level are investigated by considering the wave-dependent stress and wave breaking parameterization. Also the effects which the circulation exerts on the wind waves are tested for the coastal areas using different parameterizations. The improved skill of the coupled forecasts compared to the non-coupled ones, in particular during extreme events, justifies the further enhancements of coastal operational systems by including wind wave models.

  11. Coupling of wave and circulation models in coastal-ocean predicting systems: a case study for the German Bight

    NASA Astrophysics Data System (ADS)

    Staneva, Joanna; Wahle, Kathrin; Günther, Heinz; Stanev, Emil

    2016-06-01

    This study addresses the impact of coupling between wave and circulation models on the quality of coastal ocean predicting systems. This is exemplified for the German Bight and its coastal area known as the Wadden Sea. The latter is the area between the barrier islands and the coast. This topic reflects the increased interest in operational oceanography to reduce prediction errors of state estimates at coastal scales, which in many cases are due to unresolved non-linear feedback between strong currents and wind waves. In this study we present analysis of wave and hydrographic observations, as well as results of numerical simulations. A nested-grid modelling system is used to produce reliable nowcasts and short-term forecasts of ocean state variables, including waves and hydrodynamics. The database includes ADCP observations and continuous measurements from data stations. The individual and combined effects of wind, waves and tidal forcing are quantified. The performance of the forecast system is illustrated for the cases of several extreme events. The combined role of wave effects on coastal circulation and sea level are investigated by considering the wave-dependent stress and wave breaking parameterization. Also the response, which the circulation exerts on the waves, is tested for the coastal areas. The improved skill of the coupled forecasts compared to the non-coupled ones, in particular during extreme events, justifies the further enhancements of coastal operational systems by including wave effects in circulation models.

  12. On improving the accuracy of the M2 barotropic tides embedded in a high-resolution global ocean circulation model

    NASA Astrophysics Data System (ADS)

    Ngodock, Hans; Wallcraft, Alan; Souopgui, Innocent; Richman, James; Shriver, Jay; Arbic, Brian

    2016-04-01

    The ocean tidal velocity and elevation can be estimated concurrently with the ocean circulation by adding the astronomical tidal forcing, parameterized topographic internal wave drag, and self-attraction and loading to the general circulation physics. However, the accuracy of these tidal estimates does not yet match accuracies in the best data-assimilative barotropic tidal models. This paper investigates the application of an Augmented State Ensemble Kalman Filter (ASEnKF) to improve the accuracy of M2 barotropic tides embedded in a 1/12.5° three-dimensional ocean general circulation model. The ASEnKF is an alternative to the techniques typically used with linearized tide-only models; such techniques cannot be applied to the embedded tides in a nonlinear eddying circulation. An extra term, meant to correct for errors in the tide model due to imperfectly known topography and damping terms, is introduced into the tidal forcing. Ensembles of the model are created with stochastically generated forcing correction terms. The discrepancies for each ensemble member with TPXO, an existing data-assimilative tide model, are computed. The ASEnKF method yields an optimal estimate of the model forcing correction terms, that minimizes resultant root mean square (RMS) tidal sea surface elevation error with respect to TPXO, as well as an estimate of the tidal elevation. The deep-water, global area-averaged RMS sea surface elevation error of the principal lunar semidiurnal tide M2 is reduced from 4.4 cm in a best-case non-assimilative solution to 2.6 cm. The largest elevation errors in both the non-assimilative and ASEnKF solutions are in the North Atlantic, a highly resonant basin. Possible pathways for achieving further reductions in the RMS error are discussed.

  13. On improving the accuracy of the M2 barotropic tides embedded in a high-resolution global ocean circulation model

    NASA Astrophysics Data System (ADS)

    Ngodock, Hans E.; Souopgui, Innocent; Wallcraft, Alan J.; Richman, James G.; Shriver, Jay F.; Arbic, Brian K.

    2016-01-01

    The ocean tidal velocity and elevation can be estimated concurrently with the ocean circulation by adding the astronomical tidal forcing, parameterized topographic internal wave drag, and self-attraction and loading to the general circulation physics. However, the accuracy of these tidal estimates does not yet match accuracies in the best data-assimilative barotropic tidal models. This paper investigates the application of an augmented state ensemble Kalman Filter (ASEnKF) to improve the accuracy of M2 barotropic tides embedded in a 1/12.5° three-dimensional ocean general circulation model. The ASEnKF is an alternative to the techniques typically used with linearized tide-only models; such techniques cannot be applied to the embedded tides in a nonlinear eddying circulation. An extra term, meant to correct for errors in the tide model due to imperfectly known topography and damping terms, is introduced into the tidal forcing. Ensembles of the model are created with stochastically generated forcing correction terms. The discrepancies for each ensemble member with TPXO, an existing data-assimilative tide model, are computed. The ASEnKF method yields an optimal estimate of the model forcing correction terms, that minimizes resultant root mean square (RMS) tidal sea surface elevation error with respect to TPXO, as well as an estimate of the tidal elevation. The deep-water, global area-averaged RMS sea surface elevation error of the principal lunar semidiurnal tide M2 is reduced from 4.4 cm in a best-case non-assimilative solution to 2.6 cm. The largest elevation errors in both the non-assimilative and ASEnKF solutions are in the North Atlantic, a highly resonant basin. Possible pathways for achieving further reductions in the RMS error are discussed.

  14. Variability in deep ocean circulation from GRACE

    NASA Astrophysics Data System (ADS)

    Boening, C.; Watkins, M. M.

    2015-12-01

    Although nearly impossible to observe on a global scale, total water mass transport and inter-basin exchange are central to understanding long-term changes in ocean circulation. Of particular interest are changes in the Meridional Overturning Circulation (MOC) as they pose potential impacts in continental climtae. However, in-situ observations are limited in space and time preventing a holistic view of current variability. The representation of long-term transports in ocean models is highly dependent on the atmospheric forcing fields, which may misrepresent real interannual variability. The bottom pressure observations from the Gravity Recovery And Climate Experiment (GRACE) provide for the first time the ability to observe this global water mass transport. Here, we present the first near-global maps of variability in the depth-independent ocean circulation derived from advanced analysis of GRACE data. We find that significant variability on annual to decadal time scales exists in the deep large-scale circulation, some of which are related to the Southern Annular Mode forcing dominating Southern Ocean variability.

  15. Examination of Physical Processes Influencing Coastal Circulation over the Inner Scotian Shelf using a Five-Level Nested-Grid Ocean Circulation Model

    NASA Astrophysics Data System (ADS)

    Sheng, J.

    2008-12-01

    A multiply nested-grid ocean circulation modeling system was developed for coastal waters of the Inner Scotian Shelf (ISS) by coupling a limited-area coastal circulation model to an operational shelf circulation model known as Dalcoast. The nested-grid system has five relocatable, dynamically-downscaling five sub- components. The outermost sub-component of the system has a coarse horizontal resolution of (1/12)o for simulating storm surges and two-dimensional barotropic shelf waves over the eastern Canadian shelf (ECS) from Labrador Shelf to the Gulf of Maine, and the innermost sub-component has a fine horizontal resolution of about ~180 m for simulating three-dimensional circulation and hydrographic distributions over Lunenburg Bay of Nova Scotia in the default setup. The nested-grid system is driven by meteorological and astronomical forcing. The meteorological forcing includes sea level air pressures, wind stress and surface heat/freshwater fluxes converted from the 3 hourly weather forecasts produced by the Meteorological Service of Canada. The astronomical forcing is the tidal sea levels and depth-mean currents produced by WebTide based on pre-calculated harmonic constants of five major tidal constitutes over the ECS. In this study, the nested-grid system is used to investigate main physical processes affecting the three-dimensional (3D) circulation and hydrographic distributions over the ISS in June and July 2006. Model results demonstrate that the coastal circulation and hydrographic distributions over the study region are affected significantly by tides, local wind forcing, remotely generated coastal waves during the study period.

  16. Impacts of Sea Surface Salinity Bias Correction on North Atlantic Ocean Circulation and Climate Variability in the Kiel Climate Model

    NASA Astrophysics Data System (ADS)

    Park, Taewook; Park, Wonsun; Latif, Mojib

    2016-04-01

    We investigated impacts of correcting North Atlantic sea surface salinity (SSS) biases on the ocean circulation of the North Atlantic and on North Atlantic sector mean climate and climate variability in the Kiel Climate Model (KCM). Bias reduction was achieved by applying a freshwater flux correction over the North Atlantic to the model. The quality of simulating the mean circulation of the North Atlantic Ocean, North Atlantic sector mean climate and decadal variability is greatly enhanced in the freshwater flux-corrected integration which, by definition, depicts relatively small North Atlantic SSS biases. In particular, a large reduction in the North Atlantic cold sea surface temperature (SST) bias is observed and a more realistic Atlantic Multidecadal Variability (AMV) simulated. Improvements relative to the non-flux corrected integration also comprise a more realistic representation of deep convection sites, sea ice, gyre circulation and Atlantic Meridional Overturning Circulation (AMOC). The results suggest that simulations of North Atlantic sector mean climate and decadal variability could strongly benefit from alleviating sea surface salinity biases in the North Atlantic, which may enhance the skill of decadal predictions in that region.

  17. A Comparison between the TOPEX/POSEIDON Data and a Global Ocean General Circulation Model during 1992-1993

    NASA Technical Reports Server (NTRS)

    Chao, Yi; Fu, Lee-Lueng

    1995-01-01

    The TOPEX/POSEIDON altimetric sea level observation during 1992-1993 was used to validate the simulation made by a global ocean general circulation model (OGCM) forced by the daily wind stress and heat flux derived from the National Meteorological Center operational analysis. The OGCM is a version of the modular ocean model with a horizontal resolution of 2 deg longitude and 1 deg latitude and 22 levels in the vertical. The model simulation is compared to the observation at spatial scales of the order of 500 km and larger. Only the temporal variations are examined. The variability is composed primarily of the annual cycle and intraseasonal fluctuations (periods shorter than 100 days). The basic features of the annual cycle are simulated well by the model. Major discrepancies are found in the eastern tropical Pacific, as well as the eastern North Pacific and most of the interior of the North Atlantic. The culprit is suspected to be the inadequate heat forcing and mixing parameterizations of the model. Significant intraseasonal variability is found in the central North Pacific and the Southern Ocean. The simulation is highly correlated with the observation at periods from 20 to 100 days. The spatial scales are larger than 1000 km in many places. These variabilities are apparently the barotropic response of the ocean to wind forcing. The results of the study provide a basis for future assimilation of the data into the OGCM for improved description of the large-scale ocean variabilities.

  18. Global Ocean Circulation Modeling with an Isopycnic Coordinate Model. Final Report for May 1, 1998 - April 30, 2002

    SciTech Connect

    Bleck, R.

    2004-05-19

    The overall aim of this project was to continue development of a global version of the Miami Isopycnic Coordinate Ocean Model (MICOM) with the intent of turning it into a full-fledged oceanic component of an earth system model.

  19. Significant Findings: Seasonal Distributions of Global Ocean Chlorophyll and Nutrients With a Coupled Ocean General Circulation, Biogeochemical, and Radiative Model. 2; Comparisons With Satellite and In Situ Data

    NASA Technical Reports Server (NTRS)

    Gregg, Watson W.; Busalacchi, Antonio (Technical Monitor)

    2000-01-01

    A coupled ocean general circulation, biogeochemical, and radiative model was constructed to evaluate and understand the nature of seasonal variability of chlorophyll and nutrients in the global oceans. Biogeochemical processes in the model were determined from the influences of circulation and turbulence dynamics, irradiance availability, and the interactions among three functional phytoplankton groups (diatoms, chlorophytes, and picoplankton) and three nutrients (nitrate, ammonium, and silicate). Basin scale (>1000 km) model chlorophyll seasonal distributions were statistically positively correlated with CZCS chlorophyll in 10 of 12 major oceanographic regions, and with SeaWiFS in all 12. Notable disparities in magnitudes occurred, however, in the tropical Pacific, the spring/summer bloom in the Antarctic, autumn in the northern high latitudes, and during the southwest monsoon in the North Indian Ocean. Synoptic scale (100-1000 km) comparisons of satellite and in situ data exhibited broad agreement, although occasional departures were apparent. Model nitrate distributions agreed with in situ data, including seasonal dynamics, except for the equatorial Atlantic. The overall agreement of the model with satellite and in situ data sources indicated that the model dynamics offer a reasonably realistic simulation of phytoplankton and nutrient dynamics on basin and synoptic scales.

  20. Adaptation of an unstructured-mesh, finite-element ocean model to the simulation of ocean circulation beneath ice shelves

    NASA Astrophysics Data System (ADS)

    Kimura, Satoshi; Candy, Adam S.; Holland, Paul R.; Piggott, Matthew D.; Jenkins, Adrian

    2013-07-01

    Several different classes of ocean model are capable of representing floating glacial ice shelves. We describe the incorporation of ice shelves into Fluidity-ICOM, a nonhydrostatic finite-element ocean model with the capacity to utilize meshes that are unstructured and adaptive in three dimensions. This geometric flexibility offers several advantages over previous approaches. The model represents melting and freezing on all ice-shelf surfaces including vertical faces, treats the ice shelf topography as continuous rather than stepped, and does not require any smoothing of the ice topography or any of the additional parameterisations of the ocean mixed layer used in isopycnal or z-coordinate models. The model can also represent a water column that decreases to zero thickness at the 'grounding line', where the floating ice shelf is joined to its tributary ice streams. The model is applied to idealised ice-shelf geometries in order to demonstrate these capabilities. In these simple experiments, arbitrarily coarsening the mesh outside the ice-shelf cavity has little effect on the ice-shelf melt rate, while the mesh resolution within the cavity is found to be highly influential. Smoothing the vertical ice front results in faster flow along the smoothed ice front, allowing greater exchange with the ocean than in simulations with a realistic ice front. A vanishing water-column thickness at the grounding line has little effect in the simulations studied. We also investigate the response of ice shelf basal melting to variations in deep water temperature in the presence of salt stratification.

  1. Structure and predictability of the El Nino/Southern Oscillation phenomenon in a coupled ocean-atmosphere general circulation model

    SciTech Connect

    Latif, M.; Sterl, A.; Maier-Reimer, E.; Junge, M.M. )

    1993-04-01

    The space-time structure and predictability of the El Nino/Southern Oscillation (ENSO) phenomenon was investigated. Two comprehensive datasets were analyzed by means of an advanced statistical method, one based on observational data and other on data derived from an extended-range integration performed with a coupled ocean atmosphere general circulation model. It is shown that a considerable portion of the ENSO related low-frequency climate variability in both datasets is associated with a cycle implies the possibility of climate predictions in the tropics up to lead times of about one year. This is shown by conducting an ensemble of predictions with our coupled general circulation model. For the first time a coupled model of this type was successfully applied to ENSO predictions. 34 refs., 6 figs.

  2. Comparison of ocean surface solar irradiance in the GLA General Circulation Model and satellite-based calculations

    SciTech Connect

    Chertock, B. ); Sud, Y.C. )

    1993-03-01

    A global, 7-year satellite-based record of ocean surface solar irradiance (SSI) is used to assess the realism of ocean SSI simulated by the nine-layer Goddard Laboratory for Atmospheres (GLA) General Circulation Model (GCM). January and July climatologies of net SSI produced by the model are compared with corresponding satellite climatologies for the world oceans between 54[degrees]N and 54[degrees]S. This comparison of climatologies indicates areas of strengths and weaknesses in the GCM treatment of cloud-radiation interactions, the major source of model uncertainty. Realism of ocean SSI is also important for applications such as incorporating the GLA GCM into a coupled ocean-atmosphere GCM. The results show that the GLA GCM simulates too much SSI in the extratropics and too little in the tropics, especially in the summer hemisphere. These discrepancies reach magnitudes of 60 W m[sup [minus]2] and more. The discrepancies are particularly large in the July case off the western coast of North America. In this region of persistent marine stratus, the GCM climatological values exceed the satellite climatological values by as much as 131 W m[sup [minus]2]. Positive and negative discrepancies in SSI are shown to be consistent with discrepancies in planetary albedo.

  3. Comparison of ocean surface solar irradiance in the GLA General Circulation Model and satellite-based calculations

    NASA Technical Reports Server (NTRS)

    Chertock, Beth; Sud, Y. C.

    1993-01-01

    A global, 7-year satellite-based record of ocean surface solar irradiance (SSI) is used to assess the realism of ocean SSI simulated by the nine-layer Goddard Laboratory for Atmospheres (GLA) General Circulation Model (GCM). January and July climatologies of net SSI produced by the model are compared with corresponding satellite climatologies for the world oceans between 54 deg N and 54 deg S. This comparison of climatologies indicates areas of strengths and weaknesses in the GCM treatment of cloud-radiation interactions, the major source of model uncertainty. Realism of ocean SSI is also important for applications such as incorporating the GLA GCM into a coupled ocean-atmosphere GCM. The results show that the GLA GCM simulates too much SSI in the extratropics and too little in the tropics, especially in the summer hemisphere. These discrepancies reach magnitudes of 60 W/sq m and more. The discrepancies are particularly large in the July case off the western coast of North America. Positive and negative discrepancies in SSI are shown to be consistent with discrepancies in planetary albedo.

  4. Mixed boundary conditions in ocean general circulation models and their influence on the stability of the model`s conveyor belt

    SciTech Connect

    Mikolajewicz, U.; Maier-reimer, E.

    1994-11-01

    When driven under `mixed boundary conditions` coarse resolution ocean general circulation models (OGCMs) generally show a high sensitivity of the present-day thermohaline circulation against perturbations. We will show that an alternative formulation of the boundary condition for temperature, a mixture of prescribed heat fluxes and additional restoring of the sea surface temperature to a climatological boundary temperature with a longer time constant, drastically alters the stability of the modes of the thermohaline circulation. The results from simulations with the Hamburg large-scale geostrophic OGCM indicate that the stability of the mode of the thermohaline circulation with formation of North Atlantic deepwater increases, if the damping of sea surface temperature anomalies is reduced, whereas the opposite is true for the mode without North Atlantic deep water formation. It turns out that the formulation of the temperature boundary condition also affects the variability of the model.

  5. Prognostic residual mean flow in an ocean general circulation model and its relation to prognostic Eulerian mean flow

    SciTech Connect

    Saenz, Juan A.; Chen, Qingshan; Ringler, Todd

    2015-05-19

    Recent 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, we verify our analysis by comparing the flows in an idealized Southern Ocean configuration simulated using the TWA and conventional frameworks with the same mesoscale eddy parameterization.

  6. Prognostic residual mean flow in an ocean general circulation model and its relation to prognostic Eulerian mean flow

    DOE PAGESBeta

    Saenz, Juan A.; Chen, Qingshan; Ringler, Todd

    2015-05-19

    Recent 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 TWAmore » 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, we verify our analysis by comparing the flows in an idealized Southern Ocean configuration simulated using the TWA and conventional frameworks with the same mesoscale eddy parameterization.« less

  7. Simple ocean carbon cycle models

    SciTech Connect

    Caldeira, K.; Hoffert, M.I.; Siegenthaler, U.

    1994-02-01

    Simple ocean carbon cycle models can be used to calculate the rate at which the oceans are likely to absorb CO{sub 2} from the atmosphere. For problems involving steady-state ocean circulation, well calibrated ocean models produce results that are very similar to results obtained using general circulation models. Hence, simple ocean carbon cycle models may be appropriate for use in studies in which the time or expense of running large scale general circulation models would be prohibitive. Simple ocean models have the advantage of being based on a small number of explicit assumptions. The simplicity of these ocean models facilitates the understanding of model results.

  8. Natural variability of the climate as predicted by a simple ocean model with parameterized thermohaline circulation

    SciTech Connect

    Watts, R.G.; Li, S.

    1995-12-31

    Variability of the Earth`s climate can take place on many time scales as a result of internal features. This natural variability is important to humans since it affects such important human enterprises as agriculture, floods, droughts, etc. The authors investigate natural variability within a simple ocean model.

  9. The role of the hydrological cycle and the ocean`s thermohaline circulation in climate change: A multicomponent climate model study. Ph.D. Thesis

    SciTech Connect

    Wang, Huaxiao

    1993-12-31

    Global ocean-atmosphere and ocean-atmosphere-continental ice sheet models are developed to address the question of feedbacks between the hydrological cycle and the global thermohaline circulation capable of explaining the climate changes seen in paleoclimate records of the late Pleistocene and the last deglaciation. The ocean-atmosphere model climate system displays two distinct stable equilibria controlled by latitudinal water vapor transport and the net flux of water vapor from the Atlantic to the Pacific Ocean. If the inter-basin transport is sufficiently large, small changes in water vapor transport over the North Atlantic can effect bifurcation; maximum difference between the modes occurs in the North Atlantic. If the inter-basin transport is from the Pacific to the Atlantic and sufficiently large, latitudinal vapor transport in the North Pacific controls the bifurcations, with maximum changes occurring in the North Pacific. For intermediate values of inter-basin transport, no rapid transitions occur in either basin. In the regime with vapor flux from the Atlantic to the Pacific, one mode has strong production of deep water in the North Atlantic and a large flux of heat to the atmosphere from the high latitude North Atlantic. The other has strong deep water production in the Southern Ocean and weak production in the North Pacific and small heat transport to high-latitude North Atlantic. The ocean-atmosphere-ice sheet system displays feedbacks which produce century/millennium time scale oscillations. The thermohaline circulation plays a central role in these feedbacks because of its transport of both heat and salt. The feedbacks could potentially play a causal role in the century/milliennium climate change seen in the paleoclimate record.

  10. Data Assimilation on HBM Circulation Model within MyOcean2 project

    NASA Astrophysics Data System (ADS)

    Siiriä, Simo-Matti; Axell, Lars

    2014-05-01

    To ensure good quality of the operational marine forecasts, it is very important to keep the state of the operational ocean model as close to the real physical state of the ocean as possible. However, applying observations into a model is far from trivial. In the MyOcean project, the Baltic Monitoring and Forecasting Centre (BALMFC) aims to combine the modelling efforts around Baltic Sea. As a part of this, a data assimilation system, based on optimal interpolation, originally developed in SMHI for HIROMB model has been added in hydrodynamic HIROMB-BOOS Model (HBM). BALMFC aims to create a common framework for operational data assimilation around Baltic Sea. This is done by combining and further developing the existing implementations. As a collaborative work between FMI (Finnish Meteorological Institute), SMHI (Swedish Meteorological and Hydrological Institute), DMI (Danish Meteorological Institute) and BSH (Bundesamt für Seeschifffahrt und Hydrographie), the long term aim is to have one unified data assimilation platform for the Baltic Sea models. As initial phase, the satellite Sea Surface Temperature (SST) has been assimilated. Improvements on the forecast quality will be discussed. To further develop the assimilation system, salinity and temperature measurements from ferryboxes are discussed, as well as the possibilities of assimilating ice observations in the model. We also discuss the possibilities to use ARGO floats as a data source for data assimilation schemes.

  11. Derivation of revised formulae for eddy viscous forces used in the ocean general circulation model

    NASA Technical Reports Server (NTRS)

    Chou, Ru Ling

    1988-01-01

    Presented is a re-derivation of the eddy viscous dissipation tensor commonly used in present oceanographic general circulation models. When isotropy is imposed, the currently-used form of the tensor fails to return to the laplacian operator. In this paper, the source of this error is identified in a consistent derivation of the tensor in both rectangular and earth spherical coordinates, and the correct form of the eddy viscous tensor is presented.

  12. Modelling twentieth century global ocean circulation and iceberg flux at 48°N: implications for west Greenland iceberg discharge

    NASA Astrophysics Data System (ADS)

    Wilton, David J.; Bigg, Grant R.; Hanna, Edward

    2015-11-01

    We have used a coupled ocean-iceberg model to study the variation in global ocean circulation and North Atlantic iceberg flux from 1900 to 2008. The latter component of the study focused particularly on Greenland icebergs feeding into the Labrador Current and past Newfoundland. The model was forced with daily heat, freshwater and wind fluxes from the Twentieth Century Reanalysis. The reanalysis heat fluxes were shown to be offset from the, shorter, NCEP reanalysis and a grid-point correction was applied to this component of the forcing. The model produces a generally realistic ocean circulation, although with an enhanced Atlantic Meridional Overturning largely due to the forcing. The modelled iceberg flux at 48°N is well correlated with the long-term observed flux when using a modelled iceberg discharge that varies in a similar fashion to the highly variable observed flux at 48°N. From this model we infer changes in the spatial and temporal variability of iceberg calving from western Greenland. During the first third of the twentieth century the majority of modelled icebergs reaching 48°N derive from southern Greenland, while only after 1930 is the traditional perspective of a majority of such icebergs originating from Baffin Bay consistent with model results. Decadal-scale changes in the dominant regional sources are found, with oscillations between western Greenland and northern Baffin Bay. The latter origin was modelled to be most important in the last third of the twentieth century, although west Greenland sources have increased in importance in recent years. The model correctly reproduces the pronounced late spring peak in flux at 48°N for southern Greenland icebergs, but has an approximately six month offset for icebergs from Baffin Bay, most likely due to resolution issues leading to model icebergs not being delayed in shallow coastal waters, whereas in reality they may be grounded for some time or trapped in coastal sea-ice.

  13. Data Organization and I/O in a Parallel Ocean Circulation Model

    SciTech Connect

    Ding, Chris H.Q.; He, Yun

    1999-05-01

    We describe an efficient and scalable parallel I/0 strategy for writing out gigabytes of data generated hourly in the ocean model simulations on massively parallel distributed-memory architectures. Working with Modular Ocean Model, using net CIF file system? and implemented on Cray T3E, the strategy speedup I/0 by a factor of 50 in the sequential case. In parallel case, on 8 PEs up to 256 PEs, our implementation writes out most model dynamic fields of about 1GB to a single netCDF file in 65 seconds, independent of the number of processors. The remap-and-write parallel strategy resolves the memory limitation problem and requires minimal collective I/0 capability of the file system. Several critical optimization on memory management and file access are carried out which ensure this scalability and also speedup the numerical simulation due to improved memory management.

  14. Correcting North Atlantic sea surface salinity biases in the Kiel Climate Model: influences on ocean circulation and Atlantic Multidecadal Variability

    NASA Astrophysics Data System (ADS)

    Park, T.; Park, W.; Latif, M.

    2016-01-01

    A long-standing problem in climate models is the large sea surface salinity (SSS) biases in the North Atlantic. In this study, we describe the influences of correcting these SSS biases on the circulation of the North Atlantic as well as on North Atlantic sector mean climate and decadal to multidecadal variability. We performed integrations of the Kiel Climate Model (KCM) with and without applying a freshwater flux correction over the North Atlantic. The quality of simulating the mean circulation of the North Atlantic Ocean, North Atlantic sector mean climate and decadal variability is greatly enhanced in the freshwater flux-corrected integration which, by definition, depicts relatively small North Atlantic SSS biases. In particular, a large reduction in the North Atlantic cold sea surface temperature bias is observed and a more realistic Atlantic Multidecadal Variability simulated. Improvements relative to the non-flux corrected integration also comprise a more realistic representation of deep convection sites, sea ice, gyre circulation and Atlantic Meridional Overturning Circulation. The results suggest that simulations of North Atlantic sector mean climate and decadal variability could strongly benefit from alleviating sea surface salinity biases in the North Atlantic, which may enhance the skill of decadal predictions in that region.

  15. Dynamical budgets of the Antarctic Circumpolar Current using ocean general-circulation models

    NASA Astrophysics Data System (ADS)

    Grezio, A.; Wells, N. C.; Ivchenko, V. O.; de Cuevas, B. A.

    2005-04-01

    Three general-circulation models (FRAM, OCCAM and POP) are used to investigate the dynamics of the Antarctic Circumpolar Current (ACC) at the latitudes of the Drake Passage where the ACC is unbounded. In these general circulation models, bottom form stress balances the wind stress in the momentum budgets. In the vorticity budgets, the main balance is between wind curl and bottom pressure torque in FRAM, OCCAM and POP. Moreover, in the ACC belt all topographic features are regions of nonlinearity and bottom pressure torque variations, with the Drake Passage playing the largest role. Transient eddy Reynolds stresses (TERSs) play a different role in the three models. In the upper levels, TERSs accelerate the flow in the POP and FRAM models, but decelerate the flow in OCCAM. The behaviour of TERSs change throughout the whole water column in the ACC belt and Reynolds stresses have a dragging effect on the flow below the levels where the topography starts to obstruct the flow. The total volume transport in three models is very different. Additionally, the different spatial resolution, which results in a different level of eddy kinetic energy, has a significant influence on the transport.

  16. Slow and Steady: Ocean Circulation. The Influence of Sea Surface Height on Ocean Currents

    NASA Technical Reports Server (NTRS)

    Haekkinen, Sirpa

    2000-01-01

    The study of ocean circulation is vital to understanding how our climate works. The movement of the ocean is closely linked to the progression of atmospheric motion. Winds close to sea level add momentum to ocean surface currents. At the same time, heat that is stored and transported by the ocean warms the atmosphere above and alters air pressure distribution. Therefore, any attempt to model climate variation accurately must include reliable calculations of ocean circulation. Unlike movement of the atmosphere, movement of the ocean's waters takes place mostly near the surface. The major patterns of surface circulation form gigantic circular cells known as gyres. They are categorized according to their general location-equatorial, subtropical, subpolar, and polar-and may run across an entire ocean. The smaller-scale cell of ocean circulation is known' as an eddy. Eddies are much more common than gyres and much more difficult to track in computer simulations of ocean currents.

  17. Modeling evidences for global warming, Arctic seawater freshening, and sluggish oceanic circulation during the Early Toarcian anoxic event

    NASA Astrophysics Data System (ADS)

    Dera, Guillaume; Donnadieu, Yannick

    2012-06-01

    The paleoecological disturbances recorded during the Early Toarcian warming event (183 Myr ago), including marine anoxia, sea level rise, seawater acidification, carbonate production crisis, and species extinctions, are often regarded as past examples of Earth's possible responses to the rapid emergence of super greenhouse conditions. However, physical mechanisms explaining both the global and local expressions of paleoenvironmental events are still highly debated. Here we analyze the paleoclimatic and paleoceanographic consequences of increases in atmospheric pCO2 levels at a multiscale resolution using a fully coupled ocean-atmosphere model (FOAM). We show that, in association with stronger high-latitude precipitation rates and enhanced continental runoff, the demise of polar sea ice due to the global warming event involved a regional freshening of Arctic surface seawaters. These disturbances lead to progressive slowdowns of the global oceanic circulation accountable for widespread ocean stratification and bottom anoxia processes in deep oceanic settings and epicontinental basins. In agreement with very negative oxygen isotope values measured on fossil shells from the NW Tethys, our simulations also show that recurrent discharges of brackish and nutrient-rich Arctic surface waters through the Viking Corridor could have led to both vertical and geographical gradients in salinity and seawater δ18O in the NW Tethyan seas. Locally contrasted conditions in water mass density and rises in productivity rates due to strong nutrient supplies could partly explain the regional severity of the anoxic event in the restricted Euro-boreal domains, as it has been previously suggested and modeled regionally.

  18. Carbon-nitrogen interactions regulate climate-carbon cycle feedbacks: results from an atmosphere-ocean general circulation model

    SciTech Connect

    Thornton, Peter E; Doney, Scott C.; Lindsay, Keith; Moore, Jefferson Keith; Mahowald, Natalie; Randerson, James T; Fung, Inez; Lamarque, Jean-Francois H; Feddema, Johan J.

    2009-01-01

    Inclusion of fundamental ecological interactions between carbon and nitrogen cycles in the land component of an atmosphere-ocean general circulation model (AOGCM) leads to decreased carbon uptake associated with CO{sub 2} fertilization, and increased carbon uptake associated with warming of the climate system. The balance of these two opposing effects is to reduce the fraction of anthropogenic CO{sub 2} predicted to be sequestered in land ecosystems. The primary mechanism responsible for increased land carbon storage under radiatively forced climate change is shown to be fertilization of plant growth by increased mineralization of nitrogen directly associated with increased decomposition of soil organic matter under a warming climate, which in this particular model results in a negative gain for the climate-carbon feedback. Estimates for the land and ocean sink fractions of recent anthropogenic emissions are individually within the range of observational estimates, but the combined land plus ocean sink fractions produce an airborne fraction which is too high compared to observations. This bias is likely due in part to an underestimation of the ocean sink fraction. Our results show a significant growth in the airborne fraction of anthropogenic CO{sub 2} emissions over the coming century, attributable in part to a steady decline in the ocean sink fraction. Comparison to experimental studies on the fate of radio-labeled nitrogen tracers in temperate forests indicates that the model representation of competition between plants and microbes for new mineral nitrogen resources is reasonable. Our results suggest a weaker dependence of net land carbon flux on soil moisture changes in tropical regions, and a stronger positive growth response to warming in those regions, than predicted by a similar AOGCM implemented without land carbon-nitrogen interactions. We expect that the between-model uncertainty in predictions of future atmospheric CO{sub 2} concentration and

  19. Influence of the Central American Seaway and Drake Passage on ocean circulation and neodymium isotopes: A model study

    NASA Astrophysics Data System (ADS)

    Pfister, Patrik L.; Stocker, Thomas F.; Rempfer, Johannes; Ritz, Stefan P.

    2014-12-01

    The sensitivity of the neodymium isotopic composition (ɛNd) to tectonic rearrangements of seaways is investigated using an Earth System Model of Intermediate Complexity. The shoaling and closure of the Central American Seaway (CAS) is simulated, as well as the opening and deepening of Drake Passage (DP). Multiple series of equilibrium simulations with various intermediate depths are performed for both seaways, providing insight into ɛNd and circulation responses to progressive throughflow evolutions. Furthermore, the sensitivity of these responses to the Atlantic Meridional Overturning Circulation (AMOC) and the neodymium boundary source is examined. Modeled ɛNd changes are compared to sediment core and ferromanganese (Fe-Mn) crust data. The model results indicate that the North Atlantic ɛNd response to the CAS shoaling is highly dependent on the AMOC state, i.e., on the AMOC strength before the shoaling to shallow depths (preclosure). Three scenarios based on different AMOC forcings are discussed, of which the model-data agreement favors a shallow preclosure (Miocene) AMOC (˜6 Sv). The DP opening causes a rather complex circulation response, resulting in an initial South Atlantic ɛNd decrease preceding a larger increase. This feature may be specific to our model setup, which induces a vigorous CAS throughflow that is strongly anticorrelated to the DP throughflow. In freshwater experiments following the DP deepening, ODP Site 1090 is mainly influenced by AMOC and DP throughflow changes, while ODP Site 689 is more strongly influenced by Southern Ocean Meridional Overturning Circulation and CAS throughflow changes. The boundary source uncertainty is largest for shallow seaways and at shallow sites.

  20. Coupling of wave and circulation models in coastal-ocean predicting systems: A case study for the German Bight

    NASA Astrophysics Data System (ADS)

    Staneva, Joanna; Wahle, Kathrin

    2015-04-01

    This study addresses the coupling between wind wave and circulation models on the example of the German Bight and its coastal area called the Wadden Sea (the area between the barrier islands and the coast). This topic reflects the increased interest in operational oceanography to reduce prediction errors of state estimates at coastal scales. The uncertainties in most of the presently used models result from the nonlinear feedback between strong tidal currents and wind-waves, which can no longer be ignored, in particular in the coastal zone where its role seems to be dominant. A nested modelling system is used in the Helmholtz-Zentrum Geesthacht to producing reliable now- and short-term forecasts of ocean state variables, including wind waves and hydrodynamics. In this study we present analysis of wave and hydrographic observations, as well as the results of numerical simulations. The data base includes ADCP observations and continuous measurements from data stations. The individual and collective role of wind, waves and tidal forcing are quantified. The performance of the forecasting system is illustrated for the cases of several extreme events. Effects of ocean waves on coastal circulation and SST simulations are investigated considering wave-dependent stress and wave breaking parameterization during extreme events, e.g. hurricane Xavier in December, 2013. Also the effect which the circulation exerts on the wind waves is tested for the coastal areas using different parameterizations. The improved skill resulting from the new developments in the forecasting system, in particular during extreme events, justifies further enhancements of the coastal pre-operational system for the North Sea and German Bight.

  1. The Atlantic Multidecadal Oscillation without a role for ocean circulation.

    PubMed

    Clement, Amy; Bellomo, Katinka; Murphy, Lisa N; Cane, Mark A; Mauritsen, Thorsten; Rädel, Gaby; Stevens, Bjorn

    2015-10-16

    The Atlantic Multidecadal Oscillation (AMO) is a major mode of climate variability with important societal impacts. Most previous explanations identify the driver of the AMO as the ocean circulation, specifically the Atlantic Meridional Overturning Circulation (AMOC). Here we show that the main features of the observed AMO are reproduced in models where the ocean heat transport is prescribed and thus cannot be the driver. Allowing the ocean circulation to interact with the atmosphere does not significantly alter the characteristics of the AMO in the current generation of climate models. These results suggest that the AMO is the response to stochastic forcing from the mid-latitude atmospheric circulation, with thermal coupling playing a role in the tropics. In this view, the AMOC and other ocean circulation changes would be largely a response to, not a cause of, the AMO. PMID:26472908

  2. Ensemble climate simulations using a fully coupled ocean-troposphere-stratosphere general circulation model.

    PubMed

    Huebener, H; Cubasch, U; Langematz, U; Spangehl, T; Niehörster, F; Fast, I; Kunze, M

    2007-08-15

    Long-term transient simulations are carried out in an initial condition ensemble mode using a global coupled climate model which includes comprehensive ocean and stratosphere components. This model, which is run for the years 1860-2100, allows the investigation of the troposphere-stratosphere interactions and the importance of representing the middle atmosphere in climate-change simulations. The model simulates the present-day climate (1961-2000) realistically in the troposphere, stratosphere and ocean. The enhanced stratospheric resolution leads to the simulation of sudden stratospheric warmings; however, their frequency is underestimated by a factor of 2 with respect to observations.In projections of the future climate using the Intergovernmental Panel on Climate Change special report on emissions scenarios A2, an increased tropospheric wave forcing counteracts the radiative cooling in the middle atmosphere caused by the enhanced greenhouse gas concentration. This leads to a more dynamically active, warmer stratosphere compared with present-day simulations, and to the doubling of the number of stratospheric warmings. The associated changes in the mean zonal wind patterns lead to a southward displacement of the Northern Hemisphere storm track in the climate-change signal. PMID:17569652

  3. Pathways of marine debris in statistical and diagnostic ocean circulation models

    NASA Astrophysics Data System (ADS)

    Maximenko, N.; Hafner, J.; Lumpkin, R.

    2012-04-01

    Statistical and diagnostic models are used in this study to describe long-term dynamics of objects floating at the sea surface. The statistical model is based of the particle displacement probability density function, derived from trajectories of drifting buoys, and is supplemented by the probability of running aground. This model reveals five main areas of debris accumulation in the subtropical ocean, all confirmed with direct observations. It also reveals the global pattern of shores impacted by marine debris, correlated with dominant winds. The diagnostic model (SCUD - Surface CUrrents from Diagnostic) utilizes satellite data of altimetry and QuikSCAT/ASCAT winds to assess near-real time surface velocities and its parameters are optimized using drifter trajectories. Numerical experiments with various sources and life times of the model debris help to understand main pathways of the tracer and distributions of its properties within and across individual oceans. Applications of statistical and diagnostic models help to assess probable motion of the debris, generated in Japan by tsunami of March 11, 2011. The timeline, derived from the statistical model, and maps, computed with SCUD, are used to coordinate operational at-sea and on-coast observations and preparations for the debris impact. Most of debris is drifting from Japan towards east, while dispersing over increasing area. After passing Hawaii in the north it is expected to recirculate into the so-called North Pacific Garbage Patch - the area, located between Hawaii and California, where convergent surface currents collect all floating waste. Only a small fraction of tsunami debris, on the edge of the debris field, will "touch" Hawaii and US/Canada west coast. Yet the amount and composition may be anomalous. Mixed with the older waste, tsunami debris will slowly leak from the patch, polluting Hawaiian Islands.

  4. 3D modelling of the ocean circulation in the gulf of Fos

    NASA Astrophysics Data System (ADS)

    Ulses, C.; Grenz, C.; Marsaleix, P.; Schaaff, E.; Estournel, C.; Pinazo, C.

    2003-04-01

    The Gulf of Fos, near Marseille (France), is a semi-enclosed bay covering 42 km2 for a mean depth of 8 m. Freshwater inputs come mainly from the Rhone river, main river of the NW Mediterranean sea which mouth is located on the southwestern part of the gulf. This coastal zone is also influenced by the entrance of water originating from three channels in the northwestern part and from the Berre lagoon which is connected to the gulf through the Caronte channel, in the eastern part. The gulf of Fos is studied with a high horizontal resolution (200 m) three dimensional hydrodynamic model. Academic simulations under typical wind forcing conditions are described. They reveal several features of the exchange of water masses in the Gulf of Fos, in particularly the intrusion of the Rhone river plume generated by south winds. Residence times in the different areas of the Gulf are also investigated. Then a realistic simulation, where Rhone river discharge, meteorological forcing and the surrounding general circulation are taken into account, is presented. This simulation is computed by a chain of three models : a 3-km regional scale model, a 1-km continental shelf model and the coastal model. To assess the quality of the numerical procedure, the model outputs, mainly salinity fields, are compared to MODELFOS2 surveys, that took place in May 2001, as part of the OAERRE program (Oceanographic Application of Eutrophisation in Regions of Restricted Exchanges). The sensitivity of the model results to the wind direction is discussed.

  5. The Determination of the Large-Scale Circulation of the Pacific Ocean from Satellite Altimetry using Model Green's Functions

    NASA Technical Reports Server (NTRS)

    Stammer, Detlef; Wunsch, Carl

    1996-01-01

    A Green's function method for obtaining an estimate of the ocean circulation using both a general circulation model and altimetric data is demonstrated. The fundamental assumption is that the model is so accurate that the differences between the observations and the model-estimated fields obey a linear dynamics. In the present case, the calculations are demonstrated for model/data differences occurring on very a large scale, where the linearization hypothesis appears to be a good one. A semi-automatic linearization of the Bryan/Cox general circulation model is effected by calculating the model response to a series of isolated (in both space and time) geostrophically balanced vortices. These resulting impulse responses or 'Green's functions' then provide the kernels for a linear inverse problem. The method is first demonstrated with a set of 'twin experiments' and then with real data spanning the entire model domain and a year of TOPEX/POSEIDON observations. Our present focus is on the estimate of the time-mean and annual cycle of the model. Residuals of the inversion/assimilation are largest in the western tropical Pacific, and are believed to reflect primarily geoid error. Vertical resolution diminishes with depth with 1 year of data. The model mean is modified such that the subtropical gyre is weakened by about 1 cm/s and the center of the gyre shifted southward by about 10 deg. Corrections to the flow field at the annual cycle suggest that the dynamical response is weak except in the tropics, where the estimated seasonal cycle of the low-latitude current system is of the order of 2 cm/s. The underestimation of observed fluctuations can be related to the inversion on the coarse spatial grid, which does not permit full resolution of the tropical physics. The methodology is easily extended to higher resolution, to use of spatially correlated errors, and to other data types.

  6. A study of the circulation and salinity budget of the Arabian Sea with an isopycnic coordinate ocean model

    NASA Astrophysics Data System (ADS)

    Esenkov, Oleg E.; Olson, Donald B.; Bleck, Rainer

    2003-07-01

    The evolution of surface circulation and salinity budget are studied with the open-boundary version of the Miami Isopycnic Coordinate Ocean Model (MICOM) that uses a global MICOM simulation as a boundary condition. Under climatological wind and thermodynamic forcing, the model develops solutions that are in good agreement with the climatologically forced global MICOM results and with observations. When the observed winds force the model, interannual variability of the surface fields increases significantly. However, coalescence of the two large eddies off Somalia in the end of the summer monsoon suggested in earlier observations does not occur in the model. To identify what processes facilitate or restrict the merger, a series of experiments was performed with modified model parameters and forcing fields. The eddies coalesced when half-slip, rather than no-slip, boundary conditions were used. In this case, less positive vorticity was produced at the coast, resulting in reduced blocking effect on the propagation of the southern eddy. The Socotra Island, which is submerged in the standard model, hinders a northward movement of the Great Whirl, leading to a stronger interaction between the eddies, which results in their subsequent merging. A more realistic coalescence occurs in an experiment where winds are held constant after reaching the peak summer value. Freshwater fluxes from the east and south are important for the salinity budget in the Arabian Sea, where evaporation exceeds precipitation. The only significant cross-equatorial transport of low-salinity water occurs in the upper 400 m in the model. Most of this water is advected below the surface mixed layer at the western boundary. The strongest interaction between the mixed layer and the oceanic interior occurs during the summer in the coastal upwelling regions off Somalia. Almost half of all upwelled water comes from depths between 100 and 200 m, thus signifying the importance of mid-depth circulation and

  7. Simulation of Lake Victoria Circulation Patterns Using the Regional Ocean Modeling System (ROMS).

    PubMed

    Nyamweya, Chrispine; Desjardins, Christopher; Sigurdsson, Sven; Tomasson, Tumi; Taabu-Munyaho, Anthony; Sitoki, Lewis; Stefansson, Gunnar

    2016-01-01

    Lake Victoria provides important ecosystem services including transport, water for domestic and industrial uses and fisheries to about 33 million inhabitants in three East African countries. The lake plays an important role in modulating regional climate. Its thermodynamics and hydrodynamics are also influenced by prevailing climatic and weather conditions on diel, seasonal and annual scales. However, information on water temperature and circulation in the lake is limited in space and time. We use a Regional Oceanographic Model System (ROMS) to simulate these processes from 1st January 2000 to 31st December 2014. The model is based on real bathymetry, river runoff and atmospheric forcing data using the bulk flux algorithm. Simulations show that the water column exhibits annual cycles of thermo-stratification (September-May) and mixing (June-August). Surface water currents take different patterns ranging from a lake-wide northward flow to gyres that vary in size and number. An under flow exists that leads to the formation of upwelling and downwelling regions. Current velocities are highest at the center of the lake and on the western inshore waters indicating enhanced water circulation in those areas. However, there is little exchange of water between the major gulfs (especially Nyanza) and the open lake, a factor that could be responsible for the different water quality reported in those regions. Findings of the present study enhance understanding of the physical processes (temperature and currents) that have an effect on diel, seasonal, and annual variations in stratification, vertical mixing, inshore-offshore exchanges and fluxes of nutrients that ultimately influence the biotic distribution and trophic structure. For instance information on areas/timing of upwelling and vertical mixing obtained from this study will help predict locations/seasons of high primary production and ultimately fisheries productivity in Lake Victoria. PMID:27030983

  8. Simulation of Lake Victoria Circulation Patterns Using the Regional Ocean Modeling System (ROMS)

    PubMed Central

    Sigurdsson, Sven; Tomasson, Tumi; Taabu-Munyaho, Anthony; Sitoki, Lewis; Stefansson, Gunnar

    2016-01-01

    Lake Victoria provides important ecosystem services including transport, water for domestic and industrial uses and fisheries to about 33 million inhabitants in three East African countries. The lake plays an important role in modulating regional climate. Its thermodynamics and hydrodynamics are also influenced by prevailing climatic and weather conditions on diel, seasonal and annual scales. However, information on water temperature and circulation in the lake is limited in space and time. We use a Regional Oceanographic Model System (ROMS) to simulate these processes from 1st January 2000 to 31st December 2014. The model is based on real bathymetry, river runoff and atmospheric forcing data using the bulk flux algorithm. Simulations show that the water column exhibits annual cycles of thermo-stratification (September–May) and mixing (June–August). Surface water currents take different patterns ranging from a lake-wide northward flow to gyres that vary in size and number. An under flow exists that leads to the formation of upwelling and downwelling regions. Current velocities are highest at the center of the lake and on the western inshore waters indicating enhanced water circulation in those areas. However, there is little exchange of water between the major gulfs (especially Nyanza) and the open lake, a factor that could be responsible for the different water quality reported in those regions. Findings of the present study enhance understanding of the physical processes (temperature and currents) that have an effect on diel, seasonal, and annual variations in stratification, vertical mixing, inshore—offshore exchanges and fluxes of nutrients that ultimately influence the biotic distribution and trophic structure. For instance information on areas/timing of upwelling and vertical mixing obtained from this study will help predict locations/seasons of high primary production and ultimately fisheries productivity in Lake Victoria. PMID:27030983

  9. Sensitivity of near-inertial internal waves to spatial interpolations of wind stress in ocean generation circulation models

    NASA Astrophysics Data System (ADS)

    Jing, Zhao; Wu, Lixin; Ma, Xiaohui

    2016-03-01

    The oceanic near-inertial internal waves (NIWs) have been extensively studied using ocean general circulation models (OGCMs). Currently most OGCMs use the bilinear or bicubic interpolation to interpolate wind stress onto models' surface grids. In this study, we examine the influences of bilinear and bicubic interpolations on the wavenumber and frequency spectra of wind stress and on the simulated NIWs in the ocean. It is demonstrated that both the bilinear and bicubic interpolations are equivalent to spatial low-pass filters with the former leading to more significant loss of wind stress variance at high wavenumbers. When coarse (e.g., 2°) wind stress is used to force OGCMs, the bilinear and bicubic interpolations significantly damp the wavenumber spectrum of wind stress at mesoscales, leading to decreased near-inertial wind stress variance. Using the bilinear (bicubic) interpolation could weaken the near-inertial wind work by ∼43% (22%) in the subtropical region (10°N-30°N) and by ∼16% (4%) at the midlatitudes (30°N-50°N). We propose a new interpolation method, i.e., the bi-sinc-function interpolation, which is able to retain all the wind stress variance within the Nyquist wavenumber. Compared to the bilinear and bicubic interpolations, the bi-sinc-function interpolation improves the simulations of NIWs and should be incorporated into OGCMs especially when coarse wind stress is used.

  10. On the effects of constraining atmospheric circulation in a coupled atmosphere-ocean Arctic regional climate model

    NASA Astrophysics Data System (ADS)

    Berg, Peter; Döscher, Ralf; Koenigk, Torben

    2015-08-01

    Impacts of spectral nudging on simulations of Arctic climate in coupled simulations have been investigated in a set of simulations with a regional climate model (RCM). The dominantly circumpolar circulation in the Arctic lead to weak constraints on the lateral boundary conditions (LBCs) for the RCM, which causes large internal variability with strong deviations from the driving model. When coupled to an ocean and sea ice model, this results in sea ice concentrations that deviate from the observed spatial distribution. Here, a method of spectral nudging is applied to the atmospheric model RCA4 in order to assess the potentials for improving results for the sea ice concentrations when coupled to the RCO ocean-sea ice model. The spectral nudging applied to reanalysis driven simulations significantly improves the generated sea ice regarding its temporal evolution, extent and inter-annual trends, compared to simulations with standard LBC nesting. The method is furthermore evaluated with driving data from two CMIP5 GCM simulations for current and future conditions. The GCM biases are similar to the RCA4 biases with ERA-Interim, however, the spectral nudging still improves the surface winds enough to show improvements in the simulated sea ice. For both GCM downscalings, the spectrally nudged version retains a larger sea ice extent in September further into the future. Depending on the sea ice formulation in the GCM, the temporal evolution of the regional sea ice model can deviate strongly.

  11. On the effects of constraining atmospheric circulation in a coupled atmosphere-ocean Arctic regional climate model

    NASA Astrophysics Data System (ADS)

    Berg, Peter; Döscher, Ralf; Koenigk, Torben

    2016-06-01

    Impacts of spectral nudging on simulations of Arctic climate in coupled simulations have been investigated in a set of simulations with a regional climate model (RCM). The dominantly circumpolar circulation in the Arctic lead to weak constraints on the lateral boundary conditions (LBCs) for the RCM, which causes large internal variability with strong deviations from the driving model. When coupled to an ocean and sea ice model, this results in sea ice concentrations that deviate from the observed spatial distribution. Here, a method of spectral nudging is applied to the atmospheric model RCA4 in order to assess the potentials for improving results for the sea ice concentrations when coupled to the RCO ocean-sea ice model. The spectral nudging applied to reanalysis driven simulations significantly improves the generated sea ice regarding its temporal evolution, extent and inter-annual trends, compared to simulations with standard LBC nesting. The method is furthermore evaluated with driving data from two CMIP5 GCM simulations for current and future conditions. The GCM biases are similar to the RCA4 biases with ERA-Interim, however, the spectral nudging still improves the surface winds enough to show improvements in the simulated sea ice. For both GCM downscalings, the spectrally nudged version retains a larger sea ice extent in September further into the future. Depending on the sea ice formulation in the GCM, the temporal evolution of the regional sea ice model can deviate strongly.

  12. An overlooked problem in model simulations of the thermohaline circulation and heat transport in the Atlantic Ocean

    SciTech Connect

    Boening, C.W.; Holland, W.R.; Bryan, F.O.; Danabasoglu, G.; Mcwilliams, J.C. |

    1995-03-01

    Many models of the large-scale thermohaline circulation in the ocean exhibit strong zonally integrated upwelling in the midlatitude North Atlantic that significantly decreases the amount of deep water that is carried from the formation regions in the subpolar North Atlantic toward low latitudes and across the equator. In an analysis of results from the Community Modeling Effort using a suite of models with different horizontal resolution, wind and thermohaline forcing, and mixing parameters, it is shown that the upwelling is always concentrated in the western boundary layer between roughly 30 deg and 40 deg N. The vertical transport across 1000 m appears to be controlled by local dynamics and strongly depends on the horizontal resolution and mixing parameters of the model. It is suggested that in models with a realistic deep-water formation rate in the subpolar North Atlantic, the excessive upwelling can be considered as the prime reason for the typically too low meridional overturning rates and northward heat transports in the subtropical North Atlantic. A new isopycnal advection and mixing parameterization of tracer transports by mesoscale eddies yield substantial improvements in these integral measures of the circulation.

  13. A Reduced Grid Method for a Parallel Global Ocean General Circulation Model

    SciTech Connect

    Wickett, M.E.

    1999-12-01

    A limitation of many explicit finite-difference global climate models is the timestep restriction caused by the decrease in cell size associated with the convergence of meridians near the poles. A computational grid in which the number of cells in the longitudinal direction is reduced toward high-latitudes, keeping the longitudinal width of the resulting cells as uniform as possible and increasing the allowable timestep, is applied to a three-dimensional primitive equation ocean-climate model. This ''reduced'' grid consists of subgrids which interact at interfaces along their northern and southern boundaries, where the resolution changes by a factor of three. Algorithms are developed to extend the finite difference techniques to this interface, focusing on the conservation required to perform long time integrations, while preserving the staggered spatial arrangement of variables and the numerics used on subgrids. The reduced grid eliminates the common alternative of filtering high-frequency modes from the solution at high-latitudes to allow a larger timestep and reduces execution time per model step by roughly 20 percent. The reduced grid model is implemented for parallel computer architectures with two-dimensional domain decomposition and message passing, with speedup results comparable to those of the original model. Both idealized and realistic model runs are presented to show the effect of the interface numerics on the model solution. First, a rectangular, mid-latitude, at-bottomed basin with vertical walls at the boundaries is driven only by surface wind stress to compare three resolutions of the standard grid to reduced grid cases which use various interface conditions. Next, a similar basin with wind stress, heat, and fresh water forcing is used to compare the results of a reduced grid with those of a standard grid result while exercising the full set of model equations. Finally, global model runs, with topography, forcing, and physical parameters similar to

  14. Validating and assessing the sensitivity of the climate model with an ocean general circulation model developed at the Institute of Atmospheric Physics, Russian Academy of Sciences

    NASA Astrophysics Data System (ADS)

    Muryshev, K. E.; Eliseev, A. V.; Mokhov, I. I.; Diansky, N. A.

    2009-08-01

    A new version of the Institute of Atmospheric Physics, Russian Academy of Sciences (IAP RAS), climate model (CM) has been developed using an ocean general circulation model instead of the statistical-dynamical ocean model applied in the previous version. The spatial resolution of the new ocean model is 3° in latitude and 5° in longitude, with 25 unevenly spaced vertical levels. In the previous version of the oceanic model, as in the atmospheric model, the horizontal resolution was 4.5° in latitude and 6° in longitude, with four vertical levels (the upper quasi-homogeneous layer, seasonal thermocline, abyssal ocean, and bottom friction layer). There is no correction for the heat and momentum fluxes between the atmosphere and ocean in the new version of the IAP RAS CM. Numerical experiments with the IAP RAS CM have been performed under current initial and boundary conditions, as well as with an increasing concentration of atmospheric carbon dioxide. The main simulated atmospheric and oceanic fields agree quite well with observational data. The new version’s equilibrium temperature sensitivity to atmospheric CO2 doubling was found to be 2.9 K. This value lies in the mid-range of estimates (2-4.5 K) obtained from simulations with state-of-the-art models of different complexities.

  15. Anthropogenic CO2 uptake, transport, storage, and dynamical controls in the ocean imposed by the meridional overturning circulation: A modeling study

    NASA Astrophysics Data System (ADS)

    Nakano, H.; Ishii, M.; Rodgers, K. B.; Tsujino, H.; Yamanaka, G.

    2015-10-01

    Using an ocean carbon cycle model embedded in an ocean general circulation model, we examine how the budget of anthropogenic CO2 (Cant) is controlled by ocean dynamics. To complement recent studies showing only vertically integrated budgets, we provide a step-by-step description by making use of three different coarse grainings of the full vertical resolution of the ocean model in our budget analysis. For the 11 subdomains of the global ocean, these coarse grainings are (1) a one-layer (vertically integrated) budget, (2) a three-layer budget, and (3) an 11-layer budget. We largely focus on the Pacific circulation. We identify and quantify substantial carbon transport associated with the subtropical cells (STCs), which are dominant contributors to the meridional overturning circulation in the upper ocean in the tropics and subtropics, as playing a fundamental role in governing the ocean interior distribution of Cant. The upper branch of the STCs transports Cant-rich water from the tropics to the subtropics, contributing to the precondition for the high Cant inventory in mode waters. The lower branch of the STCs carries about two thirds of the transported Cant back to the tropics, while it largely excludes Subtropical Mode Waters. This work implies that the reemergence of Cant through recirculation within the STCs may lead to a reduced capacity for further Cant uptake via gas exchange into the surface ocean, potentially contributing to a positive carbon-climate feedback.

  16. Cold-air outbreaks over the ocean at high latitudes and associated mesoscale atmospheric circulations: Problems of numerical modelling

    NASA Astrophysics Data System (ADS)

    Chechin, D. G.; Pichugin, M. K.

    2015-12-01

    A review of the current state of research in the field of numerical modelling and forecasting of cold-air outbreaks over the ocean at high latitudes and associated mesoscale circulations is presented. It is shown that the most relevant tasks are as follows: (1) the improvement of predictability and the adequacy of reproduction of polar mesocyclones, (2) a more adequate representation of the marginal sea-ice zone in the numerical models, and (3) solving problems of the parametrization and explicit reproduction of organized convection and orographic jets in numerical atmosphere models. It is demonstrated that these tasks only can be accomplished as a result of a comprehensive development of different components of the climatic system models and technology of the numerical weather prediction (NWP). One of the most promising approaches to overcome the identified problems is to develop and use methods of satellite remote sensing of the atmosphere and underlying surface in NWP technology. The high potential of analyzing the satellite multisensor data for quantifying parameters of different-scale atmospheric circulations is demonstrated using the example of cold-air outbreaks over the seas of the Far East.

  17. A consistent formulation of the anisotropic stress tensor for use in models of the large-scale ocean circulation

    SciTech Connect

    Wajsowicz, R.C. )

    1993-04-01

    Subgrid-scale dissipation of momentum in numerical models of the large-scale ocean circulation is commonly parameterized as a viscous diffusion resulting from the divergence of a stress tensor of the form [omega] = Au. The form of the fourth-order coefficient tensor A is derived for anisotropic dissipation with an axis of rotational symmetry. Sufficient conditions for A to be positive definite for incompressible flows, so guaranteeing a net positive dissipation of kinetic energy, are found. The divergence of the stress tensor, in Cartesian and spherical polar coordinates, is given for A with constant and spatially varying elements. A consistent form of A and [omega] for use in models based on the Arakawa B- and C-grids is also derived. 16 refs.

  18. A Curvilinear Version of the Bryan-Cox-Semtner Ocean Model and Its Representation of the Arctic Circulation

    NASA Astrophysics Data System (ADS)

    Murray, Ross J.; Reason, C. J. C.

    2001-07-01

    Continuous and finite difference forms of the governing equations are derived for a version of the Bryan-Cox-Semtner ocean general circulation model which has been recast in orthogonal, transversely curvilinear coordinates. The coding closely follows the style of the Geophysical Fluid Dynamics Laboratory modular ocean model No. 1. Curvilinear forms are given for the tracer, internal momentum, and stream function calculations, with the options of horizontal and isopycnal diffusion, eddy-induced transport, nonlinear viscosity, and semiimplicit treatment of the Coriolis force. The model is designed to operate on a rectangular three-dimensional array of points and can accommodate reentrant boundary conditions at both 'northern' and 'east-west' boundaries. Horizontal grid locations are taken as input and need to be supplied by a separate grid generation program. The advantages of using a better behaved and more economical grid in the north polar region are investigated by comparing simulations performed on two curvilinear grids with one performed on a latitude-longitude grid and by comparing filtered and unfiltered latitude-longitude simulations. Resolution of horizontally separated currents in Fram Strait emerges as a key challenge for representing exchanges with the Arctic in global models.

  19. Assessment of the numerical efficiency of ocean circulation model : Hycom contribution to the COMODO project

    NASA Astrophysics Data System (ADS)

    Lathuilière, Cyril; Baraille, Rémy; Le Boyer, Arnaud

    2015-04-01

    The French navy hydrographic service uses a modified version of the Hybrid coordinate ocean model (HYCOM) for operational oceanographic applications. In the framework of the COMODO project, a series of test cases has been carried out to measure the numerical efficiency of the model. It addresses a wide panel of oceanic processes (baroclinic eddy, baroclinic jet, coastal upwelling, internal tides) and is useful to examine most of numerical schemes (advection schemes, time stepping, pressure gradient, …). The objectives of this study are first to assess the numerical performance of the present model to guide the modelers to make the suitable choices, and second to examine how the performances may be improved in the next years. We examine the sensitivity of the main choices for Hycom (2th or 4th order advection schemes, and viscosity values) in baroclinic eddy and baroclinic jet test cases. Both test cases are run using increasing resolution. The highest resolution provides a reference for studying the coarser resolutions. In the baroclinic vortex test case, the second order vector form scheme is well performing whereas the 4th order scheme appears to be more accurate in the baroclinic jet test case. This is probably due to the lack of fine scale energy in the baroclinic vortex test case allowing simulations with very tiny dissipation rates. We focus then on the sensitivity of the performance to vertical coordinate choices. The ability of Hycom to switch between isopycnal coordinate and quasi geopotential coordinate provides useful insights for example on the sensitivity of numerical diapycnal mixing to remapping scheme. This is particularly visible on the internal tide test case. The type of vertical coordinate is also important for potential vorticity structures. The shape of the baroclinic vortex is found to be different in geopotential and isopycnal coordinates. At coarse resolution, the potential vorticity structures seem to be better resolved in isopycnal

  20. Numerical simulation of 137Cs and (239,240)Pu concentrations by an ocean general circulation model.

    PubMed

    Tsumune, Daisuke; Aoyama, Michio; Hirose, Katsumi

    2003-01-01

    We simulated the spatial distributions and the temporal variations of 137Cs and (239,240)Pu concentrations in the ocean by using the ocean general circulation model which was developed by National Center of Atmospheric Research. These nuclides are introduced into seawaters from global fallout due to atmospheric nuclear weapons tests. The distribution of radioactive deposition on the world ocean is estimated from global precipitation data and observed values of annual deposition of radionuclides at the Meteorological Research Institute in Japan and several observed points in New Zealand. Radionuclides from global fallout have been transported by advection, diffusion and scavenging, and this concentration reduces by radioactive decay in the ocean. We verified the results of the model calculations by comparing simulated values of 137Cs and (239,240)Pu in seawater with the observed values included in the Historical Artificial Radionuclides in the HAM database, which has been constructed by the Meteorological Research Institute. The vertical distributions of the calculated 137Cs concentrations were in good agreement and are in good agreement with the observed profiles in the 1960s up to 250 m, in the 1970s up to 500 m, in the 1980s up to 750 m and in the 1990s up to 750 m. However, the calculated 137Cs concentrations were underestimated compared with the observed 137Cs at the deeper layer. This may suggest other transport processes of 137Cs to deep waters. The horizontal distributions of 137Cs concentrations in surface water could be simulated. A numerical tracer release experiment was performed to explain the horizontal distribution pattern. A maximum (239,240)Pu concentration layer occurs at an intermediate depth for both observed and calculated values, which is formed by particle scavenging. The horizontal distributions of the calculated (239,240)Pu concentrations in surface water could be simulated by considering the scavenging effect. PMID:12860090

  1. Inter-comparison of the mean circulation in the Coral and Solomon Sea simulated by high resolution ocean models

    NASA Astrophysics Data System (ADS)

    Maes, C.; Durand, F.; Gasparin, F.; Melet, A.; Ganachaud, A.

    2010-12-01

    Of primary importance to the properties of water masses transported by the northern limb of the South Pacific subtropical gyre toward the equatorial band, the transfer within the Coral and, ultimately, the Solomon Sea is perturbed by the labyrinthine topography of the region. It results in highly energetic currents and complex pathways through the Vanuatu Archipelago and New Caledonia, at the entrance of the Coral Sea, and through the Solomon Sea once the flow has bifurcated northward along the coasts of Australia and of the Louisiade Archipelago of Papua New Guinea. In the Coral Sea, the existence of the North Vanuatu Jet and North Caledonian Jet is now well established but their variations as well as their detailed characteristics, including for instance their vertical extension, remain largely unknown. In this study, recourse to ocean simulations is made in order to highlight the representation of such complex circulation of the south western Pacific Ocean and to analyze the long term variability and physical mechanism implied in the jet dynamics. A brief overview of recent observations collected through the comprehensive observational SPICE program (CLIVAR/WCRP) will first be presented in order to set the context. Then, 6 different state-of-the-art numerical experiments with high horizontal resolution, ranging from 1/10 to 1/12 degree, and realistic topography regionally focused on the Coral and Solomon Sea or extracted from global experiments, are analyzed. Here, we will consider OGCMs forced by realistic and observed atmospheric fields but each model has its own strategy in terms of diffusion, topography representation and boundaries condition when appropriate. The focus is set primarily on the annual mean circulation of the upper ocean layers (above the 1000-m depth) and on the water mass transports simulated in the vicinity of the various topographic obstacles. The results will underline that most of high resolution numerical models have reached a high

  2. Reactive transport modeling of hydrothermal circulation in oceanic crust: effect of anhydrite precipitation on the dynamics of submarine hydrothermal systems

    NASA Astrophysics Data System (ADS)

    Yang, J.

    2009-12-01

    Hydrothermal fluid circulation represents an extremely efficient mechanism for the exchange of heat and matter between seawater and oceanic crust. Precipitation and dissolution of minerals associated with hydrothermal flow at ridge axes can alter the crustal porosity and permeability and hence influence the dynamics of hydrothermal systems. In this study, a fully coupled fluid flow, heat transfer and reactive mass transport model was developed using TOUGHREACT to evaluate the role of mineral precipitation and dissolution on the evolution of hydrothermal flow systems, with a particular attention focused on anhydrite precipitation upon heating of seawater in recharge zones and the resultant change in the crustal porosity and permeability. A series of numerical case studies were carried out to assess the effect of temperature and aqueous phase inflow concentrations on the reactive geochemical system. The impact of chemically induced porosity and permeability changes on the dynamics of hydrothermal systems was also addressed.

  3. Equator-to-Pole and Ocean-Land Temperature Gradients in CMIP5 models and their Relation to Midlatitude Atmospheric Circulation

    NASA Astrophysics Data System (ADS)

    Karamperidou, C.; Booth, J. F.; Lall, U.

    2013-12-01

    Zonal and meridional surface temperature gradients are associated with mean zonal circulation and storm-track variability. We investigate the projected changes in the equator-to-pole gradient and the ocean-land contrast in the suite of models participating in the Coupled Model Intercomparison Project 5 (CMIP5). The projected decrease in the gradients is in accordance with the poleward amplification of temperature increases and the faster warming of land compared to the ocean. However, we note differences in the projections between the Northern and the Southern Hemisphere, and among ocean basins in the Northern Hemisphere, that are indicative of competing mechanisms that underlie the projected shifts in the mean zonal circulation and storm tracks. As an additional indicator of the position and strength of midlatitude mean and transient atmospheric circulation, as well as the expansion of the tropics, we study the projected changes in the latitude of maximum meridional surface temperature gradient.

  4. Changes in Mediterranean circulation and water characteristics due to restriction of the Atlantic connection: a high-resolution ocean model

    NASA Astrophysics Data System (ADS)

    Topper, R. P. M.; Meijer, P. Th.

    2015-02-01

    A high-resolution parallel ocean model is set up to examine how the sill depth of the Atlantic connection affects circulation and water characteristics in the Mediterranean Basin. An analysis of the model performance, comparing model results with observations of the present-day Mediterranean, demonstrates its ability to reproduce observed water characteristics and circulation (including deep water formation). A series of experiments with different sill depths in the Atlantic-Mediterranean connection is used to assess the sensitivity of Mediterranean circulation and water characteristics to sill depth. Basin-averaged water salinity and, to a lesser degree, temperature rise when the sill depth is shallower and exchange with the Atlantic is lower. Lateral and interbasinal differences in the Mediterranean are, however, largely unchanged. The strength of the upper overturning cell in the western basin is proportional to the magnitude of the exchange with the Atlantic, and hence to sill depth. Overturning in the eastern basin and deep water formation in both basins, on the contrary, are little affected by the sill depth. The model results are used to interpret the sedimentary record of the Late Miocene preceding and during the Messinian Salinity Crisis. In the western basin, a correlation exists between sill depth and rate of refreshment of deep water. On the other hand, because sill depth has little effect on the overturning and deep water formation in the eastern basin, the model results do not support the notion that restriction of the Atlantic-Mediterranean connection may cause lower oxygenation of deep water in the eastern basin. However, this discrepancy may be due to simplifications in the surface forcing and the use of a bathymetry different from that in the Late Miocene. We also tentatively conclude that blocked outflow, as found in experiments with a sill depth ≤10 m, is a plausible scenario for the second stage of the Messinian Salinity Crisis during which

  5. Acoustic Studies of the Large Scale Ocean Circulation

    NASA Technical Reports Server (NTRS)

    Menemenlis, Dimitris

    1999-01-01

    Detailed knowledge of ocean circulation and its transport properties is prerequisite to an understanding of the earth's climate and of important biological and chemical cycles. Results from two recent experiments, THETIS-2 in the Western Mediterranean and ATOC in the North Pacific, illustrate the use of ocean acoustic tomography for studies of the large scale circulation. The attraction of acoustic tomography is its ability to sample and average the large-scale oceanic thermal structure, synoptically, along several sections, and at regular intervals. In both studies, the acoustic data are compared to, and then combined with, general circulation models, meteorological analyses, satellite altimetry, and direct measurements from ships. Both studies provide complete regional descriptions of the time-evolving, three-dimensional, large scale circulation, albeit with large uncertainties. The studies raise serious issues about existing ocean observing capability and provide guidelines for future efforts.

  6. Characteristics of the Sinking Branch of the Atlantic Meridional Overturning Circulation in a Global Ocean Model - the Impacts of Model Resolution

    NASA Astrophysics Data System (ADS)

    Katsman, C. A.; Burrillon, E.; Drijfhout, S. S.; Dijkstra, H. A.; Spall, M. A.

    2014-12-01

    The Atlantic Meridional Overturning Circulation (AMOC) plays an important role in climate. The classical view of an ocean conveyor belt with northward surface currents and southward return currents transporting convectively-formed waters from the subpolar North Atlantic Ocean to other ocean basins suggests a tight relation between convection and sinking. However, convection regions feature a large vertical heat and salt transport, but very little vertical mass transport. Instead, it has been argued that the net sinking of dense waters that constitute the sinking branch of the AMOC must take place near boundaries and steep topography rather than in the ocean interior. So far, this theoretical result has been confirmed in highly idealized regional model studies and in laboratory experiments. It is, however, unclear how well the sinking of dense waters is represented in the current generation of ocean models and climate models, and whether the factors driving and controlling the sinking are in accordance with the developed theory. The latter is of crucial importance for the reliability of the projected future behavior of the AMOC and its impacts on climate. In this study, we address this issue by analyzing the outcomes of two global ocean models that differ only in their horizontal resolution (an eddy-permitting version, and a climate-model like version). We analyze the characteristics of the sinking, like the amount and spatial pattern. Moreover, the partition between sinking in the boundary current region and sinking in the interior is quantified. It appears that model resolution (and applied numerical diffusion) have a strong impact on the characteristics of the modeled sinking. These impacts are discussed in light of differences in the characteristics of the subpolar gyre circulation.

  7. Experiences modeling ocean circulation problems on a 30 node commodity cluster with 3840 GPU processor cores.

    NASA Astrophysics Data System (ADS)

    Hill, C.

    2008-12-01

    for which this technology is currently most useful. However, many interesting problems fit within this envelope. Looking forward, we extrapolate our experience to estimate full-scale ocean model performance and applicability. Finally we describe preliminary hybrid mixed 32-bit and 64-bit experiments with graphics cards that support 64-bit arithmetic, albeit at a lower performance.

  8. An empirical model of global climate - Part 1: Reduced impact of volcanoes upon consideration of ocean circulation

    NASA Astrophysics Data System (ADS)

    Canty, T.; Mascioli, N. R.; Smarte, M.; Salawitch, R. J.

    2012-09-01

    Observed reductions in Earth's surface temperature following explosive volcanic eruptions have been used as a proxy for geo-engineering of climate by the artificial enhancement of stratospheric sulfate. Earth cools following major eruptions due to an increase in the reflection of sunlight caused by a dramatic enhancement of the stratospheric sulfate aerosol burden. Significant global cooling has been observed following the four major eruptions since 1900: Santa María, Mount Agung, El Chichón, and Mount Pinatubo, leading IPCC (2007) to state "major volcanic eruptions can thus cause a drop in global mean surface temperature of about half a degree Celsius that can last for months and even years". We use a multiple linear regression model applied to the global surface temperature anomaly to suggest that exchange of heat between the atmosphere and ocean, driven by variations in the strength of the Atlantic Meridional Overturning Circulation (AMOC), has been a factor in the decline of global temperature following these eruptions. The veracity of this suggestion depends on whether the Atlantic Multidecadal Oscillation (AMO) truly represents a proxy for the strength of the AMOC and the precise quantification of global cooling due to volcanoes depends on how the AMO is detrended. If the AMO is detrended using anthropogenic radiative forcing of climate, we find that surface cooling attributed to Mount Pinatubo, using the Hadley Centre/University of East Anglia surface temperature record, maximizes at 0.15 °C globally and 0.35 °C over land. These values are about a factor of 2 less than found when the AMO is neglected in the model and quite a bit lower than the canonical 0.5 °C cooling usually attributed to Pinatubo. The AMO had begun to decrease prior to the four major eruptions, suggesting that exchange of heat between the atmosphere and ocean due to variations in the strength of the AMOC drives the climate system, rather than responds to volcanic perturbations. The

  9. EXPLORING THE FEEDBACKS BETWEEN CRETACEOUS OCEAN CIRCULATION, OCEANIC REDOX DYNAMICS AND SEDIMENT DIAGENESIS

    NASA Astrophysics Data System (ADS)

    Arndt, S.; Godderis, Y.; Donnadieu, Y.; Regnier, P.

    2009-12-01

    The Mid-Cretaceous oceanic anoxic events (OAEs) are witnesses of major perturbations of the Earth climate, which resulted from important changes in structure of the ocean-atmosphere system and its biogeochemical functioning. They are globally well documented by the ubiquitous presence of organic carbon-rich black shale layers. However, the exact nature and functioning of the palaeo-environment that fostered the massive and almost ubiquitous deposition of organic carbon-rich sediments is still a matter of debate. Numerous outstanding questions remain, not only concerning the dependence of black shale deposition on ocean circulation and redox zonation, but also its influence on the global ocean-atmosphere system. A new version of the coupled Earth system model GEOCLIM, which combines a climate model (FOAM 3-D GCM) with a vertically resolved diffusion-advection box model of the global ocean, a pelagic biogeochemical model and a fully formulated diagenetic model (BNRS) is used to examine the feedbacks between paleocirculation, ocean redox dynamics, sediment diagenesis and global climate. Different scenarios are designed to assess the influence of the global circulation on the biogeochemical functioning of the ocean during a mid-Cretaceous OAE. Simulation results illustrate the strong feedbacks between Cretaceous ocean circulation, oceanic geochemical dynamics, bioproductivity and sediment diagenesis. A weakening of the deep ocean ventilation increases the importance of diagenetic processes on the geochemical characteristics of the ocean. Ocean anoxia/euxinia can easily develop if the sedimentary nutrient recycling is high enough to sustain enhanced primary production. Thus, the earth system model provides a rational support for a detailed quantitative understanding of the ocean's biogeochemical response to potential circulation changes during a mid-Cretaceous OAE. It helps identify plausible scenarios for black shale deposition which are compared with simulation

  10. Sustaining observations of the unsteady ocean circulation.

    PubMed

    Frajka-Williams, E

    2014-09-28

    Sustained observations of ocean properties reveal a global warming trend and rising sea levels. These changes have been documented by traditional ship-based measurements of ocean properties, whereas more recent Argo profiling floats and satellite records permit estimates of ocean changes on a near real-time basis. Through these and newer methods of observing the oceans, scientists are moving from quantifying the 'state of the ocean' to monitoring its variability, and distinguishing the physical processes bringing signals of change. In this paper, I give a brief overview of the UK contributions to the physical oceanographic observations, and the role they have played in the wider global observing systems. While temperature and salinity are the primary measurements of physical oceanography, new transbasin mooring arrays also resolve changes in ocean circulation on daily timescales. Emerging technologies permit routine observations at higher-than-ever spatial resolutions. Following this, I then give a personal perspective on the future of sustained observations. New measurement techniques promise exciting discoveries concerning the role of smaller scales and boundary processes in setting the large-scale ocean circulation and the ocean's role in climate. The challenges now facing the scientific community include sustaining critical observations in the case of funding system changes or shifts in government priorities. These long records will enable a determination of the role and response of the ocean to climate change. PMID:25157191

  11. Modeling the Pacific Ocean

    SciTech Connect

    Johnson, M.A.; O'Brien, J.J. )

    1990-01-01

    Two numerical models utilizing primitive equations (two momentum equations and a mass continuity equation) simulate the oceanography of the Pacific Ocean from 20{degrees}S to 50{degrees}N. The authors examine the abundant model data through visualization , by animating the appropriate model fields and viewing the time history of each model simulation as a color movie. The animations are used to aid understanding of ocean circulation.

  12. Design and Implementation of a Parallel Multivariate Ensemble Kalman Filter for the Poseidon Ocean General Circulation Model

    NASA Technical Reports Server (NTRS)

    Keppenne, Christian L.; Rienecker, Michele M.; Koblinsky, Chester (Technical Monitor)

    2001-01-01

    A multivariate ensemble Kalman filter (MvEnKF) implemented on a massively parallel computer architecture has been implemented for the Poseidon ocean circulation model and tested with a Pacific Basin model configuration. There are about two million prognostic state-vector variables. Parallelism for the data assimilation step is achieved by regionalization of the background-error covariances that are calculated from the phase-space distribution of the ensemble. Each processing element (PE) collects elements of a matrix measurement functional from nearby PEs. To avoid the introduction of spurious long-range covariances associated with finite ensemble sizes, the background-error covariances are given compact support by means of a Hadamard (element by element) product with a three-dimensional canonical correlation function. The methodology and the MvEnKF configuration are discussed. It is shown that the regionalization of the background covariances; has a negligible impact on the quality of the analyses. The parallel algorithm is very efficient for large numbers of observations but does not scale well beyond 100 PEs at the current model resolution. On a platform with distributed memory, memory rather than speed is the limiting factor.

  13. A Spectral Element Ocean Model on the Cray T3D: the interannual variability of the Mediterranean Sea general circulation

    NASA Astrophysics Data System (ADS)

    Molcard, A. J.; Pinardi, N.; Ansaloni, R.

    A new numerical model, SEOM (Spectral Element Ocean Model, (Iskandarani et al, 1994)), has been implemented in the Mediterranean Sea. Spectral element methods combine the geometric flexibility of finite element techniques with the rapid convergence rate of spectral schemes. The current version solves the shallow water equations with a fifth (or sixth) order accuracy spectral scheme and about 50.000 nodes. The domain decomposition philosophy makes it possible to exploit the power of parallel machines. The original MIMD master/slave version of SEOM, written in F90 and PVM, has been ported to the Cray T3D. When critical for performance, Cray specific high-performance one-sided communication routines (SHMEM) have been adopted to fully exploit the Cray T3D interprocessor network. Tests performed with highly unstructured and irregular grid, on up to 128 processors, show an almost linear scalability even with unoptimized domain decomposition techniques. Results from various case studies on the Mediterranean Sea are shown, involving realistic coastline geometry, and monthly mean 1000mb winds from the ECMWF's atmospheric model operational analysis from the period January 1987 to December 1994. The simulation results show that variability in the wind forcing considerably affect the circulation dynamics of the Mediterranean Sea.

  14. Response of Northern Hemisphere storm tracks to Indian-western Pacific Ocean warming in atmospheric general circulation models

    NASA Astrophysics Data System (ADS)

    Chu, Cuijiao; Yang, Xiuqun; Ren, Xuejuan; Zhou, Tianjun

    2013-04-01

    With 40 yr integration output of two atmospheric general circulation models (GAMIL/IAP and HadAM3/UKMO) forced with identical prescribed seasonally-varying sea surface temperature, this study examines the effect of the observed Indian-western Pacific Ocean (IWP) warming on the Northern Hemisphere storm tracks (NHSTs). Both models indicate that the observed IWP warming tends to cause both the North Pacific storm track (NPST) and the North Atlantic storm track (NAST) to move northward. Such a consistent effect on the two storm tracks is closely associated with the changes in the low-level atmospheric baroclinicity, high-level jet stream and upper-level geopotential height. The IWP warming can excite a wavelike circum-global teleconnection in the geopotential height that gives rise to an anticyclonic anomaly over the midlatitude North Pacific and a positive-phase NAO anomaly over the North Atlantic. These geopotential height anomalies tend to enhance upper-level zonal westerly winds north of the climatological jet axes and increase low-level baroclinicity and eddy growth rates, thus favoring transient eddy more active north of the climatological storm track axes, responsible for the northward shift of the both storm tracks. The IWP warming-induced northward shift of the NAST is quite similar to the observed, suggesting that the IWP warming can be one of key factors to cause decadal northward shift of the NAST since the 1980s. However, the IWP warming-induced northward shift of the NPST is completely opposite to the observed, implying that the observed southward shift of the NPST since the 1980s would be primarily attributed to other reasons, although the IWP warming can have a cancelling effect against those reasons. Keywords: Northern Hemisphere storm tracks, Indian-western Pacific Ocean warming, baroclinicity, eddy growth rate

  15. Simulation of anthropogenic CO2 uptake in the CCSM3.1 ocean circulation-biogeochemical model: comparison with data-based estimates

    NASA Astrophysics Data System (ADS)

    Wang, S.; Moore, J. K.; Primeau, F. W.; Khatiwala, S.

    2011-11-01

    The global ocean has taken up a large fraction of the CO2 released by human activities since the industrial revolution. Quantifying the oceanic anthropogenic carbon (Cant) inventory and its variability is important for predicting the future global carbon cycle. The detailed comparison of data-based and model-based estimates is essential for the validation and continued improvement of our prediction capabilities. So far, three global estimates of oceanic Cant inventory that are "data-based" and independent of global ocean circulation models have been produced: one based on the ΔC* method, and two are based on reconstructions of the Green function for the surface-to-interior transport, the TTD method and the maximum entropy inversion method (KPH). The KPH method, in particular, is capable of reconstructing the history of Cant inventory through the industrial era. In the present study we use forward model simulations of the Community Climate System Model (CCSM3.1) to estimate the Cant inventory and compare the results with the data-based estimates. We also use the simulations to test several assumptions of the KPH method, including the assumption of constant climate and circulation, which is common to all the data-based estimates. Though the integrated estimates of global Cant inventories are consistent with each other, the regional estimates show discrepancies up to 50 %. The CCSM3 model underestimates the total Cant inventory, in part due to weak mixing and ventilation in the North Atlantic and Southern Ocean. Analyses of different simulation results suggest that key assumptions about ocean circulation and air-sea disequilibrium in the KPH method are generally valid on the global scale, but may introduce significant errors in Cant estimates on regional scales. The KPH method should also be used with caution when predicting future oceanic anthropogenic carbon uptake.

  16. Simulating transoceanic migrations of young loggerhead sea turtles: merging magnetic navigation behavior with an ocean circulation model.

    PubMed

    Putman, Nathan F; Verley, Philippe; Shay, Thomas J; Lohmann, Kenneth J

    2012-06-01

    Young loggerhead sea turtles (Caretta caretta) from eastern Florida, USA, undertake a transoceanic migration in which they gradually circle the Sargasso Sea before returning to the North American coast. Loggerheads possess a 'magnetic map' in which regional magnetic fields elicit changes in swimming direction along the migratory pathway. In some geographic areas, however, ocean currents move more rapidly than young turtles can swim. Thus, the degree to which turtles can control their migratory movements has remained unclear. In this study, the movements of young turtles were simulated within a high-resolution ocean circulation model using several different behavioral scenarios, including one in which turtles drifted passively and others in which turtles swam briefly in accordance with experimentally derived data on magnetic navigation. Results revealed that small amounts of oriented swimming in response to regional magnetic fields profoundly affected migratory routes and endpoints. Turtles that engaged in directed swimming for as little as 1-3 h per day were 43-187% more likely than passive drifters to reach the Azores, a productive foraging area frequented by Florida loggerheads. They were also more likely to remain within warm-water currents favorable for growth and survival, avoid areas on the perimeter of the migratory route where predation risk and thermal conditions pose threats, and successfully return to the open-sea migratory route if carried into coastal areas. These findings imply that even weakly swimming marine animals may be able to exert strong effects on their migratory trajectories and open-sea distributions through simple navigation responses and minimal swimming. PMID:22573765

  17. Importance of ocean circulation in ecological modeling: An example from the North Sea

    NASA Astrophysics Data System (ADS)

    Skogen, Morten D.; Moll, Andreas

    2005-09-01

    There is an increasing number of ecological models for the North Sea around. Skogen and Moll (2000) [Skogen, M.D., Moll, A. 2000. Interannual variability of the North Sea primary production: comparison from two model studies. Continental Shelf Research 20 (2), 129-151] compared the interannual variability of the North Sea primary production using two state-of-the-art ecological models, NORWECOM and ECOHAM1. Their conclusion was that the two models agreed on an annual mean primary production, its variability and the timing and size of the peak production. On the other hand, there was a low (even negative dependent of area) correlation in the production in different years between the two models. In the present work, these conclusions are brought further. To try to better understand the observed differences between the two models, the two ecological models are run in an identical physical setting. With such a set-up also the interannual variability between the two models is in agreement, and it is concluded that the single most important factor for a reliable modeling of phytoplankton and nutrient distributions and transports within the North Sea is a proper physical model.

  18. Exploring the feedbacks between Cretaceous ocean circulation, oceanic redox dynamics and sediment diagenesis

    NASA Astrophysics Data System (ADS)

    Arndt, Sandra; Regnier, Pierre; Donnadieu, Yannick; Godderis, Yves

    2010-05-01

    The Mid-Cretaceous oceanic anoxic events (OAEs) are witnesses of major perturbations of the Earth climate, which resulted from important changes in structure of the ocean-atmosphere system and its biogeochemical functioning. They are globally well documented by the ubiquitous presence of organic carbon-rich black shale layers. However, the exact nature and functioning of the palaeo-environment that fostered the massive and almost ubiquitous deposition of organic carbon-rich sediments is still a matter of debate. Numerous outstanding questions remain, not only concerning the dependence of black shale deposition on ocean circulation and redox zonation, but also its influence on the global ocean-atmosphere system. A new version of the coupled Earth system model GEOCLIM, which combines a climate model (FOAM 3-D GCM) with a vertically resolved diffusion-advection box model of the global ocean, a pelagic biogeochemical model and a fully formulated diagenetic model (BNRS) is used to examine the feedbacks between paleocirculation, ocean redox dynamics, sediment diagenesis and global climate. Different scenarios are designed to assess the influence of the global circulation on the biogeochemical functioning of the ocean during a mid-Cretaceous OAE. Simulation results illustrate the strong feedbacks between Cretaceous ocean circulation, oceanic geochemical dynamics, bioproductivity and sediment diagenesis. A weakening of the deep ocean ventilation increases the importance of diagenetic processes on the geochemical characteristics of the ocean. Ocean anoxia/euxinia can easily develop if the sedimentary nutrient recycling is high enough to sustain enhanced primary production. Thus, the earth system model provides a rational support for a detailed quantitative understanding of the ocean's biogeochemical response to potential circulation changes during a mid-Cretaceous OAE.

  19. Topographic Effects On Wind Driven Oceanic Circulation

    NASA Astrophysics Data System (ADS)

    Bigorre, S.; Dewar, W. K.

    A large scale oceanic anticyclone has been recently observed above the Zapiola Drift in the Argentine Basin. Its transports are comparable to those of the Gulf Stream. Its proximity to the Malvinas-Brazil current confluence render it potentially important to several aspects of the South Atlantic oceanic climate. A conceptual multilayer turbu- lent quasigeostrophic model simulated a comparable anticyclonic circulation in the presence of an isolated topography. The model is able to generate an upslope eddy mass flux, in agreement with downgradient eddy potential vorticity diffusion. Maps of EKE are consistent with the eddy kinetic energy minimum observed by TOPEX above the Zapiola Drift. This paper investigates the time dependent dynamics of the flow, from a 150 years long simulation. Compared to the flat bottom case, the spectrum over the bump is redder, a multi-year (7 years) band is energized, and the mesoscale band is comparatively suppressed. The presence of the 7 years oscillation is variable and connected to an apparent tendency for the flow regime to switch between 'sta- ble' and 'unstable' states. During unstable periods, the phenomenology of the oscil- lation consists of the slow development of a large potential vorticity anomaly above the seamount driven by surface Ekman pumping. This is followed by a rapid ejection phase. In stable regimes, the potential vorticity anomaly can persist for longer peri- ods and is accompanied by a stronger eddy variability. Eddy potential vorticity fluxes show that relative vorticity flux, caused by vortex tube stretching along the slope of the seamount is dominant. A low order relaxation oscillator model has successfully reproduced the results of the turbulent numerical model.

  20. The buoyancy-driven ocean circulation with realistic bathymetry

    NASA Astrophysics Data System (ADS)

    Gjermundsen, Ada; LaCasce, Joseph H.; Denstad, Liv

    2015-04-01

    In contrast to the wind-driven ocean circulation, where the concept of a Sverdrup interior and western boundary currents is generally accepted, we lack a simple dynamical framework for rationalizing the buoyancy-driven circulation. Thus most of our intuition is based on numerical solutions, primarily in idealized basins (e.g. Huck et al., 1999; Park and Bryan, 2001). Here we examine numerical solutions of the global circulation with realistic bathymetry, driven solely by surface buoyancy forcing. Explicit wind forcing is excluded, although vertical mixing is retained. The model (the MITgcm) is run with a hybrid resolution scheme, to capture approximately the variation of the deformation radius. The character of the resulting flow is consistent in many ways with the observed ocean circulation. There is inflow to and sinking in the Nordic Seas, baroclinic western boundary currents and an overturning streamfunction which closely resembles those obtained in full GCMs and in observations. Furthermore, the solutions share many features with solutions obtained with a linear analytical model (Pedlosky, 1969; LaCasce, 2004), suggesting the latter may be conceptually useful, despite lacking bathymetry. We discuss these points, as well as implications for the climate system in general. References: Pedlosky, J. (1969). Linear theory of the circulation of a stratified ocean. Journal of Fluid Mechanics, 35, 185-205. Huck, T., A. J. Weaver and A. Colin de Verdière (1999). On the influence of the parameterization of lateral boundary layers on the thermohaline circulation in coarse-resolution ocean models. Journal of Marine Research, 57(3), 387-426. Park, Y. G. and K. Bryan (2001). Comparison of thermally driven circulations from a depth-coordinate model and an isopycnal-layer model. Part II: The difference and structure of the circulations. Journal of Physical Oceanography, 31(9), 2612-2624. LaCasce, J. H. (2004). Diffusivity and viscosity dependence in the linear thermocline

  1. Currents connecting communities: nearshore community similarity and ocean circulation.

    PubMed

    Watson, J R; Hays, C G; Raimondi, P T; Mitarai, S; Dong, C; McWilliams, J C; Blanchette, C A; Caselle, J E; Siegel, D A

    2011-06-01

    Understanding the mechanisms that create spatial heterogeneity in species distributions is fundamental to ecology. For nearshore marine systems, most species have a pelagic larval stage where dispersal is strongly influenced by patterns of ocean circulation. Concomitantly, nearshore habitats and the local environment are also influenced by ocean circulation. Because of the shared dependence on the seascape, distinguishing the relative importance of the local environment from regional patterns of dispersal for community structure remains a challenge. Here, we quantify the "oceanographic distance" and "oceanographic asymmetry" between nearshore sites using ocean circulation modeling results. These novel metrics quantify spatial separation based on realistic patterns of ocean circulation, and we explore their explanatory power for intertidal and subtidal community similarity in the Southern California Bight. We find that these metrics show significant correspondence with patterns of community similarity and that their combined explanatory power exceeds that of the thermal structure of the domain. Our approach identifies the unique influence of ocean circulation on community structure and provides evidence for oceanographically mediated dispersal limitation in nearshore marine communities. PMID:21797147

  2. Ocean circulation on the North Australian Shelf

    NASA Astrophysics Data System (ADS)

    Schiller, Andreas

    2011-07-01

    The ocean circulation on Australia's Northern Shelf is dominated by the Monsoon and influenced by large-scale interannual variability. These driving forces exert an ocean circulation that influences the deep Timor Sea Passage of the Indonesian Throughflow, the circulation on the Timor and Arafura Shelves and, further downstream, the Leeuwin Current. Seasonal maxima of northeastward (southwestward) volume transports on the shelf are almost symmetric and exceed 10 6 m 3/s in February (June). The associated seasonal cycle of vertical upwelling from June to August south of 8.5°S and between 124°E and 137.5°E exceeds 1.5×10 6 m 3/s across 40 m depth. During El Niño events, combined anomalies from the seasonal means of high regional wind stresses and low inter-ocean pressure gradients double the northeastward volume transport on the North Australian Shelf to 1.5×10 6 m 3/s which accounts for 20% of the total depth-integrated transport across 124°E and reduce the total transport of the Indonesian Throughflow. Variability of heat content on the shelf is largely determined by Pacific and Indian Ocean equatorial wind stress anomalies with some contribution from local wind stress forcing.

  3. Response of Northern Hemisphere storm tracks to Indian-western Pacific Ocean warming in atmospheric general circulation models

    NASA Astrophysics Data System (ADS)

    Chu, Cuijiao; Yang, Xiu-Qun; Ren, Xuejuan; Zhou, Tianjun

    2013-03-01

    With 40 years integration output of two atmospheric general circulation models (GAMIL/IAP and HadAM3/UKMO) forced with identical prescribed seasonally-varying sea surface temperature, this study examines the effect of the observed Indian-western Pacific Ocean (IWP) warming on the Northern Hemisphere storm tracks. Both models indicate that the observed IWP warming tends to cause both the North Pacific storm track (NPST) and the North Atlantic storm track (NAST) to move northward. Such a consistent effect on the two storm tracks is closely associated with the changes in the low-level atmospheric baroclinicity, high-level jet stream and upper-level geopotential height. The IWP warming can excite a wavelike circum-global teleconnection in the geopotential height that gives rise to an anticyclonic anomaly over the midlatitude North Pacific and a positive-phase NAO anomaly over the North Atlantic. These geopotential height anomalies tend to enhance upper-level zonal westerly winds north of the climatological jet axes and increase low-level baroclinicity and eddy growth rates, thus favoring transient eddy more active north of the climatological storm track axes, responsible for the northward shift of the both storm tracks. The IWP warming-induced northward shift of the NAST is quite similar to the observed, suggesting that the IWP warming can be one of the key factors to cause decadal northward shift of the NAST since the 1980s. However, the IWP warming-induced northward shift of the NPST is completely opposite to the observed, implying that the observed southward shift of the NPST since the 1980s would be primarily attributed to other reasons, although the IWP warming can have a cancelling effect against those reasons.

  4. Persistent Cold States of the Tropical Pacific Ocean in an Intermediate Coupled Model and a General Circulation Model

    NASA Astrophysics Data System (ADS)

    Ramesh, N.; Cane, M. A.; Seager, R.

    2014-12-01

    The tropical Pacific Ocean has persistently cool sea surface temperature (SST) anomalies that last several years to a decade, with either no El Niño events or very few weak El Niño events. These have been shown to cause large-scale droughts in the extratropics[i], including the major North American droughts such as the 1930s Dust Bowl, and may also be responsible for modulating the global mean surface temperature[ii]. Here we show that two models with different levels of complexity - the Zebiak-Cane model and the Geophysical Fluid Dynamics Laboratory Coupled Model version 2.1 - are able to produce such periods in a realistic manner. We then test the predictability of these periods in the Zebiak-Cane model using an ensemble of experiments with perturbed initial states. Our results show that the cool mean state is modestly predictable, while the lack of El Niño events during these cool periods is not. These results have implications for our understanding of the origins of such persistent cool states and the possibility of improving predictions of large-scale droughts. Further, we apply this method of using an ensemble of model simulations with perturbed initial states to make retrospective forecasts and to forecast the mean state of the tropical Pacific Ocean for the upcoming decade. Our results suggest, albeit with low confidence, that the current cool mean state will persist. This could imply the continuation of the drier than normal conditions that have, in general, afflicted southwest North America since the 1997/98 El Niño, as well as the current pause in global warming. [i] C. Herweijer and R. Seager, "The global footprint of persistent extra-tropical drought in the instrumental era," International Journal of Climatology, vol. 28, pp. 1761-1774, 2008. [ii] G. A. Meehl, J. M. Arblaster, J. T. Fasullo, A. Hu and K. E. Trenberth, "Model-based evidence of deep-ocean heat uptake during surface-temperature hiatus periods," Nature Climate Change, vol. 1, pp. 360

  5. Sensitivity of the North Atlantic Ocean Circulation to an abrupt change in the Nordic Sea overflow in a high resolution global coupled climate model

    NASA Astrophysics Data System (ADS)

    Zhang, Rong; Delworth, Thomas L.; Rosati, Anthony; Anderson, Whit G.; Dixon, Keith W.; Lee, Hyun-Chul; Zeng, Fanrong

    2011-12-01

    The sensitivity of the North Atlantic Ocean Circulation to an abrupt change in the Nordic Sea overflow is investigated for the first time using a high resolution eddy-permitting global coupled ocean-atmosphere model (GFDL CM2.5). The Nordic Sea overflow is perturbed through the change of the bathymetry in GFDL CM2.5. We analyze the Atlantic Meridional Overturning Circulation (AMOC) adjustment process and the downstream oceanic response to the perturbation. The results suggest that north of 34°N, AMOC changes induced by changes in the Nordic Sea overflow propagate on the slow tracer advection timescale, instead of the fast Kelvin wave timescale, resulting in a time lead of several years between subpolar and subtropical AMOC changes. The results also show that a stronger and deeper-penetrating Nordic Sea overflow leads to stronger and deeper AMOC, stronger northward ocean heat transport, reduced Labrador Sea deep convection, stronger cyclonic Northern Recirculation Gyre (NRG), westward shift of the North Atlantic Current (NAC) and southward shift of the Gulf Stream, warmer sea surface temperature (SST) east of Newfoundland and colder SST south of the Grand Banks, stronger and deeper NAC and Gulf Stream, and stronger oceanic eddy activities along the NAC and the Gulf Stream paths. A stronger/weaker Nordic Sea overflow also leads to a contracted/expanded subpolar gyre (SPG). This sensitivity study points to the important role of the Nordic Sea overflow in the large scale North Atlantic ocean circulation, and it is crucial for climate models to have a correct representation of the Nordic Sea overflow.

  6. Large-scale ocean circulation-cloud interactions reduce the pace of transient climate change

    NASA Astrophysics Data System (ADS)

    Trossman, D. S.; Palter, J. B.; Merlis, T. M.; Huang, Y.; Xia, Y.

    2016-04-01

    Changes to the large-scale oceanic circulation are thought to slow the pace of transient climate change due, in part, to their influence on radiative feedbacks. Here we evaluate the interactions between CO2-forced perturbations to the large-scale ocean circulation and the radiative cloud feedback in a climate model. Both the change of the ocean circulation and the radiative cloud feedback strongly influence the magnitude and spatial pattern of surface and ocean warming. Changes in the ocean circulation reduce the amount of transient global warming caused by the radiative cloud feedback by helping to maintain low cloud coverage in the face of global warming. The radiative cloud feedback is key in affecting atmospheric meridional heat transport changes and is the dominant radiative feedback mechanism that responds to ocean circulation change. Uncertainty in the simulated ocean circulation changes due to CO2 forcing may contribute a large share of the spread in the radiative cloud feedback among climate models.

  7. Large-scale ocean-atmosphere interactions in a simplified coupled model of the midlatitude wintertime circulation

    NASA Technical Reports Server (NTRS)

    Miller, Arthur J.

    1992-01-01

    Midlatitude ocean-atmosphere interactions are studied in simulations from a simplified coupled model that includes synoptic-scale atmospheric variability, ocean current advection of SST, and air-sea heat exchange. Although theoretical dynamical ('identical twin') predictions using this model have shown that the SST anomalies in this model indeed influence the atmosphere, it is found here that standard cross correlation and empirical orthogonal function analyses of monthly mean model output yield the standard result, familiar from observational studies, that the atmosphere forces the ocean with little or no feedback. Therefore, these analyses are inconclusive and leave open the question of whether anomalous SST is influencing the atmosphere. In contrast, it is found that compositing strong warm events of model SST is a useful indicator of ocean forcing the atmosphere. Additional evidence is presented for oceanic influence on the atmosphere, namely, that ocean current advection appears to enhance the persistence of model SST anomalies through a feedback effect that is absent when only heat flux is allowed to influence SST anomaly evolution.

  8. Early concepts and charts of ocean circulation

    NASA Astrophysics Data System (ADS)

    Peterson, R. G.; Stramma, L.; Kortum, G.

    Charts of ocean currents from the late nineteenth century show that already by then the patterns of surface circulation in regions away from polar latitudes were well understood. This fundamental knowledge accumulated gradually through centuries of sea travel and had reached a state of near correctness by the time dedicated research cruises, full-depth measurements and the practical application of the dynamical method were being instituted. Perhaps because of the foregoing, many of the pioneering works, critical to establishing what the upper-level circulation is like, the majority of the charts accompanying them, and several of the groundbreaking theoretical treatments on the physics of currents, are only poorly known to present-day oceanographers. In this paper we trace Western developments in knowledge and understanding of ocean circulation from the earliest times to the late-1800s transition into the modern era. We also discuss certain peripheral advances that proved critical to the subject. The earliest known ideas, dating from the Bronze Age and described by Homer, necessarily reflect severe limitations to geographical knowledge, as well as basic human predilections toward conjecture and exaggeration in the face of inadequate information. People considered the earth to be flat and circular, with the ocean flowing like a river around it. They also believed in horrific whirlpools, a concept that persisted into the Renaissance and which would later provide subject material for modern literature. From the Greek Classical Age, we find hydrologic theories of Earth's interior being laced with subterranean channels (Socrates) and all motion deriving from a divine force forever propelling the heavens toward the west, the primum mobile (Aristotle). These ideas, particularly the latter, dominated opinions about ocean circulation into the late Renaissance. By late Antiquity mariners had very likely acquired intimate knowledge of coastal currents in the Mediterranean, but

  9. Effect of different surface forcings on the circulation and stratification in a global model with focus on the Northwest Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Scholz, Patrick; Lohmann, Gerrit

    2016-04-01

    The subarctic oceans like the Sea of Okhotsk, the Bering Sea, the Labrador Sea or the Greenland-Irminger-Norwegian (GIN) Sea react particularly sensitive to global climate changes and have the potential to reversely regulate climate change by CO2 uptake in the other areas of the world. So far, the natural processes in the Arctic and Subarctic system, especially of the Pacific realm, remains barely studied in terms of sedimentary records, but especially in terms of numerical modeling. In this study we focus on the marginal seas of the Northwest Pacific (e.g. the Sea of Okhotsk, the Bering Sea and the Sea of Japan), which have nowadays a significant role in the climate system of the Northwest Pacific by influencing the atmospheric and oceanic circulation as well as the hydrology of the Pacific water masses. Especially the Sea of Okhotsk is characterized by a highly dynamical sea-ice coverage, where in autumn and winter due to massive sea ice formation and brine rejection, the Sea of Okhotsk Intermediate Water (SOIW) is formed contributing to the mid-depth (500-1000m) water layer of the North Pacific known as newly formed North Pacific Intermediate Water (NPIW). We use the Finite-Element Sea-Ice Ocean Model (FESOM) in a global configuration with a regional focus on the marginal sea of the Northwest Pacific Ocean with a resolution of up to 8 km. As a preliminary study we compare the influence of the Comprehensive Ocean Ice Reference Experiment version 2 (COREv2) and ECMWF Era 40/interim forcing data set on the general circulation and stratification of the Northwest Pacific Ocean. We evaluate the reliability of both forcing data sets based on a comparison with observational derived data from the World Ocean Atlas 2013.

  10. A new model for the global biogeochemical cycle of carbonyl sulfide - Part 1: Assessment of direct marine emissions with an oceanic general circulation and biogeochemistry model

    NASA Astrophysics Data System (ADS)

    Launois, T.; Belviso, S.; Bopp, L.; Fichot, C. G.; Peylin, P.

    2015-03-01

    The global budget of tropospheric carbonyl sulfide (OCS) is believed to be at equilibrium because background air concentrations have remained roughly stable over at least the last decade. Since the uptake of OCS by leaves (associated with photosynthesis) and soils have been revised significantly upwards recently, an equilibrated budget can only be obtained with a compensatory source of OCS. It has been assumed that the missing source of OCS comes from the low-latitude ocean, following the incident solar flux. The present work uses parameterizations of major production and removal processes of organic compounds in the NEMO-PISCES (Nucleus for European Modelling of the Ocean, Pelagic Interaction Scheme for Carbon and Ecosystem Studies) ocean general circulation and biogeochemistry model to assess the marine source of OCS. In addition, the OCS photo-production rates computed with the NEMO-PISCES model~were evaluated independently using the UV absorption coefficient of chromophoric dissolved organic matter (derived from satellite ocean color data) and apparent quantum yields available in the literature. Our simulations show global direct marine emissions of OCS in the range of 573-3997 GgS yr-1, depending mostly on the quantification of the absorption rate of chromophoric dissolved organic matter. The high estimates of that range are unlikely, as they correspond to a formulation that most likely overestimate photo-production process. Low and medium (813 GgS yr-1) estimates derived from the NEMO-PISCES model are however consistent spatially and temporally~with the suggested missing source of Berry et al. (2013), allowing us thus to close the global budget of OCS given the recent estimates of leaf and soil OCS uptake.

  11. Effects of reduced vertical mixing under sea ice on Atlantic meridional overturning circulation (AMOC) in a global ice-ocean model

    NASA Astrophysics Data System (ADS)

    Kim, Sang Yeob; Lee, Ho Jin; Park, Jae-Hun; Kim, Young Ho

    2015-06-01

    Most open ocean and climate models assume a constant background mixing; however, vertical mixing should be reduced under the sea ice in polar region because the sea-ice cover acts as an insulator against the momentum transfer between the atmosphere and ocean. Using a global Ocean General Circulation Model (OGCM), we show that the Atlantic meridional overturning circulation (AMOC) can be substantially affected by reduced vertical mixing under the sea ice. When the background diffusivity under the sea ice is reduced by 1 order less than that in ice-free regions, the volume transport of the AMOC in the upper 3000 m is increased by up to 14% accordingly. The numerical experiment suggests that the reduced background diffusivity makes waters denser in the Arctic Ocean and the denser water is transported into the Nordic Seas to push up the isopycnal surfaces over the Greenland- Iceland-Scotland Ridge. Consequently, the AMOC is enhanced by overflows of the denser water crossing the Denmark Strait.

  12. Early concepts and charts of ocean circulation

    NASA Astrophysics Data System (ADS)

    Peterson, R. G.; Stramma, L.; Kortum, G.

    Charts of ocean currents from the late nineteenth century show that already by then the patterns of surface circulation in regions away from polar latitudes were well understood. This fundamental knowledge accumulated gradually through centuries of sea travel and had reached a state of near correctness by the time dedicated research cruises, full-depth measurements and the practical application of the dynamical method were being instituted. Perhaps because of the foregoing, many of the pioneering works, critical to establishing what the upper-level circulation is like, the majority of the charts accompanying them, and several of the groundbreaking theoretical treatments on the physics of currents, are only poorly known to present-day oceanographers. In this paper we trace Western developments in knowledge and understanding of ocean circulation from the earliest times to the late-1800s transition into the modern era. We also discuss certain peripheral advances that proved critical to the subject. The earliest known ideas, dating from the Bronze Age and described by Homer, necessarily reflect severe limitations to geographical knowledge, as well as basic human predilections toward conjecture and exaggeration in the face of inadequate information. People considered the earth to be flat and circular, with the ocean flowing like a river around it. They also believed in horrific whirlpools, a concept that persisted into the Renaissance and which would later provide subject material for modern literature. From the Greek Classical Age, we find hydrologic theories of Earth's interior being laced with subterranean channels (Socrates) and all motion deriving from a divine force forever propelling the heavens toward the west, the primum mobile (Aristotle). These ideas, particularly the latter, dominated opinions about ocean circulation into the late Renaissance. By late Antiquity mariners had very likely acquired intimate knowledge of coastal currents in the Mediterranean, but

  13. Biogeochemical Proxies in Scleractinian Corals used to Reconstruct Ocean Circulation

    SciTech Connect

    Guilderson, T P; Kashgarian, M; Schrag, D P

    2001-02-23

    We utilize monthly {sup 14}C data derived from coral archives in conjunction with ocean circulation models to address two questions: (1) how does the shallow circulation of the tropical Pacific vary on seasonal to decadal time scales and (2) which dynamic processes determine the mean vertical structure of the equatorial Pacific thermocline. Our results directly impact the understanding of global climate events such as the El Nino-Southern Oscillation (ENSO). To study changes in ocean circulation and water mass distribution involved in the genesis and evolution of ENSO and decadal climate variability, it is necessary to have records of climate variables several decades in length. Continuous instrumental records are limited because technology for continuous monitoring of ocean currents has only recently been available, and ships of opportunity archives such as COADS contain large spatial and temporal biases. In addition, temperature and salinity in surface waters are not conservative and thus can not be independently relied upon to trace water masses, reducing the utility of historical observations. Radiocarbon ({sup 14}C) in sea water is a quasi-conservative water mass tracer and is incorporated into coral skeletal material, thus coral {sup 14}C records can be used to reconstruct changes in shallow circulation that would be difficult to characterize using instrumental data. High resolution {Delta}{sup 14}C timeseries such as these, provide a powerful constraint on the rate of surface ocean mixing and hold great promise to augment onetime surveys such as GEOSECS and WOCE. These data not only provide fundamental information about the shallow circulation of the Pacific, but can be used as a benchmark for the next generation of high resolution ocean models used in prognosticating climate change.

  14. Corrigendum to ``Sensitivity of near-inertial internal waves to spatial interpolations of wind stress in ocean generation circulation models'' [Ocean Modelling 99 (2016) 15-21

    NASA Astrophysics Data System (ADS)

    Jing, Zhao; Wu, Lixin; Ma, Xiaohui

    2016-08-01

    The authors regret that the Acknowledgements section in Jing et al. (2016) neglected to give proper credit to the model development team and to the intellectual work behind the model simulation and wish to add the following acknowledgements: We are very grateful to the developers of the coupled regional climate model (CRCM) used in this study. The CRCM was developed at Texas A&M University by Dr. Raffaele Montuoro under the direction of Dr. Ping Chang, with support from National Science Foundation Grants AGS-1067937 and AGS-1347808, Department of Energy Grant DE-SC0006824, as well as National Oceanic and Atmospheric Administration Grant NA11OAR4310154. The design of the reported CRCM simulations was led by Dr. Ping Chang and carried out by Dr. Xiaohui Ma as a part of her dissertation research under the supervision of Dr. Ping Chang, supported by National Science Foundation Grants AGS-1067937 and AGS-1347808. The authors would like to apologise for any inconvenience caused.

  15. Responses of the Tropical Pacific to Wind Forcing as Observed by Spaceborne Sensors and Simulated by an Ocean General Circulation Model

    NASA Technical Reports Server (NTRS)

    Liu, W. Timothy; Tang, Qenqing; Atlas, Robert

    1996-01-01

    In this study, satellite observations, in situ measurements, and model simulations are combined to assess the oceanic response to surface wind forcing in the equatorial Pacific. The surface wind fields derived from observations by the spaceborne special sensor microwave imager (SSM/I) and from the operational products of the European Centre for Medium-Range Weather Forecasts (ECMWF) are compared. When SSM/I winds are used to force a primitive-equation ocean general circulation model (OGCM), they produce 3 C more surface cooling than ECMWF winds for the eastern equatorial Pacific during the cool phase of an El Nino-Southern Oscillation event. The stronger cooling by SSM/I winds is in good agreement with measurements at the moored buoys and observations by the advanced very high resolution radiometer, indicating that SSM/I winds are superior to ECMWF winds in forcing the tropical ocean. In comparison with measurements from buoys, tide gauges, and the Geosat altimeter, the OGCM simulates the temporal variations of temperature, steric, and sea level changes with reasonable realism when forced with the satellite winds. There are discrepancies between model simulations and observations that are common to both wind forcing fields, one of which is the simulation of zonal currents; they could be attributed to model deficiencies. By examining model simulations under two winds, vertical heat advection and uplifting of the thermocline are found to be the dominant factors in the anomalous cooling of the ocean mixed layer.

  16. A new model for the global biogeochemical cycle of carbonyl sulfide - Part 1: Assessment of direct marine emissions with an oceanic general circulation and biogeochemistry model

    NASA Astrophysics Data System (ADS)

    Launois, T.; Belviso, S.; Bopp, L.; Fichot, C. G.; Peylin, P.

    2014-08-01

    The global budget of tropospheric carbonyl sulfide (OCS) is believed to be at equilibrium because background air concentrations have remained roughly stable over at least the last decade. Since the uptakes of OCS by leaves (associated to photosynthesis) and soils have been revised significantly upwards recently, an equilibrated budget can only be obtained with a compensatory source of OCS. It has been assumed that the missing source of OCS comes from the low latitude ocean, following the incident solar flux. The present work uses parameterizations of major production and removal processes of organic compounds in the NEMO-PISCES Ocean General Circulation and Biogeochemistry Model to assess the marine source of OCS. In addition, the OCS photo-production rates computed with the NEMO-PISCES model were evaluated independently using UV absorption coefficient of chromophoric dissolved organic matter (derived from satellite ocean color) and apparent quantum yields available in the literature. Our simulations show global direct marine emissions of COS in the range of 573-3997 Gg S yr-1, depending mostly on the quantification of the absorption rate of chromophoric dissolved organic matter. The high estimates on that range are unlikely, as they correspond to a formulation that most likely overestimate photo-production process. Low and medium (813 Gg S yr-1) estimates derived from the NEMO-PISCES model are however consistent spatially and temporally with the suggested missing source of Berry et al. (2013), allowing thus to close the global budget of OCS given the recent estimates of leaf and soil OCS uptakes.

  17. The World Ocean Circulation Experiment (WOCE): An ocean climatology for the 1990s

    SciTech Connect

    Chapman, P.; Nowlin, W.D. Jr.

    1997-11-01

    During the last ten years, scientists have made remarkable progress in predicting seasonal and interannual climate variability, based on interactions between the atmosphere and the tropical ocean. The goals of the World Ocean Circulation Experiment (WOCE) are to develop models useful for predicting climate variability on longer time scales and to collect the data from the global ocean necessary to test them. Using a variety of instrument platforms, researchers in the US and other nations have been sampling a suite of ocean variables which will be used to build up a climatology of the oceans in the 1990s and from the basis for developing both new models of ocean circulation and coupled models of the ocean and atmosphere. This paper presents some recent results from WOCE research. It includes examples of advances in the fields of sea surface temperature measurements, sea level monitoring, current velocities, upper ocean heat content, and air-sea flux measurements. In addition, we discuss some of the recent advances in modeling and the link between WOCE research and future programs such as CLIVAR, GOOS and GCOS. 27 refs., 2 tabs.

  18. The impact of oceanic heat transport on the atmospheric circulation

    NASA Astrophysics Data System (ADS)

    Knietzsch, M.-A.; Schröder, A.; Lucarini, V.; Lunkeit, F.

    2015-09-01

    A general circulation model of intermediate complexity with an idealized Earth-like aquaplanet setup is used to study the impact of changes in the oceanic heat transport on the global atmospheric circulation. Focus is on the atmospheric mean meridional circulation and global thermodynamic properties. The atmosphere counterbalances to a large extent the imposed changes in the oceanic heat transport, but, nonetheless, significant modifications to the atmospheric general circulation are found. Increasing the strength of the oceanic heat transport up to 2.5 PW leads to an increase in the global mean near-surface temperature and to a decrease in its equator-to-pole gradient. For stronger transports, the gradient is reduced further, but the global mean remains approximately constant. This is linked to a cooling and a reversal of the temperature gradient in the tropics. Additionally, a stronger oceanic heat transport leads to a decline in the intensity and a poleward shift of the maxima of both the Hadley and Ferrel cells. Changes in zonal mean diabatic heating and friction impact the properties of the Hadley cell, while the behavior of the Ferrel cell is mostly controlled by friction. The efficiency of the climate machine, the intensity of the Lorenz energy cycle and the material entropy production of the system decline with increased oceanic heat transport. This suggests that the climate system becomes less efficient and turns into a state of reduced entropy production as the enhanced oceanic transport performs a stronger large-scale mixing between geophysical fluids with different temperatures, thus reducing the available energy in the climate system and bringing it closer to a state of thermal equilibrium.

  19. Numerical simulation and prediction of coastal ocean circulation

    SciTech Connect

    Chen, P.

    1992-01-01

    Numerical simulation and prediction of coastal ocean circulation have been conducted in three cases. 1. A process-oriented modeling study is conducted to study the interaction of a western boundary current (WBC) with coastal water, and its responses to upstream topographic irregularities. It is hypothesized that the interaction of propagating WBC frontal waves and topographic Rossby waves are responsible for upstream variability. 2. A simulation of meanders and eddies in the Norwegian Coastal Current (NCC) for February and March of 1988 is conducted with a newly developed nested dynamic interactive model. The model employs a coarse-grid, large domain to account for non-local forcing and a fine-grid nested domain to resolve meanders and eddies. The model is forced by wind stresses, heat fluxes and atmospheric pressure corresponding Feb/March of 1988, and accounts for river/fjord discharges, open ocean inflow and outflow, and M[sub 2] tides. The simulation reproduced fairly well the observed circulation, tides, and salinity features in the North Sea, Norwegian Trench and NCC region in the large domain and fairly realistic meanders and eddies in the NCC in the nested region. 3. A methodology for practical coastal ocean hindcast/forecast is developed, taking advantage of the disparate time scales of various forcing and considering wind to be the dominant factor in affecting density fluctuation in the time scale of 1 to 10 days. The density field obtained from a prognostic simulation is analyzed by the empirical orthogonal function method (EOF), and correlated with the wind; these information are then used to drive a circulation model which excludes the density calculation. The method is applied to hindcast the circulation in the New York Bight for spring and summer season of 1988. The hindcast fields compare favorably with the results obtained from the prognostic circulation model.

  20. The Seasonal Variability of the South Indian Ocean Circulation

    NASA Astrophysics Data System (ADS)

    Matano, R. P.; Beier, E. J.; Strub, P. T.

    2006-07-01

    This article compares the seasonal variability patterns of the South Indian Ocean circulation derived from a global, eddy-permitting, numerical model and altimeter observations. The seasonal variability of the Indian Ocean circulation is driven by the inflow from the Indonesian Passages and by the local wind forcing. Our analysis indicates that the influence of the Indonesian throughflow is confined to the easternmost portion of the basin, while the influence of the wind stress forcing is important everywhere. Model and observations indicates that, between ~105°E and 75°E, the seasonal variability is characterized by the southwestward propagation of an annual wave in a lapse of ~4 months. Preliminary calculations using Pathfinder data also indicates that, in the western region, there are seasonal perturbations that originates in the tropics and propagates poleward through the Mozambique Channel.

  1. Global environmental cycling of gamma-HCH and DDT in the 1980s--a study using a coupled atmosphere and ocean general circulation model.

    PubMed

    Guglielmo, Francesca; Lammel, Gerhard; Maier-Reimer, Ernst

    2009-09-01

    A coupled atmosphere-ocean general circulation model, ECHAM5-MPIOM, was used to study the multicompartmental cycling and long-range transport of persistent and semivolatile organics. Multiphase systems in air and ocean are covered by submodels for atmospheric aerosols, HAM, and marine biogeochemistry, HAMOCC5, respectively. The model, furthermore, encompasses 2D surface compartments, i.e. top soil, vegetation surfaces and sea-ice. The total environmental fate of gamma-hexachlorocyclohexane (gamma-HCH, lindane) and dichlorophenyltrichloroethane (DDT) in agriculture were studied. DDT is mostly present in the soils, the water-soluble gamma-HCH in soils and ocean. DDT has the longest residence time in almost all compartments. Quasi-steady state with regard to substance accumulation is reached within a few years in air and vegetation surfaces. In seawater the partitioning to suspended and sinking particles contributes to the vertical transport of substances. On the global scale deep water formation is, however, found to be more efficient. Up to 30% of DDT but only less than 0.2% of gamma-HCH in seawater are stored in particulate matter. On the time scale studied (1 decade) and on global scale substance transport in the environment is determined by the fast atmospheric circulation. The meridional transport mechanism, for both compounds, is significantly enhanced by multi-hopping. Net meridional transport in the ocean is effective only regionally, mostly by currents along the western boundaries of Africa and the Americas. The total environmental burdens of the substances experience a net northward migration from their source regions, which is more pronounced for DDT than for gamma-HCH. Due to the application distribution, however, after 10 years of simulation 21% of the global environmental burden of gamma-HCH and 12% of DDT have accumulated in the Arctic. PMID:19576616

  2. Ocean Surface Circulation with Implication for Marine Debris Distribution

    NASA Astrophysics Data System (ADS)

    Hafner, Jan; Maximenko, Nikolai; Niiler, Peter

    2010-05-01

    Modern, multi-instrumental Global Ocean Observing System (GOOS) includes satellites and in situ observations, monitoring the ocean state at the highest accuracy and resolution ever. By combining data of satellite altimetry, surface drifters, wind and gravity, ocean currents can be assessed globally and at research quality. The map of the mean surface currents shows a complex pattern of oceanic fronts and gyres. Distinct are the convergences of Ekman currents in subtropical gyres that, through the Sverdrup mechanism, are feeding anticyclonic circulation in the gyres. Drifter trajectories can also be utilized to simulate the evolution of the marine debris. Main problem is the inhomogeneous drifter data density, both due to convergence/divergence of the ocean currents and due to the drifter deployment scheme. A model constructed from statistics of the drifters exchange between small bins corrects this bias and was run from the uniform initial condition to study the fate of debris in the ocean. In addition to such actively studied debris accumulation areas as the Great Garbage Patch in the North Pacific, a new so far unrecognized, the world-strongest convergence is discovered in the South Pacific from the model solution. The same model reveals a complex pattern of convergence/divergence on the cold/warm flanks of major oceanic fronts. This pattern is studied in the framework of nonlinear interaction between Ekman drift and geostrophic baroclinic fronts outcropping at the sea surface. Results are generalized to assess the dynamics of internal Ekman layer distributed along the thermocline and controlling the secondary circulation at the fronts.

  3. Reconstructing Ocean Circulation using Coral (triangle)14C Time Series

    SciTech Connect

    Kashgarian, M; Guilderson, T P

    2001-02-23

    We utilize monthly {sup 14}C data derived from coral archives in conjunction with ocean circulation models to address two questions: (1) how does the shallow circulation of the tropical Pacific vary on seasonal to decadal time scales and (2) which dynamic processes determine the mean vertical structure of the equatorial Pacific thermocline. Our results directly impact the understanding of global climate events such as the El Nino-Southern Oscillation (ENSO). To study changes in ocean circulation and water mass distribution involved in the genesis and evolution of ENSO and decadal climate variability, it is necessary to have records of climate variables several decades in length. Continuous instrumental records are limited because technology for continuous monitoring of ocean currents (e.g. satellites and moored arrays) has only recently been available, and ships of opportunity archives such as COADS contain large spatial and temporal biases. In addition, temperature and salinity in surface waters are not conservative and thus can not be independently relied upon to trace water masses, reducing the utility of historical observations. Radiocarbon in sea water is a quasi-conservative water mass tracer and is incorporated into coral skeletal material, thus coral {sup 14}C records can be used to reconstruct changes in shallow circulation that would be difficult to characterize using instrumental data. High resolution {Delta}{sup 14}C timeseries such as ours, provide a powerful constraint on the rate of surface ocean mixing and hold great promise to augment one time oceanographic surveys. {Delta}{sup 14}C timeseries such as these, not only provide fundamental information about the shallow circulation of the Pacific, but can also be directly used as a benchmark for the next generation of high resolution ocean models used in prognosticating climate. The measurement of {Delta}{sup 14}C in biological archives such as tree rings and coral growth bands is a direct record of

  4. Consequences of future increased Arctic runoff on Arctic Ocean stratification, circulation, and sea ice cover

    NASA Astrophysics Data System (ADS)

    Nummelin, Aleksi; Ilicak, Mehmet; Li, Camille; Smedsrud, Lars H.

    2016-01-01

    The Arctic Ocean has important freshwater sources including river runoff, low evaporation, and exchange with the Pacific Ocean. In the future, we expect even larger freshwater input as the global hydrological cycle accelerates, increasing high-latitude precipitation, and river runoff. Previous modeling studies show some robust responses to high-latitude freshwater perturbations, including a strengthening of Arctic stratification and a weakening of the large-scale ocean circulation; some idealized modeling studies also document a stronger cyclonic circulation within the Arctic Ocean itself. With the broad range of scales and processes involved, the overall effect of increasing runoff requires an understanding of both the local processes and the broader linkages between the Arctic and surrounding oceans. Here we adopt a more comprehensive modeling approach by increasing river runoff to the Arctic Ocean in a coupled ice-ocean general circulation model, and show contrasting responses in the polar and subpolar regions. Within the Arctic, the stratification strengthens, the halocline and Atlantic Water layer warm, and the cyclonic circulation spins up, in agreement with previous work. In the subpolar North Atlantic, the model simulates a colder and fresher water column with weaker barotropic circulation. In contrast to the estuarine circulation theory, the volume exchange between the Arctic Ocean and the surrounding oceans does not increase with increasing runoff. While these results are robust in our model, we require experiments with other model systems and more complete observational syntheses to better constrain the sensitivity of the climate system to high-latitude freshwater perturbations.

  5. Temporal variations and trends of CFC11 and CFC12 surface-water saturations in Antarctic marginal seas: Results of a regional ocean circulation model

    NASA Astrophysics Data System (ADS)

    Rodehacke, Christian B.; Roether, Wolfgang; Hellmer, Hartmut H.; Hall, Timothy

    2010-02-01

    The knowledge of chlorofluorocarbon (CFC11, CFC12) concentrations in ocean surface waters is a prerequisite for deriving formation rates of, and water mass ages in, deep and bottom waters on the basis of CFC data. In the Antarctic coastal region, surface-layer data are sparse in time and space, primarily due to the limited accessibility of the region. To help filling this gap, we carried out CFC simulations using a regional ocean general circulation model (OGCM) for the Southern Ocean, which includes the ocean-ice shelf interaction. The simulated surface layer saturations, i.e. the actual surface concentrations relative to solubility-equilibrium values, are verified against available observations. The CFC surface saturations driven by concentration gradients between atmosphere and ocean are controlled mainly by the sea ice cover, sea surface temperature, and salinity. However, no uniform explanation exists for the controlling mechanisms. Here, we present simulated long-term trends and seasonal variations of surface-layer saturation at Southern Ocean deep and bottom water formation sites and other key regions, and we discuss differences between these regions. The amplitudes of the seasonal saturation cycle vary from 22% to 66% and their long-term trends range from 0.1%/year to 0.9%/year. The seasonal surface saturation maximum lags the ice cover minimum by two months. By utilizing observed bottle data the full seasonal CFC saturation cycle can be determined offering the possibility to predict long-term trends in the future. We show that ignoring the trends and using instead the saturations actually observed can lead to systematic errors in deduced inventory-based formation rates by up to 10% and suggest an erroneous decline with time.

  6. OCEAN CIRCULATION. Observing the Atlantic Meridional Overturning Circulation yields a decade of inevitable surprises.

    PubMed

    Srokosz, M A; Bryden, H L

    2015-06-19

    The importance of the Atlantic Meridional Overturning Circulation (AMOC) heat transport for climate is well acknowledged. Climate models predict that the AMOC will slow down under global warming, with substantial impacts, but measurements of ocean circulation have been inadequate to evaluate these predictions. Observations over the past decade have changed that situation, providing a detailed picture of variations in the AMOC. These observations reveal a surprising degree of AMOC variability in terms of the intraannual range, the amplitude and phase of the seasonal cycle, the interannual changes in strength affecting the ocean heat content, and the decline of the AMOC over the decade, both of the latter two exceeding the variations seen in climate models. PMID:26089521

  7. Interannual variability in the stratospheric-tropospheric circulation in a coupled ocean-atmosphere GCM

    SciTech Connect

    Kitoh, Akio; Koide, Hiroshi; Kodera, Kunihiko

    1996-03-01

    The authors look for interannual variations in circulation patterns in the stratosphere/troposphere circulation and sea surface temperatures within the Meteorological Research Institute coupled ocean-atmosphere general circulation model. They are able to identify two modes in this model which exhibit this type of variability. One involves the stratospheric polar vortex, coupled via tropospheric circulation to SST variations. The second mode involves El Nino type phenomena coupled into the tropospheric subtropical jet.

  8. A model of the general ocean circulation determined from a joint solution for the Earth's gravity field

    NASA Technical Reports Server (NTRS)

    Nerem, R. S.; Tapley, B. D.; Shum, C. K.; Yuan, D. N.

    1989-01-01

    If the geoid and the satellite position are known accurately, satellite altimetry can be used to determine the geostrophic velocity of the surface ocean currents. The purpose of this investigation is to simultaneously estimate the sea surface topography, zeta, the model for the gravity field, and the satellite orbit. Satellite tracking data from fourteen satellites were used; along with Seasat and Geosat altimeter data as well as surface gravity data for the solution. The estimated model of zeta compares well at long wavelengths with the hydrographic model of zeta. Covariance studies show that the geoid is separable from zeta up to degree 9, at which point geoid error becomes comparable to the signal of zeta.

  9. Simulated Atlantic Meridional Overturning Circulation in the 20th century with an ocean model forced by reanalysis-based atmospheric data sets

    NASA Astrophysics Data System (ADS)

    He, Yan-Chun; Drange, Helge; Gao, Yongqi; Bentsen, Mats

    2016-04-01

    Global ocean hindcast simulations for the period 1871-2009 have been run with the ocean-sea ice component of the Norwegian Earth System Model (NorESM-O), forced by an adjusted version of the Twentieth Century Reanalysis version 2 data set (20CRv2 data set), as well as by the commonly used second version of atmospheric forcing data set for the Coordinated Ocean-ice Reference Experiments phase-II (CORE-II) for the period 1948-2007 (hereafter CORE.v2 data set). The simulated Atlantic Meridional Overturning Circulation (AMOC) in the 20CR and the CORE simulations have comparable variability as well as mean strength during the last three decades of the integration. The simulated AMOC undergoes, however, distinctly different evolutions during the period 1948-1970, with a sharply declining strength in CORE but a gradual increase in 20CR. Sensitivity experiments suggest that differences in the wind forcing between CORE and 20CR have major impact on the simulated AMOCs during this period. It is furthermore found that differences in the air temperature between the two data sets do contribute to the differences in AMOC, but to a much lesser degree than the wind. An additional factor for the diverging AMOC in the two decades following 1948 is the inevitable switching of atmospheric forcing fields in 1948 in the CORE.v2-based runs due to the cyclic spin-up procedure of the ocean model. The latter is a fundamental issue for any ocean hindcast simulation. The ocean initial state mainly influence the actual value but to a lesser degree also the temporal evolution (variability) of AMOC. It may take about two decades for the AMOC to adjust to a new atmospheric state during the spin-up, although a dynamically balanced ocean initial state tends to reduce the adjustment time and the magnitude of the deviation, implying that an ocean model run with atmospheric forcing fields extending back in time, like 20CRv2, can be used to extend the reliable duration of CORE-type of simulations.

  10. Simulated Atlantic Meridional Overturning Circulation in the 20th century with an ocean model forced by reanalysis-based atmospheric data sets

    NASA Astrophysics Data System (ADS)

    He, Yan-Chun; Drange, Helge; Gao, Yongqi; Bentsen, Mats

    2016-04-01

    Global ocean hindcast simulations for the period 1871--2009 have been run with the ocean-sea ice component of the Norwegian Earth System Model (NorESM-O), forced by an adjusted version of the Twentieth Century Reanalysis version 2 data set (20CRv2 data set), as well as by the commonly used second version of atmospheric forcing data set for the Coordinated Ocean-ice Reference Experiments phase-II (CORE-II) for the period 1948--2007 (hereafter CORE.v2 data set). The simulated Atlantic Meridional Overturning Circulation (AMOC) in the 20CR and the CORE simulations have comparable variability as well as mean strength during the last three decades of the integration. The simulated AMOC undergoes, however, distinctly different evolutions during the period 1948--1970, with a sharply declining strength in CORE but a gradual increase in 20CR. Sensitivity experiments suggest that differences in the wind forcing between CORE and 20CR have major impact on the simulated AMOCs during this period. It is furthermore found that differences in the air temperature between the two data sets do contribute to the differences in AMOC, but to a much lesser degree than the wind. An additional factor for the diverging AMOC in the two decades following 1948 is the inevitable switching of atmospheric forcing fields in 1948 in the CORE.v2-based runs due to the cyclic spin-up procedure of the ocean model. The latter is a fundamental issue for any ocean hindcast simulation. The ocean initial state mainly influence the actual value but to a lesser degree also the temporal evolution (variability) of AMOC. It may take about two decades for the AMOC to adjust to a new atmospheric state during the spin-up, although a dynamically balanced ocean initial state tends to reduce the adjustment time and the magnitude of the deviation, implying that an ocean model run with atmospheric forcing fields extending back in time, like 20CRv2, can be used to extend the reliable duration of CORE-type of simulations.

  11. Multiple-scale hydrothermal circulation in 135 Ma oceanic crust of the Japan Trench outer rise: Numerical models constrained with heat flow observations

    NASA Astrophysics Data System (ADS)

    Ray, Labani; Kawada, Yoshifumi; Hamamoto, Hideki; Yamano, Makoto

    2015-09-01

    Anomalous high heat flow is observed within 150 km seaward of the trench axis at the Japan Trench offshore of Sanriku, where the old Pacific Plate (˜135 Ma) is subducting. Individual heat flow values range between 42 and 114 mW m-2, with an average of ˜70 mW m-2. These values are higher than those expected from the seafloor age based on thermal models of the oceanic plate, i.e., ˜50 mW m-2. The heat flow exhibits spatial variations at multiple scales: regional high average heat flow (˜100 km) and smaller-scale heat flow peaks (˜1 km). We found that hydrothermal mining of heat from depth due to gradual thickening of an aquifer in the oceanic crust toward the trench axis can yield elevated heat flow of the spatial scale of ˜100 km. Topographic effects combined with hydrothermal circulation may account for the observed smaller-scale heat flow variations. Hydrothermal circulation in high-permeability faults may result in heat flow peaks of a subkilometer spatial scale. Volcanic intrusions are unlikely to be a major source of heat flow variations at any scale because of limited occurrence of young volcanoes in the study area. Hydrothermal heat transport may work at various scales on outer rises of other subduction zones as well, since fractures and faults have been well developed due to bending of the incoming plate.

  12. World Ocean Circulation Experiment (WOCE) Young Investigator Workshops

    NASA Technical Reports Server (NTRS)

    Austin, Meg

    2004-01-01

    The World Ocean Circulation Experiment (WOCE) Young Investigator Workshops goals and objectives are: a) to familiarize Young Investigators with WOCE models, datasets and estimation procedures; b) to offer intensive hands-on exposure to these models ard methods; c) to build collaborations among junior scientists and more senior WOCE investigators; and finally, d) to generate ideas and projects leading to fundable WOCE synthesis projects. To achieve these goals and objectives, the Workshop will offer a mixture of tutorial lectures on numerical models and estimation procedures, advanced seminars on current WOCE synthesis activities and related projects, and the opportunity to conduct small projects which put into practice the techniques advanced in the lectures.

  13. The seasonal variation of the upper layers of the South China Sea (SCS) circulation and the Indonesian through flow (ITF): An ocean model study

    NASA Astrophysics Data System (ADS)

    Xu, Danya; Malanotte-Rizzoli, Paola

    2013-09-01

    The upper layer, wind-driven circulation of the South China Sea (SCS), its through-flow (SCSTF) and the Indonesian through flow (ITF) are simulated using a high resolution model, FVCOM (finite volume coastal ocean model) in a regional domain comprising the Maritime Continent. The regional model is embedded in the MIT global ocean general circulation model (ogcm) which provides surface forcing and boundary conditions of all the oceanographic variables at the lateral open boundaries in the Pacific and Indian oceans. A five decade long simulation is available from the MITgcm and we choose to investigate and compare the climatologies of two decades, 1960-1969 and 1990-1999. The seasonal variability of the wind-driven circulation produced by the monsoon system is realistically simulated. In the SCS the dominant driving force is the monsoon wind and the surface circulation reverses accordingly, with a net cyclonic tendency in winter and anticyclonic in summer. The SCS circulation in the 90s is weaker than in the 60s because of the weaker monsoon system in the 90s. In the upper 50 m the interaction between the SCSTF and ITF is very important. The southward ITF can be blocked by the SCSTF at the Makassar Strait during winter. In summer, part of the ITF feeds the SCSTF flowing into the SCS through the Karimata Strait. Differently from the SCS, the ITF is primarily controlled by the sea level difference between the western Pacific and eastern Indian Ocean. The ITF flow, consistently southwestward below the surface layer, is stronger in the 90s. The volume transports for winter, summer and yearly are estimated from the simulation through all the interocean straits. On the annual average, there is a ∼5.6 Sv of western Pacific water entering the SCS through the Luzon Strait and ∼1.4 Sv exiting through the Karimata Strait into the Java Sea. Also, ∼2 Sv of SCS water enters the Sulu Sea through the Mindoro Strait, while ∼2.9 Sv flow southwards through the Sibutu Strait

  14. The Ocean`s Thermohaline Circulation in a Fish Tank

    NASA Astrophysics Data System (ADS)

    Lavender, K.; Joyce, P.; Graziano, L.; Harris, S.; Jaroslow, G.; Lea, C.; Schell, J.; Witting, J.

    2005-12-01

    This demonstration develops intuition about density stratification, a concept critical to understanding the ocean`s thermohaline circulation. In addition, students learn how temperature and salinity affect density, how these characteristics may be density-compensating, and students gain practice in graphing and interpreting vertical profiles and temperature-salinity (T-S) diagrams. The demonstration requires a rectangular fish tank (5-10 gallons) with a plexiglass partition, preparation of three colored ''water masses'' representing surface water (warm and fresh), ''mystery'' Mediterranean Water (warm and salty), and North Atlantic Deep Water (NADW; cold and salty), a kitchen sponge, and a temperature and salinity probe. Density may be computed using an Equation of State calculator (e.g. online version at http://fermi.jhuapl.edu/denscalc.html). The larger side of the fish tank is filled halfway with NADW, then surface water is layered on top by carefully pouring it on a floating sponge. A student volunteer measures the temperature and salinity of the two water masses, while another computes the densities. Students draw vertical profiles and T-S diagrams representing the temperature, salinity, and density of the water column. The properties of the ''mystery'' water are measured and students predict what will happen when the water is poured on the opposite side of the partition and is allowed to overflow into the layered water. If the density gradients are sufficiently large, a beautiful internal wave develops as the mystery water overflows the sill and becomes intermediate Mediterranean Water. If time permits, having a student blow on the surface illustrates the limited influence of ''wind'' with depth; an internal wave may by forced by depressing the thermocline with a large, flat spoon; and pouring extra NADW on the sponge floating at the surface may illustrate deep convection.

  15. A note on the symmetric and antisymmetric constituents of weakly nonlinear solutions of a classical wind-driven ocean circulation model

    NASA Astrophysics Data System (ADS)

    Crisciani, Fulvio; Badin, Gualtiero

    2014-07-01

    A classical model of wind-driven ocean circulation is studied in the weakly nonlinear approximation. An asymptotic expansion for small Rossby number is applied to the separate symmetric and asymmetric components of the stream function, where the symmetry refers to a north-south reflection transformation. The asymptotic expansion allows for the formulation of a coupled set of nonlinear partial differential equations for the two components. Results show that the asymmetric component is responsible for the formation of steady cyclones and anticyclones that cause the deformation of the total stream function of the system. Higher-order components of the stream function in the asymptotic expansion are forced by an effective wind stress arising from lower-order entries in the Jacobian term, and these effective stresses act only to redistribute vorticity.

  16. Changes in Mediterranean circulation and water characteristics due to restriction of the Atlantic connection: a high-resolution parallel ocean model

    NASA Astrophysics Data System (ADS)

    Topper, R. P. M.; Meijer, P. Th.

    2014-07-01

    A high-resolution parallel ocean model is set up to examine how the sill depth of the Atlantic connection affects circulation and water characteristics in the Mediterranean Basin. An analysis of the model performance, comparing model results with observations on the present-day Mediterranean, demonstrates its ability to reproduce observed water characteristics and circulation (including deep water formation). A series of experiments with different sill depths in the Atlantic-Mediterranean connection is used to assess the sensitivity of Mediterranean circulation and water characteristics to sill depth. Basin-averaged water salinity and, to a lesser degree, temperature rise when the sill depth is less and exchange with the Atlantic is lower. Lateral and interbasinal differences in the Mediterranean are, however, largely unchanged. The strength of the upper overturning cell in the western basin is proportional to the magnitude of the exchange with the Atlantic, and hence to sill depth. Overturning in the eastern basin and deep water formation in both basins, on the contrary, are little affected by the sill depth. The model results are used to interpret the sedimentary record of the Late Miocene preceding and during the Messinian Salinity Crisis. In the western basin a correlation exists between sill depth and rate of refreshment of deep water. On the other hand, because sill depth has little effect on the overturning and deep water formation in the eastern basin, the model results do not support the notion that restriction of the Atlantic-Mediterranean connection may cause lower oxygenation of deep water in the eastern basin. However, this discrepancy may be due to simplifications in the surface forcing and the use of a bathymetry different from that in the Late Miocene. We also tentatively conclude that blocked outflow, as found in experiments with a sill depth ≤10 m, is a plausible scenario for the second stage of the Messinian Salinity Crisis during which

  17. Interpolation of On-Line Data of the Argo Float System for Data Assimilation in the World Ocean Circulation Model

    NASA Astrophysics Data System (ADS)

    Zakharova, N. B.; Lebedev, S. A.

    2010-12-01

    For many years parameters of the World ocean state were measured by traditional contact methods that lacked in efficiency and the ability to measure temperature much beneath the surface. The ARGO float system involves both contact and distance ocean parameters measure methods. Sea temperature and salinity profiles are measured by contact methods, but data communication is made using satellites. Therefore, the ARGO float system has added efficiency and greater reliability to ocean parameters measurements. Interpolation and extrapolation methods of input information are important among numerical mathematical methods used for solving data assimilation problems. Thus the development of such algorithms and programs based on up-to-date approaches is a timely problem.

  18. Global thermohaline circulation and ocean-atmosphere coupling

    NASA Astrophysics Data System (ADS)

    Wang, Xiaoli

    1997-09-01

    A global ocean general circulation model (GCM) with idealized geometry (two basins of equal size, Marotzke and Willebrand, 1991) is coupled to an energy balance atmospheric model with nonlinear parameterizations of meridional atmospheric transports of heat and moisture. With the coupled model that prescribes the atmospheric heat and moisture transports, the North Atlantic meridional mass overturning rates at equilibrium increases as the global hydrological cycle strength increases. Furthermore, the equilibrium overturning rate is primarily controlled by the hydrological cycle of the Southern Hemisphere, whereas the Northern Hemispheric hydrological cycle has little impact. The transition of the thermohaline circulation from the conveyor belt to the southern sinking state is controlled by two factors, the hydrological cycle in Northern Hemisphere, and the ratio of hydrological cycle strengths between the Northern Hemisphere and the Southern Hemisphere. Increasing either of them destabilizes the thermohaline circulation. The large-scale dynamics of the North Atlantic overturning is mainly interhemispheric, with the bulk of the overturning rising in the Southern Hemisphere. Multiple intermediate states exist that are only quantitatively different, under very small salinity perturbations. The coupled feedbacks between the thermohaline circulation and the atmospheric heat and moisture transports are demonstrated to exist in the coupled model, and all of them are positive. In addition, it is identified that the coupled feedbacks associated with the atmospheric transports in the Southern Hemisphere are also positive. Two different flux adjustments are used in the coupled model, with one adjusting the atmospheric transports efficiencies, the other adjusting the surface fluxes. Different flux adjustments influence the coupled feedback intensities, and hence the stability of the thermohaline circulation. (Copies available exclusively from MIT Libraries, Rm. 14

  19. The Southwest Pacific Ocean circulation and climate experiment (SPICE)

    NASA Astrophysics Data System (ADS)

    Ganachaud, A.; Cravatte, S.; Melet, A.; Schiller, A.; Holbrook, N. J.; Sloyan, B. M.; Widlansky, M. J.; Bowen, M.; Verron, J.; Wiles, P.; Ridgway, K.; Sutton, P.; Sprintall, J.; Steinberg, C.; Brassington, G.; Cai, W.; Davis, R.; Gasparin, F.; Gourdeau, L.; Hasegawa, T.; Kessler, W.; Maes, C.; Takahashi, K.; Richards, K. J.; Send, U.

    2014-11-01

    The Southwest Pacific Ocean Circulation and Climate Experiment (SPICE) is an international research program under the auspices of CLIVAR. The key objectives are to understand the Southwest Pacific Ocean circulation and the South Pacific Convergence Zone (SPCZ) dynamics, as well as their influence on regional and basin-scale climate patterns. South Pacific thermocline waters are transported in the westward flowing South Equatorial Current (SEC) toward Australia and Papua-New Guinea. On its way, the SEC encounters the numerous islands and straits of the Southwest Pacific and forms boundary currents and jets that eventually redistribute water to the equator and high latitudes. The transit in the Coral, Solomon, and Tasman Seas is of great importance to the climate system because changes in either the temperature or the amount of water arriving at the equator have the capability to modulate the El Niño-Southern Oscillation, while the southward transports influence the climate and biodiversity in the Tasman Sea. After 7 years of substantial in situ oceanic observational and modeling efforts, our understanding of the region has much improved. We have a refined description of the SPCZ behavior, boundary currents, pathways, and water mass transformation, including the previously undocumented Solomon Sea. The transports are large and vary substantially in a counter-intuitive way, with asymmetries and gating effects that depend on time scales. This paper provides a review of recent advancements and discusses our current knowledge gaps and important emerging research directions.

  20. A numerical method for the study of the circulation of the world ocean

    SciTech Connect

    Bryan, K.

    1997-08-01

    This paper describes a detail computational procedure involving a finite difference numerical schemes to study the circulation models of the world oceans. To obtain an efficient numerical method for low-frequency, large-scale current systems, surfaces gravity-inertial waves are filtered out by the rigid-lid approximation. Special features of the ocean circulation are resolved in the numerical model by allowing for a variable spacing in either the zonal or meridional direction. 20 refs., 5 figs., 1 tab.

  1. Extensive analysis of potentialities and limitations of a maximum cross-correlation technique for surface circulation by using realistic ocean model simulations

    NASA Astrophysics Data System (ADS)

    Doronzo, Bartolomeo; Taddei, Stefano; Brandini, Carlo; Fattorini, Maria

    2015-08-01

    As shown in the literature, ocean surface circulation can be estimated from sequential satellite imagery by using the maximum cross-correlation (MCC) technique. This approach is very promising since it offers the potential to acquire synoptic-scale coverage of the surface currents on a quasi-continuous temporal basis. However, MCC has also many limits due, for example, to cloud cover or the assumption that Sea Surface Temperature (SST) or other surface parameters from satellite imagery are considered as conservative passive tracers. Also, since MCC can detect only advective flows, it might not work properly in shallow water, where local heating and cooling, upwelling and other small-scale processes have a strong influence. Another limitation of the MCC technique is the impossibility of detecting currents moving along surface temperature fronts. The accuracy and reliability of MCC can be analysed by comparing the estimated velocities with those measured by in situ instrumentation, but the low number of experimental measurements does not allow a systematic statistical study of the potentials and limitations of the method. Instead, an extensive analysis of these features can be done by applying the MCC to synthetic imagery obtained from a realistic numerical ocean model that takes into account most physical phenomena. In this paper a multi-window (MW-) MCC technique is proposed, and its application to synthetic imagery obtained by a regional high-resolution implementation of the Regional Ocean Modeling System (ROMS) is discussed. An application of the MW-MCC algorithm to a real case and a comparison with experimental measurements are then shown.

  2. A paleoceanographic circulation and chemistry model

    SciTech Connect

    Southam, J.R. )

    1990-01-09

    We have developed a 3-D circulation and tracer field model for paleoceanographic applications. The development of the model was motivated by the desire to explore Cretaceous Oceanic Anoxic Events and ocean chemistry during glacial and interglacial modes of circulation. The bulk of paleoceanographic data is the consequences of biological processes operating in ancient oceans. This type of data represents the response to environmental conditions and can be used to reconstruct water mass properties. To infer both wind driven and thermohaline components of circulation in ancient oceans requires a model which relates circulation and water mass properties. With this motivation in mind we have formulated a model which satisfies the following criteria: (1) geostrophically balanced interior, (2) multiple sites for deep water production, (3) deep water production described by entraining plumes, (4) high vertical resolution in both velocity and property fields, (5) meridional varibility in wind stress and evaporation-precipitation rate, (6) applicable to basin scale where exchange with adjacent oceans described by flux conditions, and (7) the chemistry is coupled through the flux of particulate carbon sinking through the interior.

  3. The seasonal and inter-annual variability of sea-ice, ocean circulation and marine ecosystems in the Barents Sea: model results against satellite data

    NASA Astrophysics Data System (ADS)

    Dvornikov, Anton; Sein, Dmitry; Ryabchenko, Vladimir; Gorchakov, Victor; Pugalova, Svetlana

    2015-04-01

    This study is aimed at modelling the seasonal and inter-annual variability of sea-ice, ocean circulation and marine ecosystems in the Barents Sea in the modern period. Adequate description of marine ecosystems in the ice-covered seas crucially depends on the accuracy in determining of thicknesses of ice and snow on the sea surface which control penetrating photosynthetically active radiation under the ice. One of the few models of ice able to adequately reproduce the dynamics of sea ice is the sea ice model HELMI [1], containing 7 different categories of ice. This model has been imbedded into the Princeton Ocean Model. With this coupled model 2 runs for the period 1998-2007 were performed under different atmospheric forcing prescribed from NCEP/NCAR and ERA-40 archives. For prescribing conditions at the open boundary, all the necessary information about the horizontal velocity, level, temperature and salinity of the water, ice thickness and compactness was taken from the results of the global ocean general circulation model of the Max Planck Institute for Meteorology (Hamburg, Germany) MPIOM [2]. The resulting solution with NCEP forcing with a high accuracy simulates the seasonal and inter-annual variability of sea surface temperature (SST) estimated from MODIS data. The maximum difference between the calculated and satellite-derived SSTs (averaged over 4 selected areas of the Barents Sea) during the period 2000-2007 does not exceed 1.5 °C. Seasonal and inter-annual variations in the area of ice cover are also in good agreement with satellite-derived estimates. Pelagic ecosystem model developed in [3] has been coupled into the above hydrodynamic model and used to calculate the changes in the characteristics of marine ecosystems under NCEP forcing. Preliminarily the ecosystem model has been improved by introducing a parameterization of detritus deposition on the bottom and through the selection of optimal parameters for photosynthesis and zooplankton grazing

  4. Antarctic glaciation caused ocean circulation changes at the Eocene-Oligocene transition.

    PubMed

    Goldner, A; Herold, N; Huber, M

    2014-07-31

    Two main hypotheses compete to explain global cooling and the abrupt growth of the Antarctic ice sheet across the Eocene-Oligocene transition about 34 million years ago: thermal isolation of Antarctica due to southern ocean gateway opening, and declining atmospheric CO2 (refs 5, 6). Increases in ocean thermal stratification and circulation in proxies across the Eocene-Oligocene transition have been interpreted as a unique signature of gateway opening, but at present both mechanisms remain possible. Here, using a coupled ocean-atmosphere model, we show that the rise of Antarctic glaciation, rather than altered palaeogeography, is best able to explain the observed oceanographic changes. We find that growth of the Antarctic ice sheet caused enhanced northward transport of Antarctic intermediate water and invigorated the formation of Antarctic bottom water, fundamentally reorganizing ocean circulation. Conversely, gateway openings had much less impact on ocean thermal stratification and circulation. Our results support available evidence that CO2 drawdown--not gateway opening--caused Antarctic ice sheet growth, and further show that these feedbacks in turn altered ocean circulation. The precise timing and rate of glaciation, and thus its impacts on ocean circulation, reflect the balance between potentially positive feedbacks (increases in sea ice extent and enhanced primary productivity) and negative feedbacks (stronger southward heat transport and localized high-latitude warming). The Antarctic ice sheet had a complex, dynamic role in ocean circulation and heat fluxes during its initiation, and these processes are likely to operate in the future. PMID:25079555

  5. Southern Ocean origin for the resumption of Atlantic thermohaline circulation during deglaciation.

    PubMed

    Knorr, Gregor; Lohmann, Gerrit

    2003-07-31

    During the two most recent deglaciations, the Southern Hemisphere warmed before Greenland. At the same time, the northern Atlantic Ocean was exposed to meltwater discharge, which is generally assumed to reduce the formation of North Atlantic Deep Water. Yet during deglaciation, the Atlantic thermohaline circulation became more vigorous, in the transition from a weak glacial to a strong interglacial mode. Here we use a three-dimensional ocean circulation model to investigate the impact of Southern Ocean warming and the associated sea-ice retreat on the Atlantic thermohaline circulation. We find that a gradual warming in the Southern Ocean during deglaciation induces an abrupt resumption of the interglacial mode of the thermohaline circulation, triggered by increased mass transport into the Atlantic Ocean via the warm (Indian Ocean) and cold (Pacific Ocean) water route. This effect prevails over the influence of meltwater discharge, which would oppose a strengthening of the thermohaline circulation. A Southern Ocean trigger for the transition into an interglacial mode of circulation provides a consistent picture of Southern and Northern hemispheric climate change at times of deglaciation, in agreement with the available proxy records. PMID:12891352

  6. Massively Parallel Assimilation of TOGA/TAO and Topex/Poseidon Measurements into a Quasi Isopycnal Ocean General Circulation Model Using an Ensemble Kalman Filter

    NASA Technical Reports Server (NTRS)

    Keppenne, Christian L.; Rienecker, Michele; Borovikov, Anna Y.; Suarez, Max

    1999-01-01

    A massively parallel ensemble Kalman filter (EnKF)is used to assimilate temperature data from the TOGA/TAO array and altimetry from TOPEX/POSEIDON into a Pacific basin version of the NASA Seasonal to Interannual Prediction Project (NSIPP)ls quasi-isopycnal ocean general circulation model. The EnKF is an approximate Kalman filter in which the error-covariance propagation step is modeled by the integration of multiple instances of a numerical model. An estimate of the true error covariances is then inferred from the distribution of the ensemble of model state vectors. This inplementation of the filter takes advantage of the inherent parallelism in the EnKF algorithm by running all the model instances concurrently. The Kalman filter update step also occurs in parallel by having each processor process the observations that occur in the region of physical space for which it is responsible. The massively parallel data assimilation system is validated by withholding some of the data and then quantifying the extent to which the withheld information can be inferred from the assimilation of the remaining data. The distributions of the forecast and analysis error covariances predicted by the ENKF are also examined.

  7. Constraints on the Lost City Hydrothermal System from borehole thermal data; 3-D models of heat flow and hydrothermal circulation in an oceanic core complex.

    NASA Astrophysics Data System (ADS)

    Titarenko, S.; McCaig, A. M.

    2014-12-01

    A perennial problem in near-ridge hydrothermal circulation is that the only directly measurable data to test models is often vent fluid temperature. Surface heat flow measurements may be available but without the underlying thermal structure it is not known if they are transient and affected by local hydrothermal flow, or conductive. The Atlantis Massif oceanic core complex at 30 °N on the mid-Atlantic Ridge, offers a unique opportunity to better constrain hydrothermal circulation models. The temperature profile in gabbroic rocks of IODP Hole 1309D was measured in IODPExpedition 340T, and found to be near-conductive, but with a slight inflexion at ~750 mbsf indicating downward advection of fluid above that level. The lack of deep convection is especially remarkable given that the long-lived Lost City Hydrothermal Field (LCHF) is located only 5km to the south. We have modelled hydrothermal circulation in the Massif using Comsol Multiphysics, comparing 2-D and 3-D topographic models and using temperature-dependent conductivity to give the best estimate of heatflow into the Massif. We can constrain maximum permeability in gabbro below 750 mbsf to 5e-17 m2. The thermal gradient in the upper part of the borehole can be matched with a permeability of 3e-14 m2 in a 750 m thick layer parallel to the surface of the massif, with upflow occurring in areas of high topography and downflow at the location of the borehole. However in 3-D the precise flow pattern is quite model dependent, and the thermal structure can be matched either by downflow centred on the borehole at lower permeability or centred a few hundred metres from the borehole at higher permeability. The borehole gradient is compatible with the longevity (>120 kyr) and outflow temperature (40-90 °C) of the LCHF either with a deep more permeable (1e-14 m2 to 1e-15 m2) domain beneath the vent site in 2-D or a permeable fault slot 500 to 1000m wide and parallel to the transform fault in 3-D. In both cases topography

  8. Ocean water cycle: its recent amplification and impact on ocean circulation

    NASA Astrophysics Data System (ADS)

    Vinogradova, Nadya

    2016-04-01

    Oceans are the largest reservoir of the world's water supply, accounting for 97% of the Earth's water and supplying more than 75% of the evaporated and precipitated water in the global water cycle. Therefore, in order to predict the future of the global hydrological cycle, it is essential to understand the changes in its largest component, which is the flux of freshwater over the oceans. Here we examine the change in the ocean water cycle and the ocean's response to such changes that were happening during the last two decades. The analysis is based on a data-constrained ocean state estimate that synthesizes all of the information available in the surface fluxes, winds, observations of sea level, temperature, salinity, geoid, etc., as well as in the physical constraints, dynamics, and conservation statements that are embedded in the equations of the MIT general circulation model. Closeness to observations and dynamical consistency of the solution ensures a physically realistic correspondence between the atmospheric forcing and oceanic fluxes, including the ocean's response to freshwater input. The results show a robust pattern of change in the ocean water cycle in the last twenty years. The pattern of changes indicates a general tendency of drying of the subtropics, and wetting in the tropics and mid-to-high latitudes, following the "rich get richer and the poor get poorer" paradigm in many ocean regions. Using a closed property budget analysis, we then investigate the changes in the oceanic state (salinity, temperature, sea level) during the same twenty-year period. The results are discussed in terms of the origin of surface signatures, and differentiated between those that are attributed to short-term natural variability and those that result from an intensified hydrological cycle due to warming climate.

  9. Assessment of an ensemble system that assimilates Jason-1/Envisat altimeter data in a probabilistic model of the North Atlantic ocean circulation

    NASA Astrophysics Data System (ADS)

    Candille, G.; Brankart, J.-M.; Brasseur, P.

    2015-06-01

    A realistic circulation model of the North Atlantic ocean at 0.25° resolution (NATL025 NEMO configuration) has been adapted to explicitly simulate model uncertainties. This is achieved by introducing stochastic perturbations in the equation of state to represent the effect of unresolved scales on the model dynamics. The main motivation for this work is to develop ensemble data assimilation methods, assimilating altimetric data from past missions Jason-1 and Envisat. The assimilation experiment is designed to provide a description of the uncertainty associated with the Gulf Stream circulation for years 2005/2006, focusing on frontal regions which are predominantly affected by unresolved dynamical scales. An ensemble based on such stochastic perturbations is first produced and evaluated using along-track altimetry observations. Then each ensemble member is updated by a square root algorithm based on the SEEK (singular evolutive extended Kalman) filter (Brasseur and Verron, 2006). These three elements - stochastic parameterization, ensemble simulation and 4-D observation operator - are then used together to perform a 4-D analysis of along-track altimetry over 10-day windows. Finally, the results of this experiment are objectively evaluated using the standard probabilistic approach developed for meteorological applications (Toth et al., 2003; Candille et al., 2007). The results show that the free ensemble - before starting the assimilation process - correctly reproduces the statistical variability over the Gulf Stream area: the system is then pretty reliable but not informative (null probabilistic resolution). Updating the free ensemble with altimetric data leads to a better reliability with an information gain of around 30% (for 10-day forecasts of the SSH variable). Diagnoses on fully independent data (i.e. data that are not assimilated, like temperature and salinity profiles) provide more contrasted results when the free and updated ensembles are compared.

  10. Assessment of an ensemble system that assimilates Jason-1/Envisat altimeter data in a probabilistic model of the North Atlantic ocean circulation

    NASA Astrophysics Data System (ADS)

    Candille, G.; Brankart, J. M.; Brasseur, P.

    2014-12-01

    A realistic circulation model of the North Atlantic ocean at 1/4° resolution (NATL025 NEMO configuration) has been adapted to explicitly simulate model uncertainties. This is achieved by introducing stochastic perturbations in the equation of state to represent the effect of unresolved scales on the model dynamics. The main motivation for this work is to develop ensemble data assimilation methods, assimilating altimetric data from past missions JASON-1 and ENVISAT. The assimilation experiment is designed to better control the Gulf Stream circulation for years 2005/06, focusing on frontal regions which are predominantly affected by unresolved dynamical scales. An ensemble based on such stochastic perturbations is first produced and evaluated using along-track altimetry observations. The Incremental Analysis Update (IAU) scheme is applied in order to obtain an ensemble of continuous trajectories all over the 2005/06 assimilation period. These three elements - stochastic parameterization, ensemble simulation and 4-D observation operator - are then used together to perform a 4-D analysis of along-track altimetry over 10 day windows. Finally, the results of this experiment are objectively evaluated using the standard probabilistic approach developed for meteorological applications (Toth et al., 2003; Candille et al., 2007). The results show that the free ensemble - before starting the assimilation process - correctly reproduces the statistical variability over the Gulf Stream area: the system is then pretty reliable but not informative (null probabilistic resolution). Updating the free ensemble with altimetric data leads to a better reliability with an information gain around 30% (for 10 day forecasts of the SSH variable). Diagnoses on fully independent data (i.e. data that are not assimilated, like temperature and salinity profiles) provide more contrasted results when the free and updated ensembles are compared.