Science.gov

Sample records for circulation model simulations

  1. Thermohaline circulation and its box models simulation

    NASA Astrophysics Data System (ADS)

    Bazyura, Kateryna; Polonsky, Alexander; Sannikov, Viktor

    2014-05-01

    Ocean Thermochaline circulation (THC) is the part of large-scale World Ocean circulation and one of the main climate system components. It is generated by global meridional density gradients, which are controlled by surface heat and freshwater fluxes. THC regulates climate variability on different timescales (from decades to thousands years) [Stocker (2000), Clark (2002)]. Study of paleoclimatic evidences of abrupt and dramatic changes in ocean-atmosphere system in the past (such as, Dansgaard-Oeschger and Heinrich events or Younger Dryas, see e.g., [Rahmstorf (2002), Alley & Clark(1999)]) shows that these events are connected with THC regimes. At different times during last 120,000 years, three THC modes have prevailed in the Atlantic. They can be labeled as stadial, interstadial and Heinrich modes or as cold, warm and off mode. THC collapse (or thermohaline catastrophe) can be one of the consequences of global warming (including modern anthropogenic climate changes occurring at the moment). The ideas underlying different box-model studies, possibility of thermochaline catastrophe in present and past are discussed in this presentation. Response of generalized four box model of North Atlantic thermohaline circulation [developing the model of Griffies & Tzippermann (1995)] on periodic, stochastic and linear forcing is studied in details. To estimate climatic parameters of the box model we used monthly salinity and temperature data of ECMWF operational Ocean Reanalysis System 3 (ORA-S3) and data from atmospheric NCEP/NCAR reanalysis on precipitation, and heat fluxes for 1959-2011. Mean values, amplitude of seasonal cycle, amplitudes and periods of typical interdecadal oscillations, white noise level, linear trend coefficients and their significance level were estimated for every hydrophysical parameter. In response to intense freshwater or heat forcing, THC regime can change resulting in thermohaline catastrophe. We analyze relevant thresholds of external forcing in

  2. Simulations of the Amazon basin circulation with a regional model

    SciTech Connect

    Horel, J.D.; Pechmann, J.B.; Hahmann, A.N.; Geisler, J.E. )

    1994-01-01

    Numerical simulations of the atmospheric circulation over tropical South America are performed with a regional model developed at the Pennsylvania State University and the National Center for Atmospheric Research and commonly referred to as the MM4. The authors focus on a 5-day period beginning at 1200 UTC 27 February 1990. The observed circulation is evaluated in terms of initialized analysis of standard meterological variables from the National Meteorological Center, outgoing longwave radiation from polar orbiting satellites, and surface observations. The NMC analysis are also used to specify the initial conditions, as well as provide the lateral boundary conditions, for the 5-day simulations. The impacts on the simulated circulation of major changes to the standard MM4 are assessed. When an improved treatment of radiative processes is included, excessive rainfall develops over then Andes Mountains and over the Amazon Basin. The excessive rainfall is concentrated in gridpoint' storms that are not climated when the surface physical parameterizations are improved. Modifications to the treatment of the vertical transport of moisture are required to diminish the excessive rainfall. Even with these and other changes included in the model, the simulated basin-averaged rainfall continues to exhibit unrealistic features. The improved, thought still imperfect, model simulations are used to diagnose the temporal and spatial evolution of the circulation with an emphasis on equatorial-subtropical interactions.

  3. Strengthening of the Walker circulation under globalwarming in an aqua-planet general circulation model simulation

    NASA Astrophysics Data System (ADS)

    Li, Tim; Zhang, Lei; Murakami, Hiroyuki

    2015-11-01

    Most climate models project a weakening of theWalker circulation under global warming scenarios. It is argued, based on a global averaged moisture budget, that this weakening can be attributed to a slower rate of rainfall increase compared to that of moisture increase, which leads to a decrease in ascending motion. Through an idealized aqua-planet simulation in which a zonal wavenumber-1 SST distribution is prescribed along the equator, we find that the Walker circulation is strengthened under a uniform 2-K SST warming, even though the global mean rainfall-moisture relationship remains the same. Further diagnosis shows that the ascending branch of the Walker cell is enhanced in the upper troposphere but weakened in the lower troposphere. As a result, a "double-cell" circulation change pattern with a clockwise (anti-clockwise) circulation anomaly in the upper (lower) troposphere forms, and the upper tropospheric circulation change dominates. The mechanism for the formation of the "double cell" circulation pattern is attributed to a larger (smaller) rate of increase of diabatic heating than static stability in the upper (lower) troposphere. The result indicates that the future change of the Walker circulation cannot simply be interpreted based on a global mean moisture budget argument.

  4. Relations between winter precipitation and atmospheric circulation simulated by the Geophysical Fluid Dynamics Laboratory general circulation model

    USGS Publications Warehouse

    McCabe, G.J., Jr.; Dettinger, M.D.

    1995-01-01

    General circulation model (GCM) simulations of atmospheric circulation are more reliable than GCM simulations of temperature and precipitation. In this study, temporal correlations between 700 hPa height anomalies simulated winter precipitation at eight locations in the conterminous United States are compared with corresponding correlations in observations. The objectives are to 1) characterize the relations between atmospheric circulation and winter precipitation simulated by the GFDL, GCM for selected locations in the conterminous USA, ii) determine whether these relations are similar to those found in observations of the actual climate system, and iii) determine if GFDL-simulated precipitation is forced by the same circulation patterns as in the real atmosphere. -from Authors

  5. Comparison of Cenozoic atmospheric general circulation model simulations

    SciTech Connect

    Barron, E.J.

    1985-01-01

    Paleocene, Eocene, Miocene and present day (with polar ice) geography are specified as the lower boundary condition in a mean annual, energy balance ocean version of the Community Climate Model (CCM), a spectral General Circulation Model of the Atmosphere developed at the National Center for Atmospheric Research. This version of the CCM has a 4.5/sup 0/ latitudinal and 7.5/sup 0/ longitudinal resolution with 9 vertical levels and includes predictions for pressure, winds, temperature, evaporation, precipitation, cloud cover, snow cover and sea ice. The model simulations indicate little geographically-induced climates changes from the Paleocene to the Miocene, but substantial differences between the Miocene and the present simulations. The simulated climate differences between the Miocene and present day include: 1) cooler present temperatures (2/sup 0/C in tropics, 15-35 C in polar latitudes) with the exception of warmer subtropical desert conditions, 2) a generally weaker present hydrologic cycle, with greater subtropical aridity, 3) strengthened present day westerly jets with a slight poleward displacement, and 4) the largest regional climate changes associated with Antarctica. The results of the climate model sensitivity experiments have considerable implications for understanding how geography influences climate.

  6. Modeling and simulation of circulating tumor cells in flow

    NASA Astrophysics Data System (ADS)

    Lee, Angela Meeyoun

    In this thesis, we mathematically model and computationally simulate several aspects associated with the dynamics of circulating tumor cells in the bloodstream. We focus on physical processes that initiate cancer metastasis, such as intravasation and the subsequent diffusion of thrombin by the expression of tissue factor (TF) on the surface of the circulating tumor cells that are of epithelial origin. In Part I, we develop a low-dimensional parametric deformation model of a cancer cell under shear flow. The surface deformation of MDA-MB-213 cells is imaged using DIC microscopy imaging techniques until the cell releases into the flow. We post-process the time sequence of images using an Active Shape Model (ASM) to obtain the principal components of deformation, which are then used as parameters in an empirical constitutive equation to model the cell deformations as a function of the fluid normal and shear forces imparted. The cell surface is modeled as a 2D Gaussian interface with three active parameters: height, x-width, and y-width. Fluid forces are calculated on the cell surface by discretizing the surface with regularized Stokeslets, and the flow is driven by a stochastically fluctuating pressure gradient. The Stokeslet strengths are obtained so that viscous boundary conditions are enforced on the surface of the cell and the surrounding plate. We show that the low-dimensional model is able to capture the principal deformations of the cell reasonably well and argue that Active Shape Models can be exploited further as a useful tool to bridge the gap between experiments, models, and numerical simulations in this biological setting. In Part II, we describe a mathematical and computational model for diffusion-limited procoagulant circulating tumor cells (CTCs) in flow. We first build a model based on an exact formulation of Green's function solutions for domains with a blood vessel wall and for closed domains. Time-dependent gradient trackers are used to highlight

  7. Sensitivity simulations of superparameterised convection in a general circulation model

    NASA Astrophysics Data System (ADS)

    Rybka, Harald; Tost, Holger

    2015-04-01

    Cloud Resolving Models (CRMs) covering a horizontal grid spacing from a few hundred meters up to a few kilometers have been used to explicitly resolve small-scale and mesoscale processes. Special attention has been paid to realistically represent cloud dynamics and cloud microphysics involving cloud droplets, ice crystals, graupel and aerosols. The entire variety of physical processes on the small-scale interacts with the larger-scale circulation and has to be parameterised on the coarse grid of a general circulation model (GCM). Since more than a decade an approach to connect these two types of models which act on different scales has been developed to resolve cloud processes and their interactions with the large-scale flow. The concept is to use an ensemble of CRM grid cells in a 2D or 3D configuration in each grid cell of the GCM to explicitly represent small-scale processes avoiding the use of convection and large-scale cloud parameterisations which are a major source for uncertainties regarding clouds. The idea is commonly known as superparameterisation or cloud-resolving convection parameterisation. This study presents different simulations of an adapted Earth System Model (ESM) connected to a CRM which acts as a superparameterisation. Simulations have been performed with the ECHAM/MESSy atmospheric chemistry (EMAC) model comparing conventional GCM runs (including convection and large-scale cloud parameterisations) with the improved superparameterised EMAC (SP-EMAC) modeling one year with prescribed sea surface temperatures and sea ice content. The sensitivity of atmospheric temperature, precipiation patterns, cloud amount and types is observed changing the embedded CRM represenation (orientation, width, no. of CRM cells, 2D vs. 3D). Additionally, we also evaluate the radiation balance with the new model configuration, and systematically analyse the impact of tunable parameters on the radiation budget and hydrological cycle. Furthermore, the subgrid

  8. Hospitable archean climates simulated by a general circulation model.

    PubMed

    Wolf, E T; Toon, O B

    2013-07-01

    Evidence from ancient sediments indicates that liquid water and primitive life were present during the Archean despite the faint young Sun. To date, studies of Archean climate typically utilize simplified one-dimensional models that ignore clouds and ice. Here, we use an atmospheric general circulation model coupled to a mixed-layer ocean model to simulate the climate circa 2.8 billion years ago when the Sun was 20% dimmer than it is today. Surface properties are assumed to be equal to those of the present day, while ocean heat transport varies as a function of sea ice extent. Present climate is duplicated with 0.06 bar of CO2 or alternatively with 0.02 bar of CO2 and 0.001 bar of CH4. Hot Archean climates, as implied by some isotopic reconstructions of ancient marine cherts, are unattainable even in our warmest simulation having 0.2 bar of CO2 and 0.001 bar of CH4. However, cooler climates with significant polar ice, but still dominated by open ocean, can be maintained with modest greenhouse gas amounts, posing no contradiction with CO2 constraints deduced from paleosols or with practical limitations on CH4 due to the formation of optically thick organic hazes. Our results indicate that a weak version of the faint young Sun paradox, requiring only that some portion of the planet's surface maintain liquid water, may be resolved with moderate greenhouse gas inventories. Thus, hospitable late Archean climates are easily obtained in our climate model. PMID:23808659

  9. Mars atmospheric dynamics as simulated by the NASA AMES General Circulation Model. I - The zonal-mean circulation

    NASA Astrophysics Data System (ADS)

    Haberle, R. M.; Pollack, J. B.; Barnes, J. R.; Zurek, R. W.; Leovy, C. B.; Murphy, J. R.; Lee, H.; Schaeffer, J.

    1993-02-01

    The characteristics of the zonal-mean circulation and how it responds to seasonal variations and dust loading are described. This circulation is the main momentum-containing component of the general circulation, and it plays a dominant role in the budgets of heat and momentum. It is shown that in many ways the zonal-mean circulation on Mars, at least as simulated by the model, is similar to that on earth, having Hadley and Ferrel cells and high-altitude jet streams. However, the Martian systems tend to be deeper, more intense, and much more variable with season. Furthermore, the radiative effects of suspended dust particles, even in small amounts, have a major influence on the general circulation.

  10. Large eddy simulation using the general circulation model ICON

    NASA Astrophysics Data System (ADS)

    Dipankar, Anurag; Stevens, Bjorn; Heinze, Rieke; Moseley, Christopher; Zängl, Günther; Giorgetta, Marco; Brdar, Slavko

    2015-09-01

    ICON (ICOsahedral Nonhydrostatic) is a unified modeling system for global numerical weather prediction (NWP) and climate studies. Validation of its dynamical core against a test suite for numerical weather forecasting has been recently published by Zängl et al. (2014). In the present work, an extension of ICON is presented that enables it to perform as a large eddy simulation (LES) model. The details of the implementation of the LES turbulence scheme in ICON are explained and test cases are performed to validate it against two standard LES models. Despite the limitations that ICON inherits from being a unified modeling system, it performs well in capturing the mean flow characteristics and the turbulent statistics of two simulated flow configurations—one being a dry convective boundary layer and the other a cumulus-topped planetary boundary layer.

  11. Seasonal changes in the atmospheric heat balance simulated by the GISS general circulation model

    NASA Technical Reports Server (NTRS)

    Stone, P. H.; Chow, S.; Helfand, H. M.; Quirk, W. J.; Somerville, R. C. J.

    1975-01-01

    Tests of the ability of numerical general circulation models to simulate the atmosphere have focussed so far on simulations of the January climatology. These models generally present boundary conditions such as sea surface temperature, but this does not prevent testing their ability to simulate seasonal changes in atmospheric processes that accompany presented seasonal changes in boundary conditions. Experiments to simulate changes in the zonally averaged heat balance are discussed since many simplified models of climatic processes are based solely on this balance.

  12. 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

  13. Numerical Study on an Autonomous Decentralized Model-Based Simulation of Resources Circulation Systems

    NASA Astrophysics Data System (ADS)

    Matsumoto, Takuya; Tamaki, Hisashi; Murao, Hajime; Kitamura, Shinzo

    In this paper, a methodology for modeling and controlling of resources circulation systems is studied. We propose a model structure by introducing two kinds of sub-models: a physical model and an information model. The physical model is used for simulating the flow of materials, products and also money, while the information model is used for representing flow of information and decision-making on production, consumption, recycling/reuse, discard, etc. Moreover, we introduce an additional top-level component, a supervisor, who observes the global behavior of the system and controls it indirectly. Based on the proposed approach, we implement a prototype of simulation model including producers, consumers and recyclers. Through some computer simulations based on the model, it is shown that the model has price adjustment function and its global behavior is very complicated. Then, we examine influences of the informational as well as the physical indirect control on the resources circulation.

  14. A simulation of the winter and summer circulations with the NMC Global Spectral Model

    NASA Technical Reports Server (NTRS)

    Kinter, J. L., III; Shukla, J.; Marx, L.; Schneider, E. K.

    1988-01-01

    The medium range forecast model of the NMC has been integrated to produce winter and summer simulations. It is found that the model climatology is similar to that of the observed atmosphere as well as climatologies of other general circulation models. The stationary and transient features of the model circulation are described, including both tropical and extratropical regions. The model hydrological cycle, radiative balance, and surface heat budget are discussed. Comparison with observations shows that the model is colder than that observed in the troposphere and cools in the lower stratosphere in the tropics and near the poles in both simulations. It is suggested that the upper branch of the Hadley cell is poorly simulated in the integrated model. The simulations are in reasonable agreement with the observations in sea level pressure, the structure of the tropospheric zonal jets, and the winter hemispheric stationary waves.

  15. 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.

  16. Recent results from the GISS model of the global atmosphere. [circulation simulation for weather forecasting

    NASA Technical Reports Server (NTRS)

    Somerville, R. C. J.

    1975-01-01

    Large numerical atmospheric circulation models are in increasingly widespread use both for operational weather forecasting and for meteorological research. The results presented here are from a model developed at the Goddard Institute for Space Studies (GISS) and described in detail by Somerville et al. (1974). This model is representative of a class of models, recently surveyed by the Global Atmospheric Research Program (1974), designed to simulate the time-dependent, three-dimensional, large-scale dynamics of the earth's atmosphere.

  17. 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.

  18. The Early Jurassic climate: General circulation model simulations and the paleoclimate record

    SciTech Connect

    Chandler, M.A.

    1992-01-01

    This thesis presents the results of several general circulation model simulations of the Early Jurassic climate. The general circulation model employed was developed at the Goddard Institute for Space Studies while most paleoclimate data were provided by the Paleographic Atlas Project of the University of Chicago. The first chapter presents an Early Jurassic base simulation, which uses detailed reconstructions of paleogeography, vegetation, and sea surface temperature as boundary condition data sets. The resulting climatology reveals an Earth 5.2[degrees]C warmer, globally, than at present and a latitudinal temperature gradient dominated by high-latitude warming (+20[degrees]C) and little tropical change (+1[degrees]C). Comparisons show a good correlation between simulated results and paleoclimate data. Sensitivity experiments are used to investigate any model-data mismatches. Chapters two and three discuss two important aspects of Early Jurassic climate, continental aridity and global warming. Chapter two focuses on the hydrological capabilities of the general circulation model. The general circulation model's hydrologic diagnostics are evaluated, using the distribution of modern deserts and Early Jurassic paleoclimate data as validating constraints. A new method, based on general circulation model diagnostics and empirical formulae, is proposed for evaluating moisture balance. Chapter three investigates the cause of past global warming, concentrating on the role of increased ocean heat transport. Early Jurassic simulations show that increased ocean heat transports may have been a major factor in past climates. Increased ocean heat transports create latitudinal temperature gradients that closely approximate paleoclimate data and solve the problem of tropical overheating that results from elevated atmospheric carbon dioxide. Increased carbon dioxide cannot duplicate the Jurassic climate without also including increased ocean heat transports.

  19. Dynamic modeling for simulation and control of a circulating fluidized-bed combustor

    SciTech Connect

    Muir, J.R.; Brereton, C.; Grace, J.R.; Lim, C.J.

    1997-05-01

    A dynamic model has been developed to predict the transient behavior of the temperature, the heat removal rate by the in-bed heat exchanger, and the flue-gas oxygen concentration for a circulating fluidized-bed (CFB) combustor. The model was incorporated into a control simulator to reproduce the combustion process within the overall program. The simulator predicts the behavior of the combustor under manual or automatic control to allow testing of control strategies. The model is validated by comparison with step-response tests carried out on a pilot CFB combustor. Discrepancies are attributable to unmodeled disturbances. Further validation, necessary to ensure the applicability of the simulator to control development, is provided by comparing control models identified experimentally using the pilot CFB to those obtained by simulation. Favorable comparison suggests that the dynamic model is suitable for use in control simulation.

  20. General circulation model simulations of winter and summer sea-level pressures over North America

    USGS Publications Warehouse

    McCabe, G.J., Jr.; Legates, D.R.

    1992-01-01

    In this paper, observed sea-level pressures were used to evaluate winter and summer sea-level pressures over North America simulated by the Goddard Institute for Space Studies (GISS) and the Geophysical Fluid Dynamics Laboratory (GFDL) general circulation models. The objective of the study is to determine how similar the spatial and temporal distributions of GCM-simulated daily sea-level pressures over North America are to observed distributions. Overall, both models are better at reproducing observed within-season variance of winter and summer sea-level pressures than they are at simulating the magnitude of mean winter and summer sea-level pressures. -from Authors

  1. Simulation of the great plains low-level jet and associated clouds by general circulation models

    SciTech Connect

    Ghan, S.J.; Bian, X.; Corsetti, L.

    1996-07-01

    The low-level jet frequently observed in the Great Plains of the United States forms preferentially at night and apparently influences the timing of the thunderstorms in the region. The authors have found that both the European Centre for Medium-Range Weather Forecasts general circulation model and the National Center for Atmospheric Research Community Climate Model simulate the low-level jet rather well, although the spatial distribution of the jet frequency simulated by the two GCM`s differ considerably. Sensitivity experiments have demonstrated that the simulated low-level jet is surprisingly robust, with similar simulations at much coarser horizontal and vertical resolutions. However, both GCM`s fail to simulate the observed relationship between clouds and the low-level jet. The pronounced nocturnal maximum in thunderstorm frequency associated with the low-level jet is not simulated well by either GCM, with only weak evidence of a nocturnal maximum in the Great Plains. 36 refs., 20 figs.

  2. Reproduction of links between circulation types and precipitation in Central Europe in regional climate model simulations

    NASA Astrophysics Data System (ADS)

    Plavcová, Eva; Kyselý, Jan; Štěpánek, Petr

    2014-05-01

    The study evaluates relationships between large-scale atmospheric circulation (represented by circulation indices and circulation types derived from gridded mean sea level pressure) and daily precipitation amounts over three regions in the Czech Republic (Central Europe) with different precipitation regimes. We examine how ENSEMBLES regional climate model (RCM) simulations driven by re-analysis reproduce the observed links and capture differences in the links between the regions (lowlands vs. highlands) and seasons. We study the links of circulation to (i) mean precipitation over the regions, (ii) probability of wet days, and (iii) probability of extreme daily precipitation (exceeding threshold defined by a high quantile of precipitation distribution in a given season). Relatively strong links between atmospheric circulation and the precipitation characteristics are found in the observed data. The links are generally more pronounced for highland than lowland regions. More wet days and higher precipitation amounts are found for cyclonic and stronger flows, and for westerly and north-easterly flows. The RCMs are generally able to capture basic features of the links; nevertheless, they have difficulties to reproduce some more specific features and differences in the links between the regions. The results also suggest that good performance in some precipitation characteristics may be due to compensating errors rather than model's perfection. Reference: Plavcová E., Kyselý J., Štěpánek P., 2014: Links between circulation types and precipitation in Central Europe in the observed data and regional climate model simulations. International Journal of Climatology, doi 10.1002/joc.3882.

  3. A heuristic simulation model of Lake Ontario circulation and mass balance transport

    USGS Publications Warehouse

    McKenna, J.E., Jr.; Chalupnicki, M.A.

    2011-01-01

    The redistribution of suspended organisms and materials by large-scale currents is part of natural ecological processes in large aquatic systems but can contribute to ecosystem disruption when exotic elements are introduced into the system. Toxic compounds and planktonic organisms spend various lengths of time in suspension before settling to the bottom or otherwise being removed. We constructed a simple physical simulation model, including the influence of major tributaries, to qualitatively examine circulation patterns in Lake Ontario. We used a simple mass balance approach to estimate the relative water input to and export from each of 10 depth regime-specific compartments (nearshore vs. offshore) comprising Lake Ontario. Despite its simplicity, our model produced circulation patterns similar to those reported by more complex studies in the literature. A three-gyre pattern, with the classic large counterclockwise central lake circulation, and a simpler two-gyre system were both observed. These qualitative simulations indicate little offshore transport along the south shore, except near the mouths of the Niagara River and Oswego River. Complex flow structure was evident, particularly near the Niagara River mouth and in offshore waters of the eastern basin. Average Lake Ontario residence time is 8 years, but the fastest model pathway indicated potential transport of plankton through the lake in as little as 60 days. This simulation illustrates potential invasion pathways and provides rough estimates of planktonic larval dispersal or chemical transport among nearshore and offshore areas of Lake Ontario. ?? 2011 Taylor & Francis.

  4. Simulation of West African monsoon circulation in four atmospheric general circulation models forced by prescribed sea surface temperature

    NASA Astrophysics Data System (ADS)

    Moron, Vincent; Philippon, Nathalie; Fontaine, Bernard

    2004-12-01

    The mean evolution of the West African monsoon (WAM) circulation and its interannual variability have been studied using an ensemble of 21 simulations (common period 1961-1994) performed with four different atmospheric general circulation models (AGCMs) (European Center/Hamburg (ECHAM) 3, ECHAM 4, Action de Recherche Petite Echelle Grande Echelle (ARPEGE), and Goddard Institute for Space Studies (GISS)) and forced by the same observed sea surface temperature (SST) data set. The results have been compared with European Centre for Medium-Range Weather Forecasts reanalyses (ERA-40). The climatological means of WAM winds for the AGCMs are similar to the ERA-40 ones. However, the AGCMs tend to underestimate the southern wind component at low levels around 10°N compared to the ERA-40. The simulated Tropical Easterly Jet (TEJ) is usually shifted northward and also too weak for ECHAM 3 and ECHAM 4 compared to ERA-40. The interannual variability of an atmospheric WAM index (WAMI) is quite successfully reproduced (the correlations between the mean ensemble of each AGCM and ERA-40 time series over 1961-1994 range between 0.51 and 0.64). In particular, the four AGCMs reproduce quite well the mean teleconnection structure with El Niño-Southern Oscillation, i.e., a strong (weak) monsoon during La Niña (El Niño) events, even if the largest absolute correlations between WAMI and SST in the eastern and central equatorial Pacific are weaker than in ERA-40. On a yearly basis, WAMI is more predictable and skillful during the cold ENSO years than during the warm ENSO ones. The unskillful warm ENSO events are associated with a significant cooling over the equatorial Atlantic and Western Pacific Ocean and a significant warming in the tropical Indian Ocean.

  5. Simulation of 18O in precipitation by the regional circulation model REMOiso

    NASA Astrophysics Data System (ADS)

    Sturm, Kristof; Hoffmann, Georg; Langmann, Bärbel; Stichler, Willibald

    2005-11-01

    The first results of a regional circulation model REMOiso fitted with water isotope diagnostics are compared with various isotope series from central Europe. A 2 year case study is conducted from March 1997 to February 1999 centred over Europe, analysing daily and monthly measurements. Isotope signals over Europe are dominated by the typical isotopic effects such as temperature, continental and altitude effects, both on annual and seasonal scales. These well-known isotopic effects are successfully reproduced by REMOiso, using two different boundary data sets. In a first simulation, the European Centre for Medium-range Weather Forecasts (ECMWF) analyses serve as boundary conditions, where water isotopes were parameterized by a simple temperature dependence. In a second simulation, boundary conditions both for climatic and isotopic variables are taken from the ECHAMiso general circulation model output. The comparison of both simulations shows a very high sensitivity of the simulated 18O signal to boundary conditions. The ECMWF-nested simulation shows an average offset of -4.5 in mean 18O values and exaggerated seasonal amplitude. The ECHAM-nested simulation represents correctly the observed mean 18O values, although with a dampened seasonality. REMOiso's isotope module is further validated against daily 18O measurements at selected stations (Nordeney, Arkona and Hohenpeissenberg) situated in Germany. Copyright

  6. Multiscale dynamical analysis of a high-resolution numerical model simulation of the Solomon Sea circulation

    NASA Astrophysics Data System (ADS)

    Djath, Bughsin'; Verron, Jacques; Melet, Angelique; Gourdeau, Lionel; Barnier, Bernard; Molines, Jean-Marc

    2014-09-01

    A high 1/36° resolution numerical model is used to study the ocean circulation in the Solomon Sea. An evaluation of the model with (the few) available observation shows that the 1/36° resolution model realistically simulates the Solomon Sea circulations. The model notably reproduces the high levels of mesoscale eddy activity observed in the Solomon Sea. With regard to previous simulations at 1/12° resolution, the average eddy kinetic energy levels are increased by up to ˜30-40% in the present 1/36° simulation, and the enhancement extends at depth. At the surface, the eddy kinetic energy level is maximum in March-April-May and is minimum in December-January-February. The high subsurface variability is related to the variability of the western boundary current (New Guinea Coastal Undercurrent). Moreover, the emergence of submesoscales is clearly apparent in the present simulations. A spectral analysis is conducted in order to evidence and characterize the modeled submesoscale dynamics and to provide a spectral view of scales interactions. The corresponding spectral slopes show a strong consistency with the Surface Quasi-Geostrophic turbulence theory.

  7. Computer simulation of the cooling effect due to circulation in four geothermal well models

    SciTech Connect

    Duda, L.E.

    1984-11-01

    Computer calculations of wellbore transient temperatures, using the geothermal wellbore thermal simulator code GEOTEMP2, were made on four well models. The well models studied were from the Baca geothermal area, the East Mesa geothermal area, and a shallow and a deep well from the Salton Sea geothermal area. Calculations for one day of water circulation followed by one day of shut-in at flow rates of 100, 250, 500, and 1000 gpm were made to investigate the cooling effects produced by the circulation. Additional calculations were made using the Baca and Salton Sea well models. In the former, the effect on the cooling due to different soil thermal conductivity values and different circulating fluids (a high viscosity mud and air) were investigated. In the latter, the number of casings in the wellbore and the diameter of the tubing were notified. Plots of the calculated temperatures as a function of circulation and shut-in time and depth are given for each case.

  8. 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.

  9. The Tropical Subseasonal Variability Simulated in the NASA GISS General Circulation Model

    NASA Technical Reports Server (NTRS)

    Kim, Daehyun; Sobel, Adam H.; DelGenio, Anthony D.; Chen, Yonghua; Camargo, Suzana J.; Yao, Mao-Sung; Kelley, Maxwell; Nazarenko, Larissa

    2012-01-01

    The tropical subseasonal variability simulated by the Goddard Institute for Space Studies general circulation model, Model E2, is examined. Several versions of Model E2 were developed with changes to the convective parameterization in order to improve the simulation of the Madden-Julian oscillation (MJO). When the convective scheme is modified to have a greater fractional entrainment rate, Model E2 is able to simulate MJO-like disturbances with proper spatial and temporal scales. Increasing the rate of rain reevaporation has additional positive impacts on the simulated MJO. The improvement in MJO simulation comes at the cost of increased biases in the mean state, consistent in structure and amplitude with those found in other GCMs when tuned to have a stronger MJO. By reinitializing a relatively poor-MJO version with restart files from a relatively better-MJO version, a series of 30-day integrations is constructed to examine the impacts of the parameterization changes on the organization of tropical convection. The poor-MJO version with smaller entrainment rate has a tendency to allow convection to be activated over a broader area and to reduce the contrast between dry and wet regimes so that tropical convection becomes less organized. Besides the MJO, the number of tropical-cyclone-like vortices simulated by the model is also affected by changes in the convection scheme. The model simulates a smaller number of such storms globally with a larger entrainment rate, while the number increases significantly with a greater rain reevaporation rate.

  10. Simulation of hydrodynamics using large eddy simulation-second-order moment model in circulating fluidized beds

    NASA Astrophysics Data System (ADS)

    Juhui, Chen; Yanjia, Tang; Dan, Li; Pengfei, Xu; Huilin, Lu

    2013-07-01

    Flow behavior of gas and particles is predicted by the large eddy simulation of gas-second order moment of solid model (LES-SOM model) in the simulation of flow behavior in CFB. This study shows that the simulated solid volume fractions along height using a two-dimensional model are in agreement with experiments. The velocity, volume fraction and second-order moments of particles are computed. The second-order moments of clusters are calculated. The solid volume fraction, velocity and second order moments are compared at the three different model constants.

  11. Numerical Simulations and Tracer Studies as a Tool to Support Water Circulation Modeling in Breeding Reservoirs

    NASA Astrophysics Data System (ADS)

    Zima, Piotr

    2014-12-01

    The article presents a proposal of a method for computer-aided design and analysis of breeding reservoirs in zoos and aquariums. The method applied involves the use of computer simulations of water circulation in breeding pools. A mathematical model of a pool was developed, and a tracer study was carried out. A simplified model of two-dimensional flow in the form of a biharmonic equation for the stream function (converted into components of the velocity vector) was adopted to describe the flow field. This equation, supplemented by appropriate boundary conditions, was solved numerically by the finite difference method. Next, a tracer migration equation was solved, which was a two-dimensional advection-dispersion equation describing the unsteady transport of a non-active, permanent solute. In order to obtain a proper solution, a tracer study (with rhodamine WT as a tracer) was conducted in situ. The results of these measurements were compared with numerical solutions obtained. The results of numerical simulations made it possible to reconstruct water circulation in the breading pool and to identify still water zones, where water circulation was impeded.

  12. Decadal Variations of the Atlantic Meridional Overturning Circulation as simulated by the VIKING20 Model

    NASA Astrophysics Data System (ADS)

    Handmann, Patricia; Fischer, Jürgen; Visbeck, Martin; Behrens, Erik; Patara, Lavinia

    2015-04-01

    Time series of observed deep circulation transports and water mass properties in the subpolar North Atlantic are beginning to be long enough to investigate multiannual to decadal variability of the deep water. At the same time high resolution ocean circulation models (1/20° resolution VIKING20 model) can be used to compare observations with model simulation. The models also allow to diagnose the deep water circulation processes more completely and to relate local to basin scale signals. North Atlantic Deep Water (NADW) is a complex combination of water masses from different origins and pathways that meet at the exit of the Labrador Sea. The lower part of NADW is formed by water masses entering the subpolar basin over the Greenland-Scotland ridge. Iceland-Scotland Overflow Water (ISOW) from the eastern sills has the longest pathway and joins the densest deep water component from Denmark Strait (DSOW) after crossing the Mid-Atlantic-Ridge through Charlie-Gibbs Fracture Zone (CGFZ); together, they form the Lower NADW. The upper component of the NADW is composed of Labrador Sea Water (LSW), which is formed and modified through deep convection in the Labrador Sea. Using 60 year long time series of North Atlantic water masses and currents produced by the Viking20 model driven by observed monthly winds, a comparison of transport variability of observed and modeled data will be presented at three locations: Deep flow at the exit of the Labrador Sea at 53°N; upper layer transports between New Jersey and Bermuda (OLEANDER section) and between the southern tip of Greenland and Portugal (OVIDE section). Is the model reproducing the observed long-term behavior of the different components in phase and amplitude? Do the results permit identification of the processes leading to these variations in transport variability? Finally, is it possible to extend the observed variability pattern over the observed time span (15 years) to the total time range of the model simulations (60

  13. Simulation of the equatorially asymmetric mode of the Hadley circulation in CMIP5 models

    NASA Astrophysics Data System (ADS)

    Feng, Juan; Li, Jianping; Zhu, Jianlei; Li, Fei; Sun, Cheng

    2015-08-01

    The tropical Hadley circulation (HC) plays an important role in influencing the climate in the tropics and extra-tropics. The realism of the climatological characteristics, spatial structure, and temporal evolution of the long-term variation of the principal mode of the annual mean HC (i.e., the equatorially asymmetric mode, EAM) was examined in model simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5). The results showed that all the models are moderately successful in capturing the HC's climatological features, including the spatial pattern, meridional extent, and intensity, but not the spatial or temporal variation of the EAM. The possible reasons for the poor simulation of the long-term variability of the EAM were explored. None of the models can successfully capture the differences in the warming rate between the tropical Southern Hemisphere (SH) and Northern Hemisphere (NH), which is considered to be an important driver for the variation of the AM. Most of the models produce a faster warming in the NH than in the SH, which is the reverse of the observed trend. This leads to a reversed trend in the meridional gradient between the SH and NH, and contributes to the poor simulation of EAM variability. Thus, this aspect of the models should be improved to provide better simulations of the variability of the HC. This study suggests a possible reason for the poor simulation of the HC, which may be helpful for improving the skill of the CMIP5 models in the future.

  14. Mars atmospheric dynamics as simulated by the NASA AMES General Circulation Model. II - Transient baroclinic eddies

    NASA Astrophysics Data System (ADS)

    Barnes, J. R.; Pollack, J. B.; Haberle, R. M.; Leovy, C. B.; Zurek, R. W.; Lee, H.; Schaeffer, J.

    1993-02-01

    A large set of experiments performed with the NASA Ames Mars General Circulation Model is analyzed to determine the properties, structure, and dynamics of the simulated transient baroclinic eddies. There is strong transient baroclinic eddy activity in the extratropics of the Northern Hemisphere during the northern autumn, winter, and spring seasons. The eddy activity remains strong for very large dust loadings, though it shifts northward. The eastward propagating eddies are characterized by zonal wavenumbers of 1-4 and periods of about 2-10 days. The properties of the GCM baroclinic eddies in the northern extratropics are compared in detail with analogous properties inferred from Viking Lander meteorology observations.

  15. Simulation of Venus polar vortices with the non-hydrostatic general circulation model

    NASA Astrophysics Data System (ADS)

    Rodin, Alexander V.; Mingalev, Oleg; Orlov, Konstantin

    2012-07-01

    The dynamics of Venus atmosphere in the polar regions presents a challenge for general circulation models. Numerous images and hyperspectral data from Venus Express mission shows that above 60 degrees latitude atmospheric motion is substantially different from that of the tropical and extratropical atmosphere. In particular, extended polar hoods composed presumably of fine haze particles, as well as polar vortices revealing mesoscale wave perturbations with variable zonal wavenumbers, imply the significance of vertical motion in these circulation elements. On these scales, however, hydrostatic balance commonly used in the general circulation models is no longer valid, and vertical forces have to be taken into account to obtain correct wind field. We present the first non-hydrostatic general circulation model of the Venus atmosphere based on the full set of gas dynamics equations. The model uses uniform grid with the resolution of 1.2 degrees in horizontal and 200 m in the vertical direction. Thermal forcing is simulated by means of relaxation approximation with specified thermal profile and time scale. The model takes advantage of hybrid calculations on graphical processors using CUDA technology in order to increase performance. Simulations show that vorticity is concentrated at high latitudes within planetary scale, off-axis vortices, precessing with a period of 30 to 40 days. The scale and position of these vortices coincides with polar hoods observed in the UV images. The regions characterized with high vorticity are surrounded by series of small vortices which may be caused by shear instability of the zonal flow. Vertical velocity component implies that in the central part of high vorticity areas atmospheric flow is downwelling and perturbed by mesoscale waves with zonal wavenumbers 1-4, resembling observed wave structures in the polar vortices. Simulations also show the existence of areas with strong vertical flow, concentrated in spiral branches extending

  16. Dust Emissions, Transport, and Deposition Simulated with the NASA Finite-Volume General Circulation Model

    NASA Technical Reports Server (NTRS)

    Colarco, Peter; daSilva, Arlindo; Ginoux, Paul; Chin, Mian; Lin, S.-J.

    2003-01-01

    Mineral dust aerosols have radiative impacts on Earth's atmosphere, have been implicated in local and regional air quality issues, and have been identified as vectors for transporting disease pathogens and bringing mineral nutrients to terrestrial and oceanic ecosystems. We present for the first time dust simulations using online transport and meteorological analysis in the NASA Finite-Volume General Circulation Model (FVGCM). Our dust formulation follows the formulation in the offline Georgia Institute of Technology-Goddard Global Ozone Chemistry Aerosol Radiation and Transport Model (GOCART) using a topographical source for dust emissions. We compare results of the FVGCM simulations with GOCART, as well as with in situ and remotely sensed observations. Additionally, we estimate budgets of dust emission and transport into various regions.

  17. A comparison between general circulation model simulations using two sea surface temperature datasets for January 1979

    NASA Technical Reports Server (NTRS)

    Ose, Tomoaki; Mechoso, Carlos; Halpern, David

    1994-01-01

    Simulations with the UCLA atmospheric general circulation model (AGCM) using two different global sea surface temperature (SST) datasets for January 1979 are compared. One of these datasets is based on Comprehensive Ocean-Atmosphere Data Set (COADS) (SSTs) at locations where there are ship reports, and climatology elsewhere; the other is derived from measurements by instruments onboard NOAA satellites. In the former dataset (COADS SST), data are concentrated along shipping routes in the Northern Hemisphere; in the latter dataset High Resolution Infrared Sounder (HIRS SST), data cover the global domain. Ensembles of five 30-day mean fields are obtained from integrations performed in the perpetual-January mode. The results are presented as anomalies, that is, departures of each ensemble mean from that produced in a control simulation with climatological SSTs. Large differences are found between the anomalies obtained using COADS and HIRS SSTs, even in the Northern Hemisphere where the datasets are most similar to each other. The internal variability of the circulation in the control simulation and the simulated atmospheric response to anomalous forcings appear to be linked in that the pattern of geopotential height anomalies obtained using COADS SSTs resembles the first empirical orthogonal function (EOF 1) in the control simulation. The corresponding pattern obtained using HIRS SSTs is substantially different and somewhat resembles EOF 2 in the sector from central North America to central Asia. To gain insight into the reasons for these results, three additional simulations are carried out with SST anomalies confined to regions where COADS SSTs are substantially warmer than HIRS SSTs. The regions correspond to warm pools in the northwest and northeast Pacific, and the northwest Atlantic. These warm pools tend to produce positive geopotential height anomalies in the northeastern part of the corresponding oceans. Both warm pools in the Pacific produce large

  18. Simulating Titan’s tropospheric circulation with the Portable University Model of the Atmosphere

    NASA Astrophysics Data System (ADS)

    Grieger, B.; Segschneider, J.; Keller, H. U.; Rodin, A. V.; Lunkeit, F.; Kirk, E.; Fraedrich, K.

    2004-01-01

    The Portable University Model of the Atmosphere (PUMA) is a general circulation model of intermediate complexity. In the model setup used herein, the dynamics is driven by restoration to a prescribed temperature field. Given an observed three-dimensional field of restoration temperatures, the feedback of aerosol distribution to the radiation scheme and hence to the dynamics is excluded from calculations. PUMA is adapted to Titan conditions and used to carry out a series of experiments with temperature fields based on radio occultation and infrared spectroscopy measurements taken by Voyager 1 in 1980. The resultant winds are prograde with maximum wind speeds of about 14 m/s in the troposphere. This simulation demonstrates capabilities of a restricted complexity model and provides a contribution to the prediction of the descent trajectory of the Huygens lander in January 2005.

  19. 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.

  20. Venus atmosphere simulated by a high-resolution general circulation model

    NASA Astrophysics Data System (ADS)

    Sugimoto, Norihiko

    2016-07-01

    An atmospheric general circulation model (AGCM) for Venus on the basis of AFES (AGCM For the Earth Simulator) have been developed (e.g., Sugimoto et al., 2014a) and a very high-resolution simulation is performed. The highest resolution of the model is T319L120; 960 times 480 horizontal grids (grid intervals are about 40 km) with 120 vertical layers (layer intervals are about 1 km). In the model, the atmosphere is dry and forced by the solar heating with the diurnal and semi-diurnal components. The infrared radiative process is simplified by adopting Newtonian cooling approximation. The temperature is relaxed to a prescribed horizontally uniform temperature distribution, in which a layer with almost neutral static stability observed in the Venus atmosphere presents. A fast zonal wind in a solid-body rotation is given as the initial state. Starting from this idealized superrotation, the model atmosphere reaches a quasi-equilibrium state within 1 Earth year and this state is stably maintained for more than 10 Earth years. The zonal-mean zonal flow with weak midlatitude jets has almost constant velocity of 120 m/s in latitudes between 45°S and 45°N at the cloud top levels, which agrees very well with observations. In the cloud layer, baroclinic waves develop continuously at midlatitudes and generate Rossby-type waves at the cloud top (Sugimoto et al., 2014b). At the polar region, warm polar vortex zonally surrounded by a cold latitude band (cold collar) is well reproduced (Ando et al., 2016). As for horizontal kinetic energy spectra, divergent component is broadly (k>10) larger than rotational component compared with that on Earth (Kashimura et al., in preparation). Finally, recent results for thermal tides and small-scale waves will be shown in the presentation. Sugimoto, N. et al. (2014a), Baroclinic modes in the Venus atmosphere simulated by GCM, Journal of Geophysical Research: Planets, Vol. 119, p1950-1968. Sugimoto, N. et al. (2014b), Waves in a Venus general

  1. The cyclonic circulation in the Australian-Antarctic basin simulated by an eddy-resolving general circulation model

    NASA Astrophysics Data System (ADS)

    Aoki, Shigeru; Sasai, Yoshikazu; Sasaki, Hideharu; Mitsudera, Humio; Williams, Guy D.

    2010-06-01

    Flow structure in the Australian-Antarctic basin is investigated using an eddy-resolving general ocean circulation model and validated with iceberg and middepth float trajectories. A cyclonic circulation system between the Antarctic Circumpolar Current and Antarctic Slope Current consists of a large-scale gyre in the west (80-110° E) and a series of eddies in the east (120-150° E). The western gyre has an annual mean westward transport of 22 Sv in the southern limb. Extending west through the Princess Elizabeth Trough, 5 Sv of the gyre recirculates off Prydz Bay and joins the western boundary current off the Kerguelen Plateau. Iceberg trajectories from QuickScat and ERS-1/2 support this recirculation and the overall structure of the Antarctic Slope Current against isobath in the model. Argo float trajectories also reveal a consistent structure of the deep westward slope current. This study indicates the presence of a large cyclonic circulation in this basin, which is comparable to the Weddell and Ross gyres.

  2. Large eddy simulation model for wind-driven sea circulation in coastal areas

    NASA Astrophysics Data System (ADS)

    Petronio, A.; Roman, F.; Nasello, C.; Armenio, V.

    2013-12-01

    In the present paper a state-of-the-art large eddy simulation model (LES-COAST), suited for the analysis of water circulation and mixing in closed or semi-closed areas, is presented and applied to the study of the hydrodynamic characteristics of the Muggia bay, the industrial harbor of the city of Trieste, Italy. The model solves the non-hydrostatic, unsteady Navier-Stokes equations, under the Boussinesq approximation for temperature and salinity buoyancy effects, using a novel, two-eddy viscosity Smagorinsky model for the closure of the subgrid-scale momentum fluxes. The model employs: a simple and effective technique to take into account wind-stress inhomogeneity related to the blocking effect of emerged structures, which, in turn, can drive local-scale, short-term pollutant dispersion; a new nesting procedure to reconstruct instantaneous, turbulent velocity components, temperature and salinity at the open boundaries of the domain using data coming from large-scale circulation models (LCM). Validation tests have shown that the model reproduces field measurement satisfactorily. The analysis of water circulation and mixing in the Muggia bay has been carried out under three typical breeze conditions. Water circulation has been shown to behave as in typical semi-closed basins, with an upper layer moving along the wind direction (apart from the anti-cyclonic veering associated with the Coriolis force) and a bottom layer, thicker and slower than the upper one, moving along the opposite direction. The study has shown that water vertical mixing in the bay is inhibited by a large level of stable stratification, mainly associated with vertical variation in salinity and, to a minor extent, with temperature variation along the water column. More intense mixing, quantified by sub-critical values of the gradient Richardson number, is present in near-coastal regions where upwelling/downwelling phenomena occur. The analysis of instantaneous fields has detected the presence of

  3. Variable-resolution frameworks for the simulation of tropical cyclones in global atmospheric general circulation models

    NASA Astrophysics Data System (ADS)

    Zarzycki, Colin

    The ability of atmospheric General Circulation Models (GCMs) to resolve tropical cyclones in the climate system has traditionally been difficult. The challenges include adequately capturing storms which are small in size relative to model grids and the fact that key thermodynamic processes require a significant level of parameterization. At traditional GCM grid spacings of 50-300 km tropical cyclones are severely under-resolved, if not completely unresolved. This thesis explores a variable-resolution global model approach that allows for high spatial resolutions in areas of interest, such as low-latitude ocean basins where tropical cyclogenesis occurs. Such GCM designs with multi-resolution meshes serve to bridge the gap between globally-uniform grids and limited area models and have the potential to become a future tool for regional climate assessments. A statically-nested, variable-resolution option has recently been introduced into the Department of Energy/National Center for Atmospheric Research (DoE/NCAR) Community Atmosphere Model's (CAM) Spectral Element (SE) dynamical core. Using an idealized tropical cyclone test, variable-resolution meshes are shown to significantly lessen computational requirements in regional GCM studies. Furthermore, the tropical cyclone simulations are free of spurious numerical errors at the resolution interfaces. Utilizing aquaplanet simulations as an intermediate test between idealized simulations and fully-coupled climate model runs, climate statistics within refined patches are shown to be well-matched to globally-uniform simulations of the same grid spacing. Facets of the CAM version 4 (CAM4) subgrid physical parameterizations are likely too scale sensitive for variable-resolution applications, but the newer CAM5 package is vastly improved in performance at multiple grid spacings. Multi-decadal simulations following 'Atmospheric Model Intercomparison Project' protocols have been conducted with variable-resolution grids. Climate

  4. Simulated pre-industrial climate in Bergen Climate Model (version 2): model description and large-scale circulation features

    NASA Astrophysics Data System (ADS)

    Otterâ, O. H.; Bentsen, M.; Bethke, I.; Kvamstø, N. G.

    2009-11-01

    The Bergen Climate Model (BCM) is a fully-coupled atmosphere-ocean-sea-ice model that provides state-of-the-art computer simulations of the Earth's past, present, and future climate. Here, a pre-industrial multi-century simulation with an updated version of BCM is described and compared to observational data. The model is run without any form of flux adjustments and is stable for several centuries. The simulated climate reproduces the general large-scale circulation in the atmosphere reasonably well, except for a positive bias in the high latitude sea level pressure distribution. Also, by introducing an updated turbulence scheme in the atmosphere model a persistent cold bias has been eliminated. For the ocean part, the model drifts in sea surface temperatures and salinities are considerably reduced compared to earlier versions of BCM. Improved conservation properties in the ocean model have contributed to this. Furthermore, by choosing a reference pressure at 2000 m and including thermobaric effects in the ocean model, a more realistic meridional overturning circulation is simulated in the Atlantic Ocean. The simulated sea-ice extent in the Northern Hemisphere is in general agreement with observational data except for summer where the extent is somewhat underestimated. In the Southern Hemisphere, large negative biases are found in the simulated sea-ice extent. This is partly related to problems with the mixed layer parametrization, causing the mixed layer in the Southern Ocean to be too deep, which in turn makes it hard to maintain a realistic sea-ice cover here. However, despite some problematic issues, the pre-industrial control simulation presented here should still be appropriate for climate change studies requiring multi-century simulations.

  5. Martian atmospheric gravity waves simulated by a high-resolution general circulation model

    NASA Astrophysics Data System (ADS)

    Kuroda, Takeshi; Yiǧit, Erdal; Medvedev, Alexander S.; Hartogh, Paul

    2016-07-01

    Gravity waves (GWs) significantly affect temperature and wind fields in the Martian middle and upper atmosphere. They are also one of the observational targets of the MAVEN mission. We report on the first simulations with a high-resolution general circulation model (GCM) and present a global distributions of small-scale GWs in the Martian atmosphere. The simulated GW-induced temperature variances are in a good agreement with available radio occultation data in the lower atmosphere between 10 and 30 km. For the northern winter solstice, the model reveals a latitudinal asymmetry with stronger wave generation in the winter hemisphere and two distinctive sources of GWs: mountainous regions and the meandering winter polar jet. Orographic GWs are filtered upon propagating upward, and the mesosphere is primarily dominated by harmonics with faster horizontal phase velocities. Wave fluxes are directed mainly against the local wind. GW dissipation in the upper mesosphere generates a body force per unit mass of tens of m s^{-1} per Martian solar day (sol^{-1}), which tends to close the simulated jets. The results represent a realistic surrogate for missing observations, which can be used for constraining GW parameterizations and validating GCMs.

  6. Simulations of the Amazon Basin circulation using the Pennsylvania State University/National Center for Atmospheric Research mesoscale model

    SciTech Connect

    Hahmann, A.N.

    1992-01-01

    A regional model has been used to investigate dynamical processes that control the circulation over the Amazon Basin. The application of a regional model to the Amazon Basin is unique and the method in which the model output is diagnosed is distinct. Two synoptic cases describe the ability of the regional model to simulate the circulation over the Amazon Basin. The first case, 15-17 April 1990, represents an example of the dominant circulation over the basin during the summer. The second case study occurs 27 February-1 March 1990. At the onset of this period, a vigorous trough is located in the subtropical westerlies of the Southern Hemisphere, which promotes advection of drier air by the low-level southerly flow into the southern part of the Basin. There is limited agreement between the observed circulation and the model simulations for the case studies. The model appears to simulate a number of dynamical processes known to take place. The timing of individual rain bands and their locations differ significantly from those observed. The sensitivity of the model simulation to the size of the grid spacing and the domain reveal that the regional circulation is most economically simulated with a nested domain and 60 km grid spacing. Larger grid spacings lead to excessive rainfall totals near the Andes Mountains and circulations that are unrealistic. Restricted domains (Amazon Basin only) produce excessive precipitation along the horizontal boundaries. Model simulations using several different combinations of convective and explicit precipitation parameterizations are performed. Experiments using the explicit moisture scheme without a cumulus parameterization scheme show the development of grid point instabilities. These instabilities result from interaction processes among latent heat release, large-scale moisture convergence, and surface pressure. When the Kuo-Anthes cumulus parameterization is included, grid point instabilities are substantially reduced.

  7. Simulated pre-industrial climate in Bergen Climate Model (version 2): model description and large-scale circulation features

    NASA Astrophysics Data System (ADS)

    Otterå, O. H.; Bentsen, M.; Bethke, I.; Kvamstø, N. G.

    2009-05-01

    The Bergen Climate Model (BCM) is a fully-coupled atmosphere-ocean-sea-ice model that provides state-of-the-art computer simulations of the Earth's past, present, and future climate. Here, a pre-industrial multi-century simulation with an updated version of BCM is described and compared to observational data. The model is run without any form of flux adjustments and is stable for several centuries. The simulated climate reproduces the general large scale circulation in the atmosphere reasonably well, except for a positive bias in the high latitude sea level pressures distribution. Also, by introducing an updated turbulence scheme in the atmosphere model a persistent cold bias has been eliminated. For the ocean part, the model drifts in sea surface temperatures and salinities are considerably reduced compared to earlier versions of BCM. Improved conservation properties in the ocean have contributed to this. Furthermore, by choosing a reference pressure at 2000 m and including thermobaric effects in the ocean model, a more realistic meridional overturning circulation is simulated in the Atlantic Ocean. The simulated sea-ice extent in the Northern Hemisphere is in general agreement with observational data except for summer where the extent is somewhat underestimated. In the Southern Hemisphere, large negative biases are found in the simulated sea-ice extent. This is partly related to problems with the mixed layer parametrization, causing the mixed layer in the Southern Ocean to be too deep, which in turn makes it hard to maintain a realistic sea-ice cover here. However, despite some problematic issues, the pre-industrial control simulation presented here should still be appropriate for climate change studies requiring multi-century simulations.

  8. 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

  9. 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

  10. Simulating Titan's methane cycle with the TitanWRF General Circulation Model

    NASA Astrophysics Data System (ADS)

    Newman, Claire E.; Richardson, Mark I.; Lian, Yuan; Lee, Christopher

    2016-03-01

    Observations provide increasing evidence of a methane hydrological cycle on Titan. Earth-based and Cassini-based monitoring has produced data on the seasonal variation in cloud activity and location, with clouds being observed at increasingly low latitudes as Titan moved out of southern summer. Lakes are observed at high latitudes, with far larger lakes and greater areal coverage in the northern hemisphere, where some shorelines extend down as far as 50°N. Rainfall at some point in the past is suggested by the pattern of flow features on the surface at the Huygens landing site, while recent rainfall is suggested by surface change. As with the water cycle on Earth, the methane cycle on Titan is both impacted by tropospheric dynamics and likely able to impact this circulation via feedbacks. Here we use the 3D TitanWRF General Circulation Model (GCM) to simulate Titan's methane cycle. In this initial work we use a simple large-scale condensation scheme with latent heat feedbacks and a finite surface reservoir of methane, and focus on large-scale dynamical interactions between the atmospheric circulation and methane, and how these impact seasonal changes and the long term (steady state) behavior of the methane cycle. We note five major conclusions: (1) Condensation and precipitation in the model is sporadic in nature, with interannual variability in its timing and location, but tends to occur in association with both (a) frequent strong polar upwelling during spring and summer in each hemisphere, and (b) the Inter-Tropical Convergence Zone (ITCZ), a region of increased convergence and upwelling due to the seasonally shifting Hadley cells. (2) An active tropospheric methane cycle affects the stratospheric circulation, slightly weakening the stratospheric superrotation produced. (3) Latent heating feedback strongly influences surface and near-surface temperatures, narrowing the latitudinal range of the ITCZ, and changing the distribution - and generally weakening the

  11. Evaluating Parameterizations in General Circulation Models: Climate Simulation Meets Weather Prediction

    SciTech Connect

    Phillips, T J; Potter, G L; Williamson, D L; Cederwall, R T; Boyle, J S; Fiorino, M; Hnilo, J J; Olson, J G; Xie, S; Yio, J J

    2004-05-06

    To significantly improve the simulation of climate by general circulation models (GCMs), systematic errors in representations of relevant processes must first be identified, and then reduced. This endeavor demands that the GCM parameterizations of unresolved processes, in particular, should be tested over a wide range of time scales, not just in climate simulations. Thus, a numerical weather prediction (NWP) methodology for evaluating model parameterizations and gaining insights into their behavior may prove useful, provided that suitable adaptations are made for implementation in climate GCMs. This method entails the generation of short-range weather forecasts by a realistically initialized climate GCM, and the application of six-hourly NWP analyses and observations of parameterized variables to evaluate these forecasts. The behavior of the parameterizations in such a weather-forecasting framework can provide insights on how these schemes might be improved, and modified parameterizations then can be tested in the same framework. In order to further this method for evaluating and analyzing parameterizations in climate GCMs, the U.S. Department of Energy is funding a joint venture of its Climate Change Prediction Program (CCPP) and Atmospheric Radiation Measurement (ARM) Program: the CCPP-ARM Parameterization Testbed (CAPT). This article elaborates the scientific rationale for CAPT, discusses technical aspects of its methodology, and presents examples of its implementation in a representative climate GCM.

  12. 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.

  13. Simulation of Indian Monsoon Variability in the Medieval Warm Period using ECHAM5 General Circulation Model

    NASA Astrophysics Data System (ADS)

    Polanski, Stefan; Fallah, Bijan; Prasad, Sushma; Cubasch, Ulrich

    2013-04-01

    Within the framework of the DFG research group HIMPAC, the general circulation model ECHAM5 has been used to simulate the Indian monsoon and its variability during the Medieval Warm Period (MWP; 900-1100 AD) and for recent climate (REC; 1800-2000 AD). The focus is on the analysis of internal and external drivers leading to extreme rainfall events over India from interannual to multidecadal time scale. An evaluation of spatio-temporal monsoon patterns with present-day observation data is in agreement with other state-of-the-art monsoon modeling studies. The simulated monsoon intensity on multidecadal time scale is weakened (enhanced) in summer (winter) due to colder (warmer) SSTs in the Indian Ocean. Variations in solar insolation are the main drivers for these SST anomalies, verified by very high temporal correlations between Total Solar Irradiance and All-India-Monsoon-Rainfall in summer monsoon months (-0.95). The external solar forcing is coupled and overlain by internal climate modes of the Ocean (ENSO and IOD) with asynchronous intensities and lengths of periods. In addition, the model simulations have been compared with a relative moisture index derived from paleoclimatic reconstructions based on various proxies and archives in India (Anoop et al., 2012 (under revision); Bhattacharya et al., 2007; Chauhan et al., 2000; Denniston et al., 2000; Ely et al., 1999; Kar et al., 2002; Ponton et al., 2012; Prasad et al., 2012 (under revision)). In this context, the reconstructed climate of the well-dated Lonar record in Central India has been highlighted and evaluated the first time (Anoop et al., 2012 (under revision); Prasad et al., 2012 (under revision)). Particularly with regard to the long continuously chronology of the last 11000 years, the Lonar site gives a unique possibility for a comparison of long-term climate time series. The simulated relative annual rainfall anomalies ("MWP" minus "REC") are in agreement with the reconstructed moisture index. The dry

  14. Internal versus SST-forced atmospheric variability as simulated by an atmospheric general circulation model

    SciTech Connect

    Harzallah, A.; Sadourny, R.

    1995-03-01

    The variability of atmospheric flow is analyzed by separating it into an internal part due to atmospheric dynamics only and an external (or forced) part due to the variability of sea surface temperature forcing. The two modes of variability are identified by performing an ensemble of seven independent long-term simulations of the atmospheric response to observed SST (1970-1988) with the LMD atmospheric general circulation model. The forced variability is defined from the analysis of the ensemble mean and the internal variability from the analysis of deviations from the ensemble mean. Emphasis is put on interannual variability of sea level pressure and 500-hPa geopotential height for the Northern Hemisphere winter. In view of the large systematic errors related to the relatively small number of realizations, unbiased variance estimators have been developed. Although statistical significance is not reached in some extratropical regions, large significant extratropical responses are found at the North Pacific-Alaska sector for SLP and over western Canada and the Aleutians for 500-hPa geopotential height. The influence of SST variations on internal variability is also examined by using a 7-year simulation using the climatological SST seasonal cycle. It is found that interannual SST changes strongly influence the geographical distribution of internal variability; in particular, it tends to increase it over oceans. EOF decompositions, showing that the model realistically simulates the leading observed variability modes. The geographical structure of internal variability patterns is found to be similar to that of total variability, although similar modes tend to evolve rather differently in time. The zonally symmetric seesaw dominates the internal variability for both observed and climatologically prescribed SST. 46 refs., 15 figs., 3 tabs.

  15. a Mesoscale Planetary Boundary Layer Numerical Model for Simulations of Topographically Induced Circulations.

    NASA Astrophysics Data System (ADS)

    Huang, Ching-Yuang Albert

    1990-01-01

    A mesoscale planetary boundary layer (PBL) numerical model is developed to investigate airflow over complex topography. The model physics includes PBL turbulent transfer, atmospheric longwave and shortwave radiation, diurnal energy budgets over ground, cloud microphysics and subgrid cumulus parameterization. The model utilizes a new fourth order Crowley advection scheme which preserves phase and amplitude much better than other Crowley schemes. Turbulence closures using the turbulent kinetic energy (TKE) and dissipation (varepsilon ) equations are investigated with the level 2.5 scheme of Mellor and Yamada (1982) to better determine eddy diffusivities. One-dimensional (1-D) model results show that the PBL flows under various stability conditions are not significantly sensitive to the modified Blackadar's and Kolmogorov's eddy mixing length formations, although the latter yields excessively large mixing lengths in the entrainment region of the upper PBL. With the same prognostic TKE equation, the model results show insensitivity of the 1-D flow to the details of diagnostic formulations in the closures and to eddy Prandtl numbers. A 2-D model is used to stimulate January 28 cold -air outbreak over the Gulf Stream region during the IOP -2 (Intensive Observation Period) of the 1986 Genesis of Atlantic Lows Experiment (GALE). The modeled 2-D circulation system is found to be sensitive to Prandtl number, in contrast to the 1-D model results. Prandtl number becomes increasingly important as the clouds begin to interact with the marine boundary layer (MBL). Using the E-varepsilon closure, the model predicts the observed MBL structure that includes a low level jet west of the Gulf Stream warm core and a constrained boundary layer height due to the middle-level stable layer. Two cases with 3-D idealized flow are also simulated for the same GALE IOP. For the easterly onshore ambient flow, a confluence zone appears near the coastline in response to the strong oceanic

  16. Acute effects of a large bolide impact simulated by a global atmospheric circulation model

    NASA Technical Reports Server (NTRS)

    Thompson, Starley L.; Crutzen, P. J.

    1988-01-01

    The goal is to use a global three-dimensional atmospheric circulation model developed for studies of atmospheric effects of nuclear war to examine the time evolution of atmospheric effects from a large bolide impact. The model allows for dust and NOx injection, atmospheric transport by winds, removal by precipitation, radiative transfer effects, stratospheric ozone chemistry, and nitric acid formation and deposition on a simulated Earth having realistic geography. Researchers assume a modest 2 km-diameter impactor of the type that could have formed the 32 km-diameter impact structure found near Manson, Iowa and dated at roughly 66 Ma. Such an impact would have created on the order of 5 x 10 to the 10th power metric tons of atmospheric dust (about 0.01 g cm(-2) if spread globally) and 1 x 10 to the 37th power molecules of NO, or two orders of magnitude more stratospheric NO than might be produced in a large nuclear war. Researchers ignore potential injections of CO2 and wildfire smoke, and assume the direct heating of the atmosphere by impact ejecta on a regional scale is not large compared to absorption of solar energy by dust. Researchers assume an impact site at 45 N in the interior of present day North America.

  17. Response of the Tropical Atmospheric Circulation to Glacial Boundary Conditions Simulated by an Ensemble of Coupled Climate Models

    NASA Astrophysics Data System (ADS)

    di Nezio, P. N.; Clement, A. C.; Vecchi, G. A.

    2009-12-01

    The response of the tropical atmospheric circulation to Last Glacial Maximum (LGM) boundary conditions is analyzed using an ensemble of coordinated climate model experiments performed for the Paleoclimate Modelling Intercomparison Project Phase II. The multi-model changes in the surface circulation of the Tropical Pacific are dominated by cross-equatorial winds flowing from the Northern hemisphere (NH) to the Southern hemisphere (SH) along with a strengthening of the easterlies over the equatorial Pacific. The anomalous cross-equatorial winds have been typically associated with an anomalous Hadley cell with the ascending branch in the SH and the descending branch in the NH compensating changes in atmospheric heat transport. However, in this ensemble of coupled General Circulation Models (GCMs) the changes in the tropical circulation result from different forcing in each hemisphere. In the NH hemisphere the changes are dominated by the topography of the ice sheets, while in the SH the changes result from cooling due to decreased CO2. The changes in circulation due to the topography of the icesheets are diagnosed using a steady s-coordinate primitive equation model linearized about a zonally symmetric basic state that solves for the eddy component of the circulation. The solutions from this model for each GCM indicate that differences in the simulation of the mean climate result in differences in the response to LGM topography. The multi-model atmospheric response in the NH is analogous to the expansion of the Aleutian low during boreal winter in the present climate, when the NH subtropical high is squeezed southeastward by an expanded Aleutian low. In the SH the models simulate an eastward expansion of the South Pacific Convergence Zone and contraction of the eastern Pacific dry zone consistent with reduced subsidence associated with a slowing down of the SH Hadley cell. This eastward shift in the mean climatology results in weakened trade winds. In addition to the

  18. General circulation model simulations of recent cooling in the east-central United States

    NASA Astrophysics Data System (ADS)

    Robinson, Walter A.; Reudy, Reto; Hansen, James E.

    2002-12-01

    In ensembles of retrospective general circulation model (GCM) simulations, surface temperatures in the east-central United States cool between 1951 and 1997. This cooling, which is broadly consistent with observed surface temperatures, is present in GCM experiments driven by observed time varying sea-surface temperatures (SSTs) in the tropical Pacific, whether or not increasing greenhouse gases and other time varying climate forcings are included. Here we focus on ensembles with fixed radiative forcing and with observed varying SST in different regions. In these experiments the trend and variability in east-central U.S. surface temperatures are tied to tropical Pacific SSTs. Warm tropical Pacific SSTs cool U.S. temperatures by diminishing solar heating through an increase in cloud cover. These associations are embedded within a year-round response to warm tropical Pacific SST that features tropospheric warming throughout the tropics and regions of tropospheric cooling in midlatitudes. Precipitable water vapor over the Gulf of Mexico and the Caribbean and the tropospheric thermal gradient across the Gulf Coast of the United States increase when the tropical Pacific is warm. In observations, recent warming in the tropical Pacific is also associated with increased precipitable water over the southeast United States. The observed cooling in the east-central United States, relative to the rest of the globe, is accompanied by increased cloud cover, though year-to-year variations in cloud cover, U.S. surface temperatures, and tropical Pacific SST are less tightly coupled in observations than in the GCM.

  19. Interannual tropical rainfall variability in general circulation model simulations associated with the atmospheric model intercomparison project

    SciTech Connect

    Sperber, K.R.; Palmer, T.N.

    1996-11-01

    The interannual variability of rainfall over the Indian subcontinent, the African Sahel, and the Nordeste region of Brazil have been evaluated in 32 models for the period 1979 - 88 as part of the Atmospheric Model Intercomparison Project (AMIP). The interannual variations of Nordeste rainfall are the most readily captured, owing to the intimate link with Pacific and Atlantic sea surface temperatures. The precipitation variations over India and the Sahel are less well simulated. Additionally, an Indian monsoon wind shear index was calculated for each model. This subset of models also had a rainfall climatology that was in better agreement with observations, indicating a link between systematic model error and the ability to simulate interannual variations. A suite of six European Centre for Medium-Range Weather Forecasts (ECMWF) AMIP runs (differing only in their initial conditions) have also been examined. As observed, all-India rainfall was enhanced in 1988 relative to 1987 in each of these realizations. All-India rainfall variability during other years showed little or no predictability, possibly due to internal chaotic dynamics associated with intraseasonal monsoon fluctuations and/or unpredictable land surface process interactions. The interannual variations of Nordeste rainfall were best represented. The State University of New York at Albany /National Center for Atmospheric Research Genesis model was run in five initial condition realizations. In this model, the Nordeste rainfall variability was also best reproduced. However, for all regions the skill was less than that of the ECMWF model. The relationships of the all-India and Sahel rainfall/SST teleconnections with horizontal resolution, convection scheme closure, and numerics have been evaluated. 64 refs., 13 figs., 3 tabs.

  20. Simulation of the Low-Level-Jet by general circulation models

    SciTech Connect

    Ghan, S.J.

    1996-04-01

    To what degree is the low-level jet climatology and it`s impact on clouds and precipitation being captured by current general circulation models? It is hypothesised that a need for a pramaterization exists. This paper describes this parameterization need.

  1. Role of a cumulus parameterization scheme in simulating atmospheric circulation and rainfall in the nine-layer Goddard Laboratory for Atmospheres General Circulation Model

    NASA Technical Reports Server (NTRS)

    Sud, Y. C.; Chao, Winston C.; Walker, G. K.

    1992-01-01

    The influence of a cumulus convection scheme on the simulated atmospheric circulation and hydrologic cycle is investigated by means of a coarse version of the GCM. Two sets of integrations, each containing an ensemble of three summer simulations, were produced. The ensemble sets of control and experiment simulations are compared and differentially analyzed to determine the influence of a cumulus convection scheme on the simulated circulation and hydrologic cycle. The results show that cumulus parameterization has a very significant influence on the simulation circulation and precipitation. The upper-level condensation heating over the ITCZ is much smaller for the experiment simulations as compared to the control simulations; correspondingly, the Hadley and Walker cells for the control simulations are also weaker and are accompanied by a weaker Ferrel cell in the Southern Hemisphere. Overall, the difference fields show that experiment simulations (without cumulus convection) produce a cooler and less energetic atmosphere.

  2. The Response of the South Asian Summer Monsoon Circulation to Intensified Irrigation in Global Climate Model Simulations

    NASA Technical Reports Server (NTRS)

    Shukla, Sonali P.; Puma, Michael J.; Cook, Benjamin I.

    2013-01-01

    Agricultural intensification in South Asia has resulted in the expansion and intensification of surface irrigation over the twentieth century. The resulting changes to the surface energy balance could affect the temperature contrasts between the South Asian land surface and the equatorial Indian Ocean, potentially altering the South Asian Summer Monsoon (SASM) circulation. Prior studies have noted apparent declines in the monsoon intensity over the twentieth century and have focused on how altered surface energy balances impact the SASM rainfall distribution. Here, we use the coupled Goddard Institute for Space Studies ModelE-R general circulation model to investigate the impact of intensifying irrigation on the large-scale SASM circulation over the twentieth century, including how the effect of irrigation compares to the impact of increasing greenhouse gas (GHG) forcing. We force our simulations with time-varying, historical estimates of irrigation, both alone and with twentieth century GHGs and other forcings. In the irrigation only experiment, irrigation rates correlate strongly with lower and upper level temperature contrasts between the Indian sub-continent and the Indian Ocean (Pearson's r = -0.66 and r = -0.46, respectively), important quantities that control the strength of the SASM circulation. When GHG forcing is included, these correlations strengthen: r = -0.72 and r = -0.47 for lower and upper level temperature contrasts, respectively. Under irrigated conditions, the mean SASM intensity in the model decreases only slightly and insignificantly. However, in the simulation with irrigation and GHG forcing, inter-annual variability of the SASM circulation decreases by *40 %, consistent with trends in the reanalysis products. This suggests that the inclusion of irrigation may be necessary to accurately simulate the historical trends and variability of the SASM system over the last 50 years. These findings suggest that intensifying irrigation, in concert with

  3. Experiments in monthly mean simulation of the atmosphere with a coarse-mesh general circulation model

    NASA Technical Reports Server (NTRS)

    Lutz, R. J.; Spar, J.

    1978-01-01

    The Hansen atmospheric model was used to compute five monthly forecasts (October 1976 through February 1977). The comparison is based on an energetics analysis, meridional and vertical profiles, error statistics, and prognostic and observed mean maps. The monthly mean model simulations suffer from several defects. There is, in general, no skill in the simulation of the monthly mean sea-level pressure field, and only marginal skill is indicated for the 850 mb temperatures and 500 mb heights. The coarse-mesh model appears to generate a less satisfactory monthly mean simulation than the finer mesh GISS model.

  4. The global distribution of natural tritium in precipitation simulated with an Atmospheric General Circulation Model and comparison with observations

    NASA Astrophysics Data System (ADS)

    Cauquoin, A.; Jean-Baptiste, P.; Risi, C.; Fourré, É.; Stenni, B.; Landais, A.

    2015-10-01

    The description of the hydrological cycle in Atmospheric General Circulation Models (GCMs) can be validated using water isotopes as tracers. Many GCMs now simulate the movement of the stable isotopes of water, but here we present the first GCM simulations modelling the content of natural tritium in water. These simulations were obtained using a version of the LMDZ General Circulation Model enhanced by water isotopes diagnostics, LMDZ-iso. To avoid tritium generated by nuclear bomb testing, the simulations have been evaluated against a compilation of published tritium datasets dating from before 1950, or measured recently. LMDZ-iso correctly captures the observed tritium enrichment in precipitation as oceanic air moves inland (the so-called continental effect) and the observed north-south variations due to the latitudinal dependency of the cosmogenic tritium production rate. The seasonal variability, linked to the stratospheric intrusions of air masses with higher tritium content into the troposphere, is correctly reproduced for Antarctica with a maximum in winter. LMDZ-iso reproduces the spring maximum of tritium over Europe, but underestimates it and produces a peak in winter that is not apparent in the data. This implementation of tritium in a GCM promises to provide a better constraint on: (1) the intrusions and transport of air masses from the stratosphere, and (2) the dynamics of the modelled water cycle. The method complements the existing approach of using stable water isotopes.

  5. Modeling and simulation of liquid-solid circulating fluidized bed ion exchange system for continuous protein recovery.

    PubMed

    Mazumder, Jahirul; Zhu, Jingxu; Bassi, Amarjeet S; Ray, Ajay K

    2009-09-01

    Liquid-solid circulating fluidized bed (LSCFB) is an integrated two-column (downcomer and riser) system which can accommodate two separate processes (adsorption and desorption) in the same unit with continuous circulation of the solid particles between the two columns. In this study, a mathematical model based on the assumption of homogeneous fluidization was developed considering hydrodynamics, adsorption-desorption kinetics and liquid-solid mass transfer. The simulation results showed good agreement with the available experimental results for continuous protein recovery. A parametric sensitivity study was performed to better understand the influence of different operating parameters on the BSA adsorption and desorption capacity of the system. The model developed can easily be extended to other applications of LSCFB. PMID:19466748

  6. 3D Simulations of the Early Mars Climate with a General Circulation Model

    NASA Technical Reports Server (NTRS)

    Forget, F.; Haberle, R. M.; Montmessin, F.; Cha, S.; Marcq, E.; Schaeffer, J.; Wanherdrick, Y.

    2003-01-01

    The environmental conditions that existed on Mars during the Noachian period are subject to debate in the community. In any case, there are compelling evidence that these conditions were different than what they became later in the amazonian and possibly the Hesperian periods. Indeed, most of the old cratered terrains are disected by valley networks (thought to have been carved by flowing liquid water), whereas younger surface are almost devoid of such valleys. In addition, there are evidence that the erosion rate was much higher during the early noachian than later. Flowing water is surprising on early Mars because the solar luminosity was significantly lower than today. Even with the thick atmosphere (up to several bars).To improve our understanding of the early Mars Climate, we have developed a 3D general circulation model similar to the one used on current Earth or Mars to study the details of the climate today. Our first objective is to answer the following questions : how is the Martian climate modified if 1) the surface pressure is increased up to several bars (our baseline: 2 bars) and 2) if the sun luminosity is decreased by 25 account the heat possibly released by impacts during short periods, although it may have played a role .For this purpose, we have coupled the Martian General Circulation model developed at LMD with a sophisticated correlated k distribution model developped at NASA Ames Research Center. It is a narrow band model which computes the radiative transfer at both solar and thermal wavelengths (from 0.3 to 250 microns).

  7. A nesting model for bias correction of variability at multiple time scales in general circulation model precipitation simulations

    NASA Astrophysics Data System (ADS)

    Johnson, Fiona; Sharma, Ashish

    2012-01-01

    Climate change impact assessments of water resources systems require simulations of precipitation and evaporation that exhibit distributional and persistence attributes similar to the historical record. Specifically, there is a need to ensure general circulation model (GCM) simulations of rainfall for the current climate exhibit low-frequency variability that is consistent with observed data. Inability to represent low-frequency variability in precipitation and flow leads to biased estimates of the security offered by water resources systems in a warmer climate. This paper presents a method to postprocess GCM precipitation simulations by imparting correct distributional and persistence attributes, resulting in sequences that are representative of observed records across a range of time scales. The proposed approach is named nesting bias correction (NBC), the rationale being to correct distributional and persistence bias from fine to progressively longer time scales. In the results presented here, distributional attributes have been represented by order 1 and 2 moments with persistence represented by lag 1 autocorrelation coefficients at monthly and annual time scales. The NBC method was applied to the Commonwealth Scientific and Industrial Research Organisation (CSIRO) Mk3.5 and MIROC 3.2 hires rainfall simulations for Australia. It was found that the nesting method worked well to correct means, standard deviations, and lag 1 autocorrelations when the biases in the raw GCM outputs were not too large. While the bias correction improves the representation of distributional and persistence attributes at the time scales considered, there is room for representation of longer-term persistence by extending to time scales longer than a year.

  8. Simulation of the mantle and crustal Helium isotope signature in the Mediterranean Sea using a high resolution regional circulation model

    NASA Astrophysics Data System (ADS)

    Ayache, Mohamed; Dutay, Jean-claude; Jean-baptiste, Philippe

    2015-04-01

    Helium isotopes (3He, 4He) are useful tracers for investigating the deep ocean circulation and for evaluating ocean general circulation models, because helium is a stable and conservative nuclide that does not take part in any chemical or biological processes. Helium in the ocean originates from three different sources: namely, (i) gas dissolution in equilibrium with atmospheric helium, (ii) helium-3 addition by radioactive decay of tritium (called tritiugenic helium), and (iii) injection of helium-3 and helium-4 by the submarine volcanic activity which occurs mainly at plate boundaries, and also addition of helium-4 from the crust and sedimentary cover by α-decay of uranium and thorium contained in various minerals (called terrigenic helium). Here we present the first simulation of the helium isotope distribution in the whole Mediterranean Sea, using a high resolution model (NEMO-MED12). The simulation was produced by building a simple source function for helium produced by submarine volcanic degassing in the main active areas of the Mediterranean, and by crustal degassing at sea bottom, based on previous estimates of the total flux of helium into the oceans. In addition to providing constraints on the degassing flux, our work provides information on the variability of the thermohaline circulation and the ventilation of the deep waters to constrain the degree to which the NEMO-MED12 can reproduce correctly the main hydrographic features of the Mediterranean Sea circulation. This study is part of the work carried out to assess the robustness of the NEMO-MED12 model, which will be used to study the evolution of the climate and its effect on the biogeochemical cycles in the Mediterranean Sea, and to improve our ability to predict the future evolution of the Mediterranean Sea under the increasing anthropogenic pressure.

  9. Modeling blood flow circulation in intracranial arterial networks: a comparative 3D/1D simulation study.

    PubMed

    Grinberg, L; Cheever, E; Anor, T; Madsen, J R; Karniadakis, G E

    2011-01-01

    We compare results from numerical simulations of pulsatile blood flow in two patient-specific intracranial arterial networks using one-dimensional (1D) and three-dimensional (3D) models. Specifically, we focus on the pressure and flowrate distribution at different segments of the network computed by the two models. Results obtained with 1D and 3D models with rigid walls show good agreement in massflow distribution at tens of arterial junctions and also in pressure drop along the arteries. The 3D simulations with the rigid walls predict higher amplitude of the flowrate and pressure temporal oscillations than the 1D simulations with compliant walls at various segments even for small time-variations in the arterial cross-sectional areas. Sensitivity of the flow and pressure with respect to variation in the elasticity parameters is investigated with the 1D model. PMID:20661645

  10. Multidecadal Variability Simulated With an Atmospheric General Circulation Model Forced With Observed Sea Surface Temperature

    NASA Astrophysics Data System (ADS)

    Grosfeld, K.; Rimbu, N.; Lohmann, G.; Lunkeit, F.

    2002-12-01

    We investigate the response of an atmospheric general circulation model to observed sea surface temperature for the instrumental period 1856-2000. The model used is the {nderline P}ortable {nderline U}niversity {nderline M}odel of the {nderline A}tmosphere (PUMA) developed at the University of Hamburg for long-term climate studies. When the model is forced with global sea surface temperatures (SSTs) the model interdecadal variability is dominated by the Atlantic Interdecadal Mode (AIM) and its associated teleconnection patterns. The modeled interdecadal variability sea surface patterns are in good agreement with analysis of observational time series in an ensemble mode integration. Positive SST anomalies and a sea level pressure (SLP) dipole pattern dominate the North Atlantic while a strong positive anomaly in SLP is characteristic for the North Pacific Ocean. Although the observational database is short, investigations of the typical AIM patterns before and after the climate shift in the 1970's suggest an oscillatory multidecadal mode rather than a singular event for that period. Additional experiments with ''Atlantic only'' forcing depict strong sensitivities of the relative roles of Atlantic and Pacific SST data initiating variability at multidecadal time scales. Our results have implications for climate predictability on long time scales from observed SST data.

  11. 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.

  12. 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.

  13. 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

  14. A Variable Resolution Stretched Grid General Circulation Model: Regional Climate Simulation

    NASA Technical Reports Server (NTRS)

    Fox-Rabinovitz, Michael S.; Takacs, Lawrence L.; Govindaraju, Ravi C.; Suarez, Max J.

    2000-01-01

    The development of and results obtained with a variable resolution stretched-grid GCM for the regional climate simulation mode, are presented. A global variable resolution stretched- grid used in the study has enhanced horizontal resolution over the U.S. as the area of interest The stretched-grid approach is an ideal tool for representing regional to global scale interaction& It is an alternative to the widely used nested grid approach introduced over a decade ago as a pioneering step in regional climate modeling. The major results of the study are presented for the successful stretched-grid GCM simulation of the anomalous climate event of the 1988 U.S. summer drought- The straightforward (with no updates) two month simulation is performed with 60 km regional resolution- The major drought fields, patterns and characteristics such as the time averaged 500 hPa heights precipitation and the low level jet over the drought area. appear to be close to the verifying analyses for the stretched-grid simulation- In other words, the stretched-grid GCM provides an efficient down-scaling over the area of interest with enhanced horizontal resolution. It is also shown that the GCM skill is sustained throughout the simulation extended to one year. The developed and tested in a simulation mode stretched-grid GCM is a viable tool for regional and subregional climate studies and applications.

  15. The Simulation of Stationary and Transient Geopotential-Height Eddies in January and July with a Spectral General Circulation Model.

    NASA Astrophysics Data System (ADS)

    Malone, Robert C.; Pitcher, Eric J.; Blackmon, Maurice L.; Puri, Kamal; Bourke, William

    1984-04-01

    We examine the characteristics of stationary and transient eddies in the geopotential-height field as simulated by a spectral general circulation model. The model possesses a realistic distribution of continents and oceans and realistic, but smoothed, topography. Two simulations with perpetual January and July forcing by climatological sea surface temperatures, sea ice, and insulation were extended to 1200 days, of which the final 600 days were used for the results in this study.We find that the stationary waves are well simulated in both seasons in the Northern Hemisphere, where strong forcing by orography and land-sea thermal contrasts exists. However, in the Southern Hemisphere, where no continents are present in midlatitudes, the stationary waves have smaller amplitude than that observed in both seasons.In both hemispheres, the transient eddies are well simulated in the winter season but are too weak in the summer season. The model fails to generate a sufficiently intense summertime midlatitude jet in either hemisphere, and this results in a low level of transient activity. The variance in the tropical troposphere is very well simulated. We examine the geographical distribution and vertical structure of the transient eddies. Fourier analysis in zonal wavenumber and temporal filtering am used to display the wavelength and frequency characteristics of the eddies.

  16. Earth radiation budget and cloudiness simulations with a general circulation model

    NASA Technical Reports Server (NTRS)

    HARSHVARDHAN; Randall, David A.; Corsetti, Thomas G.; Dazlich, Donald A.

    1989-01-01

    A GCM with new parameterizations of solar and terrestrial radiation, parameterized cloud optical properties, and a simple representation of the cloud liquid water feedback is used with several observational data sets to analyze the effects of cloudiness on the earth's radiation budget. The January and July results from the model are in reasonable agreement with data from Nimbus-7. It is found that the simulated cloudiness overpredicts subtropical and midlatitude cloudiness. The simulated atmospheric cloud radiative forcing is examined. The clear-sky radiation fields obtained by two methods of Cess and Potter (1987) are compared. Also, a numerical experiment was performed to determine the effects of the water vapor continuum on the model results.

  17. Comparison of spectral surface albedos and their impact on the general circulation model simulated surface climate

    NASA Astrophysics Data System (ADS)

    Roesch, A.; Wild, M.; Pinker, R.; Ohmura, A.

    2002-07-01

    This study investigates the impact of spectrally resolved surface albedo on the total surface albedo. The neglect of albedo variation within the shortwave spectrum may lead to substantial errors as the atmospheric water greatly influences the spectral distribution of the incoming radiation. It is shown that ignoring the spectral dependence of the surface albedo will affect the predicted climate. The study reveals substantial changes in the climate over northern Africa when modifying the surface albedo of the Sahara deserts. Detailed information is given how the European Center/Hamburg General Circulation Model (ECHAM4) can be extended to include surface boundary conditions for both the visible and near-infrared incoming radiation. This comprises global climatologies for both the visible and near-infrared albedo for snow-free conditions, as well as the corresponding albedo values over snow, land-/sea ice and over snow covered forests. Comparisons between several available surface albedo climatologies and a newly compiled albedo data set show substantial scatter in estimated albedos. The largest albedo differences are found in snow covered forest regions as well as in arid and semi-arid terrains.

  18. The use of a numerical model to simulate the cavo-pulmonary assistance in Fontan circulation: a preliminary verification.

    PubMed

    Di Molfetta, Arianna; Amodeo, Antonio; Fresiello, Libera; Filippelli, Sergio; Pilati, Mara; Iacobelli, Roberta; Adorisio, Rachele; Colella, Dionisio; Ferrari, Gianfranco

    2016-06-01

    The lack of an established experience on the use of VAD for the cavo-pulmonary assistance leads to the need of dedicated VADs development and animal experiments. A dedicated numerical model could support clinical and experimental strategies design and new VADs testing. The aim of this work is to perform a preliminary verification of a lumped parameter model of the cardiovascular system to simulate Fontan physiology and the effect of cavo-pulmonary assistance. Literature data of 4 pigs were used to simulate animals' baseline, and then the model was tested in simulating Fontan circulation and cavo-pulmonary-assisted condition comparing the simulation outcome (Sim) with measured literature data (Me). The results show that the numerical model can well reproduce experimental data in all three conditions (baseline, Fontan and assisted Fontan) [cardiac output (l/min): Me = 2.8 ± 1.7, Sim = 2.8 ± 1.8; ejection fraction (%): Me = 57 ± 17, Sim = 54 ± 17; arterial systemic pressure (mmHg): Me = 41.8 ± 18.6, Sim = 43.8 ± 18.1; pulmonary arterial pressure (mmHg): Me = 15.4 ± 8.9, Sim = 17.7 ± 9.9; caval pressure (mmHg): Me = 6.8 ± 4.1, Sim = 7 ± 4.6]. Systolic elastance, arterial systemic and arterial pulmonary resistances increase (10, 69, and 100 %) passing from the biventricular circulation to the Fontan physiology and then decrease (21, 39, and 50 %) once the VAD was implanted. The ventricular external work decreases (71 %) passing from the biventricular circulation to the Fontan physiology and it increases three times after the VAD implantation in parallel with the VAD power consumption. A numerical model could support clinicians in an innovative and challenging field as the use of VAD to assist the Fontan physiology and it could be helpful to personalize the VAD insertion on the base of ventricular systo-diastolic function, circulatory parameters and energetic variables. PMID:26545595

  19. The atmospheric chemistry general circulation model ECHAM5/MESSy1: consistent simulation of ozone from the surface to the mesosphere

    NASA Astrophysics Data System (ADS)

    Jöckel, P.; Tost, H.; Pozzer, A.; Brühl, C.; Buchholz, J.; Ganzeveld, L.; Hoor, P.; Kerkweg, A.; Lawrence, M. G.; Sander, R.; Steil, B.; Stiller, G.; Tanarhte, M.; Taraborrelli, D.; van Aardenne, J.; Lelieveld, J.

    2006-11-01

    The new Modular Earth Submodel System (MESSy) describes atmospheric chemistry and meteorological processes in a modular framework, following strict coding standards. It has been coupled to the ECHAM5 general circulation model, which has been slightly modified for this purpose. A 90-layer model setup up to 0.01 hPa was used at spectral T42 resolution to simulate the lower and middle atmosphere. With the high vertical resolution the model simulates the Quasi-Biennial Oscillation. The model meteorology has been tested to check the influence of the changes to ECHAM5 and the radiation interactions with the new representation of atmospheric composition. In the simulations presented here a Newtonian relaxation technique was applied in the tropospheric part of the domain to weakly nudge the model towards the analysed meteorology during the period 1998-2005. This allows an efficient and direct evaluation with satellite and in-situ data. It is shown that the tropospheric wave forcing of the stratosphere in the model suffices to reproduce major stratospheric warming events leading e.g. to the vortex split over Antarctica in 2002. Characteristic features such as dehydration and denitrification caused by the sedimentation of polar stratospheric cloud particles and ozone depletion during winter and spring are simulated well, although ozone loss in the lower polar stratosphere is slightly underestimated. The model realistically simulates stratosphere-troposphere exchange processes as indicated by comparisons with satellite and in situ measurements. The evaluation of tropospheric chemistry presented here focuses on the distributions of ozone, hydroxyl radicals, carbon monoxide and reactive nitrogen compounds. In spite of minor shortcomings, mostly related to the relatively coarse T42 resolution and the neglect of inter-annual changes in biomass burning emissions, the main characteristics of the trace gas distributions are generally reproduced well. The MESSy submodels and the

  20. Interannual Variability of Martian Global Dust Storms: Simulations with a Low-Order Model of the General Circulation

    NASA Technical Reports Server (NTRS)

    Pankine, A. A.; Ingersoll, Andrew P.

    2002-01-01

    We present simulations of the interannual variability of martian global dust storms (GDSs) with a simplified low-order model (LOM) of the general circulation. The simplified model allows one to conduct computationally fast long-term simulations of the martian climate system. The LOM is constructed by Galerkin projection of a 2D (zonally averaged) general circulation model (GCM) onto a truncated set of basis functions. The resulting LOM consists of 12 coupled nonlinear ordinary differential equations describing atmospheric dynamics and dust transport within the Hadley cell. The forcing of the model is described by simplified physics based on Newtonian cooling and Rayleigh friction. The atmosphere and surface are coupled: atmospheric heating depends on the dustiness of the atmosphere, and the surface dust source depends on the strength of the atmospheric winds. Parameters of the model are tuned to fit the output of the NASA AMES GCM and the fit is generally very good. Interannual variability of GDSs is possible in the IBM, but only when stochastic forcing is added to the model. The stochastic forcing could be provided by transient weather systems or some surface process such as redistribution of the sand particles in storm generating zones on the surface. The results are sensitive to the value of the saltation threshold, which hints at a possible feedback between saltation threshold and dust storm activity. According to this hypothesis, erodable material builds up its a result of a local process, whose effect is to lower the saltation threshold until a GDS occurs. The saltation threshold adjusts its value so that dust storms are barely able to occur.

  1. A general circulation model simulation of the springtime Antarctic ozone decrease and its impact on mid-latitudes

    SciTech Connect

    Cariolle, D.; Lasserre-Bigorry, A.; Royer, J.F. ); Geleyn, J.F. )

    1990-02-20

    Ozone is treated as an interactive variable calculated by means of a continuity equation which takes account of advection and photochemical production and loss. The ozone concentration is also used to compute the heating and cooling rates due to the absorption of solar ultraviolet radiation, and the infrared emission in the stratosphere. The daytime ozone decrease due to the perturbed chlorine chemistry found at high southern latitudes is introduced as an extra loss in the ozone continuity equation. Results of the perturbed simulation show a very good agreement with the ozone measurements made during spring 1987. The simulation also shows the development of a high-latitude anomalous circulation, with a warming of the upper stratosphere resulting mainly from dynamical heating. In addition, a substantial ozone decrease is found at mid-latitudes in a thin stratospheric layer located between the 390 and the 470 K {theta} surfaces. A significant residual ozone decrease is found at the end of the model integration, 7 months after the final warming and the vortex breakdown. If there is a significant residual ozone decrease in the atmosphere, the ozone trends predicted by photochemical models which do not take into account the high-latitude perturbed chemistry are clearly inadequate. Finally, it is concluded that further model simulations at higher horizontal resolution, possibly with a better representation of the heterogeneous chemistry, will be needed to evaluate with more confidence the magnitude of the mid-latitudinal ozone depletion induced by the ozone hole formation.

  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. Variability of the Martian thermosphere during eight Martian years as simulated by a ground-to-exosphere global circulation model

    NASA Astrophysics Data System (ADS)

    González-Galindo, F.; López-Valverde, M. A.; Forget, F.; García-Comas, M.; Millour, E.; Montabone, L.

    2015-11-01

    Using a ground-to-exosphere general circulation model for Mars we have simulated the variability of the dayside temperatures at the exobase during eight Martian years (MY, from MY24 to MY31, approximately from 1998 to 2013), taking into account the observed day-to-day solar and dust load variability. We show that the simulated temperatures are in good agreement with the exospheric temperatures derived from Precise Orbit Determination of Mars Global Surveyor. We then study the effects of the solar variability and of two planetary-encircling dust storms on the simulated temperatures. The seasonal effect produced by the large eccentricity of the Martian orbit translates in an aphelion-to-perihelion temperature contrast in every simulated year. However, the magnitude of this seasonal temperature variation is strongly affected by the solar conditions, ranging from 50 K for years corresponding to solar minimum conditions to almost 140 K during the last solar maximum. The 27 day solar rotation cycle is observed on the simulated temperatures at the exobase, with average amplitude of the temperature oscillation of 2.6 K but with a significant interannual variability. These two results highlight the importance of taking into account the solar variability when simulating the Martian upper atmosphere and likely have important implications concerning the atmospheric escape rate. We also show that the global dust storms in MY25 and MY28 have a significant effect on the simulated temperatures. In general, they increase the exospheric temperatures over the low latitude and midlatitude regions and decrease them in the polar regions.

  4. The atmospheric chemistry general circulation model ECHAM5/MESSy1: consistent simulation of ozone from the surface to the mesosphere

    NASA Astrophysics Data System (ADS)

    Jöckel, P.; Tost, H.; Pozzer, A.; Brühl, C.; Buchholz, J.; Ganzeveld, L.; Hoor, P.; Kerkweg, A.; Lawrence, M. G.; Sander, R.; Steil, B.; Stiller, G.; Tanarhte, M.; Taraborrelli, D.; van Aardenne, J.; Lelieveld, J.

    2006-07-01

    The new Modular Earth Submodel System (MESSy) describes atmospheric chemistry and meteorological processes in a modular framework, following strict coding standards. It has been coupled to the ECHAM5 general circulation model, which has been slightly modified for this purpose. A 90-layer model version up to 0.01 hPa was used at T42 resolution (~2.8 latitude and longitude) to simulate the lower and middle atmosphere. The model meteorology has been tested to check the influence of the changes to ECHAM5 and the radiation interactions with the new representation of atmospheric composition. A Newtonian relaxation technique was applied in the tropospheric part of the domain to weakly nudge the model towards the analysed meteorology during the period 1998-2005. It is shown that the tropospheric wave forcing of the stratosphere in the model suffices to reproduce the Quasi-Biennial Oscillation and major stratospheric warming events leading e.g. to the vortex split over Antarctica in 2002. Characteristic features such as dehydration and denitrification caused by the sedimentation of polar stratospheric cloud particles and ozone depletion during winter and spring are simulated accurately, although ozone loss in the lower polar stratosphere is slightly underestimated. The model realistically simulates stratosphere-troposphere exchange processes as indicated by comparisons with satellite and in situ measurements. The evaluation of tropospheric chemistry presented here focuses on the distributions of ozone, hydroxyl radicals, carbon monoxide and reactive nitrogen compounds. In spite of minor shortcomings, mostly related to the relatively coarse T42 resolution and the neglect of interannual changes in biomass burning emissions, the main characteristics of the trace gas distributions are generally reproduced well. The MESSy submodels and the ECHAM5/MESSy1 model output are available through the internet on request.

  5. Zonal wavenumber three traveling waves in the northern hemisphere of Mars simulated with a general circulation model

    NASA Astrophysics Data System (ADS)

    Wang, Huiqun; Richardson, Mark I.; Toigo, Anthony D.; Newman, Claire E.

    2013-04-01

    Observations suggest a strong correlation between curvilinear shaped traveling dust storms (observed in wide angle camera images) and eastward traveling zonal wave number m = 3 waves (observed in thermal data) in the northern mid and high latitudes during the fall and winter. Using the MarsWRF General Circulation Model, we have investigated the seasonality, structure and dynamics of the simulated m = 3 traveling waves and tested the hypothesis that traveling dust storms may enhance m = 3 traveling waves under certain conditions. Our standard simulation using a prescribed "MGS dust scenario" can capture the observed major wave modes and strong near surface temperature variations before and after the northern winter solstice. The same seasonal pattern is also shown by the simulated near surface meridional wind, but not by the normalized surface pressure. The simulated eastward traveling 1.4 < T < 10 sol m = 3 waves are confined near the surface in terms of the temperature perturbation, EP flux and eddy available potential energy, and they extend higher in terms of the eddy winds and eddy kinetic energy. The signature of the simulated m = 3 traveling waves is stronger in the near surface meridional wind than in the near surface temperature field. Compared with the standard simulation, our test simulations show that the prescribed m = 3 traveling dust blobs can enhance the simulated m = 3 traveling waves during the pre- and post-solstice periods when traveling dust storms are frequently observed in images, and that they have negligible effect during the northern winter solstice period when traveling dust storms are absent. The enhancement is even greater in our simulation when dust is concentrated closer to the surface. Our simulations also suggest that dust within the 45-75°N band is most effective at enhancing the simulated m = 3 traveling waves. There are multiple factors influencing the strength of the simulated m = 3 traveling waves. Among those, our study

  6. Multiyear Simulations of the Martian Water Cycle with the Ames General Circulation Model

    NASA Technical Reports Server (NTRS)

    Haberle, R. M.; Schaeffer, J. R.; Nelli, S. M.; Murphy, J. R.

    2003-01-01

    Mars atmosphere is carbon dioxide dominated with non-negligible amounts of water vapor and suspended dust particles. The atmospheric dust plays an important role in the heating and cooling of the planet through absorption and emission of radiation. Small dust particles can potentially be carried to great altitudes and affect the temperatures there. Water vapor condensing onto the dust grains can affect the radiative properties of both, as well as their vertical extent. The condensation of water onto a dust grain will change the grain s fall speed and diminish the possibility of dust obtaining high altitudes. In this capacity, water becomes a controlling agent with regard to the vertical distribution of dust. Similarly, the atmosphere s water vapor holding capacity is affected by the amount of dust in the atmosphere. Dust is an excellent green house catalyst; it raises the temperature of the atmosphere, and thus, its water vapor holding capacity. There is, therefore, a potentially significant interplay between the Martian dust and water cycles. Previous research done using global, 3-D computer modeling to better understand the Martian atmosphere treat the dust and the water cycles as two separate and independent processes. The existing Ames numerical model will be employed to simulate the relationship between the Martian dust and water cycles by actually coupling the two cycles. Water will condense onto the dust, allowing the particle's radiative characteristics, fall speeds, and as a result, their vertical distribution to change. Data obtained from the Viking, Mars Pathfinder, and especially the Mars Global Surveyor missions will be used to determine the accuracy of the model results.

  7. 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

  8. 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

  9. 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.

  10. Anthropogenic forcing on the Hadley circulation in CMIP5 simulations

    NASA Astrophysics Data System (ADS)

    Tao, Lijun; Hu, Yongyun; Liu, Jiping

    2016-05-01

    Poleward expansion of the Hadley circulation has been an important topic in climate change studies in the past few years, and one of the critically important issues is how it is related to anthropogenic forcings. Using simulations from the coupled model intercomparison projection phase 5 (CMIP5), we study influences of anthropogenic forcings on the width and strength of the Hadley circulation. It is found that significant poleward expansion of the Hadley circulation can be reproduced in CMIP5 historical all-forcing simulations although the magnitude of trends is much weaker than observations. Simulations with individual forcings demonstrate that among three major types of anthropogenic forcings, increasing greenhouse gases (GHGs) and stratospheric ozone depletion all cause poleward expansion of the Hadley circulation, whereas anthropogenic aerosols do not have significant influences on the Hadley circulation. Increasing GHGs cause significant poleward expansion in both hemispheres, with the largest widening of the northern cell in boreal autumn. Stratospheric ozone depletion forces significant poleward expansion of the Hadley circulation for the southern cell in austral spring and summer and for the northern cell in boreal spring. In CMIP5 projection simulations for the twenty-first century, the magnitude of poleward expansion of the Hadley circulation increases with GHG forcing. On the other hand, ozone recovery competes with increasing GHGs in determining the width of the Hadley circulation, especially in austral summer. In both historical and projection simulations, the strength of the Hadley circulation shows significant weakening in winter in both hemispheres.

  11. A revised linear ozone photochemistry parameterization for use in transport and general circulation models: multi-annual simulations

    NASA Astrophysics Data System (ADS)

    Cariolle, D.; Teyssèdre, H.

    2007-01-01

    This article describes the validation of a linear parameterization of the ozone photochemistry for use in upper tropospheric and stratospheric studies. The present work extends a previously developed scheme by improving the 2D model used to derive the coefficients of the parameterization. The chemical reaction rates are updated from a compilation that includes recent laboratory works. Furthermore, the polar ozone destruction due to heterogeneous reactions at the surface of the polar stratospheric clouds is taken into account as a function of the stratospheric temperature and the total chlorine content. Two versions of the parameterization are tested. The first one only requires the resolution of a continuity equation for the time evolution of the ozone mixing ratio, the second one uses one additional equation for a cold tracer. The parameterization has been introduced into the chemical transport model MOCAGE. The model is integrated with wind and temperature fields from the ECMWF operational analyses over the period 2000-2004. Overall, the results show a very good agreement between the modelled ozone distribution and the Total Ozone Mapping Spectrometer (TOMS) satellite data and the "in-situ" vertical soundings. During the course of the integration the model does not show any drift and the biases are generally small. The model also reproduces fairly well the polar ozone variability, with notably the formation of "ozone holes" in the southern hemisphere with amplitudes and seasonal evolutions that follow the dynamics and time evolution of the polar vortex. The introduction of the cold tracer further improves the model simulation by allowing additional ozone destruction inside air masses exported from the high to the mid-latitudes, and by maintaining low ozone contents inside the polar vortex of the southern hemisphere over longer periods in spring time. It is concluded that for the study of climatic scenarios or the assimilation of ozone data, the present

  12. The variability, structure and energy conversion of the northern hemisphere traveling waves simulated in a Mars general circulation model

    NASA Astrophysics Data System (ADS)

    Wang, Huiqun; Toigo, Anthony D.

    2016-06-01

    Investigations of the variability, structure and energetics of the m = 1-3 traveling waves in the northern hemisphere of Mars are conducted with the MarsWRF general circulation model. Using a simple, annually repeatable dust scenario, the model reproduces many general characteristics of the observed traveling waves. The simulated m = 1 and m = 3 traveling waves show large differences in terms of their structures and energetics. For each representative wave mode, the geopotential signature maximizes at a higher altitude than the temperature signature, and the wave energetics suggests a mixed baroclinic-barotropic nature. There is a large contrast in wave energetics between the near-surface and higher altitudes, as well as between the lower latitudes and higher latitudes at high altitudes. Both barotropic and baroclinic conversions can act as either sources or sinks of eddy kinetic energy. Band-pass filtered transient eddies exhibit strong zonal variations in eddy kinetic energy and various energy transfer terms. Transient eddies are mainly interacting with the time mean flow. However, there appear to be non-negligible wave-wave interactions associated with wave mode transitions. These interactions include those between traveling waves and thermal tides and those among traveling waves.

  13. Solutions to the faint young Sun paradox simulated by a general circulation model

    NASA Astrophysics Data System (ADS)

    Wolf, Eric Theodore

    The faint young Sun paradox has dominated our thinking regarding early climate. Geological evidence abounds for warm, possibly hot, seawater temperatures and the proliferation of early life during the Archean period of Earth's history (3.8-2.5 Ga). However the standard solar model indicates that the Sun was only 75 to 82 percent as bright as today, implying an apparent contradiction between warm surface temperatures and weak solar irradiance. Geological evidence also places constraints on the amount of atmospheric carbon dioxide present early in Earth's history. Over the past four decades there has been much debate amongst geological, planetary, and climate science communities regarding how to properly resolve the issue of the faint young Sun. Up until very recently, 1-dimensional radiative convective models were the standard tool for deep paleoclimate modeling studies. These studies have notably lacked the ability to treat clouds, surface ice, and meridional energy transport. However, advancements in computing technology now allow us to tackle the faint young Sun paradox using a three-dimensional climate model. Here we use a modified version of the Community Atmosphere Model version 3 from the National Center for Atmospheric Research to study early climate. We find that resolving the faint young Sun paradox becomes less problematic when viewing a full representation of the climate system. Modest amounts of carbon dioxide and methane can provide adequate warming for the Archean within given constraints. Cooler climates with large ice caps but temperate tropical regions can be supported with even less carbon dioxide. The incorporation of systematic climate system differences expected during the Archean, such as fewer cloud condensation nuclei, reduced land albedos, and increased atmospheric nitrogen, can provide additional non-greenhouse means of warming the early Earth. A warm Archean no longer appears at odds with a faint young Sun. Here, we will also discuss the

  14. Importance of the Annual Cycles of SST and Solar Irradiance for Circulation and Rainfall: A Climate Model Simulation Study

    NASA Technical Reports Server (NTRS)

    Sud, Yogesh C.; Lau, William K. M.; Walker, G. K.; Mehta, V. M.

    2001-01-01

    Annual cycle of climate and precipitation is related to annual cycle of sunshine and sea-surface temperatures. Understanding its behavior is important for the welfare of humans worldwide. For example, failure of Asian monsoons can cause widespread famine and grave economic disaster in the subtropical regions. For centuries meteorologists have struggled to understand the importance of the summer sunshine and associated heating and the annual cycle of sea-surface temperatures (SSTs) on rainfall in the subtropics. Because the solar income is pretty steady from year to year, while SSTs depict large interannual variability as consequence of the variability of ocean dynamics, the influence of SSTs on the monsoons are better understood through observational and modeling studies whereas the relationship of annual rainfall to sunshine remains elusive. However, using NASA's state of the art climate model(s) that can generate realistic climate in a computer simulation, one can answer such questions. We asked the question: if there was no annual cycle of the sunshine (and its associated land-heating) or the SST and its associated influence on global circulation, what will happen to the annual cycle of monsoon rains? By comparing the simulation of a 4-year integration of a baseline Control case with two parallel anomaly experiments: 1) with annual mean solar and 2) with annual mean sea-surface temperatures, we were able to draw the following conclusions: (1) Tropical convergence zone and rainfall which moves with the Sun into the northern and southern hemispheres, specifically over the Indian, African, South American and Australian regions, is strongly modulated by the annual cycles of SSTs as well as solar forcings. The influence of the annual cycle of solar heating over land, however, is much stronger than the corresponding SST influence for almost all regions, particularly the subtropics; (2) The seasonal circulation patterns over the vast land-masses of the Northern

  15. Seasonal Simulations of the Planetary Boundary Layer and Boundary-Layer Stratocumulus Clouds with a General Circulation Model.

    NASA Astrophysics Data System (ADS)

    Randall, David A.; Abeles, James A.; Corsetti, Thomas G.

    1985-04-01

    The UCLA general circulation model (GCM) has been used to simulate the seasonally varying planetary boundary layer (PBL), as well as boundary-layer stratus and stratocumulus clouds. The PBL depth is a prognostic variable of the GCM, incorporated through the use of a vertical coordinate system in which the PBL is identified with the lowest model layer.Stratocumulus clouds are assumed to occur whenever the upper portion of the PBL becomes saturated, provided that the cloud-top entrainment instability does not occur. As indicated by Arakawa and Schubert, cumulus clouds are assumed to originate at the PBL top, and tend to make the PBL shallow by drawing on its mass.Results are presented from a three-year simulation, starting from a 31 December initial condition obtained from an earlier run with a different version of the model. The simulated seasonally varying climates of the boundary layer and free troposphere are realistic. The observed geographical and seasonal variations of stratocumulus cloudiness are fairly well simulated. The simulation of the stratocumulus clouds associated with wintertime cold-air outbreaks is particularly realistic. Examples are given of individual events. The positions of the subtropical marine stratocumulus regimes are realistically simulated, although their observed frequency of occurrence is seriously underpredicted. The observed summertime abundance of Arctic stratus clouds is also underpredicted.In the GCM results, the layer cloud instability appears to limit the extent of the marine subtropical stratocumulus regimes. The instability also frequently occurs in association with cumulus convection over land.Cumulus convection acts as a very significant sink of PBL mass throughout the tropics, and over the midlatitude continents in summer.Three experiments have been performed to investigate the sensitivity of the GCM results to aspects of the PBL and stratocumulus parameterizations. For all three experiments, the model was started from 1

  16. A dynamic simulation model for power plants with atmospheric and pressurized circulating fluidized bed combustion -- Interactions of plant components and design studies

    SciTech Connect

    Glasmacher-Remberg, C.; Fett, F.N.

    1999-07-01

    Power plants with atmospheric or pressurized circulating fluidized bed combustion are complex technical systems. The operation characteristics of these power plants depend on the behavior of the single components and their interactions. The theoretical understanding of power plant processes of this kind as well as the design, the reliability and the practical operation can be enhanced by the application of mathematical models for the complete process. A dynamic simulation model for power plants with atmospheric circulating fluidized bed combustion (ACFBC) and pressurized circulating fluidized bed combustion (PCFBC) consisting of comprehensive submodels for the subsystems gas turbine, circulating fluidized bed combustor and water/steam cycle is presented. Apart from the investigation of the complete power plant, the simulation program enables the analysis of the three mentioned subsystems separately. Each subsystem is described by a set of unsteady-state differential and algebraic equations solved by an implicit Euler-method using a modified Newton-Raphson method. With the aid of the dynamic simulation program for a selected power plant, the effect of changes in plant operation will be examined for full and part load as well as the transient response of the system due to the carried out operation. Emphasis is laid on the characterization of the interactions between the subsystems. The dynamic simulation program can be used for design studies and it is investigated how changes of the plant design influence the operation characteristics of the example plant.

  17. Streamflow changes in the Sierra Nevada, California, simulated using a statistically downscaled general circulation model scenario of climate change

    USGS Publications Warehouse

    Wilby, Robert L.; Dettinger, Michael D.

    2000-01-01

    Simulations of future climate using general circulation models (GCMs) suggest that rising concentrations of greenhouse gases may have significant consequences for the global climate. Of less certainty is the extent to which regional scale (i.e., sub-GCM grid) environmental processes will be affected. In this chapter, a range of downscaling techniques are critiqued. Then a relatively simple (yet robust) statistical downscaling technique and its use in the modelling of future runoff scenarios for three river basins in the Sierra Nevada, California, is described. This region was selected because GCM experiments driven by combined greenhouse-gas and sulphate-aerosol forcings consistently show major changes in the hydro-climate of the southwest United States by the end of the 21st century. The regression-based downscaling method was used to simulate daily rainfall and temperature series for streamflow modelling in three Californian river basins under current-and future-climate conditions. The downscaling involved just three predictor variables (specific humidity, zonal velocity component of airflow, and 500 hPa geopotential heights) supplied by the U.K. Meteorological Office couple ocean-atmosphere model (HadCM2) for the grid point nearest the target basins. When evaluated using independent data, the model showed reasonable skill at reproducing observed area-average precipitation, temperature, and concomitant streamflow variations. Overall, the downscaled data resulted in slight underestimates of mean annual streamflow due to underestimates of precipitation in spring and positive temperature biases in winter. Differences in the skill of simulated streamflows amongst the three basins were attributed to the smoothing effects of snowpack on streamflow responses to climate forcing. The Merced and American River basins drain the western, windward slope of the Sierra Nevada and are snowmelt dominated, whereas the Carson River drains the eastern, leeward slope and is a mix of

  18. A revised linear ozone photochemistry parameterization for use in transport and general circulation models: multi-annual simulations

    NASA Astrophysics Data System (ADS)

    Cariolle, D.; Teyssèdre, H.

    2007-05-01

    This article describes the validation of a linear parameterization of the ozone photochemistry for use in upper tropospheric and stratospheric studies. The present work extends a previously developed scheme by improving the 2-D model used to derive the coefficients of the parameterization. The chemical reaction rates are updated from a compilation that includes recent laboratory work. Furthermore, the polar ozone destruction due to heterogeneous reactions at the surface of the polar stratospheric clouds is taken into account as a function of the stratospheric temperature and the total chlorine content. Two versions of the parameterization are tested. The first one only requires the solution of a continuity equation for the time evolution of the ozone mixing ratio, the second one uses one additional equation for a cold tracer. The parameterization has been introduced into the chemical transport model MOCAGE. The model is integrated with wind and temperature fields from the ECMWF operational analyses over the period 2000-2004. Overall, the results from the two versions show a very good agreement between the modelled ozone distribution and the Total Ozone Mapping Spectrometer (TOMS) satellite data and the "in-situ" vertical soundings. During the course of the integration the model does not show any drift and the biases are generally small, of the order of 10%. The model also reproduces fairly well the polar ozone variability, notably the formation of "ozone holes" in the Southern Hemisphere with amplitudes and a seasonal evolution that follow the dynamics and time evolution of the polar vortex. The introduction of the cold tracer further improves the model simulation by allowing additional ozone destruction inside air masses exported from the high to the mid-latitudes, and by maintaining low ozone content inside the polar vortex of the Southern Hemisphere over longer periods in spring time. It is concluded that for the study of climate scenarios or the assimilation of

  19. Narrowing of the Upwelling Branch of the Brewer-Dobson Circulation and Hadley Cell in Chemistry-Climate Model Simulations of the 21st Century

    NASA Technical Reports Server (NTRS)

    Li, Feng; Stolarski, Richard S.; Pawson, Steven; Newman, Paul A.; Waugh, Darryn

    2010-01-01

    Changes in the width of the upwelling branch of the Brewer-Dobson circulation and Hadley cell in the 21st Century are investigated using simulations from a coupled chemistry-climate model. In these model simulations the tropical upwelling region narrows in the troposphere and lower stratosphere. The narrowing of the Brewer-Dobson circulation is caused by an equatorward shift of Rossby wave critical latitudes and Eliassen-Palm flux convergence in the subtropical lower stratosphere. In the troposphere, the model projects an expansion of the Hadley cell's poleward boundary, but a narrowing of the Hadley rising branch. Model results suggest that the narrowing of the Hadley cell ascent is also eddy-driven.

  20. Narrowing of the Upwelling Branch of the Brewer-Dobson Circulation and Hadley Cell in Chemistry-Climate Model Simulations of the 21st Century

    NASA Technical Reports Server (NTRS)

    Li, Feng; Stolarski, Richard S.; Pawson, Steven; Newman, Paul A.; Waugh, Darryn

    2010-01-01

    Changes in the width of the upwelling branch of the Brewer-Dobson circulation and Hadley cell in the 21st Century are investigated using simulations from a coupled chemistry-climate model. In these model simulations the tropical upwelling region narrows in the troposphere and lower stratosphere. The narrowing of the Brewer-Dobson circulation is caused by an equatorward shift of Rossby wave critical latitudes and Eliassen-Palm flux convergence in the subtropical lower stratosphere. In the troposphere, the model projects an expansion of the Hadley cell's poleward boundary, but a narrowing of the Hadley cell's rising branch. Model results suggest that eddy forcing may also play a part in the narrowing of the rising branch of the Hadley cell.

  1. 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.

  2. 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

  3. 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.

  4. Simulation of short-term pressure regulation during the tilt test in a coupled 3D-0D closed-loop model of the circulation.

    PubMed

    Lau, Kevin D; Figueroa, C Alberto

    2015-08-01

    Short-term fluctuations in arterial pressures arising from normal physiological function are buffered by a negative feedback system known as the arterial baroreflex. Initiated by altered biomechanical stretch in the vessel wall, the baroreflex coordinates a systemic response that alters heart rate, cardiac contractility and peripheral vessel vasoconstriction. In this work, a coupled 3D-0D formulation for the short-term pressure regulation of the systemic circulation is presented. Including the baroreflex feedback mechanisms, a patient-specific model of the large arteries is subjected to a simulated head up tilt test. Comparative simulations with and without baroreflex control highlight the critical role that the baroreflex has in regulating variations in pressures within the systemic circulation. PMID:25567754

  5. On the reduced lifetime of nitrous oxide due to climate change induced acceleration of the Brewer-Dobson circulation as simulated by the MPI Earth System Model

    NASA Astrophysics Data System (ADS)

    Kracher, D.; Manzini, E.; Reick, C. H.; Schultz, M. G.; Stein, O.

    2014-12-01

    Greenhouse gas induced climate change will modify the physical conditions of the atmosphere. One of the projected changes is an acceleration of the Brewer-Dobson circulation in the stratosphere, as it has been shown in many model studies. This change in the stratospheric circulation consequently bears an effect on the transport and distribution of atmospheric components such as N2O. Since N2O is involved in ozone destruction, a modified distribution of N2O can be of importance for ozone chemistry. N2O is inert in the troposphere and decays only in the stratosphere. Thus, changes in the exchange between troposphere and stratosphere can also affect the stratospheric sink of N2O, and consequently its atmospheric lifetime. N2O is a potent greenhouse gas with a global warming potential of currently approximately 300 CO2-equivalents in a 100-year perspective. A faster decay in atmospheric N2O mixing ratios, i.e. a decreased atmospheric lifetime of N2O, will also reduce its global warming potential. In order to assess the impact of climate change on atmospheric circulation and implied effects on the distribution and lifetime of atmospheric N2O, we apply the Max Planck Institute Earth System Model, MPI-ESM. MPI-ESM consists of the atmospheric general circulation model ECHAM, the land surface model JSBACH, and MPIOM/HAMOCC representing ocean circulation and ocean biogeochemistry. Prognostic atmospheric N2O concentrations in MPI-ESM are determined by land N2O emissions, ocean-atmosphere N2O exchange and atmospheric tracer transport. As stratospheric chemistry is not explicitly represented in MPI-ESM, stratospheric decay rates of N2O are prescribed from a MACC MOZART simulation. Increasing surface temperatures and CO2 concentrations in the stratosphere impact atmospheric circulation differently. Thus, we conduct a series of transient runs with the atmospheric model of MPI-ESM to isolate different factors governing a shift in atmospheric circulation. From those transient

  6. A Regional Model Simulation of the 1991 Severe Precipitation Event over the Yangtze-Huai River Valley. Part I: Precipitation and Circulation Statistics.

    NASA Astrophysics Data System (ADS)

    Wang, Wei-Chyung; Gong, Wei; Wei, Helin

    2000-01-01

    The summer Mei-yu event over eastern China, which is strongly influenced by large-scale circulation, is an important aspect of East Asian climate; for example, the Mei-yu frequently brings heavy precipitation to the Yangtze-Huai River valley (YHRV). Both observations and a regional model were used to study the Mei-yu front and its relation to large-scale circulation during the summer of 1991 when severe floods occurred over YHRV. This study has two parts: the first part, presented here, analyzes the association between heavy Mei-yu precipitation and relevant large-scale circulation, while the second part, documented by W. Gong and W.-C. Wang, examines the model biases associated with the treatment of lateral boundary conditions (the objective analyses and coupling schemes) used as the driving fields for the regional model.Observations indicate that the Mei-yu season in 1991 spans 18 May-14 July, making it the longest Mei-yu period during the last 40 yr. The heavy precipitation over YHRV is found to be intimately related to the western Pacific subtropical high, upper-tropospheric westerly jet at midlatitudes, and lower-tropospheric southwest wind and moisture flux. The regional model simulates reasonably well the regional mean surface air temperature and precipitation, in particular the precipitation evolution and its association with the large-scale circulation throughout the Mei-yu season. However, the model simulates smaller precipitation intensity, which is due partly to the colder and drier model atmosphere resulting from excessive low-level clouds and the simplified land surface process scheme used in the present study.

  7. Numerical simulation of the circulation of the atmosphere of Titan

    NASA Technical Reports Server (NTRS)

    Hourdin, F.; Levan, P.; Talagrand, O.; Courtin, Regis; Gautier, Daniel; Mckay, Christopher P.

    1992-01-01

    A three dimensional General Circulation Model (GCM) of Titan's atmosphere is described. Initial results obtained with an economical two dimensional (2D) axisymmetric version of the model presented a strong superrotation in the upper stratosphere. Because of this result, a more general numerical study of superrotation was started with a somewhat different version of the GCM. It appears that for a slowly rotating planet which strongly absorbs solar radiation, circulation is dominated by global equator to pole Hadley circulation and strong superrotation. The theoretical study of this superrotation is discussed. It is also shown that 2D simulations systemically lead to instabilities which make 2D models poorly adapted to numerical simulation of Titan's (or Venus) atmosphere.

  8. Simulation of optimal arctic routes using a numerical sea ice model based on an ice-coupled ocean circulation method

    NASA Astrophysics Data System (ADS)

    Nam, Jong-Ho; Park, Inha; Lee, Ho Jin; Kwon, Mi Ok; Choi, Kyungsik; Seo, Young-Kyo

    2013-06-01

    Ever since the Arctic region has opened its mysterious passage to mankind, continuous attempts to take advantage of its fastest route across the region has been made. The Arctic region is still covered by thick ice and thus finding a feasible navigating route is essential for an economical voyage. To find the optimal route, it is necessary to establish an efficient transit model that enables us to simulate every possible route in advance. In this work, an enhanced algorithm to determine the optimal route in the Arctic region is introduced. A transit model based on the simulated sea ice and environmental data numerically modeled in the Arctic is developed. By integrating the simulated data into a transit model, further applications such as route simulation, cost estimation or hindcast can be easily performed. An interactive simulation system that determines the optimal Arctic route using the transit model is developed. The simulation of optimal routes is carried out and the validity of the results is discussed.

  9. A diabatic circulation two-dimensional model with photochemistry - Simulations of ozone and long-lived tracers with surface sources

    NASA Technical Reports Server (NTRS)

    Stordal, F.; Isaksen, I. S. A.; Horntveth, K.

    1985-01-01

    Numerous studies have been concerned with the possibility of a reduction of the stratospheric ozone layer. Such a reduction could lead to an enhanced penetration of ultraviolet (UV) radiation to the ground, and, as a result, to damage in the case of several biological processes. It is pointed out that the distributions of many trace gases, such as ozone, are governed in part by transport processes. The present investigation presents a two-dimensional photochemistry-transport model using the residual circulation. The global distribution of both ozone and components with ground sources computed in this model is in good agreement with the observations even though slow diffusion is adopted. The agreement is particularly good in the Northern Hemisphere. The results provide additional support for the idea that tracer transport in the stratosphere is mainly of advective nature.

  10. 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.

  11. The relation between AMOC, gyre circulation, and meridional heat transports in the North Atlantic in model simulations of the last millennium

    NASA Astrophysics Data System (ADS)

    Jungclaus, Johann; Moreno-Chamarro, Eduardo; Lohmann, Katja

    2016-04-01

    While it is clear that the Atlantic Meridional Overturning Circulation (AMOC) is responsible for meridional heat transfer from the South Atlantic and the tropics to the North Atlantic, the majority of the heat transport in the northern North Atlantic and the Nordic seas is carried by the gyre system. However, the detailed mechanisms determining the interaction between and the temporal modulation of the components of the northward heat transport system are not clear. Long-term climate records and model simulations can help to identify important processes and to provide background for the changes that are presently observed. Multi-centennial proxy records from the subpolar North Atlantic and the Nordic Seas indicate, for example, an out-of-phase behavior of sea surface temperature and gyre circulation between the two regions with consequences for regional climate. Paleoceanographic evidence from Fram Strait shows a pronounced modulation of heat transfer to the Arctic by the Atlantic Water layer during the last 2000 years and reconstructions from the Subpolar North Atlantic suggest a role of ocean circulation in the transition between the Medieval Climate Anomaly and the Little Ice Age. Here we explore a small ensemble of last millennium simulations, carried out with the Max Planck Institute Earth System Model, and analyze mechanisms connecting the AMOC and gyre circulation and their relation to external forcing. Our results support the important role of the Subpolar Gyre strength and the related meridional mass and temperature fluxes. We find that the modulation of the northward heat transport into the Nordic Seas and the Arctic has pronounced impact on sea-ice distribution, ocean-atmosphere interaction, and the surface climate in Scandinavia and Western Europe.

  12. 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.

  13. A thermosphere-ionosphere-mesosphere-electrodynamics general circulation model (time-GCM): Equinox solar cycle minimum simulations (30-500 km)

    SciTech Connect

    Roble, R.G.; Ridley, E.C.

    1994-03-15

    A new simulation model of the mesosphere, thermosphere, and ionosphere with coupled electrodynamics has been developed and used to calculate the global circulation, temperature and compositional structure between 30-500 km for equinox, solar cycle minimum, geomagnetic quiet conditions. The model incorporates all of the features of the NCAR thermosphere-ionosphere-electrodynamics general circulation model (TIE-GCM) but the lower boundary has been extended downward from 97 to 30 km (10 mb) and it includes the physical and chemical processes appropriate for the mesosphere and upper stratosphere. The first simulation used Rayleigh friction to represent gravity wave drag in the middle atmosphere and although it was able to close the mesospheric jets it severely damped the diurnal tide. Reduced Rayleigh friction allowed the tide to penetrate to thermospheric heights but did not close the jets. A gravity wave parameterization developed by Fritts and Lu allows both features to exist simultaneously with the structure of tides and mean flow dependent upon the strength of the gravity wave source. The model calculates a changing dynamic structure with the mean flow and diurnal tide dominant in the mesosphere, the in-situ generated semi-diurnal tide dominating the lower thermosphere and an in-situ generated diurnal tide in the upper thermosphere. The results also show considerable interaction between dynamics and composition, especially atomic oxygen between 85 and 120 km. 31 refs., 3 figs.

  14. 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.

  15. Global circulation of the Earth's atmosphere at altitudes from 0 to 135 Km simulated with the ARM model. Consideration of the solar activity contribution

    NASA Astrophysics Data System (ADS)

    Krivolutsky, A. A.; Cherepanova, L. A.; Dement'eva, A. V.; Repnev, A. I.; Klyuchnikova, A. V.

    2015-11-01

    The results of simulations of the global circulation and temperature regime in the altitude range from the lower tropospheric layers to 135 km are presented. They were obtained with the Atmospheric Research Model (ARM), an advanced modification of a version of the Cologne Middle Atmosphere Model (COMMA). The ARM is characterized by higher spatial resolution and better parameterizations of the radiation sources and heat sinks. At the lower boundary of the model, wavy sources of perturbations, which are caused by internal gravity waves and planetary waves, are specified. The results of the modeling of the global temperature and wind fields for the mean solar activity level are presented, and their changes, which are caused by variations of the UV-radiation fluxes in the solar activity cycle and by solar proton flares, are also considered.

  16. The balance of kinetic and total energy simulated by the OSU two-level atmospheric general circulation model for January and July

    NASA Technical Reports Server (NTRS)

    Wang, J.-T.; Gates, W. L.; Kim, J.-W.

    1984-01-01

    A three-year simulation which prescribes seasonally varying solar radiation and sea surface temperature is the basis of the present study of the horizontal structure of the balances of kinetic and total energy simulated by Oregon State University's two-level atmospheric general circulation model. Mechanisms responsible for the local energy changes are identified, and the energy balance requirement's fulfilment is examined. In January, the vertical integral of the total energy shows large amounts of external heating over the North Pacific and Atlantic, together with cooling over most of the land area of the Northern Hemisphere. In July, an overall seasonal reversal is found. Both seasons are also characterized by strong energy flux divergence in the tropics, in association with the poleward transport of heat and momentum.

  17. The Circulation Pattern in Simulated Contact Binaries

    NASA Astrophysics Data System (ADS)

    Motl, Patrick M.; Frank, J.; Tohline, J. E.

    2006-06-01

    We present a three-dimensional hydrodynamical simulation of an initially symmetric (equal mass) binary where both components are marginally in contact. The simulation evolves the binary through approximately 150 orbital periods and within the first 20 orbits, a global velocity field is established that carries material between both components. In the equatorial plane, the flow is along a figure eight pattern with streams of material sliding past one another in the neighborhood of the inner Lagrange point. For our chosen equation of state, mass transfer is ultimately unstable in this binary though the growth time is long compared to the orbital period. We are therefore able to observe that the circulation pattern, once established, is quite close to steady state. We explore the role that similar steady state flows may play in real contact systems.

  18. The northern wintertime divergence extrema at 200 hPa and surface cyclones as simulated in the AMIP integration of the ECMWF general circulation model

    SciTech Connect

    Boyle, J.S.

    1994-11-01

    Divergence and convergence centers at 200 hPa and mean sea level pressure (MSLP) cyclones were located every 6 hr for a 10-yr general circulation model (GCM) simulation with the ECMWF (Cycle 36) for the boreal winters from 1980 to 1988. The simulation used the observed monthly mean sea surface temperature (SST) for the decade. Analysis of the frequency, location, and strength of these centers and cyclones gives insight into the dynamical response of the model to the varying SST. The results indicate that (1) the model produces reasonable climatologies of upper-level divergence and MSLP cyclones; (2) the model distribution of anomalies of divergence and convergence centers and MSLP cyclones is consistent with observations for the 1982-83 and 1986-87 El Nifio events; (3) the tropical Indian Ocean is the region of greatest divergence activity and interannual variability in the model; (4) the variability of the divergence centers is greater than that of the convergence centers; (5) strong divergence centers occur chiefly over the ocean in the midlatitudes but are more land-based in the tropics, except in the Indian Ocean; and (6) locations of divergence and convergence centers can be a useful tool for the intercomparison of global atmospheric simulations.

  19. 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.

  20. Simulating effects of highway embankments on estuarine circulation

    USGS Publications Warehouse

    Lee, Jonathan K.; Schaffranek, Raymond W.; Baltzer, Robert A.

    1994-01-01

    A two-dimensional depth-averaged, finite-difference, numerical model was used to simulate tidal circulation and mass transport in the Port Royal Sound. South Carolina, estuarine system. The purpose of the study was to demonstrate the utility of the Surface-Water. Integrated. Flow and Transport model (SWIFT2D) for evaluating changes in circulation patterns and mass transport caused by highway-crossing embankments. A model of subregion of Port Royal Sound including the highway crossings and having a grid size of 61 m (200ft) was derived from a 183-m (600-ft) model of the entire Port Royal Sound estuarine system. The 183-m model was used to compute boundary-value data for the 61-m submodel, which was then used to simulate flow conditions with and without the highway embankments in place. The numerical simulations show that, with the highway embankment in place, mass transport between the Broad River and Battery Creek is reduced and mass transport between the Beaufort River and Battery Creek is increased. The net result is that mass transport into and out of upper Battery Creek is reduced. The presence of the embankments also alters circulation patterns within Battery Creek.

  1. Simulation of the mantle and crustal helium isotope signature in the Mediterranean Sea using a high-resolution regional circulation model

    NASA Astrophysics Data System (ADS)

    Ayache, M.; Dutay, J.-C.; Jean-Baptiste, P.; Fourré, E.

    2015-12-01

    Helium isotopes (3He, 4He) are useful tracers for investigating the deep ocean circulation and for evaluating ocean general circulation models, because helium is a stable and conservative nuclide that does not take part in any chemical or biological process. Helium in the ocean originates from three different sources, namely, (i) gas dissolution in equilibrium with atmospheric helium, (ii) helium-3 addition by radioactive decay of tritium (called tritiugenic helium), and (iii) injection of terrigenic helium-3 and helium-4 by the submarine volcanic activity which occurs mainly at plate boundaries, and also addition of (mainly) helium-4 from the crust and sedimentary cover by α-decay of uranium and thorium contained in various minerals. We present the first simulation of the terrigenic helium isotope distribution in the whole Mediterranean Sea using a high-resolution model (NEMO-MED12). For this simulation we build a simple source function for terrigenic helium isotopes based on published estimates of terrestrial helium fluxes. We estimate a hydrothermal flux of 3.5 mol3 He yr-1 and a lower limit for the crustal flux at 1.6 × 10-7 4He mol m-2 yr-1. In addition to providing constraints on helium isotope degassing fluxes in the Mediterranean, our simulations provide information on the ventilation of the deep Mediterranean waters which is useful for assessing NEMO-MED12 performance. This study is part of the work carried out to assess the robustness of the NEMO-MED12 model, which will be used to study the evolution of the climate and its effect on the biogeochemical cycles in the Mediterranean Sea, and to improve our ability to predict the future evolution of the Mediterranean Sea under the increasing anthropogenic pressure.

  2. Simulation of the mantle and crustal helium isotope signature in the Mediterranean Sea using a high-resolution regional circulation model

    NASA Astrophysics Data System (ADS)

    Ayache, M.; Dutay, J.-C.; Jean-Baptiste, P.; Fourré, P. E.

    2015-08-01

    Helium isotopes (3He, 4He) are useful tracers for investigating the deep ocean circulation and for evaluating ocean general circulation models, because helium is a stable and conservative nuclide that does not take part in any chemical or biological process. Helium in the ocean originates from three different sources: namely, (i) gas dissolution in equilibrium with atmospheric helium, (ii) helium-3 addition by radioactive decay of tritium (called tritiugenic helium), and (iii) injection of terrigenic helium-3 and helium-4 by the submarine volcanic activity which occurs mainly at plate boundaries, and also addition of (mainly) helium-4 from the crust and sedimentary cover by α-decay of uranium and thorium contained in various minerals. We present the first simulation of the terrigenic helium isotope distribution in the whole Mediterranean Sea, using a high-resolution model (NEMO-MED12). For this simulation we build a simple source function for terrigenic helium isotopes based on published estimates of terrestrial helium fluxes. We estimate a hydrothermal flux of 3.5 mol 3He yr-1 and a lower limit for the crustal flux at 1.6 10-7 mol 4He mol m-2 yr-1. In addition to providing constraints on helium isotope degassing fluxes in the Mediterranean, our simulations provide information on the ventilation of the deep Mediterranean waters which are useful for assessing NEMO-MED12 performance. This study is part of the work carried out to assess the robustness of the NEMO-MED12 model, which will be used to study the evolution of the climate and its effect on the biogeochemical cycles in the Mediterranean Sea, and to improve our ability to predict the future evolution of the Mediterranean Sea under the increasing anthropogenic pressure.

  3. Application of a Coupled Multiscale Atmospheric-Land Surface Model to Simulate the Snow Circulation in a Mountain Basin

    NASA Astrophysics Data System (ADS)

    Herrera, E.; Pomeroy, J.; Pietroniro, A.

    2009-05-01

    Snow cover spatial variability and snowmelt runoff are greatly influenced by the snow advected due to the wind- flow in the atmospheric boundary layer. Typically this has been accomplished by considering the snow as a subgrid scale problem in the atmospheric models. However, this subgrid scale approach can not be sufficient to explain the snow dynamics. Therefore a multiscale strategy where the hydrological, climatological, meteorological and physiographic conditions of a basin are related should improve the understanding of snow dynamics. This methodology was developed coupling the Global Environmental Multiscale Limited Area Model (GEM-LAM) with the Cold Regions Hydrological Model (CRHM). The GEM-LAM was used on a one-way nesting configuration to simulate the atmospheric-land fields at 100m of resolution with the Interactions between Soil, Biosphere, and Atmosphere (ISBA) soil scheme. The CRHM is used as a snow transport model at the hydrometeorological stations located in the basin. The case of study is the 4th November 2007 at Marmot Creek (50° 57' N, 115° 10' W), Alberta, Canada. This strategy has proved to be a physics based procedure to describe the snow dynamics without interpolation methods.

  4. Simulating influence of QBO phase on planetary waves during a stratospheric warming in a general circulation model of the middle atmosphere

    NASA Astrophysics Data System (ADS)

    Koval, Andrey; Gavrilov, Nikolai; Pogoreltsev, Alexander; Savenkova, Elena

    2016-04-01

    One of the important factors of dynamical interactions between the lower and upper atmosphere is energy and momentum transfer by atmospheric internal gravity waves. For numerical modeling of the general circulation and thermal regime of the middle and upper atmosphere, it is important to take into account accelerations of the mean flow and heating rates produced by dissipating internal waves. The quasi-biennial oscillations (QBOs) of the zonal mean flow at lower latitudes at stratospheric heights can affect the propagation conditions of planetary waves. We perform numerical simulation of global atmospheric circulation for the initial conditions corresponding to the years with westerly and easterly QBO phases. We focus on the changes in amplitudes of stationary planetary waves (SPWs) and traveling normal atmospheric modes (NAMs) in the atmosphere during SSW events for the different QBO phases. For these experiments, we use the global circulation of the middle and upper atmosphere model (MUAM). There is theory of PW waveguide describing atmospheric regions where the background wind and temperature allow the wave propagation. There were introduced the refractive index for PWs and found that strongest planetary wave propagation is in areas of large positive values of this index. Another important PW characteristic is the Eliassen-Palm flux (EP-flux). These characteristics are considered as useful tools for visualizing the PW propagation conditions. Sudden stratospheric warming (SSW) event has significant influence on the formation of the weather anomalous and climate changes in the troposphere. Also, SSW event may affect the dynamical and energy processes in the upper atmosphere. The major SSW events imply significant temperature rises (up to 30 - 40 K) at altitudes 30 - 50 km accompanying with corresponding decreases, or reversals, of climatological eastward zonal winds in the stratosphere.

  5. Assessing the ability of isotope-enabled General Circulation Models to simulate the variability of Iceland water vapor isotopic composition

    NASA Astrophysics Data System (ADS)

    Erla Sveinbjornsdottir, Arny; Steen-Larsen, Hans Christian; Jonsson, Thorsteinn; Ritter, Francois; Riser, Camilla; Messon-Delmotte, Valerie; Bonne, Jean Louis; Dahl-Jensen, Dorthe

    2014-05-01

    During the fall of 2010 we installed an autonomous water vapor spectroscopy laser (Los Gatos Research analyzer) in a lighthouse on the Southwest coast of Iceland (63.83°N, 21.47°W). Despite initial significant problems with volcanic ash, high wind, and attack of sea gulls, the system has been continuously operational since the end of 2011 with limited down time. The system automatically performs calibration every 2 hours, which results in high accuracy and precision allowing for analysis of the second order parameter, d-excess, in the water vapor. We find a strong linear relationship between d-excess and local relative humidity (RH) when normalized to SST. The observed slope of approximately -45 o/oo/% is similar to theoretical predictions by Merlivat and Jouzel [1979] for smooth surface, but the calculated intercept is significant lower than predicted. Despite this good linear agreement with theoretical calculations, mismatches arise between the simulated seasonal cycle of water vapour isotopic composition using LMDZiso GCM nudged to large-scale winds from atmospheric analyses, and our data. The GCM is not able to capture seasonal variations in local RH, nor seasonal variations in d-excess. Based on daily data, the performance of LMDZiso to resolve day-to-day variability is measured based on the strength of the correlation coefficient between observations and model outputs. This correlation coefficient reaches ~0.8 for surface absolute humidity, but decreases to ~0.6 for δD and ~0.45 d-excess. Moreover, the magnitude of day-to-day humidity variations is also underestimated by LMDZiso, which can explain the underestimated magnitude of isotopic depletion. Finally, the simulated and observed d-excess vs. RH has similar slopes. We conclude that the under-estimation of d-excess variability may partly arise from the poor performance of the humidity simulations.

  6. Regional climates in the GISS global circulation model - Synoptic-scale circulation

    NASA Technical Reports Server (NTRS)

    Hewitson, B.; Crane, R. G.

    1992-01-01

    A major weakness of current general circulation models (GCMs) is their perceived inability to predict reliably the regional consequences of a global-scale change, and it is these regional-scale predictions that are necessary for studies of human-environmental response. For large areas of the extratropics, the local climate is controlled by the synoptic-scale atmospheric circulation, and it is the purpose of this paper to evaluate the synoptic-scale circulation of the Goddard Institute for Space Studies (GISS) GCM. A methodology for validating the daily synoptic circulation using Principal Component Analysis is described, and the methodology is then applied to the GCM simulation of sea level pressure over the continental United States (excluding Alaska). The analysis demonstrates that the GISS 4 x 5 deg GCM Model II effectively simulates the synoptic-scale atmospheric circulation over the United States. The modes of variance describing the atmospheric circulation of the model are comparable to those found in the observed data, and these modes explain similar amounts of variance in their respective datasets. The temporal behavior of these circulation modes in the synoptic time frame are also comparable.

  7. 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

  8. A blood circulation model for reference man

    SciTech Connect

    Leggett, R.W.; Eckerman, K.F.; Williams, L.R.

    1996-12-31

    A dynamic blood circulation model that predicts the movement and gradual dispersion of a bolus of material in the circulation after its intravenous injection into an adult human. The main purpose of the model is improve the dosimetry of internally deposited radionuclides that decay in the circulation to a significant extent. The model partitions the blood volume into 24 separate organs or tissues, right heart chamber, left heart chamber, pulmonary circulation, arterial outflow to the aorta and large arteries, and venous return via the large veins. Model results were compared to data obtained from injection of carbon 11 labeled carbon monoxide or rubidium 86.

  9. Simulations of Hurricane Katrina (2005) with the 0.125 degree finite-volume General Circulation Model on the NASA Columbia Supercomputer

    NASA Technical Reports Server (NTRS)

    Shen, B.-W.; Atlas, R.; Reale, O.; Lin, S.-J.; Chern, J.-D.; Chang, J.; Henze, C.

    2006-01-01

    Hurricane Katrina was the sixth most intense hurricane in the Atlantic. Katrina's forecast poses major challenges, the most important of which is its rapid intensification. Hurricane intensity forecast with General Circulation Models (GCMs) is difficult because of their coarse resolution. In this article, six 5-day simulations with the ultra-high resolution finite-volume GCM are conducted on the NASA Columbia supercomputer to show the effects of increased resolution on the intensity predictions of Katrina. It is found that the 0.125 degree runs give comparable tracks to the 0.25 degree, but provide better intensity forecasts, bringing the center pressure much closer to observations with differences of only plus or minus 12 hPa. In the runs initialized at 1200 UTC 25 AUG, the 0.125 degree simulates a more realistic intensification rate and better near-eye wind distributions. Moreover, the first global 0.125 degree simulation without convection parameterization (CP) produces even better intensity evolution and near-eye winds than the control run with CP.

  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. 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.

  12. Simulating Mars' Dust Cycle with a Mars General Circulation Model: Effects of Water Ice Cloud Formation on Dust Lifting Strength and Seasonality

    NASA Technical Reports Server (NTRS)

    Kahre, Melinda A.; Haberle, Robert; Hollingsworth, Jeffery L.

    2012-01-01

    The dust cycle is critically important for the current climate of Mars. The radiative effects of dust impact the thermal and dynamical state of the atmosphere [1,2,3]. Although dust is present in the Martian atmosphere throughout the year, the level of dustiness varies with season. The atmosphere is generally the dustiest during northern fall and winter and the least dusty during northern spring and summer [4]. Dust particles are lifted into the atmosphere by dust storms that range in size from meters to thousands of kilometers across [5]. Regional storm activity is enhanced before northern winter solstice (Ls200 degrees - 240 degrees), and after northern solstice (Ls305 degrees - 340 degrees ), which produces elevated atmospheric dust loadings during these periods [5,6,7]. These pre- and post- solstice increases in dust loading are thought to be associated with transient eddy activity in the northern hemisphere with cross-equatorial transport of dust leading to enhanced dust lifting in the southern hemisphere [6]. Interactive dust cycle studies with Mars General Circulation Models (MGCMs) have included the lifting, transport, and sedimentation of radiatively active dust. Although the predicted global dust loadings from these simulations capture some aspects of the observed dust cycle, there are marked differences between the simulated and observed dust cycles [8,9,10]. Most notably, the maximum dust loading is robustly predicted by models to occur near northern winter solstice and is due to dust lifting associated with down slope flows on the flanks of the Hellas basin. Thus far, models have had difficulty simulating the observed pre- and post- solstice peaks in dust loading.

  13. A blood circulation model for reference man

    SciTech Connect

    Leggett, R.W.; Eckerman, K.F.; Williams, L.R.

    1999-01-01

    This paper describes a dynamic blood circulation model that predicts the movement and gradual dispersal of a bolus of material in the circulation after its intravascular injection into an adult human. The main purpose of the model is to improve the dosimetry of internally deposited radionuclides that decay in the circulation to a significant extent. The total blood volume is partitioned into the blood contents of 24 separate organs or tissues, right heart chambers, left heart chambers, pulmonary circulation, arterial outflow to the systemic tissues (aorta and large arteries), and venous return from the systemic tissues (large veins). As a compromise between physical reality and computational simplicity, the circulation of blood is viewed as a system of first-order transfers between blood pools, with the delay time depending on the mean transit time across the pool. The model allows consideration of incomplete, tissue-dependent extraction of material during passage through the circulation and return of material from tissues to plasma.

  14. Kelvin waves and ozone Kelvin waves in the quasi-biennial oscillation and semiannual oscillation: A simulation by a high-resolution chemistry-coupled general circulation model

    NASA Astrophysics Data System (ADS)

    Watanabe, Shingo; Takahashi, Masaaki

    2005-09-01

    Equatorial Kelvin waves and ozone Kelvin waves were simulated by a T63L250 chemistry-coupled general circulation model with a high vertical resolution (300 m). The model produces a realistic quasi-biennial oscillation (QBO) and a semiannual oscillation (SAO) in the equatorial stratosphere. The QBO has a period slightly longer than 2 years, and the SAO shows rapid reversals from westerly to easterly regimes and gradual descents of westerlies. Results for the zonal wave number 1 slow and fast Kelvin waves are discussed. Structure of the waves and phase relationships between temperature and ozone perturbations coincide well with satellite observations made by LIMS, CLAES, and MLS. They are generally in phase (antiphase) in the lower (upper) stratosphere as theoretically expected. The fast Kelvin waves in the temperature and ozone are dominant in the upper stratosphere because the slow Kelvin waves are effectively filtered by the QBO westerly. In this simulation, the fast Kelvin waves encounter their critical levels in the upper stratosphere when zonal asymmetry of the SAO westerly is enhanced by an intrusion of the extratropical planetary waves. In addition to the critical level filtering effect, modulations of wave properties by background winds are evident near easterly and westerly shears associated with the QBO and SAO. Enhancement of wave amplitude in the QBO westerly shear is well coincident with radiosonde observations. Increase/decrease of vertical wavelength in the QBO easterly/westerly is obvious in this simulation, which is consistent with the linear wave theory. Shortening of wave period due to the descending QBO westerly shear zone is demonstrated for the first time. Moreover, dominant periods during the QBO westerly phase are longer than those during the QBO easterly phase for both the slow and fast Kelvin waves.

  15. Modeling the circulation of the Dead Sea

    NASA Astrophysics Data System (ADS)

    Brenner, Steve; Lensky, Nadav; Gertman, Isaac

    2015-04-01

    The Dead Sea is a hypersaline, terminal lake located at the lowest point on the land surface of the Earth. Its current level is more than 429 m below MSL, and due to a negative water balance (mainly anthropogenic), the lake level has been dropping at an average rate of more than 1 m/yr for more than 30 years. The mean salinity has also been steadily increasing and today is close to 280 psu. The region of the Dead Sea is a unique landscape that has important historical, cultural, and economic value and therefore such an extreme change of the lake has significant environmental and economic consequences. In recent years there has been a notable increase in observing and monitoring of the lake through continuous measurements from several fixed buoys as well as during quasi-regular cruises. In order to complement the measurements and improve our understanding of the dynamics of this unique lake a three dimensional circulation model is being developed. Previous modeling efforts were limited mainly to a one dimensional column model which was coupled to a comprehensive physio-chemical model and used for long term multi-decadal simulations. In this study the focus is on understanding the dynamical processes that control the lake-wide circulation on time scales ranging from days to seasons. The first step was to replace the equation of state with an equation appropriate for the hypersaline conditions, in addition to some minor tuning of the turbulence closure scheme. Results will be presented from preliminary simulations of the wind driven circulation in various seasons. A case study of a recent unusual winter flooding event, during which the lake level rose by more than 20 cm over a two month period, will also be presented. The model successfully simulated the observed transition from holomictic to meromictic conditions and epilimnion dilution during this event, as well as the restoration of holomictic conditions when the level started to drop again. The relationship

  16. Numerical Simulation of Regional Circulation in the Monterey Bay Region

    NASA Technical Reports Server (NTRS)

    Tseng, Y. H.; Dietrich, D. E.; Ferziger, J. H.

    2003-01-01

    The objective of this study is to produce a high-resolution numerical model of Mon- terey Bay area in which the dynamics are determined by the complex geometry of the coastline, steep bathymetry, and the in uence of the water masses that constitute the CCS. Our goal is to simulate the regional-scale ocean response with realistic dynamics (annual cycle), forcing, and domain. In particular, we focus on non-hydrostatic e ects (by comparing the results of hydrostatic and non-hydrostatic models) and the role of complex geometry, i.e. the bay and submarine canyon, on the nearshore circulation. To the best of our knowledge, the current study is the rst to simulate the regional circulation in the vicinity of Monterey Bay using a non-hydrostatic model. Section 2 introduces the high resolution Monterey Bay area regional model (MBARM). Section 3 provides the results and veri cation with mooring and satellite data. Section 4 compares the results of hydrostatic and non-hydrostatic models.

  17. Modeling global lightning distributions in a general circulation model

    NASA Technical Reports Server (NTRS)

    Price, Colin; Rind, David

    1994-01-01

    A general circulation model (GCM) is used to model global lightning distributions and frequencies. Both total and cloud-to-ground lightning frequencies are modeled using parameterizations that relate the depth of convective clouds to lightning frequencies. The model's simulations of lightning distributions in time and space show good agreement with available observations. The model's annual mean climatology shows a global lightning frequency of 77 flashes per second, with cloud-to-ground lightning making up 25% of the total. The maximum lightning activity in the GCM occurs during the Northern Hemisphere summer, with approximately 91% of all lightning occurring over continental and coastal regions.

  18. Modeling biomass gasification in circulating fluidized beds

    NASA Astrophysics Data System (ADS)

    Miao, Qi

    In this thesis, the modeling of biomass gasification in circulating fluidized beds was studied. The hydrodynamics of a circulating fluidized bed operating on biomass particles were first investigated, both experimentally and numerically. Then a comprehensive mathematical model was presented to predict the overall performance of a 1.2 MWe biomass gasification and power generation plant. A sensitivity analysis was conducted to test its response to several gasifier operating conditions. The model was validated using the experimental results obtained from the plant and two other circulating fluidized bed biomass gasifiers (CFBBGs). Finally, an ASPEN PLUS simulation model of biomass gasification was presented based on minimization of the Gibbs free energy of the reaction system at chemical equilibrium. Hydrodynamics plays a crucial role in defining the performance of gas-solid circulating fluidized beds (CFBs). A 2-dimensional mathematical model was developed considering the hydrodynamic behavior of CFB gasifiers. In the modeling, the CFB riser was divided into two regions: a dense region at the bottom and a dilute region at the top of the riser. Kunii and Levenspiel (1991)'s model was adopted to express the vertical solids distribution with some other assumptions. Radial distributions of bed voidage were taken into account in the upper zone by using Zhang et al. (1991)'s correlation. For model validation purposes, a cold model CFB was employed, in which sawdust was transported with air as the fluidizing agent. A comprehensive mathematical model was developed to predict the overall performance of a 1.2 MWe biomass gasification and power generation demonstration plant in China. Hydrodynamics as well as chemical reaction kinetics were considered. The fluidized bed riser was divided into two distinct sections: (a) a dense region at the bottom of the bed where biomass undergoes mainly heterogeneous reactions and (b) a dilute region at the top where most of homogeneous

  19. Snow Hydrology in a General Circulation Model.

    NASA Astrophysics Data System (ADS)

    Marshall, Susan; Roads, John O.; Glatzmaier, Gary

    1994-08-01

    A snow hydrology has been implemented in an atmospheric general circulation model (GCM). The snow hydrology consists of parameterizations of snowfall and snow cover fraction, a prognostic calculation of snow temperature, and a model of the snow mass and hydrologic budgets. Previously, only snow albedo had been included by a specified snow line. A 3-year GCM simulation with this now more complete surface hydrology is compared to a previous GCM control run with the specified snow line, as well as with observations. In particular, the authors discuss comparisons of the atmospheric and surface hydrologic budgets and the surface energy budget for U.S. and Canadian areas.The new snow hydrology changes the annual cycle of the surface moisture and energy budgets in the model. There is a noticeable shift in the runoff maximum from winter in the control run to spring in the snow hydrology run. A substantial amount of GCM winter precipitation is now stored in the seasonal snow pack. Snow cover also acts as an important insulating layer between the atmosphere and the ground. Wintertime soil temperatures are much higher in the snow hydrology experiment than in the control experiment. Seasonal snow cover is important for dampening large fluctuations in GCM continental skin temperature during the Northern Hemisphere winter.Snow depths and snow extent show good agreement with observations over North America. The geographic distribution of maximum depths is not as well simulated by the model due, in part, to the coarse resolution of the model. The patterns of runoff are qualitatively and quantitatively similar to observed patterns of streamflow averaged over the continental United States. The seasonal cycles of precipitation and evaporation are also reasonably well simulated by the model, although their magnitudes are larger than is observed. This is due, in part, to a cold bias in this model, which results in a dry model atmosphere and enhances the hydrologic cycle everywhere.

  20. Snow hydrology in a general circulation model

    NASA Technical Reports Server (NTRS)

    Marshall, Susan; Roads, John O.; Glatzmaier, Gary

    1994-01-01

    A snow hydrology has been implemented in an atmospheric general circulation model (GCM). The snow hydrology consists of parameterizations of snowfall and snow cover fraction, a prognostic calculation of snow temperature, and a model of the snow mass and hydrologic budgets. Previously, only snow albedo had been included by a specified snow line. A 3-year GCM simulation with this now more complete surface hydrology is compared to a previous GCM control run with the specified snow line, as well as with observations. In particular, the authors discuss comparisons of the atmospheric and surface hydrologic budgets and the surface energy budget for U.S. and Canadian areas. The new snow hydrology changes the annual cycle of the surface moisture and energy budgets in the model. There is a noticeable shift in the runoff maximum from winter in the control run to spring in the snow hydrology run. A substantial amount of GCM winter precipitation is now stored in the seasonal snowpack. Snow cover also acts as an important insulating layer between the atmosphere and the ground. Wintertime soil temperatures are much higher in the snow hydrology experiment than in the control experiment. Seasonal snow cover is important for dampening large fluctuations in GCM continental skin temperature during the Northern Hemisphere winter. Snow depths and snow extent show good agreement with observations over North America. The geographic distribution of maximum depths is not as well simulated by the model due, in part, to the coarse resolution of the model. The patterns of runoff are qualitatively and quantitatively similar to observed patterns of streamflow averaged over the continental United States. The seasonal cycles of precipitation and evaporation are also reasonably well simulated by the model, although their magnitudes are larger than is observed. This is due, in part, to a cold bias in this model, which results in a dry model atmosphere and enhances the hydrologic cycle everywhere.

  1. Seasonal overturning circulation in the Red Sea: 1. Model validation and summer circulation

    NASA Astrophysics Data System (ADS)

    Yao, Fengchao; Hoteit, Ibrahim; Pratt, Larry J.; Bower, Amy S.; Zhai, Ping; Köhl, Armin; Gopalakrishnan, Ganesh

    2014-04-01

    The overturning circulation in the Red Sea exhibits a distinct seasonally reversing pattern and is studied using high-resolution MIT general circulation model simulations. In the first part of this study, the vertical and horizontal structure of the summer overturning circulation and its dynamical mechanisms are presented from the model results. The seasonal water exchange in the Strait of Bab el Mandeb is successfully simulated, and the structures of the intruding subsurface Gulf of Aden intermediate water are in good agreement with summer observations in 2011. The model results suggest that the summer overturning circulation is driven by the combined effect of the shoaling of the thermocline in the Gulf of Aden resulting from remote winds in the Arabian Sea and an upward surface slope from the Red Sea to the Gulf of Aden set up by local surface winds in the Red Sea. In addition, during late summer two processes associated, respectively, with latitudinally differential heating and increased salinity in the southern Red Sea act together to cause the reversal of the contrast of the vertical density structure and the cessation of the summer overturning circulation. Dynamically, the subsurface northward pressure gradient force is mainly balanced by vertical viscosity resulting from the vertical shear and boundary friction in the Strait of Bab el Mandeb. Unlike some previous studies, the three-layer summer exchange flows in the Strait of Bab el Mandeb do not appear to be hydraulically controlled.

  2. GPU Developments for General Circulation Models

    NASA Astrophysics Data System (ADS)

    Appleyard, Jeremy; Posey, Stan; Ponder, Carl; Eaton, Joe

    2014-05-01

    Current trends in high performance computing (HPC) are moving towards the use of graphics processing units (GPUs) to achieve speedups through the extraction of fine-grain parallelism of application software. GPUs have been developed exclusively for computational tasks as massively-parallel co-processors to the CPU, and during 2013 an extensive set of new HPC architectural features were developed in a 4th generation of NVIDIA GPUs that provide further opportunities for GPU acceleration of general circulation models used in climate science and numerical weather prediction. Today computational efficiency and simulation turnaround time continue to be important factors behind scientific decisions to develop models at higher resolutions and deploy increased use of ensembles. This presentation will examine the current state of GPU parallel developments for stencil based numerical operations typical of dynamical cores, and introduce new GPU-based implicit iterative schemes with GPU parallel preconditioning and linear solvers based on ILU, Krylov methods, and multigrid. Several GCMs show substantial gain in parallel efficiency from second-level fine-grain parallelism under first-level distributed memory parallel through a hybrid parallel implementation. Examples are provided relevant to science-scale HPC practice of CPU-GPU system configurations based on model resolution requirements of a particular simulation. Performance results compare use of the latest conventional CPUs with and without GPU acceleration. Finally a forward looking discussion is provided on the roadmap of GPU hardware, software, tools, and programmability for GCM development.

  3. COMPUTATIONAL MODELING OF CIRCULATING FLUIDIZED BED REACTORS

    SciTech Connect

    Ibrahim, Essam A

    2013-01-09

    Details of numerical simulations of two-phase gas-solid turbulent flow in the riser section of Circulating Fluidized Bed Reactor (CFBR) using Computational Fluid Dynamics (CFD) technique are reported. Two CFBR riser configurations are considered and modeled. Each of these two riser models consist of inlet, exit, connecting elbows and a main pipe. Both riser configurations are cylindrical and have the same diameter but differ in their inlet lengths and main pipe height to enable investigation of riser geometrical scaling effects. In addition, two types of solid particles are exploited in the solid phase of the two-phase gas-solid riser flow simulations to study the influence of solid loading ratio on flow patterns. The gaseous phase in the two-phase flow is represented by standard atmospheric air. The CFD-based FLUENT software is employed to obtain steady state and transient solutions for flow modulations in the riser. The physical dimensions, types and numbers of computation meshes, and solution methodology utilized in the present work are stated. Flow parameters, such as static and dynamic pressure, species velocity, and volume fractions are monitored and analyzed. The differences in the computational results between the two models, under steady and transient conditions, are compared, contrasted, and discussed.

  4. The Agulhas circulation simulated by the global OGCM FESOM.

    NASA Astrophysics Data System (ADS)

    Sein, Dmitry; Wang, Qiang; Sidorenko, Dmitry; Harig, Sven; Durgadoo, Jonathan; Biastoch, Arne

    2015-04-01

    The Agulhas Current system, comprising of various components, is of relevance for global and regional climate on all timescales. Work undertaken in this area over the last few years have highlighted that this region is sensitive to changes of the global overturning circulation. In particular, an increase in the amount of the Indian Ocean waters entering the Atlantic has been attributed to the changes in the wind pattern in the Southern Hemisphere. Such intrusion of additional heat and salt into the Atlantic may potentially impact the stability of the meridional overturning circulation and the heat transport into the North Atlantic. We identify critical questions of both global and regional importance and aim to address them using a numerical modelling approach. The models employed are a next generation finite-element model (FESOM) developed in AWI and a state-of-the-art nested model (INALT01) developed in GEOMAR. Both models have approximately 8 km resolution in the Agulhas region. In addition the global FESOM resolution is adjusted to the sea surface height (SSH) variance obtained from the satellite observations (AVISO), i.e. the higher is the SSH variance, the higher is the FESOM resolution, varying from 6 to 100 km. The results obtained by FESOM are validated against observations, as well as against INATL01. We investigate the FESOM ability to simulate the Agulhas system, the influence of the locally eddy-permitting resolution on the general Atlantic Ocean circulation, in particular Atlantic Meridional Overturning, and the interaction of the Agulhas system with Antarctic Circumpolar Current.

  5. Modelling the Seasonal Overturning Circulation in the Red Sea

    NASA Astrophysics Data System (ADS)

    Yao, Fengchao; Hoteit, Ibrahim; Pratt, Larry; Bower, Amy; Koehl, Armin; Gopalakrishnan, Ganesh

    2015-04-01

    The overturning circulation in the Red Sea exhibits a distinct seasonally reversing pattern and is studied using 50-year, high-resolution MIT general circulation model simulations. The seasonal water exchange in the Strait of Bab el Mandeb is successfully simulated, and the structures of the intruding subsurface Gulf of Aden intermediate water are in good agreement with summer observations in 2011. The model results suggest that the summer overturning circulation is driven by the combined effect of the shoaling of the thermocline in the Gulf of Aden resulting from remote winds in the Arabian Sea and an upward surface slope from the Red Sea to the Gulf of Aden set up by local surface winds in the Red Sea. For the winter overturning circulation, the climatological model mean results suggest that the surface inflow intensifies in a western boundary current in the southern Red Sea that switches to an eastern boundary current north of 24°N. The overturning is accomplished through a cyclonic recirculation and a cross-basin overturning circulation in the northern Red Sea, with major sinking occurring along a narrow band of width about 20 km along the eastern boundary and weaker upwelling along the western boundary. The northward pressure gradient force, strong vertical mixing, and horizontal mixing near the boundary are the essential dynamical components in the model's winter overturning circulation.

  6. Modeling the seasonal circulation in Massachusetts Bay

    USGS Publications Warehouse

    Signell, Richard P.; Jenter, Harry L.; Blumberg, Alan F.

    1994-01-01

    An 18 month simulation of circulation was conducted in Massachusetts Bay, a roughly 35 m deep, 100??50 km embayment on the northeastern shelf of the United States. Using a variant of the Blumberg-Mellor (1987) model, it was found that a continuous 18 month run was only possible if the velocity field was Shapiro filtered to remove two grid length energy that developed along the open boundary due to mismatch in locally generated and climatologically forced water properties. The seasonal development of temperature and salinity stratification was well-represented by the model once ??-coordinate errors were reduced by subtracting domain averaged vertical profiles of temperature, salinity and density before horizontal differencing was performed. Comparison of modeled and observed subtidal currents at fixed locations revealed that the model performance varies strongly with season and distance from the open boundaries. The model performs best during unstratified conditions, and in the interior of the bay. The model performs poorest during stratified conditions and in the regions where the bay is driven predominantly by remote fluctuations from the Gulf of Maine.

  7. A modeling study of shelf circulation off northern California in the region of the Coastal Ocean Dynamics Experiment 2. Simulations and comparisons with observations

    NASA Astrophysics Data System (ADS)

    Gan, Jianping; Allen, J. S.

    2002-11-01

    This is the second part of a modeling study of wind-forced flow on the continental shelf off northern California in the region (37°-40°N) of the Coastal Ocean Dynamics Experiment (CODE). [2002] analyzed the shelf flow response to idealized wind stress forcing in a process-oriented study. The study here applies forcing from observed winds and heat flux for April-May 1982 and compares the model results with moored current and temperature measurements. The Princeton Ocean Model (POM) is used in a three-dimensional limited area domain with a high-resolution curvilinear grid (approximately 1 km horizontal spacing, 60 vertical levels) and realistic coastline and bottom topography. The objectives of the study are to simulate the response of the shelf circulation field to time-varying observed wind stress and heat flux, to compare model results with oceanographic observations to establish confidence in the model, and to subsequently analyze the model fields and the model dynamical balances to help understand the behavior of the observed flow. The model variables show overall good agreement with corresponding observations. Similar to the conclusions by [2002], it is found that the alongshore variability of upwelling is mainly controlled by the interaction of the wind-forced shelf flow with the coastline and bottom topography. Different dynamical regimes in the regions north and south of the coastal capes formed by Pt. Reyes and Pt. Arena and in the more uniform region between these capes are identified and investigated. The results demonstrate that the coastal capes play a dominant role in causing alongshore variability of the upwelling flow, including the setup of an alongshore pressure gradient that forces northward currents during relaxation of southward upwelling favorable winds. An analysis of the balance of terms in the equation for potential temperature indicates that across-shore temperature advection is the major contributor to the cooling of coastal water during

  8. An online educational atmospheric global circulation model

    NASA Astrophysics Data System (ADS)

    Navarro, T.; Schott, C.; Forget, F.

    2015-10-01

    As part of online courses on exoplanets of Observatoire de Paris, an online tool designed to vizualise outputs of the Laboratoire de Métérologie Dynamique (LMD) Global Circulation Model (GCM) for various atmospheric circulation regimes has been developed. It includes the possibility for students to visualize 1D and 2D plots along with animations of atmospheric quantities such as temperature, winds, surface pressure, mass flux, etc... from a state-of-the-art model.

  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. 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.

  11. Simulations of the HDO and H2O-18 atmospheric cycles using the NASA GISS general circulation model - Sensitivity experiments for present-day conditions

    NASA Technical Reports Server (NTRS)

    Jouzel, Jean; Koster, R. D.; Suozzo, R. J.; Russell, G. L.; White, J. W. C.

    1991-01-01

    Incorporating the full geochemical cycles of stable water isotopes (HDO and H2O-18) into an atmospheric general circulation model (GCM) allows an improved understanding of global delta-D and delta-O-18 distributions and might even allow an analysis of the GCM's hydrological cycle. A detailed sensitivity analysis using the NASA/Goddard Institute for Space Studies (GISS) model II GCM is presented that examines the nature of isotope modeling. The tests indicate that delta-D and delta-O-18 values in nonpolar regions are not strongly sensitive to details in the model precipitation parameterizations. This result, while implying that isotope modeling has limited potential use in the calibration of GCM convection schemes, also suggests that certain necessarily arbitrary aspects of these schemes are adequate for many isotope studies. Deuterium excess, a second-order variable, does show some sensitivity to precipitation parameterization and thus may be more useful for GCM calibration.

  12. Minimal modeling of the extratropical general circulation

    NASA Technical Reports Server (NTRS)

    O'Brien, Enda; Branscome, Lee E.

    1989-01-01

    The ability of low-order, two-layer models to reproduce basic features of the mid-latitude general circulation is investigated. Changes in model behavior with increased spectral resolution are examined in detail. Qualitatively correct time-mean heat and momentum balances are achieved in a beta-plane channel model which includes the first and third meridional modes. This minimal resolution also reproduces qualitatively realistic surface and upper-level winds and mean meridional circulations. Higher meridional resolution does not result in substantial changes in the latitudinal structure of the circulation. A qualitatively correct kinetic energy spectrum is produced when the resolution is high enough to include several linearly stable modes. A model with three zonal waves and the first three meridional modes has a reasonable energy spectrum and energy conversion cycle, while also satisfying heat and momentum budget requirements. This truncation reproduces the basic mechanisms and zonal circulation features that are obtained at higher resolution. The model performance improves gradually with higher resolution and is smoothly dependent on changes in external parameters.

  13. Simple Model of the Circulation.

    ERIC Educational Resources Information Center

    Greenway, Clive A.

    1980-01-01

    Describes a program in BASIC-11 that explores the relationships between various variables in the circulatory system and permits manipulation of several semiindependent variables to model the effects of hemorrhage, drug infusions, etc. A flow chart and accompanying sample printout are provided; the program is listed in the appendix. (CS)

  14. Combustion model for staged circulating fluidized bed boiler

    NASA Astrophysics Data System (ADS)

    Fang, Jianhua; Lu, Qinggang; Wang, Bo; Pan, Zhonggang; Wang, Dasan

    1997-03-01

    A mathematical model for atmospheric staged circulating fluidized bed combustion, which takes fluid dynamics, combustion, heat transfer, pollutants formation and retention, into account was developed in the Institute of Engineering Thermophysics (IET) recently. The model of gas solid flow at the bottom of the combustor was treated by the two-phase theory of fluidized bed and in the upper region as a core-annulus flow structure. The chemical species CO, CO2, H2, H2O, CH4, O2 and N2 were considered in the reaction process. The mathematical model consisted of sub-models of fluid namics, coal heterogeneous and gas homogeneous chemical reactions, heat transfer, particle fragmentation and attrition, mass and energy balance etc. The developed code was applied to simulate an operating staged circulating fluidized bed combustion boiler of early design and the results were in good agreement with the operating data. The main submodels and simulation results are given in this paper.

  15. Jupiter Thermospheric General Circulation Model (jtgcm)

    NASA Astrophysics Data System (ADS)

    Majeed, T.; Waite, J. H.; Bougher, S. W.; Gladstone, G. R.

    Recent observations of infrared and FUV auroral emissions from Jupiter have shown the presence of high-speed (> 2km/s) winds in the jovian thermosphere. The Galileo probe measurements of the altitude profile of equatorial temperature exhibit wave-like oscillations at all altitudes from 1029 to 133 km above the 1-bar level. A number of recent studies interpret these oscillations as being due to upward propagating gravity waves. The transport of significant auroral energy and species to equatorial latitudes by the thermospheric winds has also been proposed to explain the measured temper- ature structure observed by the Galileo probe. We examine this hypothesis using a fully 3-D Jupiter Thermospheric General Circulation Model (JTGCM) that has been developed and exercised to address global scale temperature, wind, and neutral-ion specie distributions. It was developed from a suitable adaptation of the NCAR Ther- mosphere Ionosphere General Circulation Model (TIGCM). New code was developed to parameterize the estimated auroral and equatorial heating and ionization distribu- tions learned from Galileo, HST, ROSAT, and Voyager data. Asymmetric auroral ovals are specified separately for the north and south poles. The lower boundary is set at 20 µb in order to capture the bulk of the hydrocarbon cooling due to C2H2 and CH4 at the base of the thermosphere. The upper boundary is set at 10-4 nb, sufficiently high enough to capture most auroral heating processes and winds. An ion-drag scheme is incorporated based on the formulation described by Roble and Ridley [1987]. A con- vection electric field is estimated and corresponding ion drifts are generated using the formulation of Evitar and Barbosa [1984]. These prescriptions provide a means to test the general impact of ion drag and Joule heating on the JTGCM neutral winds. The JTGCM has been fully spun-up (closely approaching steady state) and exercised for various cases to simulate 3-component neutral winds, and corresponding

  16. 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.

  17. A Circulation Model for Busy Public Libraries.

    ERIC Educational Resources Information Center

    Bagust, A.

    1983-01-01

    Develops stochastic model of library borrowing using Negative Binomial distribution applied to circulation data obtained from Huddersfield Public Library. Evidence concerning process of popularity decay is presented and method is given by which relegation tests can be constructed to maintain optimum turnover. Eight references and statistical…

  18. Modeling of Antarctic sea ice in a general circulation model

    SciTech Connect

    Wu, Xingren; Budd, W.F.; Simmonds, I.

    1997-04-01

    A dynamic-thermodynamic sea ice model is developed and coupled with the Melbourne University general circulation model to simulate the seasonal cycle of the Antarctic sea ice distributions The model is efficient, rapid to compute, and useful for a range of climate studies. The thermodynamic part of the sea ice model is similar to that developed by Parkinson and Washington, the dynamics contain a simplified ice rheology that resists compression. The thermodynamics is based on energy conservation at the top surface of the ice/snow, the ice/water interface, and the open water area to determine the ice formation, accretion, and ablation. A lead parameterization is introduced with an effective partitioning scheme for freezing between and under the ice floes. The dynamic calculation determines the motion of ice, which is forced with the atmospheric wind, taking account of ice resistance and rafting. The simulated sea ice distribution compares reasonably well with observations. The seasonal cycle of ice extent is well simulated in phase as well as in magnitude. Simulated sea ice thickness and concentration are also in good agreement with observations over most regions and serve to indicate the importance of advection and ocean drift in the determination of the sea ice distribution. 64 refs., 15 figs., 2 tabs.

  19. Seasonal circulations in the Malay Peninsula Eastern continental shelf from a wave-tide-circulation coupled model

    NASA Astrophysics Data System (ADS)

    Tangang, Fredolin T.; Xia, Changsui; Qiao, Fangli; Juneng, Liew; Shan, Feng

    2011-09-01

    A wave-tide-circulation coupled model based on Princeton Ocean Model is established to study the seasonal circulation in the Malay Peninsula Eastern Continental Shelf region. The model successfully reconstructs the observed seasonal variation of the circulation in the region, as well as the main currents. The simulated tidal harmonic constants, sea surface temperature, and sea surface height anomaly agree with the observations well. The model results show that the upper-layer circulation in the region is mainly controlled by the monsoon winds, while there are two transitions in spring and fall. An anti-cyclonic eddy is present off the Peninsular Malaysia's east coast in summer, centered at 5°N and 105.5°E, both in the TOPEX/Poseidon data and in the model. Numerical experiments show that the wind stress curl and bathymetry steering are responsible for its formation.

  20. The impact of surface dust source exhaustion on the martian dust cycle, dust storms and interannual variability, as simulated by the MarsWRF General Circulation Model

    NASA Astrophysics Data System (ADS)

    Newman, Claire E.; Richardson, Mark I.

    2015-09-01

    Observations of albedo on Mars suggest a largely invariant long-term mean surface dust distribution, but also reveal variations on shorter (seasonal to annual) timescales, particularly associated with major dust storms. We study the impact of finite surface dust availability on the dust cycle in the MarsWRF General Circulation Model (GCM), which uses radiatively active dust with parameterized 'dust devil' and wind stress dust lifting to enable the spontaneous production of dust storms, and tracks budgets of dust lifting, deposition, and total surface dust inventory. We seek a self-consistent, long-term 'steady state' dust cycle for present day Mars, consisting of (a) a surface dust distribution that varies from year to year but is constant longer-term and in balance with current dust redistribution processes, and (b) a fixed set of dust lifting parameters that continue to produce major storms for this distribution of surface dust. We relax the GCM's surface dust inventory toward this steady state using an iterative process, in which dust lifting rate parameters are increased as progressively more surface sites are exhausted of dust. Late in the equilibration process, the GCM exhibits quasi-steady state behavior in which few new surface grid points are exhausted during a 60 year period with constant dust lifting parameters. Complex regional-scale dust redistribution occurs on time-scales from less than seasonal to decadal, and the GCM generates regional to global dust storms with many realistic features. These include merging regional storms, cross-equatorial storms, and the timing and location of several storm types, though very early major storms and large amounts of late storm activity are not reproduced. Surface dust availability in key onset and growth source regions appears vital for 'early' major storms, with replenishment of these regions required before another large storm can occur, whereas 'late' major storms appear primarily dependent on atmospheric

  1. Modeling mesoscale circulation of the Black Sea

    NASA Astrophysics Data System (ADS)

    Korotenko, K. A.

    2015-11-01

    An eddy-resolving (1/30)° version of the DieCAST low-dissipative model, adapted to the Black Sea circulation, is presented. Under mean climatological forcing, the model realistically reproduces major dominant large-scale and mesoscale structures of seasonal sea circulation, including the Rim Current, coastal anticyclonic eddies, mushroom currents, etc. Due to its extremely low dissipation and high resolution, the model makes it possible to trace the development of the baroclinic instability along the Turkish and Caucasian coasts, reproduce mesoscale structures generated by this mechanism, and assess the scales of these structures. The model also realistically reproduces short-term effects of bora winds on the evolution of subsurface layer structures.

  2. Circulating a Good Service Model at Its Core: Circulation!

    ERIC Educational Resources Information Center

    Hernandez, Edmee Sofia; Germain, Carol Anne, Ed.

    2009-01-01

    Circulation is the library's tireless foot soldier: it serves as the front gate to the library's services and resources. This service point is where most patrons enter and leave; and experience their first and last impressions--impressions that linger. In an age when academic libraries are facing meager budgets and declining usage statistics, this…

  3. Circulation and rainfall climatology of a 10-year (1979 - 1988) integration with the Goddard Laboratory for atmospheres general circulation model

    NASA Technical Reports Server (NTRS)

    Kim, J.-H.; Sud, Y. C.

    1993-01-01

    A 10-year (1979-1988) integration of Goddard Laboratory for Atmospheres (GLA) general circulation model (GCM) under Atmospheric Model Intercomparison Project (AMIP) is analyzed and compared with observation. The first momentum fields of circulation variables and also hydrological variables including precipitation, evaporation, and soil moisture are presented. Our goals are (1) to produce a benchmark documentation of the GLA GCM for future model improvements; (2) to examine systematic errors between the simulated and the observed circulation, precipitation, and hydrologic cycle; (3) to examine the interannual variability of the simulated atmosphere and compare it with observation; and (4) to examine the ability of the model to capture the major climate anomalies in response to events such as El Nino and La Nina. The 10-year mean seasonal and annual simulated circulation is quite reasonable compared to the analyzed circulation, except the polar regions and area of high orography. Precipitation over tropics are quite well simulated, and the signal of El Nino/La Nina episodes can be easily identified. The time series of evaporation and soil moisture in the 12 biomes of the biosphere also show reasonable patterns compared to the estimated evaporation and soil moisture.

  4. Tropical disturbances in relation to general circulation modeling

    NASA Technical Reports Server (NTRS)

    Estoque, M. A.

    1982-01-01

    The initial results of an evaluation of the performance of the Goddard Laboratory of Atmospheric Simulation general circulation model depicting the tropical atmosphere during the summer are presented. Because the results show the existence of tropical wave disturbances throughout the tropics, the characteristics of synoptic disturbances over Africa were studied and a synoptic case study of a selected disturbance in this area was conducted. It is shown that the model is able to reproduce wave type synoptic disturbances in the tropics. The findings show that, in one of the summers simulated, the disturbances are predominantly closed vortices; in another summer, the predominant disturbances are open waves.

  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. Treatment of cloud radiative effects in general circulation models

    SciTech Connect

    Wang, W.C.; Dudek, M.P.; Liang, X.Z.; Ding, M.

    1996-04-01

    We participate in the Atmospheric Radiation Measurement (ARM) program with two objectives: (1) to improve the general circulation model (GCM) cloud/radiation treatment with a focus on cloud verticle overlapping and layer cloud optical properties, and (2) to study the effects of cloud/radiation-climate interaction on GCM climate simulations. This report summarizes the project progress since the Fourth ARM Science Team meeting February 28-March 4, 1994, in Charleston, South Carolina.

  7. Predictive models for circulating fluidized bed combustors

    SciTech Connect

    Gidaspow, D.

    1989-11-01

    The overall objective of this investigation is to develop experimentally verified models for circulating fluidized bed (CFB) combustors. The purpose of these models is to help American industry, such as Combustion Engineering, design and scale-up CFB combustors that are capable of burning US Eastern high sulfur coals with low SO{sub x} and NO{sub x} emissions. In this report, presented as a technical paper, solids distributions and velocities were computed for a PYROFLOW circulating fluidized bed system. To illustrate the capability of the computer code an example of coal-pyrite separation is included, which was done earlier for a State of Illinois project. 24 refs., 20 figs., 2 tabs.

  8. Simulation of the Atlantic meridional overturning circulation at the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Oka, A.; Hasumi, H.; Abe-Ouchi, A.

    2008-12-01

    The ocean circulation in the Atlantic deep ocean is characterized by thermohaline circulation driven by deep convection in northern high latitudes. The heat transport associated with this circulation is comparable to that by atmosphere and has a great role in the present climate. The Atlantic meridional overturning circulation (AMOC) is believed to change in past and future climate changes. Coupled model simulations suggest that the AMOC becomes weak in the future global warming climate. Geological evidence such as carbon isotope ratio indicates that the AMOC was weaker and shallower than the present at the Last Glacial Maximum (LGM). As for global warming climate, almost all model results reach consensus that the Atlantic deep circulation weakens in global warming climate. On the other hand, there is wide discrepancy in simulation of the Atlantic deep circulation at the LGM. Weber et al. (2007) report results of Paleoclimate Modeling Intercomparison Project where half of models reproduce the weakening of the Atlantic deep circulation but the other half simulates the strengthening. The reason for this disagreement between models has not been clarified yet, and investigation on the mechanism of weakening of the Atlantic deep circulation at the LGM is one of the most important topics in the paleoclimate studies. In this study, by using results of a coupled climate model (MIROC), we focus on role of changes in the sea surface heat and freshwater fluxes and investigate their role in controlling the AMOC at the LGM. In order to individually evaluate role of heat and freshwater fluxes, we conduct additional ocean general circulation model simulations under the sea surface heat/freshwater flux conditions obtained from the present and LGM simulations by MIROC. The results suggest that the freshwater flux changes contribute to weakening of the AMOC at the LGM, whereas the heat flux changes make the AMOC at the LGM stronger than the present. In the presentation, we are

  9. Simulations of Tropical Circulation and Winter Precipitation Over North India: an Application of a Tropical Band Version of Regional Climate Model (RegT-Band)

    NASA Astrophysics Data System (ADS)

    Tiwari, P. R.; Kar, S. C.; Mohanty, U. C.; Dey, S.; Kumari, S.; Sinha, P.; Raju, P. V. S.; Shekhar, M. S.

    2016-02-01

    In the present study, simulations have been carried out to study the relationship between winter-time precipitations and the large-scale global forcing (ENSO) using the tropical band version of Regional Climate Model (RegT-Band) for 5 El Niño and 4 La Niña years. The RegT-Band model is integrated with the observed sea-surface temperature and lateral boundary conditions from National Center for Environmental Prediction (NCEP)-Department of Energy (DOE) reanalysis 2 (NCEP-DOE2). The model domain extends from 50°S to 50°N and covers the entire tropics at a grid spacing of 45 km, i.e., it includes lateral boundary forcing only at the southern and northern boundaries. The performance evaluation of the model in capturing the large-scale fields followed by ENSO response with winter-time precipitation has been carried out by using model simulations against NCEP-DOE2 and Global Precipitation Climatology Project (GPCP) precipitation data. The analysis suggests that the model is able to reproduce the upper airfields and large-scale precipitation during winter time, although the model has some systematic biases compared to the observations. A comparison of model-simulated precipitation with observed precipitation at 17 station locations has been carried out. It is noticed that the RegT-Band model simulations are able to bring out the observed features reasonably well. Therefore, this preliminary study indicates that the tropical band version of the regional climate model can be effectively used for the better understanding of the large-scale global forcing.

  10. 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.

  11. CMIP5 simulated change in the intensity of the Hadley and Walker circulations from the perspective of velocity potential

    NASA Astrophysics Data System (ADS)

    Zhou, Botao; Shi, Ying; Xu, Ying

    2016-07-01

    Based on the simulations of 31 global models in CMIP5, the performance of the models in simulating the Hadley and Walker circulations is evaluated. In addition, their change in intensity by the end of the 21st century (2080-2099) under the RCP4.5 and RCP8.5 scenarios, relative to 1986-2005, is analyzed from the perspective of 200 hPa velocity potential. Validation shows good performance of the individual CMIP5 models and the multi-model ensemble mean (MME) in reproducing the meridional (zonal) structure and magnitude of Hadley (Walker) circulation. The MME can also capture the observed strengthening tendency of the winter Hadley circulation and weakening tendency of the Walker circulation. Such secular trends can be simulated by 39% and 74% of the models, respectively. The MME projection indicates that the winter Hadley circulation and the Walker circulation will weaken under both scenarios by the end of the 21st century. The weakening amplitude is larger under RCP8.5 than RCP4.5, due to stronger external forcing. The majority of the CMIP5 models show the same projection as the MME. However, for the summer Hadley circulation, the MME shows little change under RCP4.5 and large intermodel spread is apparent. Around half of the models project an increase, and the other half project a decrease. Under the RCP8.5 scenario, the MME and 65% of the models project a weakening of the summer southern Hadley circulation.

  12. Aspects of Numerical Simulation of Circulation Control Airfoils

    NASA Technical Reports Server (NTRS)

    Swanson, R. C.; Rumsey, C. L.; Anders, S. G.

    2005-01-01

    The mass-averaged compressible Navier-Stokes equations are solved for circulation control airfoils. Numerical solutions are computed with a multigrid method that uses an implicit approximate factorization smoother. The effects of flow conditions (e.g., free-stream Mach number, angle of attack, momentum coefficient) and mesh on the prediction of circulation control airfoil flows are considered. In addition, the impact of turbulence modeling, including curvature effects and modifications to reduce eddy viscosity levels in the wall jet (i.e., Coanda flow), is discussed. Computed pressure distributions are compared with available experimental data.

  13. Contribution towards statistical intercomparison of general circulation models

    SciTech Connect

    Sengupta, S.; Boyle, J.

    1995-06-01

    The Atmospheric Model Intercomparison Project (AMIP) of the World Climate Research Programme`s Working Group on Numerical Experimentation (WGNE) is an ambitious attempt to comprehensively intercompare atmospheric General Circulation Models (GCMs). The participants in AMIP simulate the global atmosphere for the decade 1979 to 1988 using, a common solar constant and Carbon Dioxide(CO{sub 2}) concentration and a common monthly averaged sea surface temperature (SST) and sea ice data set. In this work we attempt to present a statistical framework to address the difficult task of model intercomparison and verification.

  14. The northern wintertime divergence extrema at 200 hPa and MSLP cyclones as simulated in the AMIP integration by the ECMWF general circulation model

    SciTech Connect

    Boyle, J.S. )

    1994-01-01

    Divergence and convergence centers at 200 hPa and mean sea level pressure (MSLP) cyclones are located every 6 hours for a 10-year GCM simulation for the boreal winters from 1980 to 1988. The simulation used the observed monthly mean SST for the decade. Analysis of the frequency, locations, and strengths of these centers and cyclones give insight into the dynamical response of the model to the varying SST. IT is found that (1) the model produces reasonable climatologies of upper-level divergence and MSLP cyclones. (2) The model distribution of anomalies of divergence/convergence centers and MSLP cyclones is consistent with available observations for the 1982-83 and 2986-87 El Nino events. (3) The tropical Indian Ocean is the region of greatest divergence activity and interannual variability in the model. (4) The variability of the divergence centers is greater than that of the convergence centers. (5) Strong divergence centers are chiefly oceanic events in the midlatitudes but are more land based in the tropics, except in the Indian. (6) Locations of divergence/convergence centers can be a useful tool for the intercomparison of global atmospheric simulations.

  15. Electrical Lumped Model Examination for Load Variation of Circulation System

    NASA Astrophysics Data System (ADS)

    Koya, Yoshiharu; Ito, Mitsuyo; Mizoshiri, Isao

    Modeling and analysis of the circulation system enables the characteristic decision of circulation system in the body to be made. So, many models of circulation system have been proposed. But, they are complicated because the models include a lot of elements. Therefore, we proposed a complete circulation model as a lumped electrical circuit, which is comparatively simple. In this paper, we examine the effectiveness of the complete circulation model as a lumped electrical circuit. We use normal, angina pectoris, dilated cardiomyopathy and myocardial infarction for evaluation of the ventricular contraction function.

  16. Numerical Model Studies of the Martian Mesoscale Circulations

    NASA Technical Reports Server (NTRS)

    Segal, Moti; Arritt, Raymond W.

    1997-01-01

    The study objectives were to evaluate by numerical modeling various possible mesoscale circulation on Mars and related atmospheric boundary layer processes. The study was in collaboration with J. Tillman of the University of Washington (who supported the study observationally). Interaction has been made with J. Prusa of Iowa State University in numerical modeling investigation of dynamical effects of topographically-influenced flow. Modeling simulations included evaluations of surface physical characteristics on: (i) the Martian atmospheric boundary layer and (ii) their impact on thermally and dynamically forced mesoscale flows. Special model evaluations were made in support of selection of the Pathfinder landing sites. J. Tillman's finding of VL-2 inter-annual temperature difference was followed by model simulations attempting to point out the forcing for this feature. Publication of the results in the reviewed literature in pending upon completion of the manuscripts in preparation as indicated later.

  17. Interactions Between the Thermohaline Circulation and Tropical Atlantic SST in a Coupled General Circulation Model

    NASA Technical Reports Server (NTRS)

    Miller, Ron; Jiang, Xing-Jian; Travis, Larry (Technical Monitor)

    2001-01-01

    Tropical Atlantic SST shows a (statistically well-defined) decadal time scale in a 104-year simulation of unforced variability by a coupled general circulation model (CGCM). The SST anomalies superficially resemble observed Tropical Atlantic variability (TAV), and are associated with changes in the atmospheric circulation. Brazilian rainfall is modulated with a decadal time scale, along with the strength of the Atlantic trade winds, which are associated with variations in evaporation and the net surface heat flux. However, in contrast to observed tropical Atlantic variability, the trade winds damp the associated anomalies in ocean temperature, indicating a negative feedback. Tropical SST anomalies in the CGCM, though opposed by the surface heat flux, are advected in from the Southern Hemisphere mid-latitudes. These variations modulate the strength of the thermohaline circulation (THC): warm, salty anomalies at the equator sink drawing cold, fresh mid-latitude water. Upon reaching the equator, the latter inhibit vertical overturning and advection from higher latitudes, which allows warm, salty anomalies to reform, returning the cycle to its original state. Thus, the cycle results from advection of density anomalies and the effect of these anomalies upon the rate of vertical overturning and surface advection. This decadal modulation of Tropical Atlantic SST and the thermohaline circulation is correlated with ocean heat transport to the Northern Hemisphere high latitudes and Norwegian Sea SST. Because of the central role of equatorial convection, we question whether this mechanism is present in the current climate, although we speculate that it may have operated in palaeo times, depending upon the stability of the tropical water column.

  18. 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.

  19. Numerical simulation of the general circulation of the atmosphere of Titan.

    PubMed

    Hourdin, F; Talagrand, O; Sadourny, R; Courtin, R; Gautier, D; McKay, C P

    1995-10-01

    The atmospheric circulation of Titan is investigated with a general circulation model. The representation of the large-scale dynamics is based on a grid point model developed and used at Laboratoire de Météorologie Dynamique for climate studies. The code also includes an accurate representation of radiative heating and cooling by molecular gases and haze as well as a parametrization of the vertical turbulent mixing of momentum and potential temperature. Long-term simulations of the atmospheric circulation are presented. Starting from a state of rest, the model spontaneously produces a strong superrotation with prograde equatorial winds (i.e., in the same sense as the assumed rotation of the solid body) increasing from the surface to reach 100 m sec-1 near the 1-mbar pressure level. Those equatorial winds are in very good agreement with some indirect observations, especially those of the 1989 occultation of Star 28-Sgr by Titan. On the other hand, the model simulates latitudinal temperature contrasts in the stratosphere that are significantly weaker than those observed by Voyager 1 which, we suggest, may be partly due to the nonrepresentation of the spatial and temporal variations of the abundances of molecular species and haze. We present diagnostics of the simulated atmospheric circulation underlying the importance of the seasonal cycle and a tentative explanation for the creation and maintenance of the atmospheric superrotation based on a careful angular momentum budget. PMID:11538593

  20. Design of the UCLA general circulation model

    NASA Technical Reports Server (NTRS)

    Arakawa, A.

    1972-01-01

    An edited version is reported of notes distributed at the Summer Workshop on the UCLA General Circulation Model in June 1971. It presents the computational schemes of the UCLA model, along with the mathematical and physical principles on which these schemes are based. Included are the finite difference schemes for the governing fluid-dynamical equations, designed to maintain the important integral constraints and dispersion characteristics of the motion. Also given are the principles of parameterization of cumulus convection by an ensemble of identical clouds. A model of the ground hydrology, involving the liquid, ice and snow states of water, is included. A short summary is given of the scheme for computing solar and infrared radiation transfers through clear and cloudy air.

  1. Predictive models of circulating fluidized bed combustors

    SciTech Connect

    Gidaspow, D.

    1992-07-01

    Steady flows influenced by walls cannot be described by inviscid models. Flows in circulating fluidized beds have significant wall effects. Particles in the form of clusters or layers can be seen to run down the walls. Hence modeling of circulating fluidized beds (CFB) without a viscosity is not possible. However, in interpreting Equations (8-1) and (8-2) it must be kept in mind that CFB or most other two phase flows are never in a true steady state. Then the viscosity in Equations (8-1) and (8-2) may not be the true fluid viscosity to be discussed next, but an Eddy type viscosity caused by two phase flow oscillations usually referred to as turbulence. In view of the transient nature of two-phase flow, the drag and the boundary layer thickness may not be proportional to the square root of the intrinsic viscosity but depend upon it to a much smaller extent. As another example, liquid-solid flow and settling of colloidal particles in a lamella electrosettler the settling process is only moderately affected by viscosity. Inviscid flow with settling is a good first approximation to this electric field driven process. The physical meaning of the particulate phase viscosity is described in detail in the chapter on kinetic theory. Here the conventional derivation resented in single phase fluid mechanics is generalized to multiphase flow.

  2. 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.

  3. MELCOR 1.8.5 Simulation of TMI-2 Phase 2 With an Enhanced 2-Dimensional In-Vessel Natural Circulation Model

    SciTech Connect

    Gauntt, Randall O.; Ross, Kyle; Wagner, Kenneth

    2002-07-01

    Phase 2 of the TMI-2 accident (core uncover and melting) is revisited with the latest release of MELCOR (i.e., Version 1.8.5). An enhanced multi-ring multi-level hydro nodalization of the reactor core and upper plenum was developed to permit calculation of natural convection heat transfer between the core and upper internals. Uncertainties in boundary and initial conditions are investigated with particular attention given to the distribution of liquid in the RCS at the beginning of Phase 2 and to the histories of pressure and level in the steam generators. Special attention given to modeling the boiler sides of the once-through steam generators is presented. The modeling is designed to capture the rapid condensation of RCS vapor that would result from spraying cold auxiliary feedwater directly onto the upper portion of a voided steam generator tube bundle. Presentation of key Phase-2 accident signatures including fuel temperatures and hydrogen generation are presented. Comparisons are made between MELCOR calculations, TMI-2 data, and SCDAP/RELAP simulations. A largely improved MELCOR simulation of TMI-2 Phase 2 is obtained. (authors)

  4. MERIDIONAL CIRCULATION DYNAMICS FROM 3D MAGNETOHYDRODYNAMIC GLOBAL SIMULATIONS OF SOLAR CONVECTION

    SciTech Connect

    Passos, Dário; Charbonneau, Paul; Miesch, Mark

    2015-02-10

    The form of solar meridional circulation is a very important ingredient for mean field flux transport dynamo models. However, a shroud of mystery still surrounds this large-scale flow, given that its measurement using current helioseismic techniques is challenging. In this work, we use results from three-dimensional global simulations of solar convection to infer the dynamical behavior of the established meridional circulation. We make a direct comparison between the meridional circulation that arises in these simulations and the latest observations. Based on our results, we argue that there should be an equatorward flow at the base of the convection zone at mid-latitudes, below the current maximum depth helioseismic measures can probe (0.75 R{sub ⊙}). We also provide physical arguments to justify this behavior. The simulations indicate that the meridional circulation undergoes substantial changes in morphology as the magnetic cycle unfolds. We close by discussing the importance of these dynamical changes for current methods of observation which involve long averaging periods of helioseismic data. Also noteworthy is the fact that these topological changes indicate a rich interaction between magnetic fields and plasma flows, which challenges the ubiquitous kinematic approach used in the vast majority of mean field dynamo simulations.

  5. 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.

  6. Large-Eddy Simulation of Mesoscale Circulations Forced by Inhomogeneous Urban Heat Island

    NASA Astrophysics Data System (ADS)

    Zhang, Ning; Wang, Xueyuan; Peng, Zhen

    2014-04-01

    The large-eddy simulation mode of the Weather Research and Forecasting model is employed to simulate the planetary boundary-layer characteristics and mesoscale circulations forced by an ideal urban heat island (UHI). In our simulations, the horizontal heterogeneity of the UHI intensity distribution in urban areas is considered and idealized as a cosine function. Results indicate that the UHI heating rate and the UHI intensity heterogeneity affect directly the spatial distribution of the wind field; a stronger UHI intensity produces a maximum horizontal wind speed closer to the urban centre. The strong advection of warm air from the urban area to the rural area in the upper part of the planetary boundary-layer causes a more stable atmospheric stratification over both the urban and rural areas. The mesoscale sensible heat flux caused by the UHI circulation increases with UHI intensity but vanishes when the background wind speed is sufficiently high 3.0.

  7. 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.

  8. Documentation of the GLAS fourth order general circulation model. Volume 1: Model documentation

    NASA Technical Reports Server (NTRS)

    Kalnay, E.; Balgovind, R.; Chao, W.; Edelmann, J.; Pfaendtner, J.; Takacs, L.; Takano, K.

    1983-01-01

    The volume 1, of a 3 volume technical memoranda which contains a documentation of the GLAS Fourth Order General Circulation Model is presented. Volume 1 contains the documentation, description of the stratospheric/tropospheric extension, user's guide, climatological boundary data, and some climate simulation studies.

  9. 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.

  10. Processes and Mechanisms in Simulations of the Mid-holocene African Summer Monsoon Circulation

    NASA Astrophysics Data System (ADS)

    Tomas, R. A.; Otto-Bliesner, B.

    2006-12-01

    Proxy reconstructions indicate that the Sahel and Sahara regions were considerably wetter during the early and middle Holocene (about 12 to 5 thousand years ago) than they are presently. Kutzbach (1981) and Kutzbach and Otto-Bliesner (1982) tested whether changes in the Earth's orbital parameters could have caused these climatic changes seen in the observed records. Using a low-resolution general circulation model and orbital parameters that describe conditions 9000 years ago, they found that the increased solar radiation during the summer months caused an intensified monsoon circulation over the African-Eurasian land mass. During the past 25 years, as general circulation models and coupled climate models have evolved, these experiments have been repeated, these results have been reconfirmed and our understanding of what parts of the climate system are important for the anomalous monsoon circulation has been refined. Yet, questions remain about the details of the processes and mechanisms that are important for producing the anomalous monsoon in climate model simulations and there are still some significant discrepancies between simulations and proxy records. We examine simulations of the African summer monsoon made using the latest version of the Community Climate System Model (CCSM3) developed at the National Center for Atmospheric Research (NCAR) forced with orbital parameters and greenhouse gas concentrations appropriate for 6 ka and pre-industrial periods following the protocols established by the Paleoclimate Modeling Intercomparison Project II (PMIP-2). Results from three sets of experiments are presented. In the first, we test to determine to what extent the SST's simulated by CCSM3 influence the anomalous monsoon circulation using a stand alone atmospheric model forced with 6ka orbital parameters but prescribed SST's taken from CCSM3 simulations of the 6ka and pre-industrial periods. In the second, we explore a more fundamental question regarding what

  11. 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.

  12. Future changes and uncertainties in Asian precipitation simulated by multiphysics and multi-sea surface temperature ensemble experiments with high-resolution Meteorological Research Institute atmospheric general circulation models (MRI-AGCMs)

    NASA Astrophysics Data System (ADS)

    Endo, Hirokazu; Kitoh, Akio; Ose, Tomoaki; Mizuta, Ryo; Kusunoki, Shoji

    2012-08-01

    This study focuses on projecting future changes in mean and extreme precipitation in Asia, and discusses their uncertainties. Time-slice experiments using a 20-km-mesh atmospheric general circulation (AGCM) were performed both in the present-day (1979-2003) and the future (2075-2099). To assess the uncertainty of the projections, 12 ensemble projections (i.e., combination of 3 different cumulus schemes and 4 different sea surface temperature (SST) change patterns) were conducted using 60-km-mesh AGCMs. For the present-day simulations, the models successfully reproduced the pattern and amount of mean and extreme precipitation, although the model with the Arakawa-Schubert (AS) cumulus scheme underestimated the amount of extreme precipitation. For the future climate simulations, in South Asia and Southeast Asia, mean and extreme precipitation generally increase, but their changes show marked differences among the projections, suggesting some uncertainty in their changes over these regions. In East Asia, northwestern China and Bangladesh, in contrast, mean and extreme precipitation show consistent increases among the projections, suggesting their increases are reliable for this model framework. Further investigation by analysis of variance (ANOVA) revealed that the uncertainty in the precipitation changes in South Asia and Southeast Asia are derived mainly from differences in the cumulus schemes, with an exception in the Maritime Continent where the uncertainty originates mainly from the differences in the SST pattern.

  13. (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.

  14. Development of an advanced finite difference atmospheric general circulation model

    NASA Astrophysics Data System (ADS)

    Randall, D. A.

    1994-11-01

    The essence of this research is further development of the Colorado State University (CSU) atmospheric general circulation model (AGCM). Although the CSU AGCM is currently evolving rapidly, is also being used in a variety of 'applications' in which the results of simulation performed with the model are analyzed to gain better understanding of the climate system. In parallel, a GCM development effort is also under way at UCLA. The CSU GCM was derived from the UCLA GCM of 1982, but has evolved to the point that the two models are now really quite distinct. The key distinguishing elements of the CSU model are briefly summarized. The goal of CHAMMP is 'to accelerate the development of more accurate and useful climate prediction capabilities to forecast climate change on sub-continental and smaller scales over time periods ranging from a decade to several centuries'.

  15. Fine-grid simulations of gas-solids flow in a circulating fluidized bed

    SciTech Connect

    Benyahia, S.

    2012-01-01

    This research note demonstrates that more accurate predictions of a two-fluid model for the riser section of a circulating fluidized bed are obtained as the grid size is equally refined along all the directions of the gas-particle flow. However, two-fluid simulations of large-scale fluidized beds with such a fine mesh are currently computationally prohibitive. Alternatively,subgrid models can significantly reduce the simulation time of multiphase flow by using coarse mesh, whereas maintaining a high level of accuracy.

  16. Importance of a control state for simulating the Atlantic meridional overturning circulation at the LGM

    NASA Astrophysics Data System (ADS)

    Oka, A.; Abe-Ouchi, A.; Hasumi, H.

    2009-04-01

    The ocean circulation in the Atlantic deep ocean is characterized by thermohaline circulation driven by deep convection in northern high latitudes. The heat transport associated with this circulation is comparable to that by atmosphere and has a great role in the present climate. The Atlantic meridional overturning circulation (AMOC) is believed to change in past and future climate changes. Coupled model simulations suggest that the AMOC becomes weak in the future global warming climate. Geological evidence such as carbon isotope ratio indicates that the AMOC was weaker and shallower than the present at the Last Glacial Maximum (LGM). As for global warming climate, almost all model results reach consensus that the AMOC weakens in global warming climate. On the other hand, there is wide discrepancy in simulation of the AMOC at the LGM. Weber et al. (2007) report results of Paleoclimate Modeling Intercomparison Project where half of models reproduce the weakening of the AMOC but the other half simulates the strengthening. The reason for this disagreement between models has not been clarified yet, and investigation on the mechanism of weakening of the AMOC at the LGM is one of the most important topics in the paleoclimate studies. In this study, by using results of our coupled climate model (MIROC), we focus on role of changes in the sea surface heat and freshwater fluxes and investigate their role in controlling the AMOC at the LGM. In order to individually evaluate role of heat and freshwater fluxes, we conduct additional ocean general circulation model simulations under the sea surface heat/freshwater flux conditions obtained from the present and LGM simulations by MIROC. The results suggest that the freshwater flux changes contribute to weakening of the AMOC at the LGM, whereas the heat flux changes make the AMOC at the LGM stronger than the present. We found that reproducibility of the control state significantly affects response of the AMOC to heat and

  17. Enceladus' Interior: A Liquid Circulation Model

    NASA Astrophysics Data System (ADS)

    Matson, Dennis L.; Johnson, Torrence; Lunine, Jonathan; Castillo-Rogez, Julie

    We are studying a model for Enceladus' interior in which the water, gas, dust and heat are supplied to the plumes by a relatively deeply circulating brine solution. Data indicates such a source for the erupting material. On the basis of ammonia in the plume gas Waite et al. [1] suggested that the jets might originate from a liquid water region under Enceladus' icy surface. Postberg et al. [2] noted that the presence of ". . . grains that are rich in sodium salts (0.5-2 percent by mass). . . can arise only if the plumes originate from liquid water." Waite et al. [1] also regard the some of the plume chemicals as evidence for interactions with an ice layer presumably overlying the liquid water reservoir. They suggest that this could be in the form of dissociation of clathrate hydrates [3]. Additionally, there is a large heat flow of more than 15 GW [4, 5] coming out of Enceladus' south polar region. We consider a model that brings heat and chemical species up to the surface from a reservoir or "ocean" located below the ice crust that may be many tens of kilometers thick. Water transits to the surface via vertical conduits. The Cassini INMS data suggest that the water has a relatively large gas content of order a few percent. As the water travels upward and the pressure is released, exolving gases form bubbles. Since the bubbly liquid is less dense than the ice, it moves upward. (This part of the model is a variant of the "Perrier Ocean" Europa model of Crawford and Stevenson [6]. A similar model was studied for Ganymede by Murchie and Head [7].) Postberg et al. [2] model the plume eruptions that result from the water, gases, salts, and other chemicals that our circulation model provides. In the near-surface reservoir feeding the plumes, bubbles reaching the surface of the water pop and throw a very fine spray. Some of these very small droplets of brine exit with the plume gas and provide the observed salt-rich dust particles [2]. Much of the water-borne heat is

  18. Reynolds-Averaged Navier-Stokes Simulation of a 2D Circulation Control Wind Tunnel Experiment

    NASA Technical Reports Server (NTRS)

    Allan, Brian G.; Jones, Greg; Lin, John C.

    2011-01-01

    Numerical simulations are performed using a Reynolds-averaged Navier-Stokes (RANS) flow solver for a circulation control airfoil. 2D and 3D simulation results are compared to a circulation control wind tunnel test conducted at the NASA Langley Basic Aerodynamics Research Tunnel (BART). The RANS simulations are compared to a low blowing case with a jet momentum coefficient, C(sub u), of 0:047 and a higher blowing case of 0.115. Three dimensional simulations of the model and tunnel walls show wall effects on the lift and airfoil surface pressures. These wall effects include a 4% decrease of the midspan sectional lift for the C(sub u) 0.115 blowing condition. Simulations comparing the performance of the Spalart Allmaras (SA) and Shear Stress Transport (SST) turbulence models are also made, showing the SST model compares best to the experimental data. A Rotational/Curvature Correction (RCC) to the turbulence model is also evaluated demonstrating an improvement in the CFD predictions.

  19. Investigation of Northeastern North America Coastal Circulation Using a Nested Regional Circulation Hindcast Model

    NASA Astrophysics Data System (ADS)

    Chen, K.; He, R.

    2008-12-01

    A regional coastal circulation model was used to hindcast circulation over the middle Atlantic Bight (MAB) and Gulf of Maine (GOM) shelf from November 2003 to June 2008. Realistic atmospheric forcing, tidal harmonics and real-time river runoff data were used to drive the hindcast. In addition, this regional model was nested inside the data assimilative global HYCOM, which provides dynamically consistent and numerically accurate its initial and open boundary conditions. Model hindcast solutions were gauged against in situ observations, including coastal sea levels, satellite altimeter sea surface height, mooring observed temperature and salinity time series, glider hydrographic transects, and long term means of depth-averaged current analysis. Such data/model comparisons show the nested regional model is skillful in capturing major regional shelf circulation variability, lending confidence for using 4-year of time and space continuous hindcast fields (January 2004-December 2007) to depict shelf- wide circulation dynamics, along- and cross-shelf transport and the associated momentum balances. Model hindcast solutions confirm the existence of the equatorward shelf circulation with gradually decreased alongshore transport from north to south. Mean alongshelf current is characterized by a strong shelf-break jet, whereas the cross-shelf current is characterized by complex convergence and divergence on the shelf. Mean cross-shelf transports were estimated along 200-m isobath. Momentum balance analyses further nonlinear advection, stress and diffusion term all contribute to the ageostrophic circulation in the along- isobath directions, whereas in the across-isobath direction, the nonlinear advection is predominate. Our nested regional circulation model was also coupled with a 11-component ecosystem model. Some preliminary bio-physical modeling result will also be presented.

  20. Single and two-phase natural circulation in Westinghouse pressurized water reactor simulators: Phenomena, analysis and scaling

    SciTech Connect

    Schultz, R.R.; Chapman, J.C.; Kukita, Y.; Motley, F.E.; Stumpf, H.; Chen, Y.S.; Tasaka, K.

    1987-01-01

    Natural circulation data obtained in the 1/48 scale W four loop PWR simulator - the Large Scale Test Facility (LSTF) are discussed and summarized. Core cooling modes, the primary fluid state, the primary loop mass flow and localized natural circulation phenomena occurring in the steam generator are presented. TRAC-PF1 LSTF model (using both a 1 U-tube and a 3 U-tube steam generator model) analyses of the LSTF natural circulation data including the SG recirculation patterns are presented and compared to the data. The LSTF data are then compared to similar natural circulation data obtained in the Primarkreislaufe (PKL) and the Semiscale facilities. Based on the 1/48 to 1/1705 scaling range which exists between the facilities, the implications of these data towrard natural circulation behavior in commercial plants are briefly discussed.

  1. Angular momentum conservation in a simplified Venus General Circulation Model

    NASA Astrophysics Data System (ADS)

    Lee, C.; Richardson, M. I.

    2012-11-01

    Angular momentum (AM) conservation and transport are critical components of all General Circulation Model (GCM) simulations, and particularly for simulations of the Venus atmosphere. We show that a Venus GCM based upon the Geophysical Fluid Dynamics Laboratory (GFDL) Flexible Modeling System (FMS) GCM conserves angular momentum to better than 2% per 1000 Venus years (≈225,000 Earth days) of integration under the extreme conditions of a simplified Venus simulation with low surface torques. With no topography in the GCM, physical torques due to surface/atmosphere frictional interactions dominate the acceleration of an initially stationary atmosphere and provide more than four times the angular momentum of solid body co-rotation over an integration period of 100 Venus years. During the subsequent steady state period of 200 Venus years negligible mean physical torques cause variation in the total angular momentum of less than 5% and produce a stable multi-century simulation. Diffusion and damping processes within the GCM account for AM losses of less than 0.2% per 1000 Venus years. This study provides a stable comparison point for other GCMs by employing a simplified forcing scheme. The diagnostics and analysis require little or no modification to the core GCM and are sufficiently robust to allow easy model inter-comparison.

  2. Arctic Storms in a Regionally Refined Atmospheric General Circulation Model

    NASA Astrophysics Data System (ADS)

    Roesler, E. L.; Taylor, M.; Boslough, M.; Sullivan, S.

    2014-12-01

    Regional refinement in an atmospheric general circulation model is a new tool in atmospheric modeling. A regional high-resolution solution can be obtained without the computational cost of running a global high-resolution simulation as global climate models have increasing ability to resolve smaller spatial scales. Previous work has shown high-resolution simulations, i.e. 1/8 degree, and variable resolution utilities have resolved more fine-scale structure and mesoscale storms in the atmosphere than their low-resolution counterparts. We will describe an experiment designed to identify and study Arctic storms at two model resolutions. We used the Community Atmosphere Model, version 5, with the Spectral Element dynamical core at 1/8-degree and 1 degree horizontal resolutions to simulate the climatological year of 1850. Storms were detected using a low-pressure minima and vorticity maxima - finding algorithm. It was found the high-resolution 1/8-degree simulation had more storms in the Northern Hemisphere than the low-resolution 1-degree simulation. A variable resolution simulation with a global low resolution of 1-degree and a high-resolution refined region of 1/8 degree over a region in the Arctic is planned. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. SAND NO. 2014-16460A

  3. A Model for Library Book Circulations Incorporating Loan Periods.

    ERIC Educational Resources Information Center

    Burrell, Quentin L.; Fenton, Michael R.

    1994-01-01

    Proposes and explains a modification of the mixed Poisson model for library circulations which takes into account the periods when a book is out on loan and therefore unavailable for borrowing. Highlights include frequency of circulation distributions; negative binomial distribution; and examples of the model at two universities. (Contains 34…

  4. Diversity of Planetary Atmospheric Circulations and Climates in a Simplified General Circulation Model

    NASA Astrophysics Data System (ADS)

    Wang, Yixiong; Read, Peter

    2014-04-01

    The parametric dependence of terrestrial planetary atmospheric circulations and climates on characteristic parameters is studied. A simplified general circulation model-PUMA is employed to investigate the dynamic effects of planetary rotation rate and equator-to-pole temperature difference on the circulation and climate of terrestrial planetary atmospheres. Five different types of circulation regime are identified by mapping the experimental results in a 2-D parameter space defined by thermal Rossby number and frictional Taylor number. The effect of the transfer and redistribution of radiative energy is studied by building up a new two-band semi-gray radiative-convective scheme, which is capable of modelling greenhouse and anti-greenhouse effects while keeping the tunable parameters as few as possible. The results will provide insights into predicting the habitability of terrestrial exoplanets.

  5. Application of Land Surface Data Assimilation to Simulations of Sea Breeze Circulations

    NASA Technical Reports Server (NTRS)

    Mackaro, Scott; Lapenta, William M.; Blackwell, Keith; Suggs, Ron; McNider, Richard T.; Jedlovec, Gary; Kimball, Sytske

    2003-01-01

    A technique has been developed for assimilating GOES-derived skin temperature tendencies and insolation into the surface energy budget equation of a mesoscale model so that the simulated rate of temperature change closely agrees with the satellite observations. A critical assumption of the technique is that the availability of moisture (either from the soil or vegetation) is the least known term in the model's surface energy budget. Therefore, the simulated latent heat flux, which is a function of surface moisture availability, is adjusted based upon differences between the modeled and satellite- observed skin temperature tendencies. An advantage of this technique is that satellite temperature tendencies are assimilated in an energetically consistent manner that avoids energy imbalances and surface stability problems that arise from direct assimilation of surface shelter temperatures. The fact that the rate of change of the satellite skin temperature is used rather than the absolute temperature means that sensor calibration is not as critical. The sea/land breeze is a well-documented mesoscale circulation that affects many coastal areas of the world including the northern Gulf Coast of the United States. The focus of this paper is to examine how the satellite assimilation technique impacts the simulation of a sea breeze circulation observed along the Mississippi/Alabama coast in the spring of 2001. The technique is implemented within the PSUNCAR MM5 V3-5 and applied at spatial resolutions of 12- and 4-km. It is recognized that even 4-km grid spacing is too coarse to explicitly resolve the detailed, mesoscale structure of sea breezes. Nevertheless, the model can forecast certain characteristics of the observed sea breeze including a thermally direct circulation that results from differential low-level heating across the land-sea interface. Our intent is to determine the sensitivity of the circulation to the differential land surface forcing produced via the

  6. 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.

  7. Numerical simulation of losses along a natural circulation helium loop

    NASA Astrophysics Data System (ADS)

    Knížat, Branislav; Urban, František; Mlkvik, Marek; RidzoÅ, František; Olšiak, Róbert

    2016-06-01

    A natural circulation helium loop appears to be a perspective passive method of a nuclear reactor cooling. When designing this device, it is important to analyze the mechanism of an internal flow. The flow of helium in the loop is set in motion due to a difference of hydrostatic pressures between cold and hot branch. Steady flow at a requested flow rate occurs when the buoyancy force is adjusted to resistances against the flow. Considering the fact that the buoyancy force is proportional to a difference of temperatures in both branches, it is important to estimate the losses correctly in the process of design. The paper deals with the calculation of losses in branches of the natural circulation helium loop by methods of CFD. The results of calculations are an important basis for the hydraulic design of both exchangers (heater and cooler). The analysis was carried out for the existing model of a helium loop of the height 10 m and nominal heat power 250 kW.

  8. Postural reactions of circulation and its regulation during simulated weightlessness

    NASA Astrophysics Data System (ADS)

    Sokolov, V. I.; Valyev, V. A.; Kirillov, M. V.; Gornago, V. A.

    The extention and intensification of space exploration the influence of weightlessness on human organism and the formation of a new level of adaptation. The studies of blood circulation is very important because of freguent occurance of cardiovascular disorders in the middle age sudjects. In connection with extention and intensification of space exploration the influence of weightlessness on human organism and the formation of a new level of adaptation mechanisms acguires a special significance (5, 9, 10). The data obtained in recently undertaken model experiments (1, 5, 10), and also during space flights (5, 9) indicate that weightlessness in many ways affects various physiological systems of organism, and first of all cardiovascular system with the development of reflex, humoral and metabolic reactions. It also indicates, that the changes in functioning of cardiovascular system brings about the discruption of its regular responses, which is foremost expressed in decreased antigravitational response, which manifests itself in lowered orthostatic stability (2, 4, 6). It is worth mentioning, that the changes during previous investigations of haemodynamics were mainly carried out with the subjects under forty, therefore agerelated specific features of blood circulation system response are described in a few articles (5, 8). The studies of the kind are especially important because of frequent occurence of cardiovascular disorders such as heart and brain vessels atherosclerosis, hypertension in the middle age, which can to a great extent complicate and affect the "acute" period of adaptation to weightlessness and readaptation process.

  9. 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.

  10. MFIX simulation of NETL/PSRI challenge problem of circulating fluidized bed

    DOE PAGESBeta

    Li, Tingwen; Dietiker, Jean-François; Shahnam, Mehrdad

    2012-12-01

    In this paper, numerical simulations of NETL/PSRI challenge problem of circulating fluidized bed (CFB) using the open-source code Multiphase Flow with Interphase eXchange (MFIX) are reported. Two rounds of simulation results are reported including the first-round blind test and the second-round modeling refinement. Three-dimensional high fidelity simulations are conducted to model a 12-inch diameter pilot-scale CFB riser. Detailed comparisons between numerical results and experimental data are made with respect to axial pressure gradient profile, radial profiles of solids velocity and solids mass flux along different radial directions at various elevations for operating conditions covering different fluidization regimes. Overall, the numericalmore » results show that CFD can predict the complex gas–solids flow behavior in the CFB riser reasonably well. In addition, lessons learnt from modeling this challenge problem are presented.« less

  11. MFIX simulation of NETL/PSRI challenge problem of circulating fluidized bed

    SciTech Connect

    Li, Tingwen; Dietiker, Jean-François; Shahnam, Mehrdad

    2012-12-01

    In this paper, numerical simulations of NETL/PSRI challenge problem of circulating fluidized bed (CFB) using the open-source code Multiphase Flow with Interphase eXchange (MFIX) are reported. Two rounds of simulation results are reported including the first-round blind test and the second-round modeling refinement. Three-dimensional high fidelity simulations are conducted to model a 12-inch diameter pilot-scale CFB riser. Detailed comparisons between numerical results and experimental data are made with respect to axial pressure gradient profile, radial profiles of solids velocity and solids mass flux along different radial directions at various elevations for operating conditions covering different fluidization regimes. Overall, the numerical results show that CFD can predict the complex gas–solids flow behavior in the CFB riser reasonably well. In addition, lessons learnt from modeling this challenge problem are presented.

  12. 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).

  13. THE ESC COMPUTERIZED CIRCULATION SYSTEM MODEL II.

    ERIC Educational Resources Information Center

    SHAWVER, W.; STRAIN, P.M.

    A NEW CIRCULATION SYSTEM NOW IN USE AT THE ELECTRONICS SYSTEMS CENTER (ESC) LIBRARY, PART OF INTERNATIONAL BUSINESS MACHINES CORPORATION, IS BASED UPON A PREVIOUS SYSTEM WHICH USED TABULATING CARDS, UNIT RECORD MACHINES, AND A SMALL COMPUTER. THE NEW SYSTEM IS A TRANSACTION CARD SYSTEM, IN WHICH ONE BASIC TYPE OF CARD FORMAT IS USED FOR CHARGING,…

  14. Simulating the impact of the large-scale circulation on the 2-m temperature and precipitation climatology

    EPA Science Inventory

    The impact of the simulated large-scale atmospheric circulation on the regional climate is examined using the Weather Research and Forecasting (WRF) model as a regional climate model. The purpose is to understand the potential need for interior grid nudging for dynamical downscal...

  15. A Thermospheric Circulation Model for Extrasolar Giant Planets

    NASA Astrophysics Data System (ADS)

    Koskinen, T. T.; Aylward, A. D.; Smith, C. G. A.; Miller, S.

    2007-05-01

    Several models of extrasolar giant planet (EGP) atmospheres have been developed recently. Many of them are one-dimensional or concentrate on the lower or middle atmosphere. Three-dimensional hydrodynamic models are needed to study the horizontal variations in temperature and composition of EGP atmospheres. Circulation models for the upper atmosphere are particularly important as they can be used to study the thermal structure due to stellar irradiation, radiative cooling, and atmospheric circulation in the thermospheres of close-in EGPs and hence the rate of evaporation of their atmospheres. We present a generic gas giant model that is capable of generating three-dimensional, self-consistent global simulations of stable EGP thermospheres at different orbital distances. Calculations performed by this model indicate that IR emissions from H+3 ions may play a significant role in cooling the thermospheres of EGPs at least in the range of 0.2-1 AU from a solar-type host star. In this range thermal dissociation of H2 is negligible and ion densities are small compared to the overall neutral density. Inside 0.2 AU thermal dissociation and dissociative photoionization of H2 may prevent the effective formation of H+3. In the absence of radiative cooling from H+3 the upper atmospheres reach temperatures well above 10,000 K within ~0.5 AU. In this case the upper thermospheres are entirely converted into atomic hydrogen and the temperatures are high enough for significant atmospheric loss to take place. Our model is capable of calculating the IR signal strengths for various vibrational transitions of H+3 based on the thermal state and the composition of the atmosphere. Potential detection of such signals would thus provide a validation of some of our results.

  16. System model of a natural circulation integral test facility

    NASA Astrophysics Data System (ADS)

    Galvin, Mark R.

    The Department of Nuclear Engineering and Radiation Health Physics (NE/RHP) at Oregon State University (OSU) has been developing an innovative modular reactor plant concept since being initiated with a Department of Energy (DoE) grant in 1999. This concept, the Multi-Application Small Light Water Reactor (MASLWR), is an integral pressurized water reactor (PWR) plant that utilizes natural circulation flow in the primary and employs advanced passive safety features. The OSU MASLWR test facility is an electrically heated integral effects facility, scaled from the MASLWR concept design, that has been previously used to assess the feasibility of the concept design safety approach. To assist in evaluating operational scenarios, a simulation tool that models the test facility and is based on both test facility experimental data and analytical methods has been developed. The tool models both the test facility electric core and a simulated nuclear core, allowing evaluation of a broad spectrum of operational scenarios to identify those scenarios that should be explored experimentally using the test facility or design-quality multi-physics tools. Using the simulation tool, the total cost of experimentation and analysis can be reduced by directing time and resources towards the operational scenarios of interest.

  17. Development of a hybrid cloud parameterization for general circulation models

    SciTech Connect

    Kao, C.Y.J.; Kristjansson, J.E.; Langley, D.L.

    1995-04-01

    We have developed a cloud package with state-of-the-art physical schemes that can parameterize low-level stratus or stratocumulus, penetrative cumulus, and high-level cirrus. Such parameterizations will improve cloud simulations in general circulation models (GCMs). The principal tool in this development comprises the physically based Arakawa-Schubert scheme for convective clouds and the Sundqvist scheme for layered, nonconvective clouds. The term {open_quotes}hybrid{close_quotes} addresses the fact that the generation of high-attitude layered clouds can be associated with preexisting convective clouds. Overall, the cloud parameterization package developed should better determine cloud heating and drying effects in the thermodynamic budget, realistic precipitation patterns, cloud coverage and liquid/ice water content for radiation purposes, and the cloud-induced transport and turbulent diffusion for atmospheric trace gases.

  18. 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.

  19. Development of an Accident Reproduction Simulator System Using a Hemodialysis Extracorporeal Circulation System

    PubMed Central

    Nishite, Yoshiaki; Takesawa, Shingo

    2016-01-01

    Background: Accidents that occur during dialysis treatment are notified to the medical staff via alarms raised by the dialysis apparatus. Similar to such real accidents, apparatus activation or accidents can be reproduced by simulating a treatment situation. An alarm that corresponds to such accidents can be utilized in the simulation model. Objectives: The aim of this study was to create an extracorporeal circulation system (hereinafter, the circulation system) for dialysis machines so that it sets off five types of alarms for: 1) decreased arterial pressure, 2) increased arterial pressure, 3) decreased venous pressure, 4) increased venous pressure, and 5) blood leakage, according to the five types of accidents chosen based on their frequency of occurrence and the degree of severity. Materials and Methods: In order to verify the alarm from the dialysis apparatus connected to the circulation system and the accident corresponding to it, an evaluation of the alarm for its reproducibility of an accident was performed under normal treatment circumstances. The method involved testing whether the dialysis apparatus raised the desired alarm from the moment of control of the circulation system, and measuring the time it took until the desired alarm was activated. This was tested on five main models from four dialyzer manufacturers that are currently used in Japan. Results: The results of the tests demonstrated successful activation of the alarms by the dialysis apparatus, which were appropriate for each of the five types of accidents. The time between the control of the circulatory system to the alarm signal was as follows, 1) venous pressure lower limit alarm: 7 seconds; 2) venous pressure lower limit: 8 seconds; 3) venous pressure upper limit: 7 seconds; 4) venous pressure lower limit alarm: 2 seconds; and 5) blood leakage alarm: 19 seconds. All alarms were set off in under 20 seconds. Conclusions: Thus, we can conclude that a simulator system using an extracorporeal

  20. 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.

  1. Circulation-based Modeling of Gravity Currents

    NASA Astrophysics Data System (ADS)

    Meiburg, E. H.; Borden, Z.

    2013-05-01

    Atmospheric and oceanic flows driven by predominantly horizontal density differences, such as sea breezes, thunderstorm outflows, powder snow avalanches, and turbidity currents, are frequently modeled as gravity currents. Efforts to develop simplified models of such currents date back to von Karman (1940), who considered a two-dimensional gravity current in an inviscid, irrotational and infinitely deep ambient. Benjamin (1968) presented an alternative model, focusing on the inviscid, irrotational flow past a gravity current in a finite-depth channel. More recently, Shin et al. (2004) proposed a model for gravity currents generated by partial-depth lock releases, considering a control volume that encompasses both fronts. All of the above models, in addition to the conservation of mass and horizontal momentum, invoke Bernoulli's law along some specific streamline in the flow field, in order to obtain a closed system of equations that can be solved for the front velocity as function of the current height. More recent computational investigations based on the Navier-Stokes equations, on the other hand, reproduce the dynamics of gravity currents based on the conservation of mass and momentum alone. We propose that it should therefore be possible to formulate a fundamental gravity current model without invoking Bernoulli's law. The talk will show that the front velocity of gravity currents can indeed be predicted as a function of their height from mass and momentum considerations alone, by considering the evolution of interfacial vorticity. This approach does not require information on the pressure field and therefore avoids the need for an energy closure argument such as those invoked by the earlier models. Predictions by the new theory are shown to be in close agreement with direct numerical simulation results. References Von Karman, T. 1940 The engineer grapples with nonlinear problems, Bull. Am. Math Soc. 46, 615-683. Benjamin, T.B. 1968 Gravity currents and related

  2. Computer modeling of a CFB (circulating fluidized bed) gasifier

    SciTech Connect

    Gidaspow, D.; Ding, J.

    1990-06-01

    The overall objective of this investigation is to develop experimentally verified models for circulating fluidized bed (CFB) combustors. This report presents an extension of our cold flow modeling of a CFB given in our first quarterly report of this project and published in Numerical Methods for Multiphase Flows'' edited by I. Celik, D. Hughes, C. T. Crowe and D. Lankford, FED-Vol.91, American Society of Mechanical Engineering, pp47--56 (1990). The title of the paper is Multiphase Navier-Stokes Equation Solver'' by D. Gidaspow, J. Ding and U.K. Jayaswal. To the two dimensional code described in the above paper we added the energy equations and the conservation of species equations to describe a synthesis gas from char producer. Under the simulation conditions the injected oxygen reacted near the inlet. The solid-gas mixing was sufficiently rapid that no undesirable hot spots were produced. This simulation illustrates the code's capability to model CFB reactors. 15 refs., 20 figs.

  3. Simulations of Flow Circulations and Atrazine Concentrations in a Midwest U.S. Reservoir

    NASA Astrophysics Data System (ADS)

    Zhao, Xianggui; Gu, Roy R.; Guo, Chuling; Wang, Kui; Li, Shijie

    Atrazine is the most commonly used herbicide in the spring for pre-emergent weed control in the corn cropping area in the Midwestern United States. A frequent high level of herbicide concentrations in reservoirs is a great concern for public health and aquatic ecosystems. In this study, a two-dimensional hydrodynamics and toxic contaminant transport model was applied to Saylorville Reservoir, Iowa, USA. The model simulates physical, chemical, and biological processes and predicts unsteady vertical and longitudinal distributions of a toxic chemical. Model results were validated by measured temperatures and atrazine concentrations. Simulated flow velocities, water temperatures, and chemical concentrations demonstrated that the spatial variation of atrazine concentrations was largely affected by seasonal flow circulation patterns in the reservoir. In particular, the simulated fate and transport of atrazine showed the effect of flow circulation on spatial distribution of atrazine during summer months as the river flow formed an underflow within the reservoir and resulted in greater concentrations near the surface of the reservoir. Atrazine concentrations in the reservoir peaked around the end of May and early June. A thorough understanding of the fate and transport of atrazine in the reservoir can assist in developing operation and pollution prevention strategies with respect to timing, amount, and depth of withdrawal. The responses of atrazine transport to various boundary conditions provide useful information in assessing environmental impact of alternative upstream watershed management practices on the quality of reservoir water.

  4. The impact of a realistic vertical dust distribution on the simulation of the Martian General Circulation

    NASA Astrophysics Data System (ADS)

    Guzewich, Scott D.; Toigo, Anthony D.; Richardson, Mark I.; Newman, Claire E.; Talaat, Elsayed R.; Waugh, Darryn W.; McConnochie, Timothy H.

    2013-05-01

    Limb-scanning observations with the Mars Climate Sounder and Thermal Emission Spectrometer (TES) have identified discrete layers of enhanced dust opacity well above the boundary layer and a mean vertical structure of dust opacity very different from the expectation of well-mixed dust in the lowest 1-2 scale heights. To assess the impact of this vertical dust opacity profile on atmospheric properties, we developed a TES limb-scan observation-based three-dimensional and time-evolving dust climatology for use in forcing general circulation models (GCMs). We use this to force the MarsWRF GCM and compare with simulations that use a well-mixed (Conrath-ν) vertical dust profile and Mars Climate Database version 4 (MCD) horizontal distribution dust opacity forcing function. We find that simulated temperatures using the TES-derived forcing yield a 1.18 standard deviation closer match to TES temperature retrievals than a MarsWRF simulation using MCD forcing. The climatological forcing yields significant changes to many large-scale features of the simulated atmosphere. Notably the high-latitude westerly jet speeds are 10-20 m/s higher, polar warming collar temperatures are 20-30 K warmer near northern winter solstice and tilted more strongly poleward, the middle and lower atmospheric meridional circulations are partially decoupled, the migrating diurnal tide exhibits destructive interference and is weakened by 50% outside of equinox, and the southern hemisphere wave number 1 stationary wave is strengthened by up to 4 K (45%). We find the vertical dust distribution is an important factor for Martian lower and middle atmospheric thermal structure and circulation that cannot be neglected in analysis and simulation of the Martian atmosphere.

  5. Mars Global Surveyor: Aerobraking and Observations Support Using a Mars Global Circulation Model

    NASA Technical Reports Server (NTRS)

    Hollingsworth, Jeffery L.; Bridger, Alison F. C.; Harberle, Robert M.

    1997-01-01

    This is a Final Report for a Joint Research Interchange (JRI) between NASA Ames Research Center and San Jose State University, Department of Meteorology. Using a global atmospheric circulation model for Mars, the focus of this JRI has been to provide support for the Mars Global Surveyor (MGS) spacecraft aerobraking activities and interpretation guidance of preliminary observations. ne primary atmospheric model applied in this investigation has been a high-top version of the NASA Ames Mars general circulation model (MGCM). Comparisons with an atmospheric model designed primarily for engineering purposes (Mars-GRAM) has also been carried out. From a suite of MGCM simulations, we have assessed plausible spatial and temporal variability in atmospheric density at high altitudes (e.g., 70-110 km) for seasonal dates and locations during Phase 1 aerobraking. Diagnostic tools have been developed to analyze circulation fields from the MGCM simulations, and these tools have been applied in the creation of a Mars climate catalogue database. Throughout Phase 1 aerobraking activities, analysis products have been provided to the MGS aerobraking atmospheric advisory group (AAG). Analyses of circulation variability at the coupling level between the MGCM and a Mars thermospheric global circulation model (MTGCM) has also been assessed. Finally, using a quasi-geostrophic dynamical formulation with the MGCM simulations, diagnosis of breaking planetary (Rossby) waves in Mars' middle atmosphere has been carried out. Titles of papers presented at scientific workshops and seminars, and a publication in the scientific literature are provided.

  6. Mars Global Surveyor: Aerobraking and Observations Support Using a Mars Global Circulation Model

    NASA Technical Reports Server (NTRS)

    Hollingsworth, Jeffery L.; Bridger, Alison F. C.; Haberle, Robert M.

    1997-01-01

    This is a Final Report for a Joint Research Interchange (JRI) between NASA Ames Research Center and San Jose State University, Department of Meteorology. Using a global atmospheric circulation model for Mars, the focus of this JRI has been to provide support for the Mars Global Surveyor (MGS) spacecraft aerobraking activities and interpretation guidance of preliminary observations. The primary atmospheric model applied in this investigation has been a high-top version of the NASA Ames Mars general circulation model (MGCM). Comparisons with an atmospheric model designed primarily for engineering purposes (Mars-GRAM) has also been carried out. From a suite of MGCM simulations, we have assessed plausible spatial and temporal variability in atmospheric density at high altitudes (e.g., 70-1 10 km) for seasonal dates and locations during Phase 1 aerobraking. Diagnostic tools have been developed to analyze circulation fields from the MGCM simulations, and these tools have been applied in the creation of a Mars climate catalogue database. Throughout Phase I aerobraking activities, analysis products have been provided to the MGS aerobraking atmospheric advisory group (AAG). Analyses of circulation variability at the coupling level between the MGCM and a Mars thermospheric global circulation model (MTGCM) has also been assessed. Finally, using a quasi-geostrophic dynamical formulation with the MGCM simulations, diagnosis of breaking planetary (Rossby) waves in Mars middle atmosphere has been carried out. Titles of papers presented at scientific workshops and seminars, and a publication in the scientific literature are provided.

  7. Mars Global Surveyor: Aerobraking and Observations Support Using a Mars Global Circulation Model

    NASA Technical Reports Server (NTRS)

    Hollingsworth, Jeffery L.; Bridger, Alison F. C.; Haberle, Robert M.

    1997-01-01

    This is a Final Report for a Joint Research Interchange (JRI) between NASA Ames Research Center and San Jose State University, Department of Meteorology. Using a global atmospheric circulation model for Mars, the focus of this JRI has been to provide support for the Mars Global Surveyor (MGS) spacecraft aerobraking activities and interpretation guidance of preliminary observations. The primary atmospheric model applied in this investigation has been a high-top version of the NASA Ames Mars general circulation model (MGCM). Comparisons with an atmospheric model designed primarily for engineering purposes (Mars-GRAM) has also been carried out. From a suite of MGCM simulations, we have assessed plausible spatial and temporal variability in atmospheric density at high altitudes (e.g., 70-110 km) for seasonal dates and locations during Phase I aerobraking. Diagnostic tools have been developed to analyze circulation fields from the MGCM simulations, and these tools have been applied in the creation of a Mars climate catalogue database. Throughout Phase I aerobraking activities, analysis products have been provided to the MGS aerobraking atmospheric advisory group (AAG). Analyses of circulation variability at the coupling level between the MGCM and a Mars thermospheric global circulation model (MTGCM) has also been assessed. Finally, using a quasi-geostrophic dynamical formulation with the MGCM simulations, diagnosis of breaking planetary (Rossby) waves in Mars' middle atmosphere has been carried out. Titles of papers presented at scientific workshops and seminars, and a publication in the scientific literature are provided.

  8. Role of Eurasian snow cover in wintertime circulation: Decadal simulations forced with satellite observations

    NASA Astrophysics Data System (ADS)

    Orsolini, Yvan J.; Kvamstø, Nils G.

    2009-10-01

    We investigate the impact of the Eurasian snow cover extent on the Northern Hemisphere winter circulation by performing a suite of ensemble simulations with the Météo-France "Arpege Climat" atmospheric general circulation model, spanning 2 decades (1979-2000). Observed snow cover derived from satellite infrared and visible imagery has been forced weekly into the model. Variability in autumn-early winter snow cover extent over eastern Eurasia is linked to circulation anomalies over the North Pacific that are influencing the North Atlantic sector in late winter through the development of the Aleutian-Icelandic Low Seesaw teleconnection. The forcing of realistic snow cover in the model augments potential predictability over eastern Eurasia and the North Pacific and improves the hindcast skill score of the Aleutian-Icelandic Low Seesaw teleconnection. Enhanced eastern Eurasia snow cover is associated with an anomalous upper-tropospheric wave train across Eurasia, anomalously high upward wave activity flux, and a displaced stratospheric polar vortex.

  9. The Madden-Julian Oscillation in General Circulation Models

    SciTech Connect

    Sperber, K R; Gleckler, P J; Doutriaux, C; Groups, A M; Groups, C M; Slingo, J M; Inness, P M; Gualdi, S; Li, W

    2003-10-27

    A methodology is utilized to analyze in a standardized fashion the Madden-Julian Oscillation (MJO) in general circulation models. This is attained by projecting 20-100 day bandpass filtered outgoing longwave radiation (OLR) from the models onto the two leading empirical orthogonal functions (EOF's) of observed OLR that characterize the propagation of MJO convection from the Indian Ocean to the central Pacific Ocean. The resulting principal component time series are then screened to isolate boreal winters during which they exhibit a lead-lag relationship consistent with observations. This PC subset is used for linear regression to determine the ability of the models to simulate the observed spacetime variability of the MJO. The vast majority of models underestimate the amplitude of the MJO convective anomalies by a factor of two or more, and the eastward propagation of convection is less coherent than observed, typically. For a given family of models, coupling to an ocean leads to better organization of the large-scale convection. The low-level moisture convergence mechanism for eastward propagation is represented in limited cases, as is the vertical structure of the MJO.

  10. Numerical Modelling of Circulation and Exchange through Singapore Straits

    NASA Astrophysics Data System (ADS)

    Liu, G.; Xu, M.; Chua, V. P.

    2014-12-01

    The circulation in the Singapore coastal region is complicated and influenced by the combination of tidal forcing of the surrounding seas, complex bathymetry, irregular coastlines, and seasonal monsoon and local winds. An unstructured-grid SUNTANS (Stanford Unstructured Nonhydrostatic Terrain-following Adaptive Navier-Stokes Simulator) model is employed to perform three-dimensional simulations of flow in Singapore coastal waters. The unstructured-grid has an average resolution of 50 - 100 m around Singapore and in areas close to the shoreline, while a coarse grid resolution is employed in the open waters. The model is tidally forced at the three open boundaries, located to the west, south and east of Singapore, using the 8 main tidal constituents as derived from the OSU Tidal Prediction Software (OTPS). A detailed calibration is performed, and the model-predicted water levels and currents compare well with observed data throughout the model domain. We examine the individual and combined effects of tidal and wind forcing by performing simulations with (1) tides only, (2) winds only and (3) both tides and wind. The exchange through Singapore Strait is investigated by computing volume fluxes and transport pathways at four transects, namely the Malacca Strait, Java Sea, South China Sea and Singapore transects. The transport pathways are computed by releasing particles on each side of the transects, and identifying the spatial distribution of the particles over one tidal cycle. Our results show that tidal forcing is predominant in Singapore Strait, and wind forcing is an important mechanism during the monsoon season. The residual effects, attributed to nonlinear interactions between tidal and wind forcing, is dominant during the inter-monsoon season.

  11. Large-eddy simulations of flow around a circulation control airfoil

    NASA Astrophysics Data System (ADS)

    Hahn, Seonghyeon; Shariff, Karim

    2008-11-01

    Circulation control, proposed in NASA's Cruise Efficient Short Take-off and Landing (CESTOL) concept, has the potential to increase air-traffic throughput and reduce the noise footprint. Circulation control obtains a substantial increase in lift coefficient by using a wall-jet that blows tangentially on a rounded (Coanda) surface deflected at the trailing edge. The flow has proven to be difficult to reliably predict using Reynolds-averaged models. We undertake large-eddy simulations to better understand underlying mechanisms and create a database for modelers. Simulations are patterned after Novak et al.'s (1987) experiment, which, despite its faults, is the best documented to date. A Reynolds number of 10̂6 and two cases with low and high blowing are considered using Stanford's unstructured solver CDP. The upper surface begins with laminar to turbulent transition following a region of weak shear stress. Then strong favorable pressure gradient as the jet slot is approached leads to a raised log-law. There exists a region over the Coanda surface where the mean flow development collapses very well in wall-jet similarity coordinates, indicating that a portion of the near-wall region maintains classical wall-jet characteristics. At the present time, the lower surface has delayed transition due to lack of tripping in the simulations and considerable discrepancies with the experiments for second-order statistics.

  12. In Vitro Simulation and Validation of the Circulation with Congenital Heart Defects

    PubMed Central

    Figliola, Richard S.; Giardini, Alessandro; Conover, Tim; Camp, Tiffany A.; Biglino, Giovanni; Chiulli, John; Hsia, Tain-Yen

    2010-01-01

    Despite the recent advances in computational modeling, experimental simulation of the circulation with congenital heart defect using mock flow circuits remains an important tool for device testing, and for detailing the probable flow consequences resulting from surgical and interventional corrections. Validated mock circuits can be applied to qualify the results from novel computational models. New mathematical tools, coupled with advanced clinical imaging methods, allow for improved assessment of experimental circuit performance relative to human function, as well as the potential for patient-specific adaptation. In this review, we address the development of three in vitro mock circuits specific for studies of congenital heart defects. Performance of an in vitro right heart circulation circuit through a series of verification and validation exercises is described, including correlations with animal studies, and quantifying the effects of circuit inertiance on test results. We present our experience in the design of mock circuits suitable for investigations of the characteristics of the Fontan circulation. We use one such mock circuit to evaluate the accuracy of Doppler predictions in the presence of aortic coarctation. PMID:21218147

  13. 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.

  14. Exploring ``Freeze Out'' on Mars using an Atmospheric Circulation Model

    NASA Astrophysics Data System (ADS)

    Esquivel, Michael

    2006-10-01

    In addition to observational research, computational models like the NASA Ames Mars General Circulation Model (GCM) are used for efficient and often detailed representations of physical quantities. Using this GCM model, I am studying the effects of the distribution and density of frozen carbon-dioxide located at the polar caps. I have paid attention to the effects of the resulting ground temperature, surface pressure, and ground ice through time-based 2D and 3D animations. Also, I have modified the planet's axis between 5 and 50 degrees, changed the pressure by orders of magnitude from zero to two magnitudes, and studied conditions that result to a time frame of nearly 4 billion years ago. Preliminary results show that low pressures with low degrees of tilt have resulting pressures that approach zero, often ending simulations early. The remaining frozen carbon-dioxide remains airborne which could explain the possibility of an atmospheric phenomenon called a ``freeze out.'' This type of atmospheric computational data is often tedious and cumbersome to interface between numerical data and visual format. To counteract this problem, I have built an interface using IDL to interact with raw Mars GCM data. This interface allows researchers to increase the time to study actual science and minimize the time to find and decipher data to a visual format. This interface allows modification of initial variables to allow for cold starts of the Mars GCM model as well as create new maps and view them in an animation sequence to study changes in time.

  15. 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

  16. New Insights about Meridional Circulation Dynamics from 3D MHD Global Simulations of Solar Convection and Dynamo Action

    NASA Astrophysics Data System (ADS)

    Passos, D.; Charbonneau, P.; Miesch, M. S.

    2016-04-01

    The solar meridional circulation is a "slow", large scale flow that transports magnetic field and plasma throughout the convection zone in the (r,θ) plane and plays a crucial role in controlling the magnetic cycle solutions presented by flux transport dynamo models. Observations indicate that this flow speed varies in anti-phase with the solar cycle at the solar surface. A possible explanation for the source of this variation is based on the fact that inflows into active regions alter the global surface pattern of the meridional circulation. In this work we examine the meridional circulation profile that emerges from a 3D global simulation of the solar convection zone, and its associated dynamics. We find that at the bottom of the convection zone, in the region where the toroidal magnetic field accumulates, the meridional circulation is highly modulated through the action of a magnetic torques and thus provides evidence for a new mechanism to explain the observed cyclic variations.

  17. Numerical Simulation of the tidal effects on estuarine circulation in the San Juan Bay

    NASA Astrophysics Data System (ADS)

    Garcia, Edgardo; Canals, Miguel; Capella, Jorge; Morell, Julio; Leonardi, Stefano; Caribbean Coastal Ocean Observing System Collaboration

    2012-11-01

    The regional oceanic modeling system ROMS has been implemented in San Juan Bay, Puerto Rico, to investigate quantitatively the mixing processes and as a forecast tool to support emergency planning and resource management in the area. The response of the San Juan Bay circulation to both river discharges and tidal forcing has been investigated. A hind-cast simulation is performed and compared with time series measurements and hidrographic data to validate the model. Sensitivity studies to turbulence mixing parameterization have been carried out under different forcing scenarios. A simulation without river outflow but forced with tidal constituents along the open boundaries is performed. Good agreement has been found with coastal observations with amplitudes gauges and modeled amplitudes constituents. A numerical experiment of the response of the Bay's circulation to river discharge only is performed and compared with the tide plus river forcing and tidal forcing only scenarios. Salinity distributions and vertical mixing are affected by the proximity to deep waters of the San Juan Bay Estuary, also the bulge region and plume structure in the entrance of San Juan Bay are highly affected by the bottom friction for the case with tide forcing.

  18. Multiple model identification of a cold flow circulating fluidized bed

    SciTech Connect

    Panday, Rupen; Famouri, P.; Woerner, B.D.; Turton, R.; •Ludlow, J.C.; Shadle, L.J.; Boyle, E.J.

    2008-05-13

    Solids circulation rate is an important parameter that is essential to the control and improved performance of a circulating fluidized bed system. The present work focuses on the identification of a cold flow circulating fluidized bed using a multiple model identification technique that considers the given set-up as a nonlinear dynamic system and predicts the solids circulation rate as a function of riser aeration, move air flow rate, and total riser pressure drop. The predictor model obtained from this technique is trained on glass beads data sets in which riser aeration and move air flow are varied randomly one at a time. The global linear state space model obtained from the N4SID algorithm is trained on the same data set and the prediction results of solids circulation rate from both these algorithms are tested against data obtained at operating conditions different from the training data. The comparison between the two methods shows that the prediction results obtained from the multiple model technique are better than those obtained from the global linear model. The number of local models is increased from two to five and two third order state space models are sufficient for the present sets of data.

  19. Inter-annual variability of the Mediterranean thermohaline circulation in Med-CORDEX simulations

    NASA Astrophysics Data System (ADS)

    Vittoria Struglia, Maria; Adani, Mario; Carillo, Adriana; Pisacane, Giovanna; Sannino, Gianmaria; Beuvier, Jonathan; Lovato, Tomas; Sevault, Florence; Vervatis, Vassilios

    2016-04-01

    Recent atmospheric reanalysis products, such as ERA40 and ERA-interim, and their regional dynamical downscaling prompted the HyMeX/Med-CORDEX community to perform hind-cast simulations of the Mediterranean Sea, giving the opportunity to evaluate the response of different ocean models to a realistic inter-annual atmospheric forcing. Ocean numerical modeling studies have been steadily improving over the last decade through hind-cast processing, and are complementary to observations in studying the relative importance of the mechanisms playing a role in ocean variability, either external forcing or internal ocean variability. This work presents a review and an inter-comparison of the most recent hind-cast simulations of the Mediterranean Sea Circulation, produced in the framework of the Med-CORDEX initiative, at resolutions spanning from 1/8° to 1/16°. The richness of the simulations available for this study is exploited to address the effects of increasing resolution, both of models and forcing, the initialization procedure, and the prescription of the atmospheric boundary conditions, which are particularly relevant in order to model a realistic THC, in the perspective of fully coupled regional ocean-atmosphere models. The mean circulation is well reproduced by all the simulations. However, it can be observed that the horizontal resolution of both atmospheric forcing and ocean model plays a fundamental role in the reproduction of some specific features of both sub-basins and important differences can be observed among low and high resolution atmosphere forcing. We analyze the mean circulation on both the long-term and decadal time scale, and the represented inter-annual variability of intermediate and deep water mass formation processes in both the Eastern and Western sub-basins, finding that models agree with observations in correspondence of specific events, such as the 1992-1993 Eastern Mediterranean Transient, and the 2005-2006 event in the Gulf of Lion. Long

  20. Simulation of NOx emission in circulating fluidized beds burning low-grade fuels

    SciTech Connect

    Afsin Gungor

    2009-05-15

    Nitrogen oxides are a major environmental pollutant resulting from combustion. This paper presents a modeling study of pollutant NOx emission resulting from low-grade fuel combustion in a circulating fluidized bed. The simulation model accounts for the axial and radial distribution of NOx emission in a circulating fluidized bed (CFB). The model results are compared with and validated against experimental data both for small-size and industrial-size CFBs that use different types of low-grade fuels given in the literature. The present study proves that CFB combustion demonstrated by both experimental data and model predictions produces low and acceptable levels of NOx emissions resulting from the combustion of low-grade fuels. Developed model can also investigate the effects of different operational parameters on overall NOx emission. As a result of this investigation, both experimental data and model predictions show that NOx emission increases with the bed temperature but decreases with excess air if other parameters are kept unchanged. 37 refs., 5 figs., 5 tabs.

  1. A Quasi-Equilibrium Tropical Circulation Model--Formulation*.

    NASA Astrophysics Data System (ADS)

    Neelin, J. David; Zeng, Ning

    2000-06-01

    A class of model for simulation and theory of the tropical atmospheric component of climate variations is introduced. These models are referred to as quasi-equilibrium tropical circulation models, or QTCMs, because they make use of approximations associated with quasi-equilibrium (QE) convective parameterizations. Quasi-equilibrium convective closures tend to constrain the vertical temperature profile in convecting regions. This can be used to generate analytical solutions for the large-scale flow under certain approximations. A tropical atmospheric model of intermediate complexity is constructed by using the analytical solutions as the first basis function in a Galerkin representation of vertical structure. This retains much of the simplicity of the analytical solutions, while retaining full nonlinearity, vertical momentum transport, departures from QE, and a transition between convective and nonconvective zones based on convective available potential energy. The atmospheric model is coupled to a one-layer land surface model with interactive soil moisture and simulates its own tropical climatology. In the QTCM version presented here, the vertical structure of temperature variations is truncated to a single profile associated with deep convection. Though designed to be accurate in and near regions dominated by deep convection, the model simulates the tropical and subtropical climatology reasonably well, and even has a qualitative representation of midlatitude storm tracks.The model is computationally economical, since part of the solution has been carried out analytically, but the main advantage is relative simplicity of analysis under certain conditions. The formulation suggests a slightly different way of looking at the tropical atmosphere than has been traditional in tropical meteorology. While convective scales are unstable, the large-scale motions evolve with a positive effective stratification that takes into account the partial cancellation of adiabatic

  2. An interactive computer simulator of the circulation for knowledge acquisition in cardio-anesthesia.

    PubMed

    Popp, H J; Schecke, T; Rau, G; Käsmacher, H; Kalff, G

    1991-01-01

    Knowledge-based decision support systems for use in cardio-anesthesia can provide online support to the anesthesiologist by generating intelligent alarms. However, the acquisition and validation of a consistent knowledge base for this application bears problems related to the transfer of clinical experiences into a rule system. An interactive simulator of the human circulation is presented that supports the process of knowledge acquisition and testing. The simulator can be controlled in realtime by an anesthesiologist during the simulation run thus providing a basis for interdisciplinary discussion of routine as well as critical situations. The output data can be transferred to a knowledge-based system for test purposes. The simulator is currently being used for the development of the Anesthesia Expert Assist System AES-2. With regard to the special application a model of the heart-function was integrated which enables the simulation of heart insufficiency. Simulation runs under various conditions are presented and discussed. The simulator was implemented on an ATARI ST personal computer. PMID:1779177

  3. 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.

  4. On the design of an interactive biosphere for the GLAS general circulation model

    NASA Technical Reports Server (NTRS)

    Mintz, Y.; Sellers, P. J.; Willmott, C. J.

    1983-01-01

    Improving the realism and accuracy of the GLAS general circulation model (by adding an interactive biosphere that will simulate the transfers of latent and sensible heat from land surface to atmosphere as functions of the atmospheric conditions and the morphology and physiology of the vegetation) is proposed.

  5. Simulating the impact of the large-scale circulation on the 2-m temperature and precipitation climatology

    NASA Astrophysics Data System (ADS)

    Bowden, Jared H.; Nolte, Christopher G.; Otte, Tanya L.

    2013-04-01

    The impact of the simulated large-scale atmospheric circulation on the regional climate is examined using the Weather Research and Forecasting (WRF) model as a regional climate model. The purpose is to understand the potential need for interior grid nudging for dynamical downscaling of global climate model (GCM) output for air quality applications under a changing climate. In this study we downscale the NCEP-Department of Energy Atmospheric Model Intercomparison Project (AMIP-II) Reanalysis using three continuous 20-year WRF simulations: one simulation without interior grid nudging and two using different interior grid nudging methods. The biases in 2-m temperature and precipitation for the simulation without interior grid nudging are unreasonably large with respect to the North American Regional Reanalysis (NARR) over the eastern half of the contiguous United States (CONUS) during the summer when air quality concerns are most relevant. This study examines how these differences arise from errors in predicting the large-scale atmospheric circulation. It is demonstrated that the Bermuda high, which strongly influences the regional climate for much of the eastern half of the CONUS during the summer, is poorly simulated without interior grid nudging. In particular, two summers when the Bermuda high was west (1993) and east (2003) of its climatological position are chosen to illustrate problems in the large-scale atmospheric circulation anomalies. For both summers, WRF without interior grid nudging fails to simulate the placement of the upper-level anticyclonic (1993) and cyclonic (2003) circulation anomalies. The displacement of the large-scale circulation impacts the lower atmosphere moisture transport and precipitable water, affecting the convective environment and precipitation. Using interior grid nudging improves the large-scale circulation aloft and moisture transport/precipitable water anomalies, thereby improving the simulated 2-m temperature and precipitation

  6. Hierarchical framework for coupling a biogeochemical trace gas model to a general circulation model

    SciTech Connect

    Miller, N.L.; Foster, I.T.

    1994-04-01

    A scheme is described for the computation of terrestrial biogeochemical trace gas fluxes in the context of a general circulation model. This hierarchical system flux scheme (HSFS) incorporates five major components: (1) a general circulation model (GCM), which provides a medium-resolution (i.e., 1{degrees} by 1{degrees}) simulation of the atmospheric circulation; (2) a procedure for identifying regions of defined homogeneity of surface type within GCM grid cells; (3) a set of surface process models, to be run within each homogeneous region, which include a biophysical model, the Biosphere Atmospheric Transfer Scheme (BATS), and a biogeochemical model (BGCM); (4) an interpolation/integration system that transfers information between the GCM and surface process models with finer resolution; and (5) an interactive data array based on a geographic information system (GIS), which provides land characteristic information via the interpolator. The goals of this detailed investigation are to compute the local and global sensitivities of trace gas fluxes to GCM and BATS variables, the effects of trace gas fluxes on global climate, and the effects of global climate on specific biomes.

  7. Simulation of the 1986-1987 El Niño and 1988 La Niña events with a free surface tropical Pacific Ocean general circulation model

    NASA Astrophysics Data System (ADS)

    Zhang, Rong-Hua; Endoh, Masahiro

    1994-04-01

    Observed atmospheric forcing fields over the period 1984-1989 force a free surface tropical Pacific Ocean general circulation model. Numerical simulation of the 1986-1987 El Niño and 1988 La Niña events is presented in the paper. Some quantitative comparisons between model time series and corresponding observations of sea level, and upper ocean current and temperature are made to verify the model performance. Diagnostic analyses of heat balance and available energy budget are given as well. The space-time evolution of various model variables demonstrates that the model produces interannual variations with reasonable success. Beginning in mid-1986, westerly wind over the western equatorial Pacific drives strong eastward surface currents which accomplish the massive transfer of warm surface water. The strong westerly wind in late 1986 excites the pronounced equatorial Kelvin waves, which propagate eastward toward the eastern and coastal Pacific where they depress the thermocline and raise sea level twice, and increase sea surface temperature. The eastern Pacific warming occurs primarily from the diminished cooling contribution of vertical advection, whereas in the central Pacific, eastward advection by anomalous zonal flows is the principal mechanism. The El Niño conditions in the eastern Pacific disappear in mid-1987, whereas they remain in the central and western Pacific until early 1988. Subsequently, the tropical Pacific Ocean rebounds to significant La Niña conditions. Available energy (AE) has a good phase relationship with respect to other variables characterized by warm and cold conditions. AE is anomalously high prior to a warm event, accompanying conversion from kinetic energy (KE) to available potential energy (APE). During the development of El Niño, although relaxation of trade wind reduces input of wind energy, the appearance of westerly wind in the western Pacific leads to a sharp increase in KE. This excites excessive conversion from APE to KE

  8. Numerical models of wind-driven circulation in lakes

    USGS Publications Warehouse

    Cheng, R.T.; Powell, T.M.; Dillon, T.M.

    1976-01-01

    The state-of-the-art of numerical modelling of large-scale wind-driven circulation in lakes is presented. The governing equations which describe this motion are discussed along with the appropriate numerical techniques necessary to solve them in lakes. The numerical models are categorized into three large primary groups: the layered models, the Ekman-type models, and the other three-dimensional models. Discussions and comparison of models are given and future research directions are suggested. ?? 1976.

  9. Circulation induced by subglacial discharge in glacial fjords: Results from idealized numerical simulations

    NASA Astrophysics Data System (ADS)

    Salcedo-Castro, Julio; Bourgault, Daniel; deYoung, Brad

    2011-09-01

    The flow caused by the discharge of freshwater underneath a glacier into an idealized fjord is simulated with a 2D non-hydrostatic model. As the freshwater leaves horizontally the subglacial opening into a fjord of uniformly denser water it spreads along the bottom as a jet, until buoyancy forces it to rise. During the initial rising phase, the plume meanders into complex flow patterns while mixing with the surrounding fluid until it reaches the surface and then spreads horizontally as a surface seaward flowing plume of brackish water. The process induces an estuarine-like circulation. Once steady-state is reached, the flow consists of an almost undiluted buoyant plume rising straight along the face of the glacier that turns into a horizontal surface layer thickening as it flows seaward. Over the range of parameters examined, the estuarine circulation is dynamically unstable with gradient Richardson number at the sheared interface having values of <1/4. The surface velocity and dilution factors are strongly and non-linearly related to the Froude number. It is the buoyancy flux that primarily controls the resulting circulation with the momentum flux playing a secondary role.

  10. Application of Improved Radiation Modeling to General Circulation Models

    SciTech Connect

    Michael J Iacono

    2011-04-07

    This research has accomplished its primary objectives of developing accurate and efficient radiation codes, validating them with measurements and higher resolution models, and providing these advancements to the global modeling community to enhance the treatment of cloud and radiative processes in weather and climate prediction models. A critical component of this research has been the development of the longwave and shortwave broadband radiative transfer code for general circulation model (GCM) applications, RRTMG, which is based on the single-column reference code, RRTM, also developed at AER. RRTMG is a rigorously tested radiation model that retains a considerable level of accuracy relative to higher resolution models and measurements despite the performance enhancements that have made it possible to apply this radiation code successfully to global dynamical models. This model includes the radiative effects of all significant atmospheric gases, and it treats the absorption and scattering from liquid and ice clouds and aerosols. RRTMG also includes a statistical technique for representing small-scale cloud variability, such as cloud fraction and the vertical overlap of clouds, which has been shown to improve cloud radiative forcing in global models. This development approach has provided a direct link from observations to the enhanced radiative transfer provided by RRTMG for application to GCMs. Recent comparison of existing climate model radiation codes with high resolution models has documented the improved radiative forcing capability provided by RRTMG, especially at the surface, relative to other GCM radiation models. Due to its high accuracy, its connection to observations, and its computational efficiency, RRTMG has been implemented operationally in many national and international dynamical models to provide validated radiative transfer for improving weather forecasts and enhancing the prediction of global climate change.

  11. A case study of sea breeze circulation at Thumba Coast through observations and modelling

    NASA Astrophysics Data System (ADS)

    Kunhikrishnan, P. K.; Ramachandran, Radhika; Alappattu, Denny P.; Kiran Kumar, N. V. P.; Balasubrahamanyam, D.

    2006-12-01

    A case study of sea breeze circulation at a coastal region Thumba (8.5°N, 76.9°E) was carried out using Doppler Sodar, surface wind, temperature, humidity measurements and radiosonde ascents. The analysis of surface meteorological data showed that the onset of sea breeze on 12th April 2006 was at 0945 hrs. GPS sonde observation over sea at 1425 hrs and Radiosonde observation over land at 1730 showed a well developed sea breeze circulation over Thumba coast by afternoon hours. The vertical extent of sea breeze circulation was ~1000m over sea as well as on land. The Thermal Internal Boundary Layer (TIBL) depth associated with sea breeze circulation was about 400m at 8 km away from coast. The marine mixed layer height was ~500m about 12 km away from the coast. Numerical simulation of sea breeze was made using HRM (High Resolution Model) and compared the results with the observations.

  12. Thermal hydraulic modeling of a natural circulation loop

    NASA Astrophysics Data System (ADS)

    Jiang, S. Y.; Wu, X. X.; Zhang, Y. J.; Jia, H. J.

    The experiment was carried out on the test loop HRTL-5, which simulates the geometry and system design of a 5MW nuclear heating reactor. The analysis was based on a one-dimensional two-phase flow drift model with conservation equations for mass, steam, energy and momentum. Clausius-Clapeyron equation was used for the calculation of flashing front in the riser. A set of ordinary equations, which describes the behavior of two-phase flow in the natural circulation system, was derived through integration of the above conservation equations for the subcooled boiling region, bulk boiling region in the heated section and for the riser. The method of time-domain was used for the calculation. Both static and dynamic results are presented. System pressure, inlet subcooling and heat flux are varied as input parameters. The results show that subcooled boiling in the heated section and void flashing in the riser have significant influence on the distribution of the void fraction, mass flow rate and flow instability of the system, especially at low pressure. The response of mass flow rate, after a small disturbance in the heat flux is shown, and based on it the instability map of the system is given through experiment and calculation. There exists three regions in the instability map of the investigated natural circulation system, namely, the stable two-phase flow region, the unstable bulk and subcooled boiling flow region and the stable subcooled boiling and single phase flow region. The mechanism of two-phase flow oscillation is interpreted.

  13. On the relevance of tidal forcing in modelling the Mediterranean thermohaline circulation

    NASA Astrophysics Data System (ADS)

    Sannino, G.; Carillo, A.; Pisacane, G.; Naranjo, C.

    2015-05-01

    The four dominant constituents of the semi-diurnal and diurnal tides have been implemented in a regional eddy-resolving Mediterranean version of the Massachusetts Institute of Technology general circulation model to assess the role played by tides on the simulated Mediterranean thermohaline circulation. To this aim we have compared two 10-year hindcast simulations differing only for the inclusion/omission of tidal forcing. Following the recent recommendations suggested by Sannino et al. (2014) both simulations use the same model having a substantial increment of the horizontal resolution in the region of the Strait of Gibraltar. The results suggest that application of explicit tidal forcing in a Mediterranean model has non negligible effects on the simulated circulation in addition to the expected intensification of local mixing processes. The western basin exhibits an immediate response to the different characteristics of the inflowing AW observable in the modified deep water convection processes in the Gulf of Lion. The inclusion of tidal forcing also induces changes in the intermediate circulation of the Tyrrhenian Sea bringing to a better representation of local structures and a reinforcement of the global thermohaline cell. LIW dispersal paths in the eastern basin are also affected by tides.

  14. Decadal Periodicities in a Venus Atmosphere General Circulation Model

    NASA Astrophysics Data System (ADS)

    Parish, Helen; Schubert, G.; Covey, C.; Walterscheid, R.; Grossman, A.; Lebonnois, S.

    2010-10-01

    We have modified a 3-dimensional Earth-based climate model, CAM (Community Atmosphere Model), to simulate the dynamics of Venus' atmosphere. We have removed Earth-related processes and introduced parameters appropriate for Venus. We use a simplified Newtonian cooling approximation for the radiation scheme, without seasonal or diurnal cycles or topography. We use a high resolution (1 degree in latitude and longitude) to take account of small-scale dynamical processes that might be important on Venus. Rayleigh friction is used to represent surface drag and to prevent upper boundary wave reflection. The simulations generate superrotation at cloud heights with wind velocities comparable to those found in measurements. We find a significant decadal oscillation in the zonal winds at cloud top heights and below. A vacillation cycle is seen in the cloud top mid-latitude zonal jets which wax and wane on an approximate 10 year cycle. The decadal oscillations we find may be excited by an instability near the surface, possibly a symmetric instability. Analyses of angular momentum transport show that the jets are built up by poleward transport by a meridional circulation while angular momentum is redistributed to lower latitudes primarily by transient eddies. Observations suggest that a cyclic variation similar to that found in the model might occur in the real Venus atmosphere. Observations by Mariner 10, Pioneer Venus, and Venus Express reveal variability in cloud top wind magnitudes and in the structure of Venus' cloud level mid-latitude jets with timescales of 5 to 10 years. Oscillations in CO composition and in temperature above the cloud tops also exhibit a periodicity around 10 years and changes in the atmospheric SO2 content over 40 years show a periodicity around 20 to 25 years. Venus' atmosphere must be observed over multi-year time scales and below the clouds if we are to understand its dynamics.

  15. THM modelling of hydrothermal circulation in deep geothermal reservoirs

    NASA Astrophysics Data System (ADS)

    Magnenet, Vincent; Fond, Christophe; Schmittbuhl, Jean; Genter, Albert

    2014-05-01

    Numerous models have been developped for describing deep geothermal reservoirs. Using the opensource finite element software ASTER developped by EDF R&D, we carried out 2D simulations of the hydrothermal circulation in the deep geothermal reservoir of Soultz-sous-Forêts. The model is based on the effective description of Thermo-Hydro-Mechanical (THM) coupling at large scale. Such a model has a fourfold interest: a) the physical integration of laboratory measurements (rock physics), well logging, well head parameters, geological description, and geophysics field measurements; b) the construction of a direct model mechanically based for geophysical inversion: fluid flow, fluid pressure, temperature profile, seismicity monitoring, deformation of the ground surface (INSAR/GPS) related to reservoir modification, gravity or electromagnetic geophysical measurements; c) the sensitivity analysis of the parameters involved in the hydrothermal circulation and identification of the dominant ones; d) the development of a decision tool for drilling planning, stimulation and exploitation. In our model, we introduced extended Thermo-Hydro-Mechanical coupling including not only poro-elastic behavior but also the sensitivity of the fluid density, viscosity, and heat capacity to temperature and pressure. The behavior of solid rock grains is assumed to be thermo-elastic and linear. Hydraulic and thermal phenomena are governed by Darcy and Fourier laws respectively, and most rock properties (like the specific heat at constant stress csσ(T), or the thermal conductivity Λ(T,φ)) are assumed to depend on the temperature T and/or porosity φ. The radioactivity of the rocks is taken into account through a heat source term appearing in the balance equation of enthalpy. To characterize as precisely as possible the convective movement of water and the associated heat flow, water properties (specific mass ρw(T,pw), specific enthalpy hmw(T,pw) dynamic viscosity μw(T), thermal dilation

  16. Cloud Feedback in Atmospheric General Circulation Models: An Update

    NASA Technical Reports Server (NTRS)

    Cess, R. D.; Zhang, M. H.; Ingram, W. J.; Potter, G. L.; Alekseev, V.; Barker, H. W.; Cohen-Solal, E.; Colman, R. A.; Dazlich, D. A.; DelGenio, A. D.; Dix, M. R.; Dymnikov, V.; Esch, M.; Fowler, L. D.; Fraser, J. R.; Galin, V.; Gates, W. L.; Hack, J. J.; Kiehl, J. T.; LeTreut, H.

    1996-01-01

    Six years ago, we compared the climate sensitivity of 19 atmospheric general circulation models and found a roughly threefold variation among the models; most of this variation was attributed to differences in the models' depictions of cloud feedback. In an update of this comparison, current models showed considerably smaller differences in net cloud feedback, with most producing modest values. There are, however, substantial differences in the feedback components, indicating that the models still have physical disagreements.

  17. Circulation simulator method for evaluating bank note and optical feature durability

    NASA Astrophysics Data System (ADS)

    Bartz, William J.; Crane, Timothy T.

    2006-02-01

    Effective long-term authentication of optical security features on bank notes requires a sound substrate that can withstand the rigors of circulation. Crane & Co. has developed a test method that simulates the deterioration observed in actual circulated bank notes: soiling, creasing, tearing, edge tatteredness and limpness. The method relies on the physical degradation of note specimens that are weighted on each corner and tumbled in a medium of glass beads, metal discs and synthetic soil. Durability is judged by how well a note retains its initial optical and physical properties after being subjected to the conditions of the Circulation Simulator. Much of our early research was directed at improving the paper substrate, and evaluating surface treatments that resist soiling since excessive soiling is often the primary reason bank notes are removed from circulation. Recent work has examined the correlation between Circulation Simulator results and the properties of actual bank notes culled from circulation. We also are using the Circulation Simulator method to qualitatively evaluate the potential durability and effectiveness of optical security features such as electrotypes, watermarks, windowed threads, foils and inks. This paper provides a description of the testing and analysis methods.

  18. Data Collection and Cost Modeling for Library Circulation Systems.

    ERIC Educational Resources Information Center

    Bourne, Charles P.

    The objectives of the study leading to this report were to review, analyze and summarize published library cost data; and to develop a cost model and a methodology for reporting data in a more consistent and useful way. The cost model and reporting procedure were developed and tested on the circulation system of three libraries: a large university…

  19. Optimal control of CPR procedure using hemodynamic circulation model

    DOEpatents

    Lenhart, Suzanne M.; Protopopescu, Vladimir A.; Jung, Eunok

    2007-12-25

    A method for determining a chest pressure profile for cardiopulmonary resuscitation (CPR) includes the steps of representing a hemodynamic circulation model based on a plurality of difference equations for a patient, applying an optimal control (OC) algorithm to the circulation model, and determining a chest pressure profile. The chest pressure profile defines a timing pattern of externally applied pressure to a chest of the patient to maximize blood flow through the patient. A CPR device includes a chest compressor, a controller communicably connected to the chest compressor, and a computer communicably connected to the controller. The computer determines the chest pressure profile by applying an OC algorithm to a hemodynamic circulation model based on the plurality of difference equations.

  20. Stratospheric General Circulation with Chemistry Model (SGCCM)

    NASA Technical Reports Server (NTRS)

    Rood, Richard B.; Douglass, Anne R.; Geller, Marvin A.; Kaye, Jack A.; Nielsen, J. Eric; Rosenfield, Joan E.; Stolarski, Richard S.

    1990-01-01

    In the past two years constituent transport and chemistry experiments have been performed using both simple single constituent models and more complex reservoir species models. Winds for these experiments have been taken from the data assimilation effort, Stratospheric Data Analysis System (STRATAN).

  1. SST dependence of convective aggregation in three General Circulation Models

    NASA Astrophysics Data System (ADS)

    Bony, Sandrine; Becker, Tobias; Coppin, David; Medeiros, Brian; Reed, Kevin; Stevens, Bjorn; Voigt, Aiko

    2015-04-01

    Studies using cloud-resolving models or simple models have shown that under certain conditions, the radiative-convective equilibrium state becomes unstable to large-scale overturning circulations, and leads to the phenomenon of self-aggregation of moist convection. Modeling and observational studies suggest that the degree of aggregation of moist convection can influence the large-scale atmospheric state (e.g. humidity, clouds) and its energy budget. The question thus arises as to what extent the aggregation of convection may rectify the Earth's climate, including the large-scale atmospheric circulation, hydrological sensitivity and climate feedbacks. We explore these issues by running three General Circulation Models (IPSL-CM5A-LR, ECHAM6, CAM5) in radiative-convective equilibrium, i.e. a non-rotating aqua-planet configuration forced by a globally-uniform insolation and sea surface temperature (SST). We show that in these conditions, all three models can predict the spontaneous emergence of a large-scale convective organization and overturning circulation, and that the equilibrium aggregation state depends on SST and cloud-radiative effects. We will explore the reasons why the equilibrium aggregation state depends on temperature, and the impact of convective aggregation on the global mean state. Robust behaviors will be highlighted, as well as inter-model differences. The implications of these results will be discussed.

  2. Mapping tidal residual circulations in the outer Xiangshan Bay using a numerical model

    NASA Astrophysics Data System (ADS)

    Xu, Peng; Mao, Xinyan; Jiang, Wensheng

    2016-02-01

    Xiangshan Bay, which is elongated and semi-enclosed, is characterized by strong tides. The original understanding of the tidal residual circulation in the bay was based on the Eulerian time-mean method. However, it has been theoretically proved that the Lagrangian time-mean method rather than the Eulerian one should be employed to detide. This knowledge motivated us to remap the tidal residual circulation in the bay. A three-dimensional numerical model with a Lagrangian particle-tracking module was used to simulate tides, from which the Lagrangian and Eulerian tidal residual circulations were produced. The Lagrangian residual circulation exhibited a two-branch pattern that connected the southern and northern outer seas of Xiangshan Bay, whereas the Eulerian residual circulation was characterized by eddies that are not favorable for water exchange. Through comparing to the observed salinity distribution, the Lagrangian residual current presented a reasonable spatial pattern which could explain the inter-tidal mass transport. Furthermore, the Lagrangian residual current performed better in sustaining the mass conservation as predicted by theory. A series of sensitivity experiments were conducted to investigate the effect of nonlinear mechanisms on the Lagrangian residual circulation. The results showed that nonlinear advection is dominant while the time-varying width and depth play a minor role, and the quadratic bottom friction has no influence with only M2 tide driving the model.

  3. Numerical simulation of blood flow and pressure drop in the pulmonary arterial and venous circulation.

    PubMed

    Qureshi, M Umar; Vaughan, Gareth D A; Sainsbury, Christopher; Johnson, Martin; Peskin, Charles S; Olufsen, Mette S; Hill, N A

    2014-10-01

    A novel multiscale mathematical and computational model of the pulmonary circulation is presented and used to analyse both arterial and venous pressure and flow. This work is a major advance over previous studies by Olufsen et al. (Ann Biomed Eng 28:1281-1299, 2012) which only considered the arterial circulation. For the first three generations of vessels within the pulmonary circulation, geometry is specified from patient-specific measurements obtained using magnetic resonance imaging (MRI). Blood flow and pressure in the larger arteries and veins are predicted using a nonlinear, cross-sectional-area-averaged system of equations for a Newtonian fluid in an elastic tube. Inflow into the main pulmonary artery is obtained from MRI measurements, while pressure entering the left atrium from the main pulmonary vein is kept constant at the normal mean value of 2 mmHg. Each terminal vessel in the network of 'large' arteries is connected to its corresponding terminal vein via a network of vessels representing the vascular bed of smaller arteries and veins. We develop and implement an algorithm to calculate the admittance of each vascular bed, using bifurcating structured trees and recursion. The structured-tree models take into account the geometry and material properties of the 'smaller' arteries and veins of radii ≥ 50 μm. We study the effects on flow and pressure associated with three classes of pulmonary hypertension expressed via stiffening of larger and smaller vessels, and vascular rarefaction. The results of simulating these pathological conditions are in agreement with clinical observations, showing that the model has potential for assisting with diagnosis and treatment for circulatory diseases within the lung. PMID:24610385

  4. An Intercomparison of the Dynamical Cores of Global Atmospheric Circulation Models for Mars

    NASA Technical Reports Server (NTRS)

    Hollingsworth, Jeffery L.; Bridger, Alison F. C.; Haberle, Robert M.

    1998-01-01

    This is a Final Report for a Joint Research Interchange (JRI) between NASA Ames Research Cen- ter and San Jose State University, Department of Meteorology. The focus of this JRI has been to evaluate the dynamical "cores" of two global atmospheric circulation models for Mars that are in operation at the NASA Ames Research Center. ne two global circulation models in use are fundamentally different: one uses spherical harmonics in its horizontal representation of field variables; the other uses finite differences on a uniform longitude-latitude grid. Several simulations have been conducted to assess how the dynamical processors of each of these circulation models perform using identical "simple physics" parameterizations. A variety of climate statistics (e.g., time-mean flows and eddy fields) have been compared for realistic solstitial mean basic states. Results of this research have demonstrated that the two Mars circulation models with completely different spatial representations and discretizations produce rather similar circulation statistics for first-order meteorological fields, suggestive of a tendency for convergence of numerical solutions. Second and higher-order fields can, however, vary significantly between the two models.

  5. An Intercomparison of the Dynamical Cores of Global Atmospheric Circulation Models for Mars

    NASA Technical Reports Server (NTRS)

    Hollingsworth, Jeffery L.; Bridger, Alison F. C.; Haberle, Robert M.

    1998-01-01

    This is a Final Report for a Joint Research Interchange (JRI) between NASA Ames Research Center and San Jose State University, Department of Meteorology. The focus of this JRI has been to evaluate the dynamical "cores" of two global atmospheric circulation models for Mars that are in operation at the NASA Ames Research Center. The two global circulation models in use are fundamentally different: one uses spherical harmonics in its horizontal representation of field variables; the other uses finite differences on a uniform longitude-latitude grid. Several simulations have been conducted to assess how the dynamical processors of each of these circulation models perform using identical "simple physics" parameterizations. A variety of climate statistics (e.g., time-mean flows and eddy fields) have been compared for realistic solstitial mean basic states. Results of this research have demonstrated that the two Mars circulation models with completely different spatial representations and discretizations produce rather similar circulation statistics for first-order meteorological fields, suggestive of a tendency for convergence of numerical solutions. Second and higher-order fields can, however, vary significantly between the two models.

  6. An Intercomparison of the Dynamical Cores of Global Atmospheric Circulation Models for Mars

    NASA Technical Reports Server (NTRS)

    Hollingsworth, Jeffery L.; Bridger, Alison F. C.; Haberle, Robert M.

    1998-01-01

    This is a Final Report for a Joint Research Interchange (JRI) between NASA Ames Research Center and San Jose State University, Department of Meteorology. The focus of this JRI has been to evaluate the dynamical 'cores' of two global atmospheric circulation models for Mars that are in operation at the NASA Ames Research Center. The two global circulation models in use are fundamentally different: one uses spherical harmonics in its horizontal representation of field variables; the other uses finite differences on a uniform longitude-latitude grid. Several simulations have been conducted to assess how the dynamical processors of each of these circulation models perform using identical 'simple physics' parameterizations. A variety of climate statistics (e.g., time-mean flows and eddy fields) have been compared for realistic solstitial mean basic states. Results of this research have demonstrated that the two Mars circulation models with completely different spatial representations and discretizations produce rather similar circulation statistics for first-order meteorological fields, suggestive of a tendency for convergence of numerical solutions. Second and higher-order fields can, however, vary significantly between the two models.

  7. Scaling laws for parametrizations of subgrid interactions in simulations of oceanic circulations.

    PubMed

    Kitsios, V; Frederiksen, J S; Zidikheri, M J

    2014-06-28

    Parametrizations of the subgrid eddy-eddy and eddy-meanfield interactions are developed for the simulation of baroclinic ocean circulations representative of an idealized Antarctic Circumpolar Current. Benchmark simulations are generated using a spectral spherical harmonic quasi-geostrophic model with maximum truncation wavenumber of T=504, which is equivalent to a resolution of 0.24° globally. A stochastic parametrization is used for the eddy-eddy interactions, and a linear deterministic parametrization for the eddy-meanfield interactions. The parametrization coefficients are determined from the statistics of benchmark simulations truncated back to the large eddy simulation (LES) truncation wavenumber, TRsimulations. PMID:24842029

  8. Scaling laws for parametrizations of subgrid interactions in simulations of oceanic circulations

    PubMed Central

    Kitsios, V.; Frederiksen, J. S.; Zidikheri, M. J.

    2014-01-01

    Parametrizations of the subgrid eddy–eddy and eddy–meanfield interactions are developed for the simulation of baroclinic ocean circulations representative of an idealized Antarctic Circumpolar Current. Benchmark simulations are generated using a spectral spherical harmonic quasi-geostrophic model with maximum truncation wavenumber of T=504, which is equivalent to a resolution of 0.24° globally. A stochastic parametrization is used for the eddy–eddy interactions, and a linear deterministic parametrization for the eddy–meanfield interactions. The parametrization coefficients are determined from the statistics of benchmark simulations truncated back to the large eddy simulation (LES) truncation wavenumber, TRsimulations. PMID:24842029

  9. 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

  10. Simulation study of autoregulation responses of peripheral circulation to systemic pulsatility

    PubMed Central

    Aletti, Federico; Lanzarone, Ettore; Costantino, Maria Laura; Baselli, Giuseppe

    2009-01-01

    Background This simulation study investigated potential modulations of total peripheral resistance (TPR), due to distributed peripheral vascular activity, by means of a lumped model of the arterial tree and a non linear model of microcirculation, inclusive of local controls of blood flow and tissue-capillary fluid exchange. Results Numerical simulations of circulation were carried out to compute TPR under different conditions of blood flow pulsatility, and to extract the pressure-flow characteristics of the cardiovascular system. Simulations showed that TPR seen by the large arteries was increased in absence of pulsatility, while it decreased with an augmented harmonic content. This is a typically non linear effect due to the contribution of active, non linear autoregulation of the peripheral microvascular beds, which also generated a nonlinear relationship between arterial blood pressure and cardiac output. Conclusion This simulation study, though focused on a simple effect attaining TPR modulation due to pulsatility, suggests that non-linear autoregulation mechanisms cannot be overlooked while studying the integrated behavior of the global cardiovascular system, including the arterial tree and the peripheral vascular bed. PMID:19630959

  11. Revising a statistical cloud scheme for general circulation models

    NASA Astrophysics Data System (ADS)

    Schemann, Vera; Stevens, Bjorn; Grützun, Verena; Quaas, Johannes

    2013-04-01

    Cloud cover is an important factor for global climate simulations (e.g. for radiation). But in a global climate model with a typical resolution around 100 km clouds can not be resolved. The parameterization of cloud cover still is a major reason for uncertainties in climate change simulations. The aim of this study is to revise a statistical cloud scheme with special focus on the representation of low level clouds in the trade wind region. The development is based on the assumed PDF (probability density function) scheme of Tompkins 2002, which is part of the global climate model ECHAM6. The assumed PDF approach is based on the assumption of a certain PDF family and the determination of a certain member by further assumptions or constraints. For the scheme used in this study a beta distribution is assumed and two prognostic equations are added. Besides the original prognostic equations for a shape parameter and the distribution width, adjusted equations for the higher moments variance and skewness are introduced. This change leads to an easier physical interpretation. The source and sink terms due to the physical processes of convection, turbulence and microphysics play an important role in describing the total water PDF and with this the cloud fraction in one grid box. A better understanding of these terms and their effect on the cloud fraction and their vertical distribution is essential for the evaluation and development of the statistical cloud scheme. One known problem of the scheme is the underestimation of subgrid-scale variance of total water (Quaas 2012, Weber 2011). The aim of this study is to improve the representation of subgrid-scale variability by introducing and evaluating different source terms. For this several runs with the ECHAM6 model and modified cloud schemes are performed and analyzed. The focus is placed on the trade wind region to get a better understanding of the important processes for an improved representation of shallow cumuli

  12. Examination of circulation, dispersion, and connectivity in Lunenburg Bay of Nova Scotia using a nested-grid circulation model

    NASA Astrophysics Data System (ADS)

    Sheng, Jinyu; Zhao, Jun; Zhai, Li

    2009-05-01

    A coastal ocean observatory has been established in Lunenburg Bay, Nova Scotia since summer 2002 as part of a multi-agency research program of marine environmental observation and prediction over Atlantic Canada coastal waters. The observatory was operational when a category-2 hurricane (Juan) made land fall within 50-km of the bay in September 2003. The coastal response of the bay to Hurricane Juan is examined using a nested-grid coastal circulation modelling system. The nested-grid system is forced by the local wind, tides, and remotely generated coastal waves. A comparison of model results with observed surface elevations and currents demonstrates that the nested-grid system has reasonable skills in simulating the three-dimensional (3D) storm-induced circulation in the study region. The 3D model currents are used to examine the transport and dispersion of passive tracers, local flushing time, and retention and connectivity of passive particles in the bay during Hurricane Juan. Numerical results demonstrate that local wind forcing plays a dominant role in generating large dispersion and hydrodynamic connectivity in the bay during the storm.

  13. Study on subtidal circulation and variability in the Gulf of St. Lawrence, Scotian Shelf, and Gulf of Maine using a nested-grid shelf circulation model

    NASA Astrophysics Data System (ADS)

    Urrego-Blanco, Jorge; Sheng, Jinyu

    2014-03-01

    This paper examines the subtidal circulation and associated variability in the Gulf of St. Lawrence, the Scotian Shelf, and the Gulf of Maine (GSL-SS-GOM) in 1988-2004 based on results produced by a nested-grid shelf circulation model. The model has a fine-resolution child model (˜ (1/12)°) embedded inside a coarse-resolution parent model (˜ (1/4)°) of the northwest Atlantic. The combination of the semi-prognostic method and the spectral nudging method is used to reduce the model seasonal bias and drift. The child model reproduces the general features of the observed circulation and hydrography over the study region during the study period. The child model results demonstrate that the time-mean circulation in the GSL is affected by the time-mean atmospheric forcing and inflow through the Strait of Belle Isle. The temporal variability in atmospheric forcing affects the outflow through western Cabot Strait, which in turn affects the transport of the Nova Scotian Current and the gulf-wide cyclonic circulation in the GOM. The simulated seasonal variability of salinity in the top 30 m of the GSL-SS-GOM is mainly affected by the equatorward advection of low-salinity waters from the lower St. Lawrence Estuary to the GOM through the Scotian Shelf. The simulated intraseasonal variability of circulation in the GSL is affected by the variability in the estuarine circulation in response to the temporal variability in atmospheric forcing. On the Scotian Shelf, the intraseasonal variability is mainly driven by the variability of wind forcing and mesoscale and nonlinear dynamics over the shelf break and slope region. The interannual variability in the simulated temperature and salinity are spatially coherent in the intermediate waters in the GSL, which is caused partially by the local response to atmospheric variability and partially by variabilities over the southern Newfoundland Shelf that enter the GSL through the eastern Cabot Strait. By comparison, on the Scotian Shelf

  14. 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

  15. Ensemble simulations of the magnetic field induced by global ocean circulation: Estimating the uncertainty

    NASA Astrophysics Data System (ADS)

    Irrgang, Christopher; Saynisch, Jan; Thomas, Maik

    2016-03-01

    The modeling of the ocean global circulation induced magnetic field is affected by various uncertainties that originate from errors in the input data and from the model itself. The amount of aggregated uncertainties and their effect on the modeling of electromagnetic induction in the ocean is unknown. For many applications, however, the knowledge of uncertainties in the modeling is essential. To investigate the uncertainty in the modeling of motional induction at the sea surface, simulation experiments are performed on the basis of different error scenarios and error covariance matrices. For these error scenarios, ensembles of an ocean general circulation model and an electromagnetic induction model are generated. This ensemble-based approach allows to estimate both the spatial distribution and temporal variation of the uncertainty in the ocean-induced magnetic field. The largest uncertainty in the ocean-induced magnetic field occurs in the area of the Antarctic Circumpolar Current. Local maxima reach values of up to 0.7 nT. The estimated global annual mean uncertainty in the ocean-induced magnetic field ranges from 0.1 to 0.4 nT. The relative amount of uncertainty reaches up to 30% of the signal strength with largest values in regions in the northern hemisphere. The major source of uncertainty is found to be introduced by wind stress from the atmospheric forcing of the ocean model. In addition, the temporal evolution of the uncertainty in the induced magnetic field shows distinct seasonal variations. Specific regions are identified which are robust with respect to the introduced uncertainties.

  16. Modeling 1993-2008 climatology of seasonal general circulation and thermal structure in the Great Lakes using FVCOM

    NASA Astrophysics Data System (ADS)

    Bai, Xuezhi; Wang, Jia; Schwab, David J.; Yang, Yi; Luo, Lin; Leshkevich, George A.; Liu, Songzhi

    2013-05-01

    An unstructured Finite Volume Coastal Ocean Model was applied to all five Great Lakes simultaneously to simulate circulation and thermal structure from 1993 to 2008. Model results are compared to available observations of currents and temperature and previous modeling work. Maps of climatological circulation for all five Great lakes are presented. Winter currents show a two-gyre type circulation in Lakes Ontario and Erie and one large-scale cyclonic circulation in Lakes Michigan, Huron, and Superior. During the summer, a cyclonic circulation remains in Lakes Superior; a primarily cyclonic circulation dominates upper and central Lake Huron; Lake Ontario has a single cyclonic circulation, while circulation in the central basin of Lake Erie remains two-gyre type; Lake Michigan has a cyclonic gyre in the north and an anti-cyclonic one in the south. The temperature profile during the summer is well simulated when a surface wind-wave mixing scheme is included in the model. Main features of the seasonal evolution of water temperature, such as inverse temperature stratification during the winter, the spring and autumn overturn, the thermal bar, and the stratification during summer are well reproduced. The lakes exhibit significant annual and interannual variations in current speed and temperature.

  17. Development of a hydraulic model of the human systemic circulation

    NASA Technical Reports Server (NTRS)

    Sharp, M. K.; Dharmalingham, R. K.

    1999-01-01

    Physical and numeric models of the human circulation are constructed for a number of objectives, including studies and training in physiologic control, interpretation of clinical observations, and testing of prosthetic cardiovascular devices. For many of these purposes it is important to quantitatively validate the dynamic response of the models in terms of the input impedance (Z = oscillatory pressure/oscillatory flow). To address this need, the authors developed an improved physical model. Using a computer study, the authors first identified the configuration of lumped parameter elements in a model of the systemic circulation; the result was a good match with human aortic input impedance with a minimum number of elements. Design, construction, and testing of a hydraulic model analogous to the computer model followed. Numeric results showed that a three element model with two resistors and one compliance produced reasonable matching without undue complication. The subsequent analogous hydraulic model included adjustable resistors incorporating a sliding plate to vary the flow area through a porous material and an adjustable compliance consisting of a variable-volume air chamber. The response of the hydraulic model compared favorably with other circulation models.

  18. Asian Summer Monsoon Intraseasonal Variability in General Circulation Models

    SciTech Connect

    Sperber, K R; Annamalai, H

    2004-02-24

    The goals of this report are: (1) Analyze boreal summer Asian monsoon intraseasonal variability general circulation models--How well do the models represent the eastward and northward propagating components of the convection and how well do the models represent the interactive control that the western tropical Pacific rainfall exerts on the rainfall over India and vice-versa? (2) Role of air-sea interactions--prescribed vs. interactive ocean; and (3) Mean monsoon vs. variability.

  19. A general circulation model (GCM) parameterization of Pinatubo aerosols

    SciTech Connect

    Lacis, A.A.; Carlson, B.E.; Mishchenko, M.I.

    1996-04-01

    The June 1991 volcanic eruption of Mt. Pinatubo is the largest and best documented global climate forcing experiment in recorded history. The time development and geographical dispersion of the aerosol has been closely monitored and sampled. Based on preliminary estimates of the Pinatubo aerosol loading, general circulation model predictions of the impact on global climate have been made.

  20. A January angular momentum balance in the OSU two-level atmospheric general circulation model

    NASA Technical Reports Server (NTRS)

    Kim, J.-W.; Grady, W.

    1982-01-01

    The present investigation is concerned with an analysis of the atmospheric angular momentum balance, based on the simulation data of the Oregon State University two-level atmospheric general circulation model (AGCM). An attempt is also made to gain an understanding of the involved processes. Preliminary results on the angular momentum and mass balance in the AGCM are shown. The basic equations are examined, and questions of turbulent momentum transfer are investigated. The methods of analysis are discussed, taking into account time-averaged balance equations, time and longitude-averaged balance equations, mean meridional circulation, the mean meridional balance of relative angular momentum, and standing and transient components of motion.

  1. Wave-mean flow interaction in the NCAR stratospheric general circulation model

    NASA Technical Reports Server (NTRS)

    Boville, B. A.

    1985-01-01

    A version of the NCAR General Circulation Model has been developed which extends from the surface into the mesosphere. The model was forced by climatological January sea surface temperatures and insolation and gives a fairly reasonable simulation of the troposphere and stratosphere. The transformed Eulerian formation is used to examine the interaction of the eddies with the mean flow in the winter hemisphere. The essence of the transformed Eulerian formation is an attempt to distinguish between the mean meridional circulation driven by diabatic heating and that driven by eddies. The net effect of eddies can then be determined, and is given by the Eliassen-Palm (EP) flux divergence. In practice, this method works reasonably well but is far from perfect. For instance, in the absence of eddy forcing, the winter stratosphere would go to radiative equilibrium and there would be no diabatic heating to drive a mean meridional circulation.

  2. 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.

  3. 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.

  4. Numerical modeling of circulation in high-energy estuaries: A Columbia River estuary benchmark

    NASA Astrophysics Data System (ADS)

    Kärnä, Tuomas; Baptista, António M.; Lopez, Jesse E.; Turner, Paul J.; McNeil, Craig; Sanford, Thomas B.

    2015-04-01

    Numerical modeling of three-dimensional estuarine circulation is often challenging due to complex flow features and strong density gradients. In this paper the skill of a specific model is assessed against a high-resolution data set, obtained in a river-dominated mesotidal estuary with autonomous underwater vehicles and a shipborne winched profiler. The measurements provide a detailed view of the salt wedge dynamics of the Columbia River estuary. Model skill is examined under contrasting forcing conditions, covering spring freshet and autumn low flow conditions, as well as spring and neap tides. The data set provides a rigorous benchmark for numerical circulation models. This benchmark is used herein to evaluate an unstructured grid circulation model, based on linear finite element and finite volume formulations. Advection of momentum is treated with an Eulerian-Lagrangian scheme. After the model's sensitivity to grid resolution and time step is examined, a detailed skill assessment is provided for the best model configuration. The simulations reproduce the timing and tidal asymmetry of salinity intrusion. Sharp density gradients, however, tend to be smoothed out affecting vertical mixing and gravitational circulation. We show that gravitational salt transport is underestimated in the model, but is partially compensated through tidal effects. The discrepancy becomes most pronounced when the stratification is strongest, i.e., under high river discharge and neap tide conditions.

  5. An analytical and experimental investigation of natural circulation transients in a model pressurized water reactor

    SciTech Connect

    Massoud, M

    1987-01-01

    Natural Circulation phenomena in a simulated PWR was investigated experimentally and analytically. The experimental investigation included determination of system characteristics as well as system response to the imposed transient under symmetric and asymmetric operations. System characteristics were used to obtain correlation for heat transfer coefficient in heat exchangers, system flow resistance, and system buoyancy heat. Asymmetric transients were imposed to study flow oscillation and possible instability. The analytical investigation encompassed development of mathematical model for single-phase, steady-state and transient natural circulation as well as modification of existing model for two-phase flow analysis of phenomena such as small break LOCA, high pressure coolant injection and pump coast down. The developed mathematical model for single-phase analysis was computer coded to simulate the imposed transients. The computer program, entitled ''Symmetric and Asymmetric Analysis of Single-Phase Flow (SAS),'' were employed to simulate the imposed transients. It closely emulated the system behavior throughout the transient and subsequent steady-state. Modifications for two-phase flow analysis included addition of models for once-through steam generator and electric heater rods. Both programs are faster than real time. Off-line, they can be used for prediction and training applications while on-line they serve for simulation and signal validation. The programs can also be used to determine the sensitivity of natural circulation behavior to variation of inputs such as secondary distribution and power transients.

  6. Computational model of a circulation current that controls electrochemical properties in the mammalian cochlea.

    PubMed

    Nin, Fumiaki; Hibino, Hiroshi; Murakami, Shingo; Suzuki, Toshihiro; Hisa, Yasuo; Kurachi, Yoshihisa

    2012-06-01

    Sound-evoked mechanical stimuli permit endolymphatic K(+) to enter sensory hair cells. This transduction is sensitized by an endocochlear potential (EP) of +80 mV in endolymph. After depolarizing the cells, K(+) leaves hair cells in perilymph, and it is then circulated back to endolymph across the lateral cochlear wall. In theory, this process entails a continuous and unidirectional current carried by apical K(+) channels and basolateral K(+) uptake transporters in both the marginal cell and syncytial layers of the lateral wall. The transporters regulate intracellular and extracellular [K(+)], allowing the channels to form K(+) diffusion potentials across each of the two layers. These diffusion potentials govern the EP. What remains uncertain is whether these transport mechanisms accumulating across diverse cell layers make up a continuous circulation current in the lateral wall and how this current might affect the characteristics of the endolymph. To address this question, we developed an electrophysiological model that incorporates channels and transporters of the lateral wall and channels of hair cells that derive a circulation current. The simulation replicated normal experimental EP values and reproduced experimentally measured changes in the EP and intra- and extracellular [K(+)] in the lateral wall when different transporters and channels were blocked. The model predicts that, under these different conditions, the circulation current's contribution to the EP arises from different sources. Finally, our model also accurately simulated EP loss in a mouse model of a chloride channelopathy associated with deafness. PMID:22619324

  7. Circulating microRNA Signatures in Rodent Models of Pain.

    PubMed

    Qureshi, Rehman A; Tian, Yuzhen; McDonald, Marguerite K; Capasso, Kathryn E; Douglas, Sabrina R; Gao, Ruby; Orlova, Irina A; Barrett, James E; Ajit, Seena K; Sacan, Ahmet

    2016-07-01

    MicroRNAs (miRNAs) remain stable in circulation and have been identified as potential biomarkers for a variety of conditions. We report miRNA changes in blood from multiple rodent models of pain, including spinal nerve ligation and spared nerve injury models of neuropathic pain; a complete Freund's adjuvant (CFA) model of inflammatory pain; and a chemotherapy-induced model of pain using the histone deacetylase inhibitor JNJ-26481585. The effect of celecoxib, a cyclooxygenase-2-selective nonsteroidal anti-inflammatory drug, was investigated in the CFA model as proof of principle for assessing the utility of circulating miRNAs as biomarkers in determining treatment response. Each study resulted in a unique miRNA expression profile. Despite differences in miRNAs identified from various models, computational target prediction and functional enrichment have identified biological pathways common among different models. The Wnt signaling pathway was affected in all models, suggesting a crucial role for this pathway in the pathogenesis of pain. Our studies demonstrate the utility of circulating miRNAs as pain biomarkers and suggest the potential for rigorous forward and reverse translational approaches. Evaluating alterations in miRNA fingerprints under different pain conditions and after administering therapeutic agents may be beneficial in evaluating clinical trial outcomes, predicting treatment response, and developing correlational outcomes between preclinical and human studies. PMID:26081151

  8. Effects of implementing the Simple Biosphere Model in a general circulation model

    NASA Technical Reports Server (NTRS)

    Sato, N.; Sellers, P. J.; Randall, D. A.; Schneider, E. K.; Shukla, J.

    1989-01-01

    The Simple Biosphere Model (SiB) of Sellers et al., was designed to simulate the interactions between the earth's land surface and the atmosphere by treating the vegetation explicitly and realistically, thereby incorporating the biophysical controls on the exchanges of radiation, momentum, sensible and latent heat between the two systems. This paper describes the steps taken to implement SiB in a modified version of the National Meteorological Center's global spectral general circulation model (GCM) and explores the impact of the implementation on the simulated land surface fluxes and near-surface meteorological conditions. The coupled model (SiB-GCM) was used to produce summer and winter simulations. The same GCM was used with a conventional hydrological model (Ctl-GCM) to produce comparable 'control' summer and winter simulations for comparison. It was found that SiB-GCM produced a more realistic partitioning of energy at the land surface than Ctl-GCM. Generally, SiB-GCM, produced more sensible heat flux and less latent heat flux over vegetated land than did Ctl-GCM and this resulted in a much deeper daytime planetary boundary layer and reduced precipitation rates over the continents in SiB-GCM. In the summer simulation, the 200 mb jet stream was slightly weakened in the SiB-GCM relative to the Ctl-GCM results and analyses made from observations.

  9. Decadal variations in a Venus general circulation model

    NASA Astrophysics Data System (ADS)

    Parish, Helen F.; Schubert, Gerald; Covey, Curtis; Walterscheid, Richard L.; Grossman, Allen; Lebonnois, Sebastien

    2011-03-01

    The Community Atmosphere Model (CAM), a 3-dimensional Earth-based climate model, has been modified to simulate the dynamics of the Venus atmosphere. The most current finite volume version of CAM is used with Earth-related processes removed, parameters appropriate for Venus introduced, and some basic physics approximations adopted. A simplified Newtonian cooling approximation has been used for the radiation scheme. We use a high resolution (1° by 1° in latitude and longitude) to take account of small-scale dynamical processes that might be important on Venus. A Rayleigh friction approach is used at the lower boundary to represent surface drag, and a similar approach is implemented in the uppermost few model levels providing a ‘sponge layer’ to prevent wave reflection from the upper boundary. The simulations generate superrotation with wind velocities comparable to those measured in the Venus atmosphere by probes and around 50-60% of those measured by cloud tracking. At cloud heights and above the atmosphere is always superrotating with mid-latitude zonal jets that wax and wane on an approximate 10 year cycle. However, below the clouds, the zonal winds vary periodically on a decadal timescale between superrotation and subrotation. Both subrotating and superrotating mid-latitude jets are found in the approximate 40-60 km altitude range. The growth and decay of the sub-cloud level jets also occur on the decadal timescale. Though subrotating zonal winds are found below the clouds, the total angular momentum of the atmosphere is always in the sense of superrotation. The global relative angular momentum of the atmosphere oscillates with an amplitude of about 5% on the approximate 10 year timescale. Symmetric instability in the near surface equatorial atmosphere might be the source of the decadal oscillation in the atmospheric state. Analyses of angular momentum transport show that all the jets are built up by poleward transport by a meridional circulation while

  10. On a sparse pressure-flow rate condensation of rigid circulation models.

    PubMed

    Schiavazzi, D E; Hsia, T Y; Marsden, A L

    2016-07-26

    Cardiovascular simulation has shown potential value in clinical decision-making, providing a framework to assess changes in hemodynamics produced by physiological and surgical alterations. State-of-the-art predictions are provided by deterministic multiscale numerical approaches coupling 3D finite element Navier Stokes simulations to lumped parameter circulation models governed by ODEs. Development of next-generation stochastic multiscale models whose parameters can be learned from available clinical data under uncertainty constitutes a research challenge made more difficult by the high computational cost typically associated with the solution of these models. We present a methodology for constructing reduced representations that condense the behavior of 3D anatomical models using outlet pressure-flow polynomial surrogates, based on multiscale model solutions spanning several heart cycles. Relevance vector machine regression is compared with maximum likelihood estimation, showing that sparse pressure/flow rate approximations offer superior performance in producing working surrogate models to be included in lumped circulation networks. Sensitivities of outlets flow rates are also quantified through a Sobol׳ decomposition of their total variance encoded in the orthogonal polynomial expansion. Finally, we show that augmented lumped parameter models including the proposed surrogates accurately reproduce the response of multiscale models they were derived from. In particular, results are presented for models of the coronary circulation with closed loop boundary conditions and the abdominal aorta with open loop boundary conditions. PMID:26671219

  11. Modeling Jupiter's cloud bands and decks. 1. Jet scale meridional circulations

    NASA Astrophysics Data System (ADS)

    Zuchowski, L. C.; Yamazaki, Y. H.; Read, P. L.

    2009-04-01

    We have investigated the formation of jet scale meridional circulation cells on Jupiter in response to radiative and zonal momentum forcing. In the framework of semi-geostrophic theory, the meridional streamfunction is described by an elliptic equation with a source term dependent on the sum of the latitudinal derivative of the radiative forcing and the vertical derivative of the zonal momentum forcing. Using this equation with analytic terms similar to the assumed forcing on Jupiter, we obtained two set of atmospheric circulations cells, a stratospheric and a tropospheric one. A possible shift in the overturning circulation of the high and deep atmosphere can be induced by breaking the latitudinal alignment of radiative heating with the enforced belt and zones. A series of numerical simulations was conducted with the Jovian GCM OPUS, which was initiated with observational data obtained from the Cassini CIRS temperature cross-section and a corresponding geostrophic zonal wind field. Newtonian forcing of potential temperature as well as zonal momentum was applied respectively towards latitudinally and vertically uniform equilibrium fields. In accordance with the analytic illustrations two rows of jet scale circulation cells were created. The stratospheric circulation showed the distribution of upwelling over zones and downwelling over belts, consistent with cloud observations. The tropospheric cells featured a partial reversal of the downward vertical velocity over the belts and a considerable reduction of the upward movement over the zones in the domain, consistent with recent detections of high water clouds and lightning in belts. We also used the modeled new forcing fields as source terms for the semi-geostrophic Poisson equation to attribute the origin of the modeled secondary circulation. In this analysis, the stratospheric circulation cells observed in the model are primarily generated in response to radiative forcing, while momentum forcing induces the

  12. Simulated strengthening of the Atlantic Meridional Overturning Circulation in response to abyssal ocean warming around Antarctica

    NASA Astrophysics Data System (ADS)

    Patara, L.; Boning, C. W.

    2013-12-01

    Studies of repeat hydrographic observations have revealed a conspicuous multi-decadal warming, and partly, freshening, of the frigid abyssal ocean waters originating from the fringes of the Antarctic continent. The warming and contraction of Antarctic Bottom Water (AABW) represents one of the most prominent signals of change in Earth's climate and accounts for a substantial fraction of the present global energy and sea level budgets. Here we present a set of ocean model experiments demonstrating that the ongoing loss of AABW also has important dynamical consequences for the large-scale meridional overturning circulation in the Atlantic Ocean. In conjunction with a slowdown of the bottom cell, we find that the upper cell of the Atlantic Meridional Overturning Circulation (AMOC) progressively strengthens in response to changes in density gradients in the deep South Atlantic. Changes in the AMOC are tightly connected to increased meridional heat transport and therefore have a strong influence on global and regional climate patterns in the North Atlantic. The simulations suggest that the AABW-induced strengthening of the AMOC is already extending into the North Atlantic, progressing at a rate of about 0.2 Sv per decade, implying that the process may need to be taken into account in projections of future North Atlantic climate.

  13. 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

  14. 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.

  15. A general circulation model of a Venus-like atmosphere

    NASA Astrophysics Data System (ADS)

    Rossow, W. B.

    1983-02-01

    Heat and momentum budgets are investigated for a three-dimensional general circulation model of a Venus-like, massive and slowly rotating atmosphere which is forced with an axisymmetric radiative heating/cooling distribution. Model results confirm the suggestions of Gierasch (1975) and Rossow and Williams (1979), with a mean meridional circulation which, despite its multicellular form, interacts with quasi-barotropic eddies produced by zonal flow shear instability to yield a weak superrotation of the entire model atmosphere. This process is sufficiently general to encourage the conclusion that it will occur in all slowly rotating atmospheres. Whether it can accelerate wind speeds as large as those observed on Venus cannot presently be determined.

  16. The puzzling Venusian polar atmospheric structure reproduced by a general circulation model

    PubMed Central

    Ando, Hiroki; Sugimoto, Norihiko; Takagi, Masahiro; Kashimura, Hiroki; Imamura, Takeshi; Matsuda, Yoshihisa

    2016-01-01

    Unlike the polar vortices observed in the Earth, Mars and Titan atmospheres, the observed Venus polar vortex is warmer than the midlatitudes at cloud-top levels (∼65 km). This warm polar vortex is zonally surrounded by a cold latitude band located at ∼60° latitude, which is a unique feature called ‘cold collar' in the Venus atmosphere. Although these structures have been observed in numerous previous observations, the formation mechanism is still unknown. Here we perform numerical simulations of the Venus atmospheric circulation using a general circulation model, and succeed in reproducing these puzzling features in close agreement with the observations. The cold collar and warm polar region are attributed to the residual mean meridional circulation enhanced by the thermal tide. The present results strongly suggest that the thermal tide is crucial for the structure of the Venus upper polar atmosphere at and above cloud levels. PMID:26832195

  17. The puzzling Venusian polar atmospheric structure reproduced by a general circulation model.

    PubMed

    Ando, Hiroki; Sugimoto, Norihiko; Takagi, Masahiro; Kashimura, Hiroki; Imamura, Takeshi; Matsuda, Yoshihisa

    2016-01-01

    Unlike the polar vortices observed in the Earth, Mars and Titan atmospheres, the observed Venus polar vortex is warmer than the midlatitudes at cloud-top levels (∼65 km). This warm polar vortex is zonally surrounded by a cold latitude band located at ∼60° latitude, which is a unique feature called 'cold collar' in the Venus atmosphere. Although these structures have been observed in numerous previous observations, the formation mechanism is still unknown. Here we perform numerical simulations of the Venus atmospheric circulation using a general circulation model, and succeed in reproducing these puzzling features in close agreement with the observations. The cold collar and warm polar region are attributed to the residual mean meridional circulation enhanced by the thermal tide. The present results strongly suggest that the thermal tide is crucial for the structure of the Venus upper polar atmosphere at and above cloud levels. PMID:26832195

  18. Aviation Safety Simulation Model

    NASA Technical Reports Server (NTRS)

    Houser, Scott; Yackovetsky, Robert (Technical Monitor)

    2001-01-01

    The Aviation Safety Simulation Model is a software tool that enables users to configure a terrain, a flight path, and an aircraft and simulate the aircraft's flight along the path. The simulation monitors the aircraft's proximity to terrain obstructions, and reports when the aircraft violates accepted minimum distances from an obstruction. This model design facilitates future enhancements to address other flight safety issues, particularly air and runway traffic scenarios. This report shows the user how to build a simulation scenario and run it. It also explains the model's output.

  19. Surface circulation at the Strait of Gibraltar: A combined HF radar and high resolution model study

    NASA Astrophysics Data System (ADS)

    Soto-Navarro, Javier; Lorente, Pablo; Álvarez Fanjul, Enrique; Carlos Sánchez-Garrido, Jose; García-Lafuente, Jesús

    2016-03-01

    Observations from a high frequency radar system and outputs from a high resolution operational ocean model working at the Strait of Gibraltar have been analyzed and compared during the period February 2013 to September 2014 in order to evaluate their capability to resolve the surface circulation of the region. The description of the mean circulation patterns has been statistically assessed, showing good agreement, particularly in the central region of the strait corresponding with the Atlantic Jet (AJ) stream, although some short scale features are not reproduced by the model. In the frequency domain very high concordance is observed. Tidal maps of diurnal and semidiurnal constituents are in good agreement with previous observations. The analysis of the model and radar response to the wind forcing reveals that the low resolution of the model wind-forcing field and its deeper superficial level smoothes the wind effect on the simulated currents. The first three EOF modes account for the 86% of model and radar variances. The coincidence between the observed and simulated patterns is very significant for the first two modes, which account for the mean velocity field and the latitudinal shifting of the AJ consequence of the flow-topography interaction. The third mode captures the wind-induced circulation, and greater discrepancies are found in this case. Results underline the complementary character of both systems: radar observations improve the model description, resolving short scale processes, while the model completes the radar information when the time or spatial coverage is poorer.

  20. Numerical simulation of Black Sea circulation and pollution propagation in coastal waters of the Great Sochi

    NASA Astrophysics Data System (ADS)

    Fomin, Vladimir; Gusev, Anatoly; Diansky, Nikolay

    2014-05-01

    The numerical modelling of the Black Sea (BS) is performed by using INMOM (Institute of Numerical Mathematics Ocean Model). The model is based on the primitive equations in spherical s-coordinate system with free surface boundary condition. The numerical algorithm is based on the method of multicomponent splitting and has a flexible modular structure. The splitting with respect to physical processes and spatial coordinate is used. A computational method is proposed of the polluting substances (PS) transport in the BS region adjacent to the Great Sochi. It is based on INMOM application for the BS in two versions: M1 and M2. In the M1 INMOM has a uniform spatial resolution ~4 km, while M2 has non-uniform one with refinement to 50 m in the BS region near Great Sochi coast. The M2 is used only during the periods of PS transport computation for which the initial hydrothermodynamic conditions are taken from M1. Both versions reveal complexity of the BS circulation nature, however, M2 more adequately reproduces eddy circulation due to higher horizontal resolution in its eastern part. Hence, a suggestion is made that BS eddy structure simulation requires model resolution ~1.5 km, and the major factor of quasistationary Batumi anti-cyclonic gyre formation is the topographical features in this part of the sea. A computation of PS distribution from the rivers Sochi, Host and Mzymta and from 18 pipes of deep-water sewage production was performed for the high-water period from 01.04.2007 to 30.04.2007. It is shown that the significant contribution to PS distribution from these punctual sources is made by whirlwind mesoscale formations generating complicated 3-dimensional PS distribution.

  1. Modeling and simulation

    SciTech Connect

    Hanham, R.; Vogt, W.G.; Mickle, M.H.

    1986-01-01

    This book presents the papers given at a conference on computerized simulation. Topics considered at the conference included expert systems, modeling in electric power systems, power systems operating strategies, energy analysis, a linear programming approach to optimum load shedding in transmission systems, econometrics, simulation in natural gas engineering, solar energy studies, artificial intelligence, vision systems, hydrology, multiprocessors, and flow models.

  2. 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.

  3. Modeling the periodic stratification and gravitational circulation in San Francisco Bay, California

    USGS Publications Warehouse

    Cheng, Ralph T.; Casulli, Vincenzo

    1996-01-01

    A high resolution, three-dimensional (3-D) hydrodynamic numerical model is applied to San Francisco Bay, California to simulate the periodic tidal stratification caused by tidal straining and stirring and their long-term effects on gravitational circulation. The numerical model is formulated using fixed levels in the vertical and uniform computational mesh on horizontal planes. The governing conservation equations, the 3-D shallow water equations, are solved by a semi-implicit finite-difference scheme. Numerical simulations for estuarine flows in San Francisco Bay have been performed to reproduce the hydrodynamic properties of tides, tidal and residual currents, and salt transport. All simulations were carried out to cover at least 30 days, so that the spring-neap variance in the model results could be analyzed. High grid resolution used in the model permits the use of a simple turbulence closure scheme which has been shown to be sufficient to reproduce the tidal cyclic stratification and well-mixed conditions in the water column. Low-pass filtered 3-D time-series reveals the classic estuarine gravitational circulation with a surface layer flowing down-estuary and an up-estuary flow near the bottom. The intensity of the gravitational circulation depends upon the amount of freshwater inflow, the degree of stratification, and spring-neap tidal variations.

  4. 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

  5. Simulation and optimization of airlift external circulation membrane bioreactor using computational fluid dynamics.

    PubMed

    Qing, Zhang; Rongle, Xu; Xiang, Zheng; Yaobo, Fan

    2014-01-01

    The airlift external circulation membrane bioreactor (AEC-MBR) is a new MBR consisting of a separated aeration tank and membrane tank with circulating pipes fixed between the two tanks. The circulating pipe is called a H circulating pipe (HCP) because of its shape. With the complex configuration, it was difficult but necessary to master the AEC-MBR's hydraulic characteristics. In this paper, simulation and optimization of the AEC-MBR was performed using computational fluid dynamics. The distance from diffusers to membrane modules, i.e. the height of gas-liquid mixing zone (h(m)), and its effect on velocity distribution at membrane surfaces were studied. Additionally, the role of HCP and the effect of HCP's diameter on circulation were simulated and analyzed. The results showed that non-uniformity of cross-flow velocity existed in the flat-plate membrane modules, and the problem could be alleviated by increasing hm to an optimum range (h(m)/B ≥ 0.55; B is total static depth). Also, the low velocity in the boundary layer on the membrane surface was another reason for membrane fouling. The results also suggested that HCP was necessary and it had an optimum diameter to make circulation effective in the AEC-MBR. PMID:24804658

  6. Jupiter's thermosphere general circulation model: thermal and dynamical structures

    NASA Astrophysics Data System (ADS)

    Majeed, T.; Waite, J. H.; Bougher, S. W.; Gladstone, G. R.

    2003-04-01

    Recent observations of infrared and FUV auroral emissions from Jupiter have shown the presence of high-speed (>~2km/s) winds in the jovian thermosphere. The neutral atmospheric structure measured in-situ by the Galileo probe near the jovian equator exhibited wave-like oscillations in the temperature profile at altitudes of 133--1029~km. The derived exospheric temperature was ˜940~K. While no in-situ measurement is available for the neutral atmosphere of Jupiter's auroral region, infrared and ultraviolet spectrographic imaging results indicate auroral exospheric temperatures >1200~K. We examine this hypothesis using a fully 3-D JTGCM that has been developed and exercised to address global scale temperature, wind, and neutral-ion specie distributions. It was developed from a suitable adaptation of the NCAR Thermosphere Ionosphere General Circulation Model (TIGCM). An ion drag scheme was incorporated. A convection electric field was estimated and corresponding ion drifts were generated. These prescriptions provide a means to test the general impact of ion drag and Joule heating on the JTGCM neutral winds. The JTGCM has been fully spun-up and exercised for various cases to simulate 3-component neutral winds, and corresponding temperature and density distributions. The horizontal winds at the ionospheric heights vary from 0.5 km/s to 1.6 km/s and auroral temperatures from 1000 K to 3800 K depending on the magnitude of Joule heating. The equatorial temperature profiles from the JTGCM are compared with the measured temperature structure from the Galileo ASI data. The best fit to the data implies that the major energy source for heating the equatorial atmosphere is due to adiabatic heating induced by the downward motion of the neutral atmosphere. Further details of the JTGCM code and results for moderately strong auroral heating, ion drag, and ion drag plus Joule heating will be presented.

  7. Observed and simulated inter-decadal changes in the structure of Southern Hemisphere large-scale circulation

    NASA Astrophysics Data System (ADS)

    Freitas, Ana C. V.; Frederiksen, Jorgen S.; Whelan, Jennifer; O'Kane, Terence J.; Ambrizzi, Tércio

    2015-12-01

    Several studies have identified that, in the mid-1970s to early 1980s, a major shift occurred in the structure of the large-scale circulation in both hemispheres. This work employs the CSIRO Mk3L general circulation model in ensemble simulations with observed sea surface temperatures (SSTs) and historical time-evolving carbon dioxide (CO2) concentrations to investigate the inter-decadal changes found observationally in the jet streams, temperature, Hadley circulation, mean sea level pressure and precipitation. First, the performance of the model in simulating these changes for the mean July climate fields of 1949-1968 and 1975-1994, in comparison with the corresponding observations (NCEP/NCAR Reanalysis I and the Twentieth Century Reanalysis V2), is investigated. We find that the model is quite skilful in reproducing the broad features of the important inter-decadal changes that occurred in the mid-1970s. The model simulations and the NCEP/NCAR and twentieth century reanalyses agree in the eastern hemisphere; whereas in the western hemisphere the reanalyses show differences, and the simulations combine aspects of these two datasets. The role of the direct radiative forcing due to CO2 in driving the inter-decadal changes is also examined. Results indicate that, in comparison with the indirect effect of CO2 carried by the changing SSTs, there is little additional impact of the direct radiative forcing due to CO2 on the changes in the latter period. However, our simulations with fixed CO2 concentration have shown clearly that the atmospheric simulations with historical time-evolving CO2 concentrations are more skilful in reproducing the inter-decadal changes. The sensitivity of the ensemble results to employing the same or different time evolving sea ice boundary conditions in the ensemble members is also studied. The contributions of internal and external variability are discussed.

  8. Effects of Solar Particle Event-Like Proton Radiation and/or Simulated Microgravity on Circulating Mouse Blood Cells

    PubMed Central

    Romero-Weaver, Ana L.; Lin, Liyong; Carabe-Fernandez, Alejandro; Kennedy, Ann R.

    2014-01-01

    Astronauts traveling in space missions outside of low Earth orbit will be exposed for longer times to a microgravity environment. In addition, the increased travel time involved in exploration class missions will result in an increased risk of exposure to significant doses of solar particle event (SPE) radiation. Both conditions could significantly affect the number of circulating blood cells. Therefore, it is critical to determine the combined effects of exposure to both microgravity and SPE radiation. The purpose of the present study was to assess these risks by evaluating the effects of SPE-like proton radiation and/or microgravity, as simulated with the hindlimb unloading (HU) system, on circulating blood cells using mouse as a model system. The results indicate that exposure to HU alone caused minimal or no significant changes in mouse circulating blood cell numbers. The exposure of mice to SPE-like proton radiation with or without HU treatment caused a significant decrease in the number of circulating lymphocytes, granulocytes and platelets. The reduced numbers of circulating lymphocytes, granulocytes, and platelets, resulting from the SPE-like proton radiation exposure, with or without HU treatment, in mice suggest that astronauts participating in exploration class missions may be at greater risk of developing infections and thrombotic diseases; thus, countermeasures may be necessary for these biological endpoints. PMID:25360441

  9. Effects of Solar Particle Event-Like Proton Radiation and/or Simulated Microgravity on Circulating Mouse Blood Cells.

    PubMed

    Romero-Weaver, Ana L; Lin, Liyong; Carabe-Fernandez, Alejandro; Kennedy, Ann R

    2014-08-01

    Astronauts traveling in space missions outside of low Earth orbit will be exposed for longer times to a microgravity environment. In addition, the increased travel time involved in exploration class missions will result in an increased risk of exposure to significant doses of solar particle event (SPE) radiation. Both conditions could significantly affect the number of circulating blood cells. Therefore, it is critical to determine the combined effects of exposure to both microgravity and SPE radiation. The purpose of the present study was to assess these risks by evaluating the effects of SPE-like proton radiation and/or microgravity, as simulated with the hindlimb unloading (HU) system, on circulating blood cells using mouse as a model system. The results indicate that exposure to HU alone caused minimal or no significant changes in mouse circulating blood cell numbers. The exposure of mice to SPE-like proton radiation with or without HU treatment caused a significant decrease in the number of circulating lymphocytes, granulocytes and platelets. The reduced numbers of circulating lymphocytes, granulocytes, and platelets, resulting from the SPE-like proton radiation exposure, with or without HU treatment, in mice suggest that astronauts participating in exploration class missions may be at greater risk of developing infections and thrombotic diseases; thus, countermeasures may be necessary for these biological endpoints. PMID:25360441

  10. A mock circulation model for cardiovascular device evaluation.

    PubMed

    Schampaert, S; Pennings, K A M A; van de Molengraft, M J G; Pijls, N H J; van de Vosse, F N; Rutten, M C M

    2014-04-01

    The aim of this study was to develop an integrated mock circulation system that functions in a physiological manner for testing cardiovascular devices under well-controlled circumstances. In contrast to previously reported mock loops, the model includes a systemic, pulmonary, and coronary circulation, an elaborate heart contraction model, and a realistic heart rate control model. The behavior of the presented system was tested in response to changes in left ventricular contractile states, loading conditions, and heart rate. For validation purposes, generated hemodynamic parameters and responses were compared to literature. The model was implemented in a servo-motor driven mock loop, together with a relatively simple lead-lag controller. The pressure and flow signals measured closely mimicked human pressure under both physiological and pathological conditions. In addition, the system's response to changes in preload, afterload, and heart rate indicate a proper implementation of the incorporated feedback mechanisms (frequency and cardiac function control). Therefore, the presented mock circulation allows for generic in vitro testing of cardiovascular devices under well-controlled circumstances. PMID:24622168

  11. Circulant Graph Modeling Deterministic Small-World Networks

    NASA Astrophysics Data System (ADS)

    Zhao, Chenggui

    In recent years, many research works have revealed some technological networks including internet to be small-world networks, which is attracting attention from computer scientists. One can decide if or not a real network is Small-world by whether it has high local clustering and small average path distance which are the two distinguishing characteristics of small-world networks. So far, researchers have presented many small-world models by dynamically evolving a deterministic network into a small world one by stochastic adding vertices and edges to original networks. Rather few works focused on deterministic models. In this paper, as a important kind of Cayley graph, the circulant graph is proposed as models of deterministic small-world networks, thinking if its simple structures and significant adaptability. It shows circulant graph constructed in this document takes on the two expected characteristics of small word. This work should be useful because circulant graph has serviced as some models of communication and computer networks. The small world characteristic will be helpful to design and analysis of structure and performance.

  12. Mesozoic climates: General circulation models and the rock record

    NASA Astrophysics Data System (ADS)

    Sellwood, Bruce W.; Valdes, Paul J.

    2006-08-01

    General circulation models (GCMs) use the laws of physics and an understanding of past geography to simulate climatic responses. They are objective in character. However, they tend to require powerful computers to handle vast numbers of calculations. Nevertheless, it is now possible to compare results from different GCMs for a range of times and over a wide range of parameterisations for the past, present and future (e.g. in terms of predictions of surface air temperature, surface moisture, precipitation, etc.). GCMs are currently producing simulated climate predictions for the Mesozoic, which compare favourably with the distributions of climatically sensitive facies (e.g. coals, evaporites and palaeosols). They can be used effectively in the prediction of oceanic upwelling sites and the distribution of petroleum source rocks and phosphorites. Models also produce evaluations of other parameters that do not leave a geological record (e.g. cloud cover, snow cover) and equivocal phenomena such as storminess. Parameterisation of sub-grid scale processes is the main weakness in GCMs (e.g. land surfaces, convection, cloud behaviour) and model output for continental interiors is still too cold in winter by comparison with palaeontological data. The sedimentary and palaeontological record provides an important way that GCMs may themselves be evaluated and this is important because the same GCMs are being used currently to predict possible changes in future climate. The Mesozoic Earth was, by comparison with the present, an alien world, as we illustrate here by reference to late Triassic, late Jurassic and late Cretaceous simulations. Dense forests grew close to both poles but experienced months-long daylight in warm summers and months-long darkness in cold snowy winters. Ocean depths were warm (8 °C or more to the ocean floor) and reefs, with corals, grew 10° of latitude further north and south than at the present time. The whole Earth was warmer than now by 6 °C or

  13. Impacts of Large-Scale Circulation on Convection: A 2-D Cloud Resolving Model Study

    NASA Technical Reports Server (NTRS)

    Li, X; Sui, C.-H.; Lau, K.-M.

    1999-01-01

    Studies of impacts of large-scale circulation on convection, and the roles of convection in heat and water balances over tropical region are fundamentally important for understanding global climate changes. Heat and water budgets over warm pool (SST=29.5 C) and cold pool (SST=26 C) were analyzed based on simulations of the two-dimensional cloud resolving model. Here the sensitivity of heat and water budgets to different sizes of warm and cold pools is examined.

  14. Numerical Simulations of a Circulating Fluidized Bed with a Square Cross-Section

    SciTech Connect

    Li, Tingwen

    2011-01-01

    In this study, both 2D and 3D numerical simulations of a well-documented circulating fluidized bed with a square cross-section were conducted. With some assumptions, a series of 2D simulations was first carried out to study the influence of grid resolution, initial flow field, and boundary condition on the flow hydrodynamics. It was found that 2D simulations under-predicted the solids inventory even with the finest grid (10-particle-diameter grid size). On the other hand, a 3D simulation with relatively coarse grid was found in better agreement with the experimental data. Differences between 2D and 3D simulations were briefly discussed.

  15. WHTSubmersible: a simulator for estimating transient circulation temperature in offshore wells with the semi-submersible platform

    NASA Astrophysics Data System (ADS)

    Song, Xun-cheng; Liu, Yong-wang; Guan, Zhi-chuan

    2015-10-01

    Offshore wellbore temperature field is significant to drilling fluids program, equipment selection, evaluations on potential risks caused by casing thermal stress, etc. This paper mainly describes the theoretical basis, module structure and field verification of the simulator WHTSubmersible. This computer program is a useful tool for estimating transient temperature distribution of circulating drilling fluid on semi-submersible platform. WHTSubmersible is based on a mathematical model which is developed to consider radial and axial two-dimensional heat exchange of the inner drill pipe, the annulus, the drill pipe wall, the sea water and the formation in the process of drilling fluid circulation. The solution of the discrete equations is based on finite volume method with an implicit scheme. This scheme serves to demonstrate the numerical solution procedure. Besides, the simulator also considers the heating generated by drilling fluid circulation friction, drill bit penetrating rocks, friction between the drill column and the borehole wall, and the temperature effect on thermal physical properties and rheology of the drilling fluid. These measures ensure more accurate results. The simulator has been programmed as a dynamic link library using Visual C++, the routine interface is simple, which can be connected with other computer programs conveniently. The simulator is validated with an actual well temperature filed developed on a semi-submersible platform in South China, and the error is less than 5 %.

  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. Jovian Stratospheric Circulation: Insights from Cassini Observations and Coupled Dynamical-Chemical Modeling

    NASA Astrophysics Data System (ADS)

    Zhang, X.; Cosentino, R.; Morales-Juberias, R.; West, R. A.; Coffing, S.; Dowling, T. E.; Allen, M.; Yung, Y. L.

    2011-10-01

    Simultaneous observations of stratospheric temperature and hydrocarbon species acquired by the Cassini Composite Infrared Spectrometer (CIRS) (Nixon, et al., 2010) and the vertical and latitudinal distributions of aerosol retrieved from the Cassini Imaging Science Subsystem (ISS) provide the necessary data for an accurate simulation of the state of the stratosphere of Jupiter. The hydrocarbon distributions, the spatial variation of whose abundances is controlled by the stratospheric circulation, themselves can confirm the model formulation of global mass transport processes. In this study, a two-dimensional chemical transport model will be forced by output from a physics-based three-dimensional global circulation model, providing a model-measurement inter-comparison with stratospheric tracer species that can be tied back to specific dynamical processes.

  18. Baroclinic internal wave energy distribution in the Baltic Sea derived from 45 years of circulation simulations

    NASA Astrophysics Data System (ADS)

    Rybin, Artem; Soomere, Tarmo; Kurkina, Oxana; Kurkin, Andrey; Rouvinskaya, Ekaterina; Markus Meier, H. E.

    2016-04-01

    Internal waves and internal tides are an essential component of the functioning of stratified shelf seas. They carry substantial amounts of energy through the water masses, drive key hydrophysical processes such as mixing and overturning and support the functioning of marine ecosystem in many ways. Their particular impact becomes evident near and at the bottom where they often create substantial loads to engineering structures and exert a wide range of impacts on the bottom sediments and evolution of the seabed. We analyse several properties of spatio-temporal distributions of energy of relatively long-period large-scale internal wave motions in the Baltic Sea. The analysis is based on numerically simulated pycnocline variations that are extracted from the hydrographic data calculated by the Rossby Centre Ocean circulation model (RCO) for the entire Baltic Sea for 1961-2005. This model has a horizontal resolution of 2 nautical miles and uses 41 vertical layers with a thickness between 3 m close to the surface and 12 m in 250 m depth. The model is forced with atmospheric data derived from the ERA-40 re-analysis using a regional atmosphere model with a horizontal resolution of 25 km. It also accounts for river inflow and water exchange through the Danish Straits. See (Meier, H.E.M., Höglund, A., 2013. Studying the Baltic Sea circulation with Eulerian tracers, in Soomere, T., Quak, E., eds., Preventive Methods for Coastal Protection, Springer, Cham, Heidelberg, 101-130) for a detailed description of the model and its forcing. The resolution of the model output used in this study (once in 6 hours) is sufficient for estimates of spectral amplitudes of the displacements of isopycnal surfaces with a typical period of 2-12 days. We provide the analysis of kinetic and potential energy of motions with these periods. The resulting maps of the maxima of energy and spatial distributions of near-bottom velocities have been evaluated for the entire simulation interval of 45

  19. Observations and Modeling of the Transient General Circulation of the North Pacific Basin

    NASA Technical Reports Server (NTRS)

    McWilliams, James C.

    2000-01-01

    Because of recent progress in satellite altimetry and numerical modeling and the accumulation and archiving of long records of hydrographic and meteorological variables, it is becoming feasible to describe and understand the transient general circulation of the ocean (i.e., variations with spatial scales larger than a few hundred kilometers and time scales of seasonal and longer-beyond the mesoscale). We have carried out various studies in investigation of the transient general circulation of the Pacific Ocean from a coordinated analysis of satellite altimeter data, historical hydrographic gauge data, scatterometer wind observations, reanalyzed operational wind fields, and a variety of ocean circulation models. Broadly stated, our goal was to achieve a phenomenological catalogue of different possible types of large-scale, low-frequency variability, as a context for understanding the observational record. The approach is to identify the simplest possible model from which particular observed phenomena can be isolated and understood dynamically and then to determine how well these dynamical processes are represented in more complex Oceanic General Circulation Models (OGCMs). Research results have been obtained on Rossby wave propagation and transformation, oceanic intrinsic low-frequency variability, effects of surface gravity waves, pacific data analyses, OGCM formulation and developments, and OGCM simulations of forced variability.

  20. 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.

  1. Numerical Modeling of Water Circulation and Pollutant Transport in a Shallow Basin

    NASA Astrophysics Data System (ADS)

    Charafi, My. M.; Sadok, A.; Kamal, A.; Menai, A.

    A two-dimensional numerical model was developed1-3 to simulate the sediment and pollutant transport in a shallow basin. The developed model consist of two modules: Hydrodynamic module and sediment/pollutant transport module. A numerical hydrodynamic module based on the Saint-Venant equations, is resolved by a MacCormack numerical scheme and is used to simulate the circulation pattern in the basin. The obtained flow circulation is used as an input to the sediment/pollutant transport module to simulate the transport and dispersion of a pollutant emitted into the basin. To calibrate the numerical model, the distorted scale model of the Windermere Basin4 was used. In this physical model, the flow visualization and pollutant transport experiments provide a good calibration. The simulated results were found to be in good agreement with the experimental measurements and the results in Ref. 4. With the aid of the validated model, the influence of the construction of dikes on the residence time distributions in the basin was examined.

  2. Comparing the Degree of Land-Atmosphere Interaction in Four Atmospheric General Circulation Models

    NASA Technical Reports Server (NTRS)

    Koster, Randal D.; Dirmeyer, Paul A.; Hahmann, Andrea N.; Ijpelaar, Ruben; Tyahla, Lori; Cox, Peter; Suarez, Max J.; Houser, Paul R. (Technical Monitor)

    2001-01-01

    Land-atmosphere feedback, by which (for example) precipitation-induced moisture anomalies at the land surface affect the overlying atmosphere and thereby the subsequent generation of precipitation, has been examined and quantified with many atmospheric general circulation models (AGCMs). Generally missing from such studies, however, is an indication of the extent to which the simulated feedback strength is model dependent. Four modeling groups have recently performed a highly controlled numerical experiment that allows an objective inter-model comparison of land-atmosphere feedback strength. The experiment essentially consists of an ensemble of simulations in which each member simulation artificially maintains the same time series of surface prognostic variables. Differences in atmospheric behavior between the ensemble members then indicates the degree to which the state of the land surface controls atmospheric processes in that model. A comparison of the four sets of experimental results shows that feedback strength does indeed vary significantly between the AGCMs.

  3. A simple-physics global circulation model for Venus: Sensitivity assessments of atmospheric superrotation

    NASA Astrophysics Data System (ADS)

    Hollingsworth, J. L.; Young, R. E.; Schubert, G.; Covey, C.; Grossman, A. S.

    2007-03-01

    A 3D global circulation model is adapted to the atmosphere of Venus to explore the nature of the planet's atmospheric superrotation. The model employs the full meteorological primitive equations and simplified forms for diabatic and other nonconservative forcings. It is therefore economical for performing very long simulations. To assess circulation equilibration and the occurrence of atmospheric superrotation, the climate model is run for 10,000-20,000 day integrations at 4° × 5° latitude-longitude horizontal resolution, and 56 vertical levels (denoted L56). The sensitivity of these simulations to imposed Venus-like diabatic heating rates, momentum dissipation rates, and various other key parameters (e.g., near-surface momentum drag), in addition to model configuration (e.g., low versus high vertical domain and number of atmospheric levels), is examined. We find equatorial superrotation in several of our numerical experiments, but the magnitude of superrotation is often less than observed. Further, the meridional structure of the mean zonal overturning (i.e., Hadley circulation) can consist of numerous cells which are symmetric about the equator and whose depth scale appears sensitive to the number of vertical layers imposed in the model atmosphere. We find that when realistic diabatic heating is imposed in the lowest several scales heights, only extremely weak atmospheric superrotation results.

  4. The Probability of the Collapse of the Thermohaline Circulation in an Intermediate Complexity Model

    NASA Astrophysics Data System (ADS)

    Challenor, P.; Hankin, R.; Marsh, R.

    2005-12-01

    If the thermohaline circulation were to collapse we could see very rapid climate changes, with North West Europe becoming much cooler and widespread impacts across the globe. The risk of such an event has two aspects: the first is the impact of a collapse in the circulation and the second is the probability that it will happen. In this paper we look at latter problem. In particular we investigate the probability that the thermohaline circulation will collapse by the end of the century. To calculate the probability of thermohaline collapse we use a Monte Carl method. We simulate from a climate model with uncertain parameters and estimate the probability from the number of times the model collapses compared to the number of runs. We use an intermediate complexity climate model, C-GOLDSTEIN, which includes a 3-d ocean, an energy balance atmosphere and, in the version we use, a parameterised carbon cycle. Although C-GOLDSTEIN runs quickly for a climate model it is still too slow to allow the thousands of runs needed for the Monte Carlo calculations. We therefore build an emulator of the model. An emulator is a statistical approximation to the full climate model that gives an estimate of the model output and an uncertainty measure. We use a Gaussian process as our emulator. A limited number of model runs are used to build the emulator which is then used for the simulations. We produce estimates of the probability of the collapse of the thermohaline circulation corresponding to the indicative SRES emission scenarios: A1, A1FI, A1T, A2, B1 and B2.

  5. 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.

  6. On the tidally driven circulation in the South China Sea: modeling and analysis

    NASA Astrophysics Data System (ADS)

    Nelko, Varjola; Saha, Abhishek; Chua, Vivien P.

    2014-03-01

    The South China Sea is a large marginal sea surrounded by land masses and island chains, and characterized by complex bathymetry and irregular coastlines. An unstructured-grid SUNTANS model is employed to perform depth-averaged simulations of the circulation in the South China Sea. The model is tidally forced at the open ocean boundaries using the eight main tidal constituents as derived from the OSU Tidal Prediction Software. The model simulations are performed for the year 2005 using a time step of 60 s. The model reproduces the spring-neap and diurnal and semidiurnal variability in the observed data. Skill assessment of the model is performed by comparing model-predicted surface elevations with observations. For stations located in the central region of the South China Sea, the root mean squared errors (RMSE) are less than 10 % and the Pearson's correlation coefficient ( r) is as high as 0.9. The simulations show that the quality of the model prediction is dependent on the horizontal grid resolution, coastline accuracy, and boundary locations. The maximum RMSE errors and minimum correlation coefficients occur at Kaohsiung (located in northern South China Sea off Taiwan coast) and Tioman (located in southern South China Sea off Malaysia coast). This may be explained with spectral analysis of sea level residuals and winds, which reveal dynamics at Kaohsiung and Tioman are strongly influenced by the seasonal monsoon winds. Our model demonstrates the importance of tidally driven circulation in the central region of the South China Sea.

  7. 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.

  8. 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

  9. Modeling Black Sea circulation with high resolution in the coastal zone

    NASA Astrophysics Data System (ADS)

    Zalesnyi, V. B.; Gusev, A. V.; Agoshkov, V. I.

    2016-05-01

    We present a numerical model of Black Sea circulation based on primitive equations with improved spatial resolution in the coastal zone. The model equations are formulated in a two-pole orthogonal coordinate system with arbitrary locations of the poles and a vertical σ coordinate. Increased horizontal resolution is gained by displacing the pole into the vicinity of the separated subdomain. The problem is solved over a grid with a variable step. The northern coordinate pole is displaced to the vicinity of Gelendzhik; the grid step varies from 150 m in the coastal zone to 4.6 km in the main basin. We simulated the fields of currents, sea level, temperature, and salinity under the given atmospheric forcing in 2007. The model is capable of reproducing the large-scale Black Sea circulation and submesoscale variations in the coastal currents.

  10. El Niño-related variations in the southern Pacific atmospheric circulation: model versus observations

    NASA Astrophysics Data System (ADS)

    Bhaskaran, B.; Mullan, A. B.

    2002-10-01

    Our objective is two-fold: (1) to study the influence of tropical Pacific sea surface temperature (SST) anomalies associated with the El Niño - Southern Oscillation (ENSO) on the southern Pacific atmospheric circulation using observations; and (2) to assess the ability of a fully comprehensive GCM to reproduce the observed ENSO-related variations. The observed circulation features were derived from the National Center for Environmental Prediction (NCEP) reanalyses of observations. The GCM used is the atmospheric component of the United Kingdom Meteorological Office (UKMO) unified model (UM). A detailed study of the impact of the ENSO on the seasonal mean circulation and on the intraseasonal variability on synoptic time scales has been carried out using both the model and NCEP data for austral summer season. We have also investigated the relationship between the high frequency (HF) transients and the quasi-stationary mean circulation during selected ENSO years. A regional Hadley cell intensity in the tropical Pacific has been used as an El Niño index to classify the warming and cooling years for our composite analysis. During El Niño years the regional Hadley cell acts as a medium through which the enhanced equatorial convection forces a train of Rossby waves to produce the quasi-stationary circulation anomalies in extratropics. The Hadley cell weakens during La Niña years, and the equatorial convection moves further westwards. The Rossby wave response to this situation is to reverse the phase of the quasi-stationary circulation anomalies by 180°, as expected. These features are fairly well simulated by the UM, though the extratropical circulation anomalies in response to the equatorial convection is found about 30° longitude further eastwards than observed during El Niño years. The model confirms the observational evidence that the storm track variations in the southern subtropical Pacific are largely driven by variations in the South Pacific Convergence

  11. Computer Modeling and Simulation

    SciTech Connect

    Pronskikh, V. S.

    2014-05-09

    Verification and validation of computer codes and models used in simulation are two aspects of the scientific practice of high importance and have recently been discussed by philosophers of science. While verification is predominantly associated with the correctness of the way a model is represented by a computer code or algorithm, validation more often refers to model’s relation to the real world and its intended use. It has been argued that because complex simulations are generally not transparent to a practitioner, the Duhem problem can arise for verification and validation due to their entanglement; such an entanglement makes it impossible to distinguish whether a coding error or model’s general inadequacy to its target should be blamed in the case of the model failure. I argue that in order to disentangle verification and validation, a clear distinction between computer modeling (construction of mathematical computer models of elementary processes) and simulation (construction of models of composite objects and processes by means of numerical experimenting with them) needs to be made. Holding on to that distinction, I propose to relate verification (based on theoretical strategies such as inferences) to modeling and validation, which shares the common epistemology with experimentation, to simulation. To explain reasons of their intermittent entanglement I propose a weberian ideal-typical model of modeling and simulation as roles in practice. I suggest an approach to alleviate the Duhem problem for verification and validation generally applicable in practice and based on differences in epistemic strategies and scopes

  12. Evidence for a fluctuation theorem in an atmospheric circulation model.

    PubMed

    Schalge, B; Blender, R; Wouters, J; Fraedrich, K; Lunkeit, F

    2013-05-01

    An investigation of the distribution of finite time trajectory divergence is performed on an atmospheric global circulation model. The distribution of the largest local Lyapunov exponent shows a significant probability for negative values over time spans up to 10 days. This effect is present for resolutions up to wave numbers ℓ=42 (≈250 km). The probability for a negative local largest Lyapunov exponent decreases over time, similarly to the predictions of the fluctuation theorem for entropy production. The model used is hydrostatic with variable numbers of vertical levels and different horizontal resolutions. PMID:23767493

  13. Evidence for a fluctuation theorem in an atmospheric circulation model

    NASA Astrophysics Data System (ADS)

    Schalge, B.; Blender, R.; Wouters, J.; Fraedrich, K.; Lunkeit, F.

    2013-05-01

    An investigation of the distribution of finite time trajectory divergence is performed on an atmospheric global circulation model. The distribution of the largest local Lyapunov exponent shows a significant probability for negative values over time spans up to 10 days. This effect is present for resolutions up to wave numbers ℓ=42 (≈250 km). The probability for a negative local largest Lyapunov exponent decreases over time, similarly to the predictions of the fluctuation theorem for entropy production. The model used is hydrostatic with variable numbers of vertical levels and different horizontal resolutions.

  14. Modeling of clouds and radiation for developing parameterizations for general circulation models. Annual report, 1994

    SciTech Connect

    1994-12-31

    We are using a hierarchy of numerical models of cirrus and stratus clouds and radiative transfer to improve the reliability of general circulation models. Our detailed cloud microphysical model includes all of the physical processes believed to control the lifecycle of liquid and ice clouds in the troposphere. In our one-dimensional cirrus studies, we find that the ice crystal number and size in cirrus clouds are not very sensitive to the number of condensation nuclei which are present. We have compared our three-dimensional meoscale simulations of cirrus clouds with radar, lidar satellite and other observations of water vapor and cloud fields and find that the model accurately predicts the characteristics of a cirrus cloud system. The model results reproduce several features detected by remote sensing (lidar and radar) measurements, including the appearance of the high cirrus cloud at about 15 UTC and the thickening of the cloud at 20 UTC. We have developed a new parameterizations for production of ice crystals based on the detailed one-dimensional cloud model, and are presently testing the parameterization in three-dimensional simulations of the FIRE-II November 26 case study. We have analyzed NWS radiosonde humidity data from FIRE and ARM and found errors, biases, and uncertainties in the conversion of the sensed resistance to humidity.

  15. Venusian Polar Vortex reproduced in an Atmospheric General Circulation Model

    NASA Astrophysics Data System (ADS)

    Ando, Hiroki; Imamura, Takeshi; Takagi, Masahiro; Sugimoto, Norihiko; Kashimura, Hiroki

    The Venus atmosphere has a polar vortex rotating in the retrograde direction with a period of about three days. The vortex has a warm feature surrounded by a cold collar (e.g., Taylor et al. 1980; Piccioni et al. 2006). Although the Venusian polar vortex has been reported by many observations, its mechanism is still unknown. Elson (1982, 1989) examined the structure of the polar vortex by linear calculations. However, the background zonal wind assumed in the calculations was much stronger or weaker than those retrieved in the previous measurements (e.g., Peralta et al. 2008; Kouyama et al. 2012). Lee et al. (2010) and Yamamoto and Takahashi (2012) performed numerical simulations with general circulation models (GCMs) of the Venus atmosphere and obtained vertical structure in the polar region. However, the models included artificial forcing of Kelvin and/or Rossby waves. We have developed a new Venusian GCM by modifying the Atmospheric GCM For the Earth Simulator (Sugimoto et al. 2012; 2013). The basic equations of the GCM are primitive ones in the sigma coordinate on a sphere without topography. The model resolution is T42 (i.e., about 2.8 deg x 2.8 deg grids) and L60 (Deltaz is about 2 km). Rayleigh friction (sponge layer) in the upper layer (>80 km) is applied to prevent the reflection of waves, whose effect increases gradually with height. In the model, the atmosphere is dry and forced by the solar heating and Newtonian cooling. The vertical profile of the solar heating is based on Crisp (1986), and zonally averaged distribution is used. In addition diurnal component of the solar heating, which excites the diurnal and semi-diurnal tides, is also included. Newtonian cooling relaxes the temperature to the zonally uniform basic temperature which has a virtual static stability of Venus with almost neutral layers, and its coefficient is based on Crisp (1986). To prevent numerical instability, the biharmonic hyper-diffusion is included with 0.8 days of e-folding time

  16. The influence of atmospheric circulation on the mid-Holocene climate of Europe: a data-model comparison

    NASA Astrophysics Data System (ADS)

    Mauri, A.; Davis, B. A. S.; Collins, P. M.; Kaplan, J. O.

    2014-10-01

    The atmospheric circulation is a key area of uncertainty in climate model simulations of future climate change, especially in mid-latitude regions such as Europe where atmospheric dynamics have a significant role in climate variability. It has been proposed that the mid-Holocene was characterized in Europe by a stronger westerly circulation in winter comparable with a more positive AO/NAO, and a weaker westerly circulation in summer caused by anti-cyclonic blocking near Scandinavia. Model simulations indicate at best only a weakly positive AO/NAO, whilst changes in summer atmospheric circulation have not been widely investigated. Here we use a new pollen-based reconstruction of European mid-Holocene climate to investigate the role of atmospheric circulation in explaining the spatial pattern of seasonal temperature and precipitation anomalies. We find that the footprint of the anomalies is entirely consistent with those from modern analogue atmospheric circulation patterns associated with a strong westerly circulation in winter (positive AO/NAO) and a weak westerly circulation in summer associated with anti-cyclonic blocking (positive SCAND). We find little agreement between the reconstructed anomalies and those from 14 GCMs that performed mid-Holocene experiments as part of the PMIP3/CMIP5 project, which show a much greater sensitivity to top-of-the-atmosphere changes in solar insolation. Our findings are consistent with data-model comparisons on contemporary timescales that indicate that models underestimate the role of atmospheric circulation in recent climate change, whilst also highlighting the importance of atmospheric dynamics in explaining interglacial warming.

  17. 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.

  18. Theory Modeling and Simulation

    SciTech Connect

    Shlachter, Jack

    2012-08-23

    Los Alamos has a long history in theory, modeling and simulation. We focus on multidisciplinary teams that tackle complex problems. Theory, modeling and simulation are tools to solve problems just like an NMR spectrometer, a gas chromatograph or an electron microscope. Problems should be used to define the theoretical tools needed and not the other way around. Best results occur when theory and experiments are working together in a team.

  19. Precipitation-climate sensitivity to initial conditions in an atmospheric general circulation model

    SciTech Connect

    Covey, C., LLNL

    1997-03-01

    Atmospheric climate, in contrast to weather, is traditionally considered to be determined by boundary conditions such as sea surface temperature (SST). To test this hypothesis, we examined annual mean precipitation from an ensemble of 20 general circulation model (GCM) simulations. Ensemble members were forced with identical 10-year series of SST and sea ice, but they began with slightly differing initial conditions. A surprisingly small proportion of the variance in the output is attributable to the effects of boundary forcing. This result-and similar evidence from smaller ensembles of other GCM simulations-implies that long-term precipitation variations are mostly unpredictable, even if SST forecasts are `perfect.`

  20. Simulation of three-dimensional circulation and hydrography over the Grand Banks of Newfoundland

    NASA Astrophysics Data System (ADS)

    Han, Guoqi; Ma, Zhimin; deYoung, Brad; Foreman, Mike; Chen, Nancy

    There are few ocean models that both adequately resolve the cross-shelf structure of the Labrador Current and have been sufficiently evaluated against in situ observations at tidal, synoptic and seasonal scales. We present a three-dimensional, high-resolution, prognostic, nonlinear circulation model for the Newfoundland offshore based on the finite volume coastal ocean model (FVCOM). The FVCOM uses unstructured grid in the horizontal and thus allows efficient and effective use of grid resolution to resolve coastal- and shelf-scale features. The model results are evaluated against current meter measurements, vessel-mounted acoustic Doppler current profiler (ADCP) data, and tide-gauge observations. The FVCOM climatological monthly-mean currents over the shelf and slope show good agreement with observations and substantial improvement over those from an earlier finite-element model. The simulated tidal elevations agree well (4 cm of the root-sum-square absolute error for the total tidal height) with observations, and show improvement over previous tidal models over the Labrador Shelf. The hindcasts for the spring to fall of 1999 show reasonable skill in reproducing temperature, salinity and currents. At station 27 the observed temperature and salinity have seasonal ranges of 14 °C and 1.5 psu near the surface from April to November; while the root-mean-square (RMS) differences are 2.1 °C and 0.3 psu between the model and observations. On the Flemish Cap transect the observed temperature and salinity range from -1.5 to 13.1 °C and from 31.3 to 34.9 psu on July 17-20, 1999; while the RMS differences are 1.0 °C and 0.2 psu. The model-observation velocity difference ratio is 0.53 on this transect on July 17-18, 1999.

  1. Overly persistent circulation in climate models contributes to overestimated frequency and duration of heat waves and cold spells

    NASA Astrophysics Data System (ADS)

    Plavcová, Eva; Kyselý, Jan

    2016-05-01

    The study examines links of summer heat waves and winter cold spells in Central Europe to atmospheric circulation and specifically its persistence in an ensemble of regional climate models (RCMs). We analyse 13 RCMs driven by the ERA-40 reanalysis and compare them against observations over reference period 1971-2000. Using objective classification of circulation types and an efficiency coefficient with a block resampling test, we identify circulation types significantly conducive to heat waves and cold spells. We show that the RCMs have a stronger tendency to group together days with very high or low temperature and tend to simulate too many heat waves and cold spells, especially those lasting 5 days and more. Circulation types conducive to heat waves in summer are characterized by anticyclonic, southerly and easterly flow, with increasing importance of warm advection during heat waves. Winter cold spells are typically associated with easterly and anticyclonic flow, and the onset of cold spells tends to be linked to northerly and cyclonic flow with cold advection. The RCMs are generally able to reproduce the links between circulation and heat waves or cold spells, including the radiation-to-advection effect for heat waves and the opposite advection-to-radiation effect for cold spells. They capture relatively well also changes of mean temperature anomalies during sequences of given circulation types, namely the tendency towards temperature increase (decrease) during those types conducive to heat waves (cold spells). Since mean lengths of all circulation supertypes are overestimated in the RCMs, we conclude that the overly persistent circulation in climate models contributes to the overestimated frequency of long heat waves and cold spells. As these biases are rather general among the examined RCMs and similar drawbacks are likely to be manifested in climate model simulations for the twenty-first century, the results also suggest that climate change scenarios for

  2. Integrated and spectral energetics of the GLAS general circulation model

    NASA Technical Reports Server (NTRS)

    Tenenbaum, J.

    1982-01-01

    Integrated and spectral error energetics of the GLAS General circulation model are compared with observations for periods in January 1975, 1976, and 1977. For two cases the model shows significant skill in predicting integrated energetics quantities out to two weeks, and for all three cases, the integrated monthly mean energetics show qualitative improvements over previous versions of the model in eddy kinetic energy and barotropic conversions. Fundamental difficulties remain with leakage of energy to the stratospheric level, particularly above strong initial jet streams associated in part with regions of steep terrain. The spectral error growth study represents the first comparison of general circulation model spectral energetics predictions with the corresponding observational spectra on a day by day basis. The major conclusion is that eddy kinetics energy can be correct while significant errors occur in the kinetic energy of wavenumber 3. Both the model and observations show evidence of single wavenumber dominance in eddy kinetic energy and the correlation of spectral kinetics and potential energy.

  3. Two-dimensional model for circulating fluidized-bed reactors

    SciTech Connect

    Schoenfelder, H.; Kruse, M.; Werther, J.

    1996-07-01

    Circulating fluidized bed reactors are widely used for the combustion of coal in power stations as well as for the cracking of heavy oil in the petroleum industry. A two-dimensional reactor model for circulating fluidized beds (CFB) was studied based on the assumption that at every location within the riser, a descending dense phase and a rising lean phase coexist. Fluid mechanical variables may be calculated from one measured radial solids flux profile (upward and downward). The internal mass-transfer behavior is described on the basis of tracer gas experiments. The CFB reactor model was tested against data from ozone decomposition experiments in a CFB cold flow model (15.6-m height, 0.4-m ID) operated in the ranges 2.5--4.5 m/s and 9--45 kg/(m{sup 2}{center_dot}s) of superficial gas velocity and solids mass flux, respectively. Based on effective reaction rate constants determined from the ozone exit concentration, the model was used to predict the spatial reactant distribution within the reactor. Model predictions agreed well with measurements.

  4. Design and Performance Analysis of a Massively Parallel Atmospheric General Circulation Model

    NASA Technical Reports Server (NTRS)

    Schaffer, Daniel S.; Suarez, Max J.

    1998-01-01

    In the 1990's computer manufacturers are increasingly turning to the development of parallel processor machines to meet the high performance needs of their customers. Simultaneously, atmospheric scientists study weather and climate phenomena ranging from hurricanes to El Nino to global warming that require increasingly fine resolution models. Here, implementation of a parallel atmospheric general circulation model (GCM) which exploits the power of massively parallel machines is described. Using the horizontal data domain decomposition methodology, this FORTRAN 90 model is able to integrate a 0.6 deg. longitude by 0.5 deg. latitude problem at a rate of 19 Gigaflops on 512 processors of a Cray T3E 600; corresponding to 280 seconds of wall-clock time per simulated model day. At this resolution, the model has 64 times as many degrees of freedom and performs 400 times as many floating point operations per simulated day as the model it replaces.

  5. Simulations and Observations of Circulation in the Oregon Coastal Transition Zone during the 2002-2003 Downwelling Season

    NASA Astrophysics Data System (ADS)

    Springer, S. R.; Allen, J. S.; Samelson, R. M.; Kurapov, A. L.; Egbert, G. D.; Miller, R. N.; de Rada, S.

    2008-12-01

    In comparison with summertime, relatively little is known about the circulation off Oregon during wintertime. We conducted a hindcast simulation of the period from October 1, 2002 to May 1, 2003, which coincided with a major observational field program. A non-assimilating, one-way nested model obtained initial conditions and boundary conditions from a larger scale, assimilating California Current model, and it was forced by wind stress from a regional mesoscale model, rainfall and heat fluxes calculated from a coarse resolution atmospheric model, and observed coastal river flows. At the beginning of the period, an upwelling circulation established by predominantly southward winds during the previous summer is in place. Vigorous storms in December deepen, freshen, and cool the mixed layer in the simulation, consistent with measurements along the Newport hydrographic line (44.65° N). Sensitivity studies demonstrate the importance of both rainfall and coastal river freshwater input to upper ocean stratification. Predominantly northward wind stress near the coast establishes a downwelling circulation with onshore Ekman transport, which holds freshwater input by rivers near the coast. When the wind reverses to southward for several days in early February, offshore Ekman transport spreads this freshwater feature seaward in both model simulations and high resolution hydrographic observations. During the mid to late winter, wind stress switches between strongly downwelling-favorable and weakly upwelling-favorable intervals of approximately 10-14 day duration. Comparison with moored current meters on the outer and midshelf shows that the model reproduces the corresponding reversals of the depth-averaged alongshore currents. Coastal trapped wave energy originating to the south passes into the domain and contributes to the strength of the upwelling response on the central Oregon coast.

  6. The Sensitivity of WRF Daily Summertime Simulations over West Africa to Alternative Parameterizations. Part 1: African Wave Circulation

    NASA Technical Reports Server (NTRS)

    Noble, Erik; Druyan, Leonard M.; Fulakeza, Matthew

    2014-01-01

    The performance of the NCAR Weather Research and Forecasting Model (WRF) as a West African regional-atmospheric model is evaluated. The study tests the sensitivity of WRF-simulated vorticity maxima associated with African easterly waves to 64 combinations of alternative parameterizations in a series of simulations in September. In all, 104 simulations of 12-day duration during 11 consecutive years are examined. The 64 combinations combine WRF parameterizations of cumulus convection, radiation transfer, surface hydrology, and PBL physics. Simulated daily and mean circulation results are validated against NASA's Modern-Era Retrospective Analysis for Research and Applications (MERRA) and NCEP/Department of Energy Global Reanalysis 2. Precipitation is considered in a second part of this two-part paper. A wide range of 700-hPa vorticity validation scores demonstrates the influence of alternative parameterizations. The best WRF performers achieve correlations against reanalysis of 0.40-0.60 and realistic amplitudes of spatiotemporal variability for the 2006 focus year while a parallel-benchmark simulation by the NASA Regional Model-3 (RM3) achieves higher correlations, but less realistic spatiotemporal variability. The largest favorable impact on WRF-vorticity validation is achieved by selecting the Grell-Devenyi cumulus convection scheme, resulting in higher correlations against reanalysis than simulations using the Kain-Fritch convection. Other parameterizations have less-obvious impact, although WRF configurations incorporating one surface model and PBL scheme consistently performed poorly. A comparison of reanalysis circulation against two NASA radiosonde stations confirms that both reanalyses represent observations well enough to validate the WRF results. Validation statistics for optimized WRF configurations simulating the parallel period during 10 additional years are less favorable than for 2006.

  7. Rotating-fluid experiments with an atmospheric general circulation model

    NASA Technical Reports Server (NTRS)

    Geisler, J. E.; Pitcher, E. J.; Malone, R. C.

    1983-01-01

    In order to determine features of rotating fluid flow that are dependent on the geometry, rotating annulus-type experiments are carried out with a numerical model in spherical coordinates. Rather than constructing and testing a model expressly for this purpose, it is found expedient to modify an existing general circulation model of the atmosphere by removing the model physics and replacing the lower boundary with a uniform surface. A regime diagram derived from these model experiments is presented; its major features are interpreted and contrasted with the major features of rotating annulus regime diagrams. Within the wave regime, a narrow region is found where one or two zonal wave numbers are dominant. The results reveal no upper symmetric regime; wave activity at low rotation rates is thought to be maintained by barotropic rather than baroclinic processes.

  8. Pressurized Cadaver Model in Cardiothoracic Surgical Simulation.

    PubMed

    Greene, Christina L; Minneti, Michael; Sullivan, Maura E; Baker, Craig J

    2015-09-01

    Simulation is increasingly recognized as an integral aspect of thoracic surgery education. A number of simulators have been introduced to teach component cardiothoracic skills; however, no good model exists for numerous essential skills including redo sternotomy and internal mammary artery takedown. These procedures are often relegated to thoracic surgery residents but have significant negative implications if performed incorrectly. Fresh tissue dissection is recognized as the gold standard for surgical simulation, but the lack of circulating blood volume limits surgical realism. Our aim is to describe the technique of the pressurized cadaver for use in cardiothoracic surgical procedures, focusing on internal mammary artery takedown. PMID:26354651

  9. Atmospheric model intercomparison project: Monsoon simulations

    SciTech Connect

    Sperber, K.R.; Palmer, T.N.

    1994-06-01

    The simulation of monsoons, in particular the Indian summer monsoon, has proven to be a critical test of a general circulation model`s ability to simulate tropical climate and variability. The Monsoon Numerical Experimentation Group has begun to address questions regarding the predictability of monsoon extremes, in particular conditions associated with El Nino and La Nina conditions that tend to be associated with drought and flood conditions over the Indian subcontinent, through a series of seasonal integrations using analyzed initial conditions from successive days in 1987 and 1988. In this paper the authors present an analysis of simulations associated with the Atmospheric Model Intercomparison Project (AMIP), a coordinated effort to simulate the 1979--1988 decade using standardized boundary conditions with approximately 30 atmospheric general circulation models. The 13 models analyzed to date are listed. Using monthly mean data from these simulations they have calculated indices of precipitation and wind shear in an effort to access the performance of the models over the course of the AMIP decade.

  10. 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.

  11. AGRICULTURAL SIMULATION MODEL (AGSIM)

    EPA Science Inventory

    AGSIM is a large-scale econometric simulation model of regional crop and national livestock production in the United States. The model was initially developed to analyze the aggregate economic impacts of a wide variety issues facing agriculture, such as technological change, pest...

  12. Mechanisms for decadal scale variability in a simulated Atlantic meridional overturning circulation

    NASA Astrophysics Data System (ADS)

    Medhaug, I.; Langehaug, H. R.; Eldevik, T.; Furevik, T.; Bentsen, M.

    2012-07-01

    Variability in the Atlantic Meridional Overturning Circulation (AMOC) has been analysed using a 600-year pre-industrial control simulation with the Bergen Climate Model. The typical AMOC variability has amplitudes of 1 Sverdrup (1 Sv = 106 m3 s-1) and time scales of 40-70 years. The model is reproducing the observed dense water formation regions and has very realistic ocean transports and water mass distributions. The dense water produced in the Labrador Sea (1/3) and in the Nordic Seas, including the water entrained into the dense overflows across the Greenland-Scotland Ridge (GSR; 2/3), are the sources of North Atlantic Deep Water (NADW) forming the lower limb of the AMOC's northern overturning. The variability in the Labrador Sea and the Nordic Seas convection is driven by decadal scale air-sea fluxes in the convective region that can be related to opposite phases of the North Atlantic Oscillation. The Labrador Sea convection is directly linked to the variability in AMOC. Linkages between convection and water mass transformation in the Nordic Seas are more indirect. The Scandinavian Pattern, the third mode of atmospheric variability in the North Atlantic, is a driver of the ocean's poleward heat transport (PHT), the overall constraint on northern water mass transformation. Increased PHT is both associated with an increased water mass exchange across the GSR, and a stronger AMOC.

  13. Numerical simulation on pulverized coal combustion and NOx emissions in high temperature air from circulating fluidized bed

    NASA Astrophysics Data System (ADS)

    Zhu, Jianguo; Ouyang, Ziqu; Lu, Qinggang

    2013-06-01

    High temperature air combustion is a prospecting technology in energy saving and pollutants reduction. Numerical simulation on pulverized coal combustion and NOx emissions in high temperature air from circulating fluidized bed was presented. The down-fired combustor, taken as the calculation domain, has the diameter of 220 mm and the height of 3000 mm. 2 cases with air staging combustion are simulated. Compared the simulation results with experimental data, there is a good agreement. It is found that the combustion model and NOx formation model are applicable to simulate the pulverized coal combustion and NOx emissions in high temperature air from circulating fluidized bed. The results show that there is a uniform temperature profile along the axis of the down-fired combustor. The NOx emissions are lower than those of ordinary pulverized coal combustion, and the NOx emissions are 390 mg/m3 and 352 mg/m3 in Case 1 and Case 2, respectively. At the range of 300-600 mm below the nozzle, the NO concentration decreases, mainly resulting from some homogeneous reactions and heterogeneous reaction. NO concentration has a little increase at the position of 800 mm below the nozzle as the tertiary air supplied to the combustor at the position of 600 mm below the nozzle.

  14. Investigating daily summertime circulation and precipitation over West Africa with the WRF model: a regional climate model adaptation study

    NASA Astrophysics Data System (ADS)

    Noble, Erik Ulysses

    This dissertation a) evaluates the performance of the NCAR Weather and Research Forecasting (WRF) model as a West African Sahel regional-atmospheric model and b) investigates the utility of regional modeling to meeting user-needs. This work represents the beginning of an effort to adapt the model as a regional climate model (RCM) for the Sahel. Two independent studies test WRF sensitivity to 64 configurations of alternative parameterizations in a series of September simulations. In all, 104 12-day simulations during 11 consecutive years are examined. Simulated daily and mean circulation results are validated against NASA's Modern-Era Retrospective Analysis for Research and Applications (MERRA) and NCEP Reanalysis-2. Modeled daily and total precipitation results are validated against NASA's Global Precipitation Climatology Project (GPCP) and Tropical Rainfall Measuring Mission (TRMM) data. Particular attention is given to westward-propagating precipitation maxima associated with transient African Easterly Waves (AEWs). A wide range of 700-hPa vorticity and daily precipitation validation scores demonstrates the influence of alternative parameterizations. The best WRF performers achieve circulation correlations against reanalysis of 0.40-0.60 and realistic amplitudes of spatiotemporal variability for the 2006 focus year, but they get time-longitude precipitation correlations (against GPCP) of between 0.35-0.42. A parallel-benchmark-simulation by the NASA Regional Model-3 (RM3) achieves higher correlations but less realistic spatiotemporal variability. The largest favorable impact on WRF vorticity and precipitation validation is achieved by selecting the Grell-Devenyi cumulus convection scheme, resulting in higher correlations against reanalysis and GPCP than simulations using the Kain-Fritch convection. Other parameterizations have less-obvious impact. A comparison of reanalysis circulation against two NASA-radiosonde stations confirms that both reanalyses represent

  15. Tracer water transport and subgrid precipitation variation within atmospheric general circulation models

    NASA Technical Reports Server (NTRS)

    Koster, Randal D.; Eagleson, Peter S.; Broecker, Wallace S.

    1988-01-01

    A capability is developed for monitoring tracer water movement in the three-dimensional Goddard Institute for Space Science Atmospheric General Circulation Model (GCM). A typical experiment with the tracer water model follows water evaporating from selected grid squares and determines where this water first returns to the Earth's surface as precipitation or condensate, thereby providing information on the lateral scales of hydrological transport in the GCM. Through a comparison of model results with observations in nature, inferences can be drawn concerning real world water transport. Tests of the tracer water model include a comparison of simulated and observed vertically-integrated vapor flux fields and simulations of atomic tritium transport from the stratosphere to the oceans. The inter-annual variability of the tracer water model results is also examined.

  16. North and equatorial Pacific Ocean circulation in the CORE-II hindcast simulations

    NASA Astrophysics Data System (ADS)

    Tseng, Yu-heng; Lin, Hongyang; Chen, Han-ching; Thompson, Keith; Bentsen, Mats; Böning, Claus W.; Bozec, Alexandra; Cassou, Christophe; Chassignet, Eric; Chow, Chun Hoe; Danabasoglu, Gokhan; Danilov, Sergey; Farneti, Riccardo; Fogli, Pier Giuseppe; Fujii, Yosuke; Griffies, Stephen M.; Ilicak, Mehmet; Jung, Thomas; Masina, Simona; Navarra, Antonio; Patara, Lavinia; Samuels, Bonita L.; Scheinert, Markus; Sidorenko, Dmitry; Sui, Chung-Hsiung; Tsujino, Hiroyuki; Valcke, Sophie; Voldoire, Aurore; Wang, Qiang; Yeager, Steve G.

    2016-08-01

    We evaluate the mean circulation patterns, water mass distributions, and tropical dynamics of the North and Equatorial Pacific Ocean based on a suite of global ocean-sea ice simulations driven by the CORE-II atmospheric forcing from 1963-2007. The first three moments (mean, standard deviation and skewness) of sea surface height and surface temperature variability are assessed against observations. Large discrepancies are found in the variance and skewness of sea surface height and in the skewness of sea surface temperature. Comparing with the observation, most models underestimate the Kuroshio transport in the Asian Marginal seas due to the missing influence of the unresolved western boundary current and meso-scale eddies. In terms of the Mixed Layer Depths (MLDs) in the North Pacific, the two observed maxima associated with Subtropical Mode Water and Central Mode Water formation coalesce into a large pool of deep MLDs in all participating models, but another local maximum associated with the formation of Eastern Subtropical Mode Water can be found in all models with different magnitudes. The main model bias of deep MLDs results from excessive Subtropical Mode Water formation due to inaccurate representation of the Kuroshio separation and of the associated excessively warm and salty Kuroshio water. Further water mass analysis shows that the North Pacific Intermediate Water can penetrate southward in most models, but its distribution greatly varies among models depending not only on grid resolution and vertical coordinate but also on the model dynamics. All simulations show overall similar large scale tropical current system, but with differences in the structures of the Equatorial Undercurrent. We also confirm the key role of the meridional gradient of the wind stress curl in driving the equatorial transport, leading to a generally weak North Equatorial Counter Current in all models due to inaccurate CORE-II equatorial wind fields. Most models show a larger

  17. Circulation Control Model Experimental Database for CFD Validation

    NASA Technical Reports Server (NTRS)

    Paschal, Keith B.; Neuhart, Danny H.; Beeler, George B.; Allan, Brian G.

    2012-01-01

    A 2D circulation control wing was tested in the Basic Aerodynamic Research Tunnel at the NASA Langley Research Center. A traditional circulation control wing employs tangential blowing along the span over a trailing-edge Coanda surface for the purpose of lift augmentation. This model has been tested extensively at the Georgia Tech Research Institute for the purpose of performance documentation at various blowing rates. The current study seeks to expand on the previous work by documenting additional flow-field data needed for validation of computational fluid dynamics. Two jet momentum coefficients were tested during this entry: 0.047 and 0.114. Boundary-layer transition was investigated and turbulent boundary layers were established on both the upper and lower surfaces of the model. Chordwise and spanwise pressure measurements were made, and tunnel sidewall pressure footprints were documented. Laser Doppler Velocimetry measurements were made on both the upper and lower surface of the model at two chordwise locations (x/c = 0.8 and 0.9) to document the state of the boundary layers near the spanwise blowing slot.

  18. Mars Pathfinder meteorological observations on the basis of results of an atmospheric global circulation model

    NASA Technical Reports Server (NTRS)

    Forget, Francois; Hourdin, F.; Talagrand, O.

    1994-01-01

    The Mars Pathfinder Meteorological Package (ASI/MET) will measure the local pressure, temperature, and winds at its future landing site, somewhere between the latitudes 0 deg N and 30 deg N. Comparable measurements have already been obtained at the surface of Mars by the Viking Landers at 22 deg N (VL1) and 48 deg N (VL2), providing much useful information on the martian atmosphere. In particular the pressure measurements contain very instructive information on the global atmospheric circulation. At the Laboratoire de Meteorologie Dynamique (LMD), we have analyzed and simulated these measurements with a martian atmospheric global circulation model (GCM), which was the first to simulate the martian atmospheric circulation over more than 1 year. The model is able to reproduce rather accurately many observed features of the martian atmosphere, including the long- and short-period oscillations of the surface pressure observed by the Viking landers. From a meteorological point of view, we think that a landing site located near or at the equator would be an interesting choice.

  19. Sensitivity of northwestern North Atlantic shelf circulation to surface and boundary forcing: A regional model assessment

    NASA Astrophysics Data System (ADS)

    Brennan, Catherine E.; Bianucci, Laura; Fennel, Katja

    2014-05-01

    The northwestern North Atlantic shelf circulation, influenced by both North Atlantic subpolar and subtropical gyres, is one of the hydrographically most variable regions in the North Atlantic Ocean and hosts biologically rich and productive fishing grounds. With the goal of simulating conditions in this productive and complex region, we implemented a nested regional ocean model for the northwest North Atlantic shelves including the Gulf of Maine, the Scotian Shelf, the Gulf of St. Lawrence, the Grand Banks, and the adjacent deep ocean. Configuring such a model requires choosing external data to supply surface forcing and initial and boundary conditions, as well as the consideration of nesting options. Although these selections can greatly affect model performance and results, often they are not systematically investigated. Here we assessed the sensitivity of our regional model to a suite of atmospheric forcing datasets, to sets of initial and boundary conditions constructed from multiple global ocean models and a larger scale regional ocean model, and to two variants of the model grid - one extending further off-shelf and resolving Flemish Cap topography. We conducted model simulations for a 6-year period and assessed model performance relative to a regional climatological dataset of temperature and salinity, observations collected from multiple monitoring stations and cruise transect lines, satellite sea surface temperature (SST) data, and descriptions of regional currents from literature. Based on this model assessment, we determined the model configuration that best reproduces observations. We find that while all surface forcing datasets are capable of producing model SST close to observed, the different datasets result in significant differences in model sea surface salinity (SSS). We find that initial and boundary conditions based on global ocean models do not necessary produce realistic circulation, and climatological initial and boundary conditions can

  20. THOR-ICO: a General Circulation Model for Exoplanets on an Icosahedral Grid

    NASA Astrophysics Data System (ADS)

    Mendonca, J.; Heng, K.; Grimm, S.

    2014-04-01

    The study of extrasolar planets has become important since the discovery of a large number of these astronomical objects. The diversity of planetary characteristics observed raises questions about the variety of climates. The influence of the astronomical and planetary bulk parameters in driving the atmospheric circulations continues to be poorly understood. In the solar system the results from planetary spacecraft missions have demonstrated how different the planetary climate and atmospheric circulations can be. The study of exoplanets is going to require a study of a far greater range of physical and orbital parameters than the ones that characterise our neighbour planets (in the solar system). For this reason the study of exoplanets will involve an even greater diversity of circulation and climate regimes. We are developing a dedicated General Circulation Model (GCM) for extrasolar planets called "Exoclimes Simulation Platform". This model will solve the complex physical and dynamical equations that include fundamental principles of atmospheric fluid dynamics and various idealisations of, for example, radiative transfer [1] and dry or moist convection. The interpretation and analysis of the results from this complex model will help us to have a better understanding on the diversity of climates and atmospheric circulations. Here we present the first results of our recent scheme which represents the fluid dynamical phenomena in the atmosphere. This new code solves the atmospheric fluid equations in a rotating sphere (fully compressible - elastic - nonhydrostatic system) using an icosahedral grid. The grid is also modified to improve the uniformity of the grid point distribution applying a method called spring dynamics [2]. The results shown include 3D experiments of gravity and acustic waves, Held-Suarez test case [3] and an idealized hot-Jupiter case.

  1. Circulation and effluent dilution modeling in Massachusetts Bay : model implementation, verification and results

    USGS Publications Warehouse

    Signell, Richard P.; Jenter, Harry L.; Blumberg, Alan F.

    1996-01-01

    A three-dimensional hydrodynamic model was developed as part of a cooperative U.S. Geological Survey/Massachusetts Water Resources Authority program to study contaminated sediment accumulation and transport in Massachusetts Bay. This report details the development of the model and assesses how well the model represents observed currents and water properties in the bay. It also summarizes circulation and comparative effluent dilution simulations from existing and future Boston sewage outfalls over a three-year period from October 1, 1989 to December 31, 1992. The ECOM-si model, a semi-implicit version of the Blumberg and Mellor (1987) Estuarine, Coastal and Ocean Model, is shown to reproduce many of the important hydrodynamical features of Massachusetts Bay: the seasonal evolution of the pycnocline, the mean flow pattern, and the strength of sub-tidal current fluctuations. Throughout the simulation period, during both vertically well-mixed and stratified conditions, the seasonal statistics of observed currents are well-represented by the model. The model is therefore appropriate for studying the average dilution of sewage effluent and other continuously discharged substances over seasonal time scales. The ability of the model to reproduce individual flow events varies with season and location within the bay. Flow events during unstratified conditions in western Massachusetts Bay are particularly well-represented, indicating that the model is appropriate for studying processes such as the transport of suspended material from the future outfall site due to winter storms. Individual flow events during stratified conditions and in the offshore Stellwagen Bank region, however, are less well-represented due to small length scales (caused by upwelling and river discharge events) coupled with insufficient data to specify open boundary forcing from the Gulf of Maine. Thus while the model might be used to answer issues such as the frequency with which Gulf of Maine river

  2. Observed and simulated variability of the Atlantic meridional overturning circulation and the deep western boundary current

    NASA Astrophysics Data System (ADS)

    Mielke, Charlotte; Frajka-Williams, Eleanor; Gary, Stefan; Shimizu, Kenji; Toole, John; Baehr, Johanna

    2014-05-01

    Despite the importance of Atlantic meridional overturnig circulation (AMOC) for the climate of Africa, America and Europe, continuous AMOC observations are at present restricted to two latitudes, and are available for less than ten years. We therefore investigate whether the AMOC's variability can be inferred from measurements of the deep western boundary current (DWBC), which are already available at several locations. To that end, we jointly analyze the available 26°N RAPID and the 41°N Argo-based AMOC estimates with RAPID and line W (40°N) DWBC estimates. We also compare them to a 60-year simulation with a high-resolution NCEP-forced ocean model. The DWBC and its layers are defined dynamically in the model based on a comparison of temperature-versus-salinity data in model and observations and the time-dependent velocity field. On the timescales where observations are available, the model is able to reproduce the variability of the DWBC and its individual layers at both locations. Our preliminary analysis of the observational data and model results suggests that different mechanisms dominate the DWBC's variability at different timescales. On sub-seasonal to seasonal timescales, the DWBC is mostly barotropic, and its variability is linked to local processes. Thus, the DWBC has a well-defined seasonal cycle which is opposite to the seasonal cycle of the non-Ekman component of the AMOC seasonal cycle. On interannual timescales, there is no obvious relation between AMOC and DWBC. However, on decadal timescales, our analysis indicates covariability between AMOC and DWBC. We conclude that although caution should be exercised on interannual timescales, the DWBC might be used as a proxy for long-term AMOC trends and possibly modulations of the AMOC's seasonal cycle.

  3. Physically-Derived Dynamical Cores in Atmospheric General Circulation Models

    NASA Technical Reports Server (NTRS)

    Rood, Richard B.; Lin, Shian-Kiann

    1999-01-01

    The algorithm chosen to represent the advection in atmospheric models is often used as the primary attribute to classify the model. Meteorological models are generally classified as spectral or grid point, with the term grid point implying discretization using finite differences. These traditional approaches have a number of shortcomings that render them non-physical. That is, they provide approximate solutions to the conservation equations that do not obey the fundamental laws of physics. The most commonly discussed shortcomings are overshoots and undershoots which manifest themselves most overtly in the constituent continuity equation. For this reason many climate models have special algorithms to model water vapor advection. This talk focuses on the development of an atmospheric general circulation model which uses a consistent physically-based advection algorithm in all aspects of the model formulation. The shallow-water model of Lin and Rood (QJRMS, 1997) is generalized to three dimensions and combined with the physics parameterizations of NCAR's Community Climate Model. The scientific motivation for the development is to increase the integrity of the underlying fluid dynamics so that the physics terms can be more effectively isolated, examined, and improved. The expected benefits of the new model are discussed and results from the initial integrations will be presented.

  4. Physically-Derived Dynamical Cores in Atmospheric General Circulation Models

    NASA Technical Reports Server (NTRS)

    Rood, Richard B.; Lin, Shian-Jiann

    1999-01-01

    The algorithm chosen to represent the advection in atmospheric models is often used as the primary attribute to classify the model. Meteorological models are generally classified as spectral or grid point, with the term grid point implying discretization using finite differences. These traditional approaches have a number of shortcomings that render them non-physical. That is, they provide approximate solutions to the conservation equations that do not obey the fundamental laws of physics. The most commonly discussed shortcomings are overshoots and undershoots which manifest themselves most overtly in the constituent continuity equation. For this reason many climate models have special algorithms to model water vapor advection. This talk focuses on the development of an atmospheric general circulation model which uses a consistent physically-based advection algorithm in all aspects of the model formulation. The shallow-water model is generalized to three dimensions and combined with the physics parameterizations of NCAR's Community Climate Model. The scientific motivation for the development is to increase the integrity of the underlying fluid dynamics so that the physics terms can be more effectively isolated, examined, and improved. The expected benefits of the new model are discussed and results from the initial integrations will be presented.

  5. A Simplified Teaching Model of the Heart and Circulation

    ERIC Educational Resources Information Center

    Rodbard, Simon; And Others

    1976-01-01

    Diagrams and explains the construction of a model for the heart and its valves and function of the atria and ventricles, using the contraction of a student's hand to simulate heart contraction. Approximate cost $125. (CS)

  6. Past Asian Monsoon circulation from multiple tree-ring proxies and models (Invited)

    NASA Astrophysics Data System (ADS)

    Anchukaitis, K. J.; Herzog, M.; Hernandez, M.; Martin-Benito, D.; Gagen, M.; LeGrande, A. N.; Ummenhofer, C.; Buckley, B.; Cook, E. R.

    2013-12-01

    The Asian monsoon can be characterized in terms of precipitation variability as well as features of regional atmospheric circulation across a range of spatial and temporal scales. While multicentury time series of tree-ring widths at hundreds of sites across Asia provide estimates of past rainfall, the oxygen isotope ratios of annual rings at some of these sites can reveal broader regional atmosphere-ocean dynamics. Here we present a replicated, multicentury stable isotope series from Vietnam that integrates the influence of monsoon circulation on water isotopes. Stronger (weaker) monsoon flow over Indochina is associated with lower (higher) oxygen isotope values in our long-lived tropical conifers. Ring width and isotopes show particular coherence at multidecadal time scales, and together allow past precipitation amount and circulation strength to be disentangled. Combining multiple tree-ring proxies with simulations from isotope-enabled and paleoclimate general circulation models allows us to independently assess the mechanisms responsible for proxy formation and to evaluate how monsoon rainfall is influenced by ocean-atmosphere interactions at timescales from interannual to multidecadal.

  7. Seasonal sensitivity of the eddy-driven jet to tropospheric heating in an idealized atmospheric general circulation model

    NASA Astrophysics Data System (ADS)

    McGraw, Marie C.

    A dry dynamical core is used to investigate the seasonal sensitivity of the circulation to two idealized thermal forcings--a tropical upper tropospheric forcing, and a polar lower tropospheric forcing. The circulation is modified using a set of perpetual simulations to simulate each month of the year, while the thermal forcings are held constant. The circu- lation responses to tropical warming and polar warming are studied separately, and then the response to the simultaneously applied forcings is analyzed. Finally, the seasonality of the internal variability of the circulation is explored as a possible mechanism to explain the seasonality of the responses. The primary results of these experiments are: 1) There is a seasonal sensitivity in the circulation response to both the tropical and polar forcings. 2) The jet position response to each forcing is greatest in the transition seasons, and the jet speed response exhibits a seasonal sensitivity to both forcings although the seasonal sensi- tivities are not the same. 3) The circulation response is nonlinear in the transition seasons, but approximately linear in the summer and winter months. 4) The internal variability of the unforced circulation exhibits a seasonal sensitivity that may partly explain the seasonal sensitivity of the forced response. The seasonality of the internal variability of daily MERRA reanalysis data is compared to that of the model, demonstrating that the broad conclusions drawn from this idealized modeling study may be useful for understanding the jet response to anthropogenic forcing.

  8. A Coupled General Circulation Model of the Archean Earth

    NASA Astrophysics Data System (ADS)

    Wolf, E. T.; Toon, O. B.

    2011-12-01

    We present results from a new coupled general circulation model suitable for deep paleoclimate studies. Particular interest is given to the faint young Sun paradox. The model is based on the Community Earth System Model maintained by the National Center for Atmospheric Research [1]. Prognostic atmosphere, ocean, land, ice, and hydrological cycle models are coupled. A new correlated-k radiative transfer model has been implemented allowing accurate flux calculations for anoxic atmospheres containing high concentrations of CO2 and CH4 [2, 3]. This model represents a significant improvement upon one-dimensional radiative-convective climate models used previously to study ancient climate [4]. Cloud and ice albedo feedbacks will be accurately quantified and new constraints on Archean surface temperatures will be revealed. References [1] Collins W.D. et al. "Description of the NCAR Community Atmosphere Model (CAM 3.0)." NCAR Technical Note, 2004. [2] Toon O.B., McKay, C.P., Ackerman, T.P. "Rapid Calculation of Radiative Heating Rates and Photodissociation Rates in Inhomogeneous Multiple Scattering Atmospheres." J. Geo. Res., 94(D13), 16287 - 16301, 1989. [3] Mlawer, E.J., et al. "Radiative transfer for inhomogeneous atmospheres: RRTM, a validated correlated-k model for the longwave." J. Geo. Res., 102(D14), 16663 - 16682, 1997. [4] Kasting J.F., Pollack, J.B., Crisp, D. "Effects of High CO2 Levels on Surface Temperature and Atmospheric Oxidation State of the Early Earth." J. Atm. Chem., 1, 403-428, 1984.

  9. Large-eddy simulations of a turbulent Coanda jet on a circulation control airfoil

    NASA Astrophysics Data System (ADS)

    Nishino, Takafumi; Hahn, Seonghyeon; Shariff, Karim

    2010-12-01

    Large-eddy simulations are performed of a turbulent Coanda jet separating from a rounded trailing edge of a simplified circulation control airfoil model. The freestream Reynolds number based on the airfoil chord is 0.49×106, the jet Reynolds number based on the jet slot height is 4470, and the ratio of the peak jet velocity to the freestream velocity is 3.96. Three different grid resolutions are used to show that their effect is very small on the mean surface pressure distribution, which agrees very well with experiments, as well as on the mean velocity profiles over the Coanda surface. It is observed that the Coanda jet becomes fully turbulent just downstream of the jet exit, accompanied by asymmetric alternating vortex shedding behind a thin (but blunt) jet blade splitting the jet and the external flow. A number of "backward-tilted" hairpin vortices (i.e., the head of each hairpin being located upstream of the legs) are observed around the outer edge of the jet over the Coanda surface. These hairpins create strong upwash between the legs and weak downwash around them, contributing to turbulent mixing of the high-momentum jet below the hairpins and the low-momentum external flow above them. The probability density distribution of velocity fluctuations is shown to be highly asymmetric in this region, consistent with the observation that the hairpin vortices create strong upwash and weak downwash. Turbulent structures inside the jet, its spreading rate, and self-similarity are also discussed.

  10. Numerical simulation on casing modification of a boiler water circulation pump

    NASA Astrophysics Data System (ADS)

    Li, Y. Z.; Fan, Y. Z.; Liu, S. H.; Wu, Y. L.; Zuo, Z. G.

    2012-11-01

    In this paper, hydraulic performance comparisons are made by numerical simulation method on boiler water circulation pump with casings of different shapes. The existing pump adopts a semispherical casing and a garlic-shaped casing. Results show that in the garlic-shaped casing noticeable swirling vortex can be found in the top region of the discharge nozzle, and semispherical casing has better performance in hydraulic efficiency and head.

  11. Validation of winter atmospheric circulation over Europe and the North Atlantic in CMIP5 global circulation model outputs

    NASA Astrophysics Data System (ADS)

    Stryhal, Jan; Huth, Radan

    2016-04-01

    An analysis of winter atmospheric circulation over Europe is carried out based on outputs of historical runs of thirty-two CMIP5 global circulation models (GCMs) (1961-2000). GCMs are validated against five reanalysis datasets, in terms of the frequency and persistence of circulation types (CTs). Previous research has shown that diverse results can be obtained if different classification methods are employed. Therefore, to achieve reliable results, CTs are successively defined by eight methods included in the COST733 software and for four domains (Europe, British Isles, Central Europe, and Eastern Mediterranean). The multi-model ensemble median in most cases shows an overestimation of CTs with (south)western advection over Europe, and over- and underestimation of cyclonic and anticyclonic types, respectively, both in their frequency and spatial extent of the respective pressure systems. The size and significance of these biases are, however, considerably dependent on the chosen classification method, domain, and even the reanalysis dataset.

  12. The GEOS-5 Atmospheric General Circulation Model: Mean Climate and Development from MERRA to Fortuna

    NASA Technical Reports Server (NTRS)

    Molod, Andrea; Takacs, Lawrence; Suarez, Max; Bacmeister, Julio; Song, In-Sun; Eichmann, Andrew

    2012-01-01

    This report is a documentation of the Fortuna version of the GEOS-5 Atmospheric General Circulation Model (AGCM). The GEOS-5 AGCM is currently in use in the NASA Goddard Modeling and Assimilation Office (GMAO) for simulations at a wide range of resolutions, in atmosphere only, coupled ocean-atmosphere, and data assimilation modes. The focus here is on the development subsequent to the version that was used as part of NASA s Modern-Era Retrospective Analysis for Research and Applications (MERRA). We present here the results of a series of 30-year atmosphere-only simulations at different resolutions, with focus on the behavior of the 1-degree resolution simulation. The details of the changes in parameterizations subsequent to the MERRA model version are outlined, and results of a series of 30-year, atmosphere-only climate simulations at 2-degree resolution are shown to demonstrate changes in simulated climate associated with specific changes in parameterizations. The GEOS-5 AGCM presented here is the model used for the GMAO s atmosphere-only and coupled CMIP-5 simulations.

  13. A hierarchy of thermohaline circulation models. Final report

    SciTech Connect

    Cessi, P.; Young, W.R.

    1998-04-01

    The objectives of this effort were: (1) to understand the variability caused by the competitive roles of salt and heat in the ocean circulation; (2) to understand the effect of differential advection of active tracers, such as temperature, salinity and angular momentum; and (3) to improve the parametrization of convection in models of the ocean circulation. One result of the project is the discovery that the characteristics of the quasi-periodic centennial and millennial oscillations found in OGCM`s, associated with alternating suppression and activation of high latitude convection, are extremely sensitive to the salinity flux and specific choice of convective adjustment scheme. In particular, the period of the oscillation depends crucially on the salinity fluxes (whether deterministic or with a stochastic component) and can be arbitrarily long. This result has clarified that these long-period oscillations (termed flushes) are not the result of the excitation of an intrinsic linear eigenmode of the system, but rather are relaxation-oscillations towards one of the several equilibria available to the system. This implies that it is the amplitude, rather than the period, of the oscillation which is almost independent of the salinity flux.

  14. 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.

  15. Links between circulation indices and precipitation in the Mediterranean in an ensemble of regional climate models

    NASA Astrophysics Data System (ADS)

    Beranová, Romana; Kyselý, Jan

    2016-02-01

    Spatial and temporal variability of precipitation in the Mediterranean is related to atmospheric circulation patterns such as the North Atlantic Oscillation (NAO), the Mediterranean Oscillation (MO) and the Western Mediterranean Oscillation (WeMO). This study examines ability of an ensemble of 12 regional climate model (RCM) simulations to reproduce observed links between these circulation indices and precipitation, as well as how these links may change in the late twenty-first century. We focus on the winter season and differences in precipitation amounts on the highest and lowest 25 % of days according to a given index. The relationships are evaluated against the E-OBS data set for 1961-1990. The observed pattern of differences in precipitation between positive and negative phases is generally similar for MO and NAO, which relates to the high correlation between these indices. Most regional climate models (RCMs) simulate links between the circulation indices and precipitation over most of the Mediterranean area reasonably well, especially for the MO and WeMO indices. The RCM with the largest deficiencies in reproducing the links is HadRM for all indices. The spatial patterns of differences in daily precipitation under positive and negative phases of the circulation indices for the future scenario (2070-2099) are similar to those for the control climate for all indices. This suggests that NAO, MO and WeMO are likely to play similar roles in affecting precipitation in the Mediterranean also in the future. However, increased NAO and decreased WeMO index, projected in most examined RCMs for the late twenty-first century in winter, may affect overall precipitation patterns.

  16. The NASA/Ames Mars General Circulation Model: Model Improvements and Comparison with Observations

    NASA Technical Reports Server (NTRS)

    Haberle, R. M.; Hollingsworth, J. L.; Colaprete, A.; Bridger, A. F. C.; McKay, C. P.; Murphy, J. R.; Schaeffer, J.; Freedman, R.; Fonda, Mark (Technical Monitor)

    2003-01-01

    For many years, the NASA/Ames Mars General Circulation Model (GCM) has been built around the UCLA B-grid dynamical core. An attached tracer transport scheme based on the aerosol microphysical model of Toon et al. (1988) provided a tool for studying dust storm transport and feedbacks (Murphy et al., 1995). While we still use a B-grid version of the model, the Ames group is now transitioning to the ARIES/GEOS Goddard C-grid dynamical core (Suarez and Takacs, 1995). The C-grid produces smoother fields when the model top is raised above 50 km, and has a built in transport scheme for an arbitrary number of tracers. All of our transport simulations are now carried out with the C-grid. We have also been updating our physics package. Several years ago we replaced our bulk boundary layer scheme with a level 2 type diffusive scheme, and added a multi-level soil model (Haberle et al., 2000). More recently we replaced our radiation code with a more generalized two-stream code that accounts for aerosol multiple scattering and gaseous absorption. This code gives us much more flexibility in choosing aerosol optical properties and radiatively active gases.

  17. Impacts of soil moisture content on simulated mesoscale circulations during the summer over eastern Spain

    NASA Astrophysics Data System (ADS)

    Gómez, I.; Caselles, V.; Estrela, M. J.

    2015-10-01

    The Regional Atmospheric Modeling System (RAMS) version 6.0 has been used to investigate the impact and influence of initial soil moisture distributions on mesoscale circulations. To do this, two different events have been selected from the 2011 summer season: one at the beginning of the season (June) and the other one at the end of the season (August). For each of these mesoscale frameworks a total of five distinct simulations were performed varying the initial soil moisture content: a control run and four additional sensitivity tests. The control run, corresponding to a low soil moisture content, is the one used within the real-time weather forecasting system implemented in the Valencia Region. In the corresponding sensitivity simulations this low value has been progressively increased in different steps until the original soil moisture content doubled. It has been found that high soil moisture is associated with colder near-surface temperature, a moister relative humidity and a slightly lower near-surface wind speed, whereas a drier soil resulted in a dryer relative humidity, warmer temperature and a slight low-level wind. In general, the highest soil moisture contents are required to reproduce the near-surface daily cycles of temperature and relative humidity through higher values of latent heat flux and lower values of sensible heat flux. In this regard, moistening the soil improves the previous results obtained using the RAMS configuration used within the operational forecasting system. However, the wind speed is not quite sensitive to changes in the soil moisture content over flatter terrain. Finally, although a warming and dryer mixing layer is obtained with the lowest soil moisture content, the mixing layer height remains practically unchanged when using the distinct configurations over flat terrain. These differences are enhanced over more complex terrain.

  18. 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

  19. a General Circulation Model Investigation of the Atmospheric Response to EL Nino

    NASA Astrophysics Data System (ADS)

    de Aragao, Jose Oribe Rocha

    The observed atmospheric response to sea surface temperature (SST) anomalies associated with El Nino episodes is simulated with the use of a general circulation model (GCM) of the atmosphere. A series of experiments has been performed with the Rasmusson and Carpenter six-episode (El Nino) composite SST anomaly (SSTA) in the tropical Pacific superimposed upon the prescribed climatological SST (CSST). Five independent 400-day runs were made beginning in April of the El Nino year (Year 0) and ending in May of the year after the maximum SSTA in the tropical Pacific (Year +1). Each of the integrations started from different initial conditions selected from different years in a 20 -year control run. The five-year El Nino integration was compared with the control run by analyzing the ensemble monthly, seasonal and annual mean statistics. The model's tropical response resembles the anomalous features found in previous studies. Some features are expected from the constraint imposed by the vorticity balance in the linear theory. For example, the upper level anticyclone pair and the lower level cyclonic circulation centers in the central Pacific are present for almost all months. These responses are significant and seem to be related to the location of both the maximum in CSST and the maximum in SSTA. An anomalous Walker Circulation is found in the vertical plane along the equatorial region. Rainfall departures from the long-term mean are associated with the anomalous Walker Circulation. An analysis of rainfall data over Northeast Brazil reveals sup- pressed rainfall in this area during the rainy season of Year(+1). Significant lower-than-normal rainfall is also found in the model's response during that period. This reduction in precipitation is associated with the downward branch of the anomalous Walker Circulation. The model's extratropical response is weaker than the tropical response and is not well organized. A Pacific/North American (PNA) pattern is present during the

  20. Developing emulators of a general circulation model for applications in Earth system modelling

    NASA Astrophysics Data System (ADS)

    Tran, Giang; Oliver, Kevin; Sobester, Andras; Toal, David; Holden, Philip; Marsh, Robert; Challenor, Peter; Edwards, Neil

    2015-04-01

    To study climate change on multi-millennial timescales, efficient models with simplified and parameterized processes are required. This is particularly important if observations are to be used effectively constrain models, an endeavour which demands large numbers of simulations. Unfortunately, the reduction in explicitly modelled processes can lead to underestimation of responses in the system that are essential to the understanding of palaeoclimate. To address this, we intend to replace a simple component of an efficient model with a statistical model (an emulator) of a more comprehensive one. Efficient construction of such an emulator is achieved by exploiting the relationship among different levels of the climate model hierarchy. Using a multi-level emulation technique, outputs from an atmospheric general circulation model (GCM), called PLASIM, are efficiently emulated by utilising the extra information gained from the computationally cheap atmosphere of an efficient model called GENIE-1. Even though the two atmospheric models chosen have large structural differences, useful links between them are identified and Gaussian process emulators of PLASIM 2-D surface air temperature and precipitation fields are successfully constructed. The result shows that the multi-level emulators of PLASIM's output fields can be built using only one third the amount of expensive data required by the normal single-level technique. The constructed emulators are shown to capture 95.4% and 80.3% of the variance in surface air temperature and precipitation, respectively, across a validation ensemble. GCM emulators constructed using the proposed method can potentially replace the current simple component of the efficient model, resulting in a higher fidelity version of the model without a significant increase in computational cost.

  1. The January and July performance of the OSU two-level atmospheric general circulation model

    NASA Technical Reports Server (NTRS)

    Schlesinger, M. E.; Gates, W. L.

    1980-01-01

    A modified version of the two-level atmospheric general circulation model has been developed and employed in the simulation of January and July global climates. The overall physical and numerical formation of the Oregon State University model is the same as that described by Gates and Schlesinger (1977), but in the new version water vapor at the upper level has been made a prognostic variable, the parameterizations of cumulus convection, large-scale condensation and evaporation, clouds, and radiative transfer have been changed, the surface snow mass and ground temperature have been made prognostic variables, and the treatment of the surface boundary layer has been revised. It is found that the model simulates most features of the large-scale distributions of observed January and July climate more accurately than before.

  2. Systematic large-scale secondary circulations in a regional climate model

    NASA Astrophysics Data System (ADS)

    Becker, Nico; Ulbrich, Uwe; Klein, Rupert

    2015-05-01

    Regional climate models (RCMs) are used to add the effects of nonresolved scales to coarser resolved model simulations by using a finer grid within a limited domain. We identify large-scale secondary circulations (SCs) relative to the driving global climate model (GCM) in an RCM simulation over Europe. By applying a clustering technique, we find that the SC depends on the large-scale flow prescribed by the driving GCM data. Evidence is presented that the SC is caused by the different representations of orographic effects in the RCM and the GCM. Flow modifications in the RCM caused by the Alps lead to large-scale vortices in the SC fields. These vortices are limited by the RCM boundaries, causing artificial boundary-parallel flows. The SC is associated with geopotential height and temperature anomalies between RCM and GCM and has the potential to produce systematic large-scale biases in RCMs.

  3. Stochastic resonance on a global atmospheric circulation model

    NASA Astrophysics Data System (ADS)

    Perez-Munuzuri, V.; Deza, R.; Fraedrich, K.; Kirk, E.; Lunkeit, F.

    2003-04-01

    Seeking for alternative sources of the observed climatic variability, and in the spirit of both classic (Nicolis, 1982; Benzi et al., 1982) and recent work (Ganopolski and Rahmstorg, 2002; Vélez-Belch&{acute;i} et al., 2001), we have added a space-independent, Gaussian and uncorrelated stochastic perturbation with amplitude eta, to the temperature equation of a simplified atmospheric global circulation model, the so-called PUMA (Portable University Model of the Atmosphere) (Frisius et al., 1998; Pérez-Muñuzuri et al., 2003). In the latter model, diabatic processes are parameterized by a Newtonian cooling term with typical timescale τ_c, whose reference temperature profile T_R(λ,μ,σ;t) (representing the ``equilibrium'' profile induced by solar heating) is given by T_R=overline{T}_R(λ,μ,σ)+ hat{T}_R \\cos[(2pi/Tac)t+Pac]. We show that the time averages of several forecasting magnitudes (like temperature and horizontal vorticity) at a point on the 300 hPa surface, undergo a non-monotonic behavior with regard to eta. Moreover, the normalized variance R=sqrt{-^2}/ of the interval t_p between the passage at the point of cyclonic and anticyclonic circulation regions exhibits an ``anticoherence resonance'' effect, thus maximizing climatic variability for some intermediate value of eta. A theoretical explanation is advanced in terms of activated processes with competing time scales. begin{itemize} C. Nicolis, Tellus 34, 1 (1982); Benzi et al., Tellus 34, 10 (1982). A. Ganopolski and S. Rahmstorg, Phys. Rev. Lett. 88, 038501 (2002); P. Vélez-Belch&{acute;i} et al., Geophys. Res. Lett. 28, 2053 (2001). T. Frisius, F. Lunkeit, K. Fraedrich and I.N. James. Q.J.R. Meteorol. Soc. 124, 1019 (1998); V. Pérez-Muñuzuri et al. Nonlin. Proc. Geophys. (submitted) (2003).

  4. Stationary eddies in the Mars general circulation as simulated by the NASA-Ames GCM

    NASA Technical Reports Server (NTRS)

    Barnes, J. R.; Pollack, J. B.; Haberle, Robert M.

    1993-01-01

    Quasistationary eddies are prominent in a large set of simulations of the Mars general circulation performed with the NASA-Ames GCM. Various spacecraft observations have at least hinted at the existence of such eddies in the Mars atmosphere. The GCM stationary eddies appear to be forced primarily by the large Mars topography, and (to a much lesser degree) by spatial variations in the surface albedo and thermal inertia. The stationary eddy circulations exhibit largest amplitudes at high altitudes (above 30-40 km) in the winter extratropical regions. In these regions they are of planetary scale, characterized largely by zonal wavenumbers 1 and 2. Southern Hemisphere winter appears to be dominated by a very strong wave 1 pattern, with both waves 1 and 2 being prominent in the Northern Hemisphere winter regime. This difference seems to be basically understandable in terms of differences in the topography in the two hemispheres. The stationary eddies in the northern winter extratropics are found to increase in amplitude with dust loading. This behavior appears to be at least partly associated with changes in the structure of the zonal-mean flow that favor a greater response to wave 1 topographic forcing. There are also strong stationary eddy circulations in the tropics and in the summer hemisphere. The eddies in the summer subtropics and extratropics arc substantially stronger in southern summer than in northern summer. The summer hemisphere stationary circulations are relatively shallow and are characterized by smaller zonal scales than those in the winter extratropics.

  5. A general circulation model study of atmospheric carbon monoxide

    NASA Technical Reports Server (NTRS)

    Pinto, J. P.; Rind, D.; Russell, G. L.; Lerner, J. A.; Hansen, J. E.; Yung, Y. L.; Hameed, S.

    1983-01-01

    The carbon monoxide cycle is studied by incorporating the known and hypothetical sources and sinks in a tracer model that uses the winds generated by a general circulation model. Photochemical production and loss terms, which depend on OH radical concentrations, are calculated in an interactive fashion. The computed global distribution and seasonal variations of CO are compared with observations to obtain constraints on the distribution and magnitude of the sources and sinks of CO, and on the tropospheric abundance of OH. The simplest model that accounts for available observations requires a low latitude plant source of about 1.3 x 10 to the 15th g/yr, in addition to sources from incomplete combustion of fossil fuels and oxidation of methane. The globally averaged OH concentration calculated in the model is 750,000/cu cm. Models that calculate globally averaged OH concentrations much lower than this nominal value are not consistent with the observed variability of CO. Such models are also inconsistent with measurements of CO isotopic abundances, which imply the existence of plant sources.

  6. GCM (general circulation model)-data intercomparison: The good news and the bad

    SciTech Connect

    Grotch, S.L.

    1990-09-01

    General circulation models (GCMs) are being actively used to assess possible climate change due to increasing greenhouse gas concentrations. Because such simulations provide detailed climatic predictions at a wide range of scales, they are of particular interest to those making regional assessments of climatic change. It is especially important that workers using the results of such simulations be aware of some of the limitations of these results. In this study some of the positive results from these model simulations will be shown and some of the deficiencies will also be highlighted. Following an introductory section describing the nature of GCM climate simulations the issue of the spatial scales of such simulations is examined. A comparison of the results of seven GCM simulations of the current climate and the predictions of these models for the changes due to a doubling of CO{sub 2} will be discussed. In these intercomparisons, the spatial scale over which the results are compared varies from global to zonal (longitudinally averaged at a given latitude) to individual slices through the data along specified latitudes or longitudes. Finally, the dangers and pitfalls of relying on simple averages will be highlighted. 19 refs., 9 figs., 1 tab.

  7. Modelling study of three-dimensional circulation and particle movement over the Sable Gully of Nova Scotia

    NASA Astrophysics Data System (ADS)

    Shan, Shiliang; Sheng, Jinyu; Greenan, Blair John William

    2014-01-01

    The Sable Gully is a broad deep underwater canyon located to the east of Sable Island on the edge of the Scotian Shelf. Being the home of many marine species including the endangered Northern Bottlenose Whale, the Gully was designated as a marine protected area (MPA) in 2004. Better understanding of physical environmental conditions over this MPA is needed for sustainable ecosystem management. In this study, a multi-nested ocean circulation model and a particle tracking model are used to examine the three-dimensional (3D) circulation and movement of particles carried passively by the flow over the Sable Gully. The 3D circulation model is driven by tides, wind, and surface heat/freshwater fluxes. The model performance is assessed by comparing the results with the previous numerical tidal results and current meter observations made in the Gully. The simulated tidal circulation over the Gully and adjacent waters is relatively strong on shallow banks and relatively weak on the continental slope. Below the depth of the Gully rim ( ˜ 200 m), the tidal currents are constrained by the thalweg of the Gully and amplified toward the Gully head. The simulated subtidal circulation in the Gully has a complex spatial structure and significant seasonal variability. The simulated time-dependent 3D flow fields are then used in a particle tracking model to study the particle movements, downstream and upstream areas, and residence time of the Gully. Based on the movements of particles released at the depth of the Gully rim and tracked forward in time, the e-folding residence time is estimated to be about 7 and 13 days in February and August 2006, respectively. The Gully flanks are identified as high retention areas with the typical residence time of 10 and 20 days in February and August 2006, respectively. Tracking particles with and without tides reveals that tidal circulation reduces the value of residence time in the Gully, particularly along the Gully flanks.

  8. The NASA/GISS Mars general circulation model: Preliminary experiments

    NASA Technical Reports Server (NTRS)

    Allison, Michael; Chandler, M. A.; Delgenio, A. D.; Lacis, A.; Rind, D.; Rossow, W. B.; Travis, L. D.; Zhou, W.

    1993-01-01

    The NASA/GISS Mars General Circulation Model (GCM) is an adapted version of the GISS Global Climate/Middle Atmosphere Model, specifically developed for the diagnostic validation and objective analysis of measured atmospheric temperatures from the Mars Observer Pressure Modulator Infrared Radiometer (PMIRR) experiment. The GISS Mars GCM has 23 vertical layers extending from the surface to approximately 80 km altitude, representing a vertical resolution of about 0.3 scale heights. The primitive (vertically hydrostatic) equations are solved in finite difference form on the Krakawa B grid, with a horizontal resolution of 8 deg x 10 deg (latitude-longitude). The model includes a diurnal solar cycle, heat transport within a two-layer ground, and a high-order 'slopes-scheme' for the advection of heat in the upper atmosphere. The radiative transfer scheme is based on the correlated k distribution method for the treatment of nongray gaseous absorption thermal emission, and multiple scattering, including options for suspended dust. A special feature of the model of particular importance for Mars is a parameterization of gravity-wave-induced drag incorporating orographic forcing, wind shear, convection, and radiative damping. The implementation of the GISS Mars model includes global maps of topography, roughness, and albedo.

  9. Application of thermospheric general circulation models for space weather operations

    NASA Astrophysics Data System (ADS)

    Fuller-Rowell, T.; Minter, C.; Codrescu, M.

    Solar irradiance is the dominant source of heat, ionization, and dissociation of the thermosphere, and to a large extent drives the global dynamics, and controls the neutral composition and density structure. Neutral composition is important for space weather applications because of its impact on ionospheric loss rates, and neutral density is critical for satellite drag prediction. The future for thermospheric general circulation models for space weather operations lies in their use as state propagators in data assimilation techniques. The physical models can match empirical models in accuracy provided accurate drivers are available, but their true value comes when combined with data in an optimal way. Two such applications have recently been developed. The first utilizes a Kalman filter to combine space-based observation of airglow with physical model predictions to produce global maps of neutral composition. The output of the filter will be used within the GAIM (Global Assimilation of Ionospheric Measurement) model developed under a parallel effort. The second filter uses satellite tracking and remote sensing data for specification of neutral density. Both applications rely on accurate estimates of the solar EUV and magnetospheric drivers.

  10. 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.

  11. Physical mechanisms controlling the initiation of convective self-aggregation in a General Circulation Model

    NASA Astrophysics Data System (ADS)

    Coppin, David; Bony, Sandrine

    2015-12-01

    Cloud-resolving models have shown that under certain conditions, the Radiative-Convective Equilibrium (RCE) could become unstable and lead to the spontaneous organization of the atmosphere into dry and wet areas, and the aggregation of convection. In this study, we show that this "self-aggregation" behavior also occurs in nonrotating RCE simulations performed with the IPSL-CM5A-LR General Circulation Model (GCM), and that it exhibits a strong dependence on sea surface temperature (SST). We investigate the physical mechanisms that control the initiation of self-aggregation in this model, and their dependence on temperature. At low SSTs, the onset of self-aggregation is primarily controlled by the coupling between low-cloud radiative effects and shallow circulations and the formation of "radiatively driven cold pools" in areas devoid of deep convection, while at high SSTs it is primarily controlled by the coupling between surface fluxes and circulation within convective areas. At intermediate temperatures, the occurrence of self-aggregation is less spontaneous and depends on initial conditions, but it can arise through a combination of both mechanisms. Through their coupling to circulation and surface fluxes, the radiative effects of low-level clouds play a critical role in both initiation mechanisms, and the sensitivity of boundary layer clouds to surface temperature explains to a large extent the temperature dependence of convective self-aggregation. At any SST, the presence of cloud-radiative effects in the free troposphere is necessary to the initiation, growth, and maintenance of convective aggregation.

  12. THOR-ISO: a Global Circulation Model for Exoplanets on an Icosahedral Grid

    NASA Astrophysics Data System (ADS)

    Mendonca, J.; Grimm, S.; Heng, K.

    2015-10-01

    In this presentation I will describe the details and first results of our new dynamical code for exoplanet atmospheres. This model is part of the Exoclimes Simulation Platform (ESP), and is a project of the Exoplanet and Exoclimes Group (see www.exoclime.org). The model I will present solves the complex physical and dynamical equations that include fundamental principles of atmospheric fluid dynamics and various idealisations of radiative transfer and dry convection, among others. I will also show the results of the first successful benchmark tests for this model, where we explore the results of the model for Earth-like and Hot-Jupiter like conditions. The analysis of the results from this complex and detailed model, will help us to have a better understanding of the diversity of climates and atmospheric circulations that we expect to find in the multitude of exoplanets already discovered.

  13. Modeling of M2 Tidal Circulation in Kyounggi Bay, Korea

    NASA Astrophysics Data System (ADS)

    Park, S.; Park, Y.; Kim, Y.; Jung, K.; Woo, S.

    2008-12-01

    Kyounggi Bay located along the western coast of Korea is a macrotidal zone of 7.9 m tidal range during the spring tide and tidal flats very well developed. Within the bay there are several islands, and the coast lines are crooked significantly so that the geometry of the bay is very complex. To study the tidal circulation of this area, we conducted numerical modeling using a finite volume coastal ocean model, FVCOM, which could represent the complex topography properly. The model domain is about 40 km × 53 km, and the smallest grid is about 72 m. Therefore, the narrowest waterway, Yeomha, is well resolved. Only M2 tidal forcing is considered at the open boundary. There are three rivers in the bay and experiments were conducted with or without the fresh water discharge from the three rivers. Some of the previous modeling studies showed that the fresh water discharge could reverse the direction of the residual flows in Yeomha Waterways, but in the present experiment the river discharge could not reverse the residual flow. Other aspects of the tidal flow in this area were examined.

  14. Non-condensable gas in a Mars General Circulation Model

    NASA Astrophysics Data System (ADS)

    Guo, X.; Richardson, M. I.; Newman, C.; Sprague, A. L.; Boynton, W. V.

    2007-12-01

    We model the variation of non-condensable trace gases that results from the seasonal cycle of CO2 on Mars. A simple condensation scheme has been incorporated into MarsWRF, a 3-dimensional numerical model for the atmospheres of Mars. Non-condensable trace gas (mostly N2 and Ar) mass mixing ratios are affected by the phase change of CO2 and by transport. The distribution of Ar abundance has been observed by the Gamma Ray Spectrometer on the Mars 2001 Odyssey spacecraft. We are able to qualitatively reproduce the Ar observations, including the seasonal evolving latitudinal distribution. However, the modeled magnitudes of maximum enrichment are lower than observed. Smoothing Ar enrichment in the vertical reduces susceptibility to transport by near-surface, off-cap circulation, therefore gives further enhancement of non-condensable tracer in the winter pole. We suggest that a missing process in the model may account for the underestimation. An extra buoyancy term in the dynamics should result from the vertical gradient in mean molecular mass as Ar mass mixing ratio increases.

  15. Short ensembles: an efficient method for discerning climate-relevant sensitivities in atmospheric general circulation models

    NASA Astrophysics Data System (ADS)

    Wan, H.; Rasch, P. J.; Zhang, K.; Qian, Y.; Yan, H.; Zhao, C.

    2014-09-01

    This paper explores the feasibility of an experimentation strategy for investigating sensitivities in fast components of atmospheric general circulation models. The basic idea is to replace the traditional serial-in-time long-term climate integrations by representative ensembles of shorter simulations. The key advantage of the proposed method lies in its efficiency: since fewer days of simulation are needed, the computational cost is less, and because individual realizations are independent and can be integrated simultaneously, the new dimension of parallelism can dramatically reduce the turnaround time in benchmark tests, sensitivities studies, and model tuning exercises. The strategy is not appropriate for exploring sensitivity of all model features, but it is very effective in many situations. Two examples are presented using the Community Atmosphere Model, version 5. In the first example, the method is used to characterize sensitivities of the simulated clouds to time-step length. Results show that 3-day ensembles of 20 to 50 members are sufficient to reproduce the main signals revealed by traditional 5-year simulations. A nudging technique is applied to an additional set of simulations to help understand the contribution of physics-dynamics interaction to the detected time-step sensitivity. In the second example, multiple empirical parameters related to cloud microphysics and aerosol life cycle are perturbed simultaneously in order to find out which parameters have the largest impact on the simulated global mean top-of-atmosphere radiation balance. It turns out that 12-member ensembles of 10-day simulations are able to reveal the same sensitivities as seen in 4-year simulations performed in a previous study. In both cases, the ensemble method reduces the total computational time by a factor of about 15, and the turnaround time by a factor of several hundred. The efficiency of the method makes it particularly useful for the development of high

  16. Gyrokinetic particle simulation model

    SciTech Connect

    Lee, W.W.

    1986-07-01

    A new type of particle simulation model based on the gyrophase-averaged Vlasov and Poisson equations is presented. The reduced system, in which particle gyrations are removed from the equations of motion while the finite Larmor radius effects are still preserved, is most suitable for studying low frequency microinstabilities in magnetized plasmas. It is feasible to simulate an elongated system (L/sub parallel/ >> L/sub perpendicular/) with a three-dimensional grid using the present model without resorting to the usual mode expansion technique, since there is essentially no restriction on the size of ..delta..x/sub parallel/ in a gyrokinetic plasma. The new approach also enables us to further separate the time and spatial scales of the simulation from those associated with global transport through the use of multiple spatial scale expansion. Thus, the model can be a very efficient tool for studying anomalous transport problems related to steady-state drift-wave turbulence in magnetic confinement devices. It can also be applied to other areas of plasma physics.

  17. Overly persistent circulation in climate models contributes to overestimated frequency and duration of heat waves and cold spells

    NASA Astrophysics Data System (ADS)

    Plavcova, Eva; Kysely, Jan

    2016-04-01

    The study examines links of summer heat waves and winter cold spells in Central Europe to atmospheric circulation and specifically its persistence in an ensemble of regional climate models (RCMs). We analyse 13 RCMs driven by the ERA-40 reanalysis and compare them against observations over 1971-2000. Using objective classification of circulation types and an efficiency coefficient with a block resampling test, we identify circulation types significantly conducive to heat waves and cold spells. We show that the RCMs have a stronger tendency to group together days with very high or low temperature and tend to simulate too many heat waves and cold spells, especially those lasting 5 days and more. Circulation types conducive to heat waves in summer are characterized by anticyclonic, southerly and easterly flow, with increasing importance of warm advection during heat waves. Winter cold spells are typically associated with easterly and anticyclonic flow, and the onset of cold spells tends to be linked to northerly and cyclonic flow with cold advection. The RCMs are generally able to reproduce the links between circulation and heat waves or cold spells, including the radiation-to-advection effect for heat waves and the opposite advection-to-radiation effect for cold spells. They capture relatively well also changes of mean temperature anomalies during sequences of given circulation types, namely the tendency towards an increase (decrease) of temperature during the types conducive to heat waves (cold spells). Since mean lengths of all circulation supertypes are overestimated in the RCMs, we conclude that the overly persistent circulation in climate models contributes to the overestimated frequency of long heat waves and cold spells. As these biases are rather general among the examined RCMs and similar drawbacks are likely to be manifested in climate model simulations for the 21st century, the results also suggest that climate change scenarios for spells of days with high

  18. Modeling studies of the coastal circulation off northern California: Statistics and patterns of wintertime flow

    NASA Astrophysics Data System (ADS)

    Pullen, Julie; Allen, J. S.

    2001-11-01

    We conduct modeling studies of the coastal circulation off northern California in the vicinity of the Eel River (40.6°N, the site of the 1995-2000 Strata Formation on Margins (STRATAFORM) marine geology observational program) using a series of nested hydrostatic primitive equation models to aid in the understanding of the shelf flow field that receives and transports sediments during the winter floods. The basic objectives of our numerical studies are to model the continental shelf and slope flow and to understand the dominant dynamical processes. We simulate the shelf and slope flow surrounding Cape Mendocino during 100 days in winter 1996-1997 using a 3 km resolution model embedded in a 9 km resolution regional model of the North Pacific Ocean (the Naval Research Laboratory's Pacific West Coast (PWC) model). The validity of the model simulations is assessed by comparison with current measurements from a STRATAFORM shelf tripod outfitted with an acoustic Doppler current profiler and with satellite altimetry. Good agreement is found between the amplitude and time variability of the 3 km resolution modeled and observed alongshore currents on the shelf. The 3 km resolution model outperforms the 9 km resolution PWC model. Using statistical maps of flow variables, strong alongshore variability in wintertime flow is documented. The role of the forcing supplied by wind and river runoff in establishing this flow asymmetry between regions north and south of Cape Mendocino is examined using empirical orthogonal functions. The evolution of a robust anticyclonic eddy over the shelf and slope adjacent to Cape Mendocino is described. The eddy forms when strong poleward winds weaken and reverse direction during winter storms. The important role of alongshore pressure gradients in the shelf circulation is documented.

  19. Improved short-term variability in the thermosphere-ionosphere-mesosphere-electrodynamics general circulation model

    NASA Astrophysics Data System (ADS)

    Häusler, K.; Hagan, M. E.; Baumgaertner, A. J. G.; Maute, A.; Lu, G.; Doornbos, E.; Bruinsma, S.; Forbes, J. M.; Gasperini, F.

    2014-08-01

    We report on a new source of tidal variability in the National Center for Atmospheric Research thermosphere-ionosphere-mesosphere-electrodynamics general circulation model (TIME-GCM). Lower boundary forcing of the TIME-GCM for a simulation of November-December 2009 based on 3-hourly Modern-Era Retrospective Analysis for Research and Application (MERRA) reanalysis data includes day-to-day variations in both diurnal and semidiurnal tides of tropospheric origin. Comparison with TIME-GCM results from a heretofore standard simulation that includes climatological tropospheric tides from the global-scale wave model reveal evidence of the impacts of MERRA forcing throughout the model domain, including measurable tidal variability in the TIME-GCM upper thermosphere. Additional comparisons with measurements made by the Gravity field and steady-state Ocean Circulation Explorer satellite show improved TIME-GCM capability to capture day-to-day variations in thermospheric density for the November-December 2009 period with the new MERRA lower boundary forcing.

  20. 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

  1. Evaluation of a stratiform cloud parameterization for general circulation models

    SciTech Connect

    Ghan, S.J.; Leung, L.R.; McCaa, J.

    1996-04-01

    To evaluate the relative importance of horizontal advection of cloud versus cloud formation within the grid cell of a single column model (SCM), we have performed a series of simulations with our SCM driven by a fixed vertical velocity and various rates of horizontal advection.

  2. 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.

  3. The global geochemistry of bomb-produced tritium - General circulation model compared to available observations and traditional interpretations

    NASA Technical Reports Server (NTRS)

    Koster, Randal D.; Broecker, Wallace S.; Jouzel, Jean; Suozzo, Robert J.; Russell, Gary L.; Rind, David

    1989-01-01

    Observational evidence suggests that of the tritium produced during nuclear bomb tests that has already reached the ocean, more than twice as much arrived through vapor impact as through precipitation. In the present study, the Goddard Institute for Space Studies 8 x 10 deg atmospheric general circulation model is used to simulate tritium transport from the upper atmosphere to the ocean. The simulation indicates that tritium delivery to the ocean via vapor impact is about equal to that via precipitation. The model result is relatively insensitive to several imposed changes in tritium source location, in model parameterizations, and in model resolution. Possible reasons for the discrepancy are explored.

  4. Estimation of freshwater runoff into Glacier Bay, Alaska and incorporation into a tidal circulation model

    NASA Astrophysics Data System (ADS)

    Hill, D. F.; Ciavola, S. J.; Etherington, L.; Klaar, M. J.

    2009-03-01

    Freshwater discharge is one of the most critical parameters driving water properties within fjord estuarine environments. To date, however, little attention has been paid to the issue of freshwater runoff into Glacier Bay, a recently deglaciated fjord in southeastern Alaska. Estimates of discharge into Glacier Bay and the outlying waters of Icy Strait and Cross Sound are therefore presented. Existing regression equations for southcentral and southeastern coastal Alaska are applied to Glacier Bay to arrive at the estimates. A limited set of acoustic Doppler current profiler (ADCP) measurements generally support the predictions of the regression equations. The results suggest that discharge into the bay ranges from a few hundred to a few thousand m 3 s -1 during a typical year. Peak discharges can be much higher, approximately 10,000 m 3 s -1 for the 10-year flow event. Estimates of the seasonal variation of discharge are also obtained and reveal a broad peak during the summer months. The hydrologic estimates are then coupled with a barotropic tidal circulation model (ADCIRC - ADvanced CIRCulation model) of Glacier Bay waters. This coupling is achieved by treating the entire coastline boundary as a non-zero normal-flux boundary. Numerical simulations with the inclusion of runoff allow for the estimation of parameters such as the estuarine Richardson number, which is an indicator of estuary mixing. Simulations also allow for the comparison of Lagrangian trajectories in the presence and absence of runoff. The results of the present paper are intended to complement a comprehensive and recently-published dataset on the oceanographic conditions of Glacier Bay. The results will also guide continuing efforts to model three-dimensional circulations in the bay.

  5. 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.

  6. Evaluation of clouds and radiative fluxes in the EC-Earth general circulation model

    NASA Astrophysics Data System (ADS)

    Lacagnina, Carlo; Selten, Frank

    2014-11-01

    Observations, mostly from the International Satellite Cloud Climatology (ISCCP), are used to assess clouds and radiative fluxes in the EC-Earth general circulation model, when forced by prescribed observed sea surface temperatures. An ISCCP instrument simulator is employed to consistently compare model outputs with satellite observations. The use of a satellite simulator is shown to be imperative for model evaluation. EC-Earth exhibits the largest cloud biases in the tropics. It generally underestimates the total cloud cover but overestimates the optically thick clouds, with the net result that clouds exert an overly strong cooling effect in the model. Every cloud type has its own source of bias. The magnitude of the cooling due to the shortwave cloud radiative effect () is underestimated for the stratiform low-clouds, because the model simulates too few of them. In contrast, is overestimated for trade wind cumulus clouds, because in the model these are too thick. The clouds in the deep convection regions also lead to overestimate the . These clouds are generally too thick and there are too few mid and high thin clouds. These biases are consistent with the positive precipitation bias and the overly strong mass flux for deep convective plumes. Potential sources for the various cloud biases in the model are discussed.

  7. Assessing Low Frequency Climate Signals in Global Circulation Models using an Integrated Hydrologic Model

    NASA Astrophysics Data System (ADS)

    Niswonger, R. G.; Huntington, J. L.

    2010-12-01

    Climate signals with periodicities of approximately one decade are pervasive in long-term streamflow records for streams in the western United States that receive significant baseflow. The driver of these signals is unknown but hypotheses have been presented, such as variations in solar input to the Earth, or harmonics of internal (i.e., processes in the ocean and troposphere) forcings like the Pacific Decadal Oscillation (PDO) and El Niño Southern Oscillation (ENSO). Climate signals of about 1 decade are important for several reasons, including their relation to climate extremes (i.e., droughts and floods), and because the drivers of these climate signals are clearly important for projecting future climate conditions. Furthermore, identifying the drivers of these climate signals is important for separating the relative impacts of human production of greenhouse gases on global warming verses external drivers of climate change, such as sunspot cycles. Studies using Global Circulation Models (GCMs) that do not incorporate solar forcings associated with sun spots have identified oscillations of about a decade long in certain model output. However, these oscillations can be difficult to identify in simulated precipitation data due to high frequency variations (less than 1 year) that obscure low frequency (decade) signals. We have found that simulations using an integrated hydrologic model (IHM) called GSFLOW reproduce decade-long oscillations in streamflow when driven by measured precipitation records, and that these oscillations are also present in simulated streamflow when driven by temperature and precipitation data projected by GCMs. Because the IHM acts as a low-pass filter that reveals low frequency signals (i.e. decadal oscillations), they can be used to assess GCMs in terms of their ability to reproduce important low-frequency climate oscillations. We will present results from GSFLOW applied to three basins in the eastern Sierra Nevada driven by 100 years of

  8. 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

  9. Responses of estuarine circulation and salinity to the loss of intertidal flats – A modeling study

    SciTech Connect

    Yang, Zhaoqing; Wang, Taiping

    2015-08-25

    Intertidal flats in estuaries are coastal wetlands that provide critical marine habitats to support wide ranges of marine species. Over the last century many estuarine systems have experienced significant loss of intertidal flats due to anthropogenic impacts. This paper presents a modeling study conducted to investigate the responses of estuarine hydrodynamics to the loss of intertidal flats caused by anthropogenic actions in Whidbey Basin of Puget Sound on the northwest coast of North America. Changes in salinity intrusion limits in the estuaries, salinity stratification, and circulation in intertidal flats and estuaries were evaluated by comparing model results under the existing baseline condition and the no-flat condition. Model results showed that loss of intertidal flats results in an increase in salinity intrusion, stronger mixing, and a phase shift in salinity and velocity fields in the bay front areas. Model results also indicated that loss of intertidal flats enhances two-layer circulation, especially the bottom water intrusion. Loss of intertidal flats increases the mean salinity but reduces the salinity range in the subtidal flats over a tidal cycle because of increased mixing. Salinity intrusion limits extend upstream in all three major rivers discharging into Whidbey Basin when no intertidal flats are present. Changes in salinity intrusion and estuarine circulation patterns due to loss of intertidal flats affect the nearshore habitat and water quality in estuaries and potentially increase risk of coastal hazards, such as storm surge and coastal flooding. Furthermore, model results suggested the importance of including intertidal flats and the wetting-and-drying process in hydrodynamic simulations when intertidal flats are present in the model domain.

  10. Responses of estuarine circulation and salinity to the loss of intertidal flats – A modeling study

    DOE PAGESBeta

    Yang, Zhaoqing; Wang, Taiping

    2015-08-25

    Intertidal flats in estuaries are coastal wetlands that provide critical marine habitats to support wide ranges of marine species. Over the last century many estuarine systems have experienced significant loss of intertidal flats due to anthropogenic impacts. This paper presents a modeling study conducted to investigate the responses of estuarine hydrodynamics to the loss of intertidal flats caused by anthropogenic actions in Whidbey Basin of Puget Sound on the northwest coast of North America. Changes in salinity intrusion limits in the estuaries, salinity stratification, and circulation in intertidal flats and estuaries were evaluated by comparing model results under the existingmore » baseline condition and the no-flat condition. Model results showed that loss of intertidal flats results in an increase in salinity intrusion, stronger mixing, and a phase shift in salinity and velocity fields in the bay front areas. Model results also indicated that loss of intertidal flats enhances two-layer circulation, especially the bottom water intrusion. Loss of intertidal flats increases the mean salinity but reduces the salinity range in the subtidal flats over a tidal cycle because of increased mixing. Salinity intrusion limits extend upstream in all three major rivers discharging into Whidbey Basin when no intertidal flats are present. Changes in salinity intrusion and estuarine circulation patterns due to loss of intertidal flats affect the nearshore habitat and water quality in estuaries and potentially increase risk of coastal hazards, such as storm surge and coastal flooding. Furthermore, model results suggested the importance of including intertidal flats and the wetting-and-drying process in hydrodynamic simulations when intertidal flats are present in the model domain.« less

  11. Responses of estuarine circulation and salinity to the loss of intertidal flats - A modeling study

    NASA Astrophysics Data System (ADS)

    Yang, Zhaoqing; Wang, Taiping

    2015-12-01

    Intertidal flats in estuaries are coastal wetlands that provide critical marine habitats to support wide ranges of marine species. Over the last century many estuarine systems have experienced significant loss of intertidal flats due to anthropogenic impacts. This paper presents a modeling study conducted to investigate the responses of estuarine hydrodynamics to the loss of intertidal flats in Whidbey Basin of Puget Sound on the northwest coast of North America. Changes in salinity intrusion limits in the estuaries, salinity stratification, and circulation in intertidal flats and estuaries were evaluated by comparing model results under the existing baseline condition and the no-flat condition. Model results showed that loss of intertidal flats results in an increase in salinity intrusion, stronger mixing, and a phase shift in salinity and velocity fields in the bay front areas. Model results also indicated that loss of intertidal flats enhances two-layer circulation, especially the bottom water intrusion. Loss of intertidal flats increases the mean salinity but reduces the salinity range in the subtidal flats over a tidal cycle because of increased mixing. Salinity intrusion limits extend upstream in all three major rivers discharging into Whidbey Basin when no intertidal flats are present. Changes in salinity intrusion and estuarine circulation patterns due to loss of intertidal flats affect the nearshore habitat and water quality in estuaries and potentially increase risk of coastal hazards, such as storm surge and coastal flooding. Lastly, model results suggested the importance of including intertidal flats and the wetting-and-drying process in hydrodynamic simulations when intertidal flats are present in the model domain.

  12. Influence of high-resolution surface databases on the modeling of local atmospheric circulation systems

    NASA Astrophysics Data System (ADS)

    Paiva, L. M. S.; Bodstein, G. C. R.; Pimentel, L. C. G.

    2014-08-01

    Large-eddy simulations are performed using the Advanced Regional Prediction System (ARPS) code at horizontal grid resolutions as fine as 300 m to assess the influence of detailed and updated surface databases on the modeling of local atmospheric circulation systems of urban areas with complex terrain. Applications to air pollution and wind energy are sought. These databases are comprised of 3 arc-sec topographic data from the Shuttle Radar Topography Mission, 10 arc-sec vegetation-type data from the European Space Agency (ESA) GlobCover project, and 30 arc-sec leaf area index and fraction of absorbed photosynthetically active radiation data from the ESA GlobCarbon project. Simulations are carried out for the metropolitan area of Rio de Janeiro using six one-way nested-grid domains that allow the choice of distinct parametric models and vertical resolutions associated to each grid. ARPS is initialized using the Global Forecasting System with 0.5°-resolution data from the National Center of Environmental Prediction, which is also used every 3 h as lateral boundary condition. Topographic shading is turned on and two soil layers are used to compute the soil temperature and moisture budgets in all runs. Results for two simulated runs covering three periods of time are compared to surface and upper-air observational data to explore the dependence of the simulations on initial and boundary conditions, grid resolution, topographic and land-use databases. Our comparisons show overall good agreement between simulated and observational data, mainly for the potential temperature and the wind speed fields, and clearly indicate that the use of high-resolution databases improves significantly our ability to predict the local atmospheric circulation.

  13. Effects of a Total Solar Eclipse on the Mesoscale Atmospheric Circulation over Europe - A Model Experiment

    NASA Astrophysics Data System (ADS)

    Gross, P.; Hense, A.

    On August the 11th, 1999 Central Europe saw a spectacular astronomical event, a total solar eclipse. We present a model study concerning the meteorological effects of this eclipse in central Europe using the state-of-the-art limited area forecast model Deutschland-Modell DM from the German Weather Service DWD. Under typical summer radiation conditions very strong anomalies in the surface energy flux and temperature in screen height are simulated. The main temperature signal in the lower troposphere is delayed by about one hour with respect to the surface. Furthermore it is connected with a well defined dynamical signal which is reminiscent to a large scale land - sea circulation. The event could be used as a test case for mesoscale atmospheric models.

  14. Two-Layer Variable Infiltration Capacity Land Surface Representation for General Circulation Models

    NASA Technical Reports Server (NTRS)

    Xu, L.

    1994-01-01

    A simple two-layer variable infiltration capacity (VIC-2L) land surface model suitable for incorporation in general circulation models (GCMs) is described. The model consists of a two-layer characterization of the soil within a GCM grid cell, and uses an aerodynamic representation of latent and sensible heat fluxes at the land surface. The effects of GCM spatial subgrid variability of soil moisture and a hydrologically realistic runoff mechanism are represented in the soil layers. The model was tested using long-term hydrologic and climatalogical data for Kings Creek, Kansas to estimate and validate the hydrological parameters. Surface flux data from three First International Satellite Land Surface Climatology Project Field Experiments (FIFE) intensive field compaigns in the summer and fall of 1987 in central Kansas, and from the Anglo-Brazilian Amazonian Climate Observation Study (ABRACOS) in Brazil were used to validate the mode-simulated surface energy fluxes and surface temperature.

  15. General circulation modeling of the thermosphere-ionosphere during a geomagnetic storm

    NASA Astrophysics Data System (ADS)

    Yiǧit, Erdal; Immel, Thomas; Ridley, Aaron; Frey, Harald U.; Moldwin, Mark

    2016-07-01

    Using a three-dimensional general circulation model (GCM) of the upper atmosphere, we investigate the response of the thermosphere-ionosphere system to the August 2011 major geomagnetic storm. The GCM is driven by measured storm-time input data of the Interplanetary Magnetic Field (IMF), solar activity, and auroral activity. Simulations for quiet steady conditions over the same period are performed as well in order to assess the response of the neutral and plasma parameters to the storm. During the storm, the high-latitude mean ion flows are enhanced by up to ~150%. Overall, the global mean neutral temperature increases by up to 15%, while the maximum thermal response is higher in the winter Southern Hemisphere at high-latitudes than the summer Northern Hemisphere: 40% vs. 20% increase in high-latitude mean temperature, respectively. The global mean Joule heating of the neutral atmosphere increases by more than a factor of three. There are distinct hemispheric differences in the magnitude and morphology of the horizontal ion flows and thermospheric circulation during the different phases of the storm. The thermospheric circulation demonstrates the largest amount of hemispheric differences during the later stages of the storm. Dynamical diagnostics show that advective forcing contributes to hemispheric differences.

  16. Enhanced evidence in climate models for changes in extratropical atmospheric circulation

    NASA Astrophysics Data System (ADS)

    Paeth, Heiko; Pollinger, Felix

    2010-10-01

    We investigate changes in extratropical atmospheric circulation as derived from the most recent multi-model ensemble of global climate projections. This internationally coordinated systematic data base allows for an accurate assessment of climate change signals against the background of model uncertainty. The multi-model mean time series of the northern-hemisphere (NAM) and southern-hemisphere (SAM) annular modes and of the North Atlantic Oscillation (NAO) are in line with the observed positive trends during the second half of the 20th century and project a further strengthening until the end of the 21st century. For SAM and NAM the simulated changes are unambiguously related to anthropogenic forcing and outperform the level of model uncertainty. This result may imply an enhanced probability for some severe regional impacts of climate change, in particular over extratropical land masses. The climate change signals are noticeably weaker under the B1 mitigation scenario than under the A2 business-as-usual scenario. Ozone forcing has a significant impact on the amplitude of future circulation changes, whereas no systematic effect is found with respect to the models' top-of-the-atmosphere.

  17. Modeling the influence of river discharge on salt intrusion and residual circulation in Danshuei River estuary, Taiwan

    USGS Publications Warehouse

    Liu, W.-C.; Chen, W.-B.; Cheng, R.T.; Hsu, M.-H.; Kuo, A.Y.

    2007-01-01

    A 3-D, time-dependent, baroclinic, hydrodynamic and salinity model was implemented and applied to the Danshuei River estuarine system and the adjacent coastal sea in Taiwan. The model forcing functions consist of tidal elevations along the open boundaries and freshwater inflows from the main stream and major tributaries in the Danshuei River estuarine system. The bottom friction coefficient was adjusted to achieve model calibration and verification in model simulations of barotropic and baroclinic flows. The turbulent diffusivities were ascertained through comparison of simulated salinity time series with observations. The model simulation results are in qualitative agreement with the available field data. The validated model was then used to investigate the influence of freshwater discharge on residual current and salinity intrusion under different freshwater inflow condition in the Danshuei River estuarine system. The model results reveal that the characteristic two-layered estuarine circulation prevails most of the time at Kuan-Du station near the river mouth. Comparing the estuarine circulation under low- and mean flow conditions, the circulation strengthens during low-flow period and its strength decreases at moderate river discharge. The river discharge is a dominating factor affecting the salinity intrusion in the estuarine system. A correlation between the distance of salt intrusion and freshwater discharge has been established allowing prediction of salt intrusion for different inflow conditions. ?? 2007 Elsevier Ltd. All rights reserved.

  18. Polar Warming in the Mars Lower Thermosphere : Odyssey Accelerometer Data Interpretation Using Coupled General Circulation Models

    NASA Astrophysics Data System (ADS)

    Bougher, S. W.; Murphy, J. R.

    2003-12-01

    opposite summer-to-winter circulation cell (Ls = 90) is weaker resulting in reduced dynamical heating to the Southern winter polar region. The coupled NASA Ames Mars General Circulation Model (MGCM) and the Michigan Mars Thermospheric General Circulation Model (MTGCM) are exercised for both perihelion and aphelion conditions using observed MGS Thermal Emission Spectrometer (TES) dust distributions appropriate to the Odyssey and MGS2 aerobraking periods. Improved CO2 15-micron cooling and near IR heating formulations are used in both MGCM and MTGCM codes resulting in upgraded simulations for this study. Latitudinal distributions of densities and temperatures are presented from these coupled simulations and contrasted with longitudinally averaged aerobraking data. The underlying MTGCM heating terms are displayed in order to illustrate the seasonally variable processes that contribute to polar warming in the Mars thermosphere.

  19. High pressure experiments with a Mars general circulation model

    NASA Technical Reports Server (NTRS)

    Haberle, R. M.; Pollack, J. B.; Murphy, J. R.; Schaeffer, J.; Lee, H.

    1992-01-01

    The interaction of three physical processes will determine the stability of the Martian polar caps as the surface pressure increases: the greenhouse effect, atmospheric heat transport, and the change in the CO2 frost point temperature. The contribution of each is readily determined in the Mars general circulation model (GCM). Therefore, we have initiated experiments with the GCM to determine how these processes interact, and how the atmosphere-polar cap system responds to increasing surface pressure. The experiments are carried out for northern winter solstice and generally assume the atmosphere to be free of dust. Each experiment starts from resting isothermal conditions and runs for 50 Mars days. Mars' current orbital parameters are used. The experiments are for surface pressures of 120, 480, and 960 mb, which represent 16, 64, and 128 times the current value. To date we have analyzed the 120 mb experiment and the results indicate the contrary to the simpler models, the polar caps actually advance instead of retreat. Other aspects of this investigation are presented.

  20. A new solar cycle model including meridional circulation

    NASA Technical Reports Server (NTRS)

    Wang, Y.-M.; Sheeley, N. R., Jr.; Nash, A. G.

    1991-01-01

    A kinematic model is presented for the solar cycle which includes not only the transport of magnetic flux by supergranular diffusion and a poleward bulk flow at the sun's surface, but also the effects of turbulent diffusion and an equatorward 'return flow' beneath the surface. As in the earlier models of Babcock and Leighton, the rotational shearing of a subsurface poloidal field generates toroidal flux that erupts at the surface in the form of bipolar magnetic regions. However, such eruptions do not result in any net loss of toroidal flux from the sun (as assumed by Babcock and Leighton); instead, the large-scale toroidal field is destroyed both by 'unwinding' as the local poloidal field reverses its polarity, and by diffusion as the toroidal flux is transported equatorward by the subsurface flow and merged with its opposite hemisphere counterpart. The inclusion of meridional circulation allows stable oscillations of the magnetic field, accompanied by the equatorward progression of flux eruptions, to be achieved even in the absence of a radial gradient in the angular velocity. An illustrative case in which a subsurface flow speed of order 1 m/s and subsurface diffusion rate of order 10 sq km/s yield 22-yr oscillations in qualitative agreement with observations.

  1. A vertically averaged spectral model for tidal circulation in estuaries

    USGS Publications Warehouse

    Burau, J.R.; Cheng, R.T.

    1989-01-01

    A frequency dependent computer model based on the two-dimensional vertically averaged shallow-water equations is described for general purpose application in tidally dominated embayments. This model simulates the response of both tides and tidal currents to user-specified geometries and boundary conditions. The mathematical formulation and practical application of the model are discussed in detail. Salient features of the model include the ability to specify: (1) stage at the open boundaries as well as within the model grid, (2) velocities on open boundaries (river inflows and so forth), (3) spatially variable wind stress, and (4) spatially variable bottom friction. Using harmonically analyzed field data as boundary conditions, this model can be used to make real time predictions of tides and tidal currents. (USGS)

  2. Improving the representation of turbulence and clouds in cloud resolving models and general circulation models

    NASA Astrophysics Data System (ADS)

    Bogenschutz, Peter A.

    Over the past few years a new type of general circulation model (GCM) has emerged that is known as the multiscale modeling framework (MMF). The Colorado State University (CSU) MMF represents a coupling between the Community Atmosphere Model (CAM) GCM and the System of Atmospheric Modeling (SAM) cloud resolving model (CRM). Within this MMF the embedded CRM replaces the traditionally used parameterized moist physics in CAM to represent subgrid-scale (SGS) convection. However, due to substantial increases of computational burden associated with the MMF, the embedded CRM is typically run with a horizontal grid size of 4 km. With a horizontal grid size of 4 km, a low-order closure CRM cannot adequately represent shallow convective processes, such as trade-wind cumulus or stratocumulus. A computationally inexpensive parameterization of turbulence and clouds is presented in this dissertation. An extensive a priori test is performed to determine which functional form of an assumed PDF is best suited for coarse-grid CRMs for both deep shallow and deep convection. The diagnostic approach to determine the input moments needed for the assumed PDFs uses the subgrid-scale (SGS) turbulent kinetic energy (TKE) as the basis for the parameterization. The term known as the turbulent length scale (L) is examined, as it is needed to parameterize the dissipation of turbulence and therefore is needed to better balance the budgets of SGS TKE. A new formulation of this term is added to the model code which appears to be able to partition resolved and SGS TKE fairly accurately. Results from "offline" tests of the simple diagnostic closure within SAM shows that the cloud and turbulence properties of shallow convection can be adequately represented when compared to large eddy simulation (LES) benchmark simulations. Results are greatly improved when compared to the standard version of SAM. The preliminary test of the scheme within the embedded CRM of the MMF shows promising results with the

  3. 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.

  4. 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.

  5. Development of the GEOS-5 atmospheric general circulation model: evolution from MERRA to MERRA2

    NASA Astrophysics Data System (ADS)

    Molod, A.; Takacs, L.; Suarez, M.; Bacmeister, J.

    2015-05-01

    The Modern-Era Retrospective Analysis for Research and Applications-2 (MERRA2) version of the Goddard Earth Observing System-5 (GEOS-5) atmospheric general circulation model (AGCM) is currently in use in the NASA Global Modeling and Assimilation Office (GMAO) at a wide range of resolutions for a variety of applications. Details of the changes in parameterizations subsequent to the version in the original MERRA reanalysis are presented here. Results of a series of atmosphere-only sensitivity studies are shown to demonstrate changes in simulated climate associated with specific changes in physical parameterizations, and the impact of the newly implemented resolution-aware behavior on simulations at different resolutions is demonstrated. The GEOS-5 AGCM presented here is the model used as part of the GMAO MERRA2 reanalysis, global mesoscale simulations at 10 km resolution through 1.5 km resolution, the real-time numerical weather prediction system, and for atmosphere-only, coupled ocean-atmosphere and coupled atmosphere-chemistry simulations. The seasonal mean climate of the MERRA2 version of the GEOS-5 AGCM represents a substantial improvement over the simulated climate of the MERRA version at all resolutions and for all applications. Fundamental improvements in simulated climate are associated with the increased re-evaporation of frozen precipitation and cloud condensate, resulting in a wetter atmosphere. Improvements in simulated climate are also shown to be attributable to changes in the background gravity wave drag, and to upgrades in the relationship between the ocean surface stress and the ocean roughness. The series of resolution-aware parameters related to the moist physics was shown to result in improvements at higher resolutions and result in AGCM simulations that exhibit seamless behavior across different resolutions and applications.

  6. Evaluation of the Surface Representation of the Greenland Ice Sheet in a General Circulation Model

    NASA Technical Reports Server (NTRS)

    Cullather, Richard I.; Nowicki, Sophie M. J.; Zhao, Bin; Suarez, Max J.

    2014-01-01

    Simulated surface conditions of the Goddard Earth Observing System model, version 5 (GEOS 5) atmospheric general circulation model (AGCM) are examined for the contemporary Greenland Ice Sheet (GrIS). A surface parameterization that explicitly models surface processes including snow compaction, meltwater percolation and refreezing, and surface albedo is found to remedy an erroneous deficit in the annual net surface energy flux and provide an adequate representation of surface mass balance (SMB) in an evaluation using simulations at two spatial resolutions. The simulated 1980-2008 GrIS SMB average is 24.7+/-4.5 cm yr(- 1) water-equivalent (w.e.) at.5 degree model grid spacing, and 18.2+/-3.3 cm yr(- 1) w.e. for 2 degree grid spacing. The spatial variability and seasonal cycle of the simulation compare favorably to recent studies using regional climate models, while results from 2 degree integrations reproduce the primary features of the SMB field. In comparison to historical glaciological observations, the coarser resolution model overestimates accumulation in the southern areas of the GrIS, while the overall SMB is underestimated. These changes relate to the sensitivity of accumulation and melt to the resolution of topography. The GEOS-5 SMB fields contrast with available corresponding atmospheric models simulations from the Coupled Model Intercomparison Project (CMIP5). It is found that only a few of the CMIP5 AGCMs examined provide significant summertime runoff, a dominant feature of the GrIS seasonal cycle. This is a condition that will need to be remedied if potential contributions to future eustatic change from polar ice sheets are to be examined with GCMs.

  7. Use of circulation types classifications to evaluate AR4 climate models over the Euro-Atlantic region

    NASA Astrophysics Data System (ADS)

    Pastor, M. A.; Casado, M. J.

    2012-10-01

    This paper presents an evaluation of the multi-model simulations for the 4th Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) in terms of their ability to simulate the ERA40 circulation types over the Euro-Atlantic region in winter season. Two classification schemes, k-means and SANDRA, have been considered to test the sensitivity of the evaluation results to the classification procedure. The assessment allows establishing different rankings attending spatial and temporal features of the circulation types. Regarding temporal characteristics, in general, all AR4 models tend to underestimate the frequency of occurrence. The best model simulating spatial characteristics is the UKMO-HadGEM1 whereas CCSM3, UKMO-HadGEM1 and CGCM3.1(T63) are the best simulating the temporal features, for both classification schemes. This result agrees with the AR4 models ranking obtained when having analysed the ability of the same AR4 models to simulate Euro-Atlantic variability modes. This study has proved the utility of applying such a synoptic climatology approach as a diagnostic tool for models' assessment. The ability of the models to properly reproduce the position of ridges and troughs and the frequency of synoptic patterns, will therefore improve our confidence in the response of models to future climate changes.

  8. 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.

  9. 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.

  10. Development of the GEOS-5 Atmospheric General Circulation Model: Evolution from MERRA to MERRA2.

    NASA Technical Reports Server (NTRS)

    Molod, Andrea; Takacs, Lawrence; Suarez, Max; Bacmeister, Julio

    2014-01-01

    The Modern-Era Retrospective Analysis for Research and Applications-2 (MERRA2) version of the GEOS-5 (Goddard Earth Observing System Model - 5) Atmospheric General Circulation Model (AGCM) is currently in use in the NASA Global Modeling and Assimilation Office (GMAO) at a wide range of resolutions for a variety of applications. Details of the changes in parameterizations subsequent to the version in the original MERRA reanalysis are presented here. Results of a series of atmosphere-only sensitivity studies are shown to demonstrate changes in simulated climate associated with specific changes in physical parameterizations, and the impact of the newly implemented resolution-aware behavior on simulations at different resolutions is demonstrated. The GEOS-5 AGCM presented here is the model used as part of the GMAO's MERRA2 reanalysis, the global mesoscale "nature run", the real-time numerical weather prediction system, and for atmosphere-only, coupled ocean-atmosphere and coupled atmosphere-chemistry simulations. The seasonal mean climate of the MERRA2 version of the GEOS-5 AGCM represents a substantial improvement over the simulated climate of the MERRA version at all resolutions and for all applications. Fundamental improvements in simulated climate are associated with the increased re-evaporation of frozen precipitation and cloud condensate, resulting in a wetter atmosphere. Improvements in simulated climate are also shown to be attributable to changes in the background gravity wave drag, and to upgrades in the relationship between the ocean surface stress and the ocean roughness. The series of "resolution aware" parameters related to the moist physics were shown to result in improvements at higher resolutions, and result in AGCM simulations that exhibit seamless behavior across different resolutions and applications.

  11. A global multiscale mathematical model for the human circulation with emphasis on the venous system.

    PubMed

    Müller, Lucas O; Toro, Eleuterio F

    2014-07-01

    We present a global, closed-loop, multiscale mathematical model for the human circulation including the arterial system, the venous system, the heart, the pulmonary circulation and the microcirculation. A distinctive feature of our model is the detailed description of the venous system, particularly for intracranial and extracranial veins. Medium to large vessels are described by one-dimensional hyperbolic systems while the rest of the components are described by zero-dimensional models represented by differential-algebraic equations. Robust, high-order accurate numerical methodology is implemented for solving the hyperbolic equations, which are adopted from a recent reformulation that includes variable material properties. Because of the large intersubject variability of the venous system, we perform a patient-specific characterization of major veins of the head and neck using MRI data. Computational results are carefully validated using published data for the arterial system and most regions of the venous system. For head and neck veins, validation is carried out through a detailed comparison of simulation results against patient-specific phase-contrast MRI flow quantification data. A merit of our model is its global, closed-loop character; the imposition of highly artificial boundary conditions is avoided. Applications in mind include a vast range of medical conditions. Of particular interest is the study of some neurodegenerative diseases, whose venous haemodynamic connection has recently been identified by medical researchers. PMID:24431098

  12. Simulation of the effects of proposed tide gates on circulation, flushing, and water quality in residential canals, Cape Coral Florida

    USGS Publications Warehouse

    Goodwin, Carl R.

    1991-01-01

    Decades of dredging and filling of Florida's low-lying coastal wetlands have produced thousands of miles of residential tidal canals and adjacent waterfront property. Typically, these canals are poorly flushed, and over time, accumulated organic-rich bottom materials, contribute to an increasingly severe degraded water quality. One-dimensional hydrodynamic and constituent-transport models were applied to two dead-end canal systems to determine the effects of canal system interconnection using tide gates on water circulation and constituent flushing. The model simulates existing and possible future circulation and flushing conditions in about 29 miles of the approximately 130 miles of tidally influenced canals in Cape Coral, located on the central west coast of peninsular Florida. Model results indicate that tidal water-level differences between the two canal systems can be converted to kinetic energy, in the form of increased water circulation, but the use of one-way tide gate interconnections. Computations show that construction of from one to four tide gates will cause replacement of a volume of water equivalent to the total volume of canals in both systems in 15 to 9 days, respectively. Because some canals flush faster than others, 47 and 21 percent of the original canal water will remain in both systems 50 days after start of operation of one and four tide gates, respectively. Some of the effects that such increased flushing are expected to have include reduced density stratification and associated dissolved-oxygen depletion in canal bottom waters, increased localized reaeration, and more efficient discharge of stormwater runoff entering the canals.

  13. A thermosphere/ionosphere general circulation model with coupled electrodynamics

    NASA Technical Reports Server (NTRS)

    Richmond, A. D.; Ridley, E. C.; Roble, R. G.

    1992-01-01

    A new simulation model of upper atmospheric dynamics is presented that includes self-consistent electrodynamic interactions between the thermosphere and ionosphere. This model calculates the dynamo effects of thermospheric winds, and uses the resultant electric fields and currents in calculating the neutral and plasma dynamics. A realistic geomagnetic field geometry is used. Sample simulations for solar maximum equinox conditions illustrate two previously predicted effects of the feedback. Near the magnetic equator, the afternoon uplift of the ionosphere by an eastward electric field reduces ion drag on the neutral wind, so that relatively strong eastward winds can occur in the evening. In addition, a vertical electric field is generated by the low-latitude wind, which produces east-west plasma drifts in the same direction as the wind, further reducing the ion drag and resulting in stronger zonal winds.

  14. An efficient method for discerning climate-relevant sensitivities in atmospheric general circulation models

    NASA Astrophysics Data System (ADS)

    Wan, H.; Rasch, P. J.; Zhang, K.; Qian, Y.; Yan, H.; Zhao, C.

    2014-04-01

    This paper explores the feasibility of an experimentation strategy for investigating sensitivities in fast components of atmospheric general circulation models. The basic idea is to replace the traditional serial-in-time long-term climate integrations by representative ensembles of shorter simulations. The key advantage of the proposed method lies in its efficiency: since fewer days of simulation are needed, the computational cost is less, and because individual realizations are independent and can be integrated simultaneously, the new dimension of parallelism can dramatically reduce the turnaround time in benchmark tests, sensitivities studies, and model tuning exercises. The strategy is not appropriate for exploring sensitivity of all model features, but it is very effective in many situations. Two examples are presented using the Community Atmosphere Model version 5. The first example demonstrates that the method is capable of characterizing the model cloud and precipitation sensitivity to time step length. A nudging technique is also applied to an additional set of simulations to help understand the contribution of physics-dynamics interaction to the detected time step sensitivity. In the second example, multiple empirical parameters related to cloud microphysics and aerosol lifecycle are perturbed simultaneously in order to explore which parameters have the largest impact on the simulated global mean top-of-atmosphere radiation balance. Results show that in both examples, short ensembles are able to correctly reproduce the main signals of model sensitivities revealed by traditional long-term climate simulations for fast processes in the climate system. The efficiency of the ensemble method makes it particularly useful for the development of high-resolution, costly and complex climate models.

  15. Short ensembles: An Efficient Method for Discerning Climate-relevant Sensitivities in Atmospheric General Circulation Models

    SciTech Connect

    Wan, Hui; Rasch, Philip J.; Zhang, Kai; Qian, Yun; Yan, Huiping; Zhao, Chun

    2014-09-08

    This paper explores the feasibility of an experimentation strategy for investigating sensitivities in fast components of atmospheric general circulation models. The basic idea is to replace the traditional serial-in-time long-term climate integrations by representative ensembles of shorter simulations. The key advantage of the proposed method lies in its efficiency: since fewer days of simulation are needed, the computational cost is less, and because individual realizations are independent and can be integrated simultaneously, the new dimension of parallelism can dramatically reduce the turnaround time in benchmark tests, sensitivities studies, and model tuning exercises. The strategy is not appropriate for exploring sensitivity of all model features, but it is very effective in many situations. Two examples are presented using the Community Atmosphere Model version 5. The first example demonstrates that the method is capable of characterizing the model cloud and precipitation sensitivity to time step length. A nudging technique is also applied to an additional set of simulations to help understand the contribution of physics-dynamics interaction to the detected time step sensitivity. In the second example, multiple empirical parameters related to cloud microphysics and aerosol lifecycle are perturbed simultaneously in order to explore which parameters have the largest impact on the simulated global mean top-of-atmosphere radiation balance. Results show that in both examples, short ensembles are able to correctly reproduce the main signals of model sensitivities revealed by traditional long-term climate simulations for fast processes in the climate system. The efficiency of the ensemble method makes it particularly useful for the development of high-resolution, costly and complex climate models.

  16. 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.

  17. Numerical model of circulation and residence times in the Persian Gulf

    NASA Astrophysics Data System (ADS)

    O'Donncha, Fearghal; Ragnoli, Emanuele

    2014-05-01

    The Persian Gulf is a semi-enclosed, marginal sea that is exposed to arid, subtropical climate. As a consequence of the extreme climate, evaporation is greater than freshwater inflow resulting in a net loss of water and associated, reverse flow, estuarine circulation as the highly saline waters exit the basin through the Straits of Hormuz, into the Gulf of Oman. Because of their consistent direction, these density currents are central in the distribution and removal of pollutants from the gulf. Tidal forcing impacts circulation in the region, particularly on smaller scales of length and time. Wind forcing can be significant, particularly the Shamal weather phenomenon; wind that sets in with great abruptness and force, and is related to synoptic weather systems to the Northwest. Output from high resolution (~1km) numerical simulations, using NEMO (Nucleus for European Modelling of the Ocean), provide insight into the physical oceanography of the region. The model was forced by 0.75° European Centre for Medium-Range Weather Forecasts (ECMWF) atmospheric data and tidal constituents extracted from the Oregon State University Tidal Prediction Software (OTPS/TPXO). Model results permit a detailed examination of the three primary forcing processes, namely: tidal forces, wind forces, and density differences. To assess fundamental model performance, results are compared with two historical observation datasets: (1) a comprehensive dataset of velocity and CTD measurements collected by Reynolds (1993) and (2) time series measurements recorded in the Strait of Hormuz from December 1996 to March 1998 by Johns et al. (2003). Model results exhibit close agreement to field values validating the model for a more detailed analysis of circulations patterns within the gulf. To better elucidate the dominant forcing processes, classical tidal analysis decomposed the flow currents by fitting the flow profile to a finite set of sinusoids at specific frequencies related to astronomical

  18. Examination of Ventricular Contraction Function Using Electrical Lumped Circuit Model of Circulation System

    NASA Astrophysics Data System (ADS)

    Ito, Mitsuyo; Koya, Yoshiharu; Mizoshiri, Isao

    Presently, many of the already proposed blood circulation models are mainly partial models although they are precise models. A complete model that is a combination of these partial models are difficult to analyze because it is complicated to consider both the viscosity of blood and circulatory details at the same time. So, it is difficult to control the model parameters in order to adapt to various cases of circulatory diseases. This paper proposes a complete circulation model as a lumped electrical circuit, which is comparatively simple. In the circuit model, total blood is modeled as seven lumped capacitors, representing the functions of atriums, ventricles, arteries, veins and lungs. We regard the variation of the ventricle capacitance as the driving force of the complete circulation model. In our model, we considered only the variation of pressure between each part and the blood capacity of each part. In particular, the contraction function of the left ventricle is examined under the consideration of whole blood circulation.

  19. A Third Note on Ageing in a Library Circulation Model: Applications to Future Use and Relegation.

    ERIC Educational Resources Information Center

    Burrell, Quentin L.

    1987-01-01

    Describes a circulation model for academic research libraries which uses the mixed Poisson model, incorporating ageing of library materials, to predict future use of monographs and to suggest weeding procedures based on frequency of circulation. Longitudinal studies are examined and statistical details are appended. (Author/LRW)

  20. 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.

  1. 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.

  2. 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.

  3. Ensemble formulation of surface fluxes and improvement in evapotranspiration and cloud parameterizations in a GCM. [General Circulation Model

    NASA Technical Reports Server (NTRS)

    Sud, Y. C.; Smith, W. E.

    1984-01-01

    The influence of some modifications to the parameters of the current general circulation model (GCM) is investigated. The aim of the modifications was to eliminate strong occasional bursts of oscillations in planetary boundary layer (PBL) fluxes. Smoothly varying bulk aerodynamic friction and heat transport coefficients were found by ensemble averaging of the PBL fluxes in the current GCM. A comparison was performed of the simulations of the modified model and the unmodified model. The comparison showed that the surface fluxes and cloudiness in the modified model simulations were much more accurate. The planetary albedo in the model was also realistic. Weaknesses persisted in the models positioning of the Inter-tropical convergence zone (ICTZ) and in the temperature estimates for polar regions. A second simulation of the model following reparametrization of the cloud data showed improved results and these are described in detail.

  4. The Hornsund fjord - modeling of the general circulation, heat exchange and water masses transport.

    NASA Astrophysics Data System (ADS)

    Przyborska, Anna; Jakacki, Jaromir; Kosecki, Szymon; Sundfjord, Arild

    2015-04-01

    The MIKE3D hydrodynamic model has been implemented for diagnosis an ecosystem status in the most southern fjord of the Svalbard Archipelago. The model is based on MIKE 3 Flow Model FM that uses flexible mesh grid. The spatial discretization in solutions of equations is performed by the finite element method. The regional scale of the model implicated implementation of external data at the lateral boundary region. In our case Flather's boundary condition let us to force the model with combined information. At the same time tidal ordinate and barotropic component of velocity that reflects the West Spitsbergen Current are implemented. Also salinity and temperature were nested at the boundary area. The upper boundary conditions was also introduced. The data for the boundary were taken from Global Tide Model (all tidal components), an 800 m ROMS simulation of the Svalbard area made by the Norwegian Institute of Marine Research (bartoropic velocities, temperature and salinity), European Centre for Medium Weather Forecast (ECMWF) and also from Global Data Assimilation System (GDAS). Implemented model was validated and the mean circulation and its seasonal variability will be presented. Also influence of the shelf water masses on the fjord will be discussed. Fresh water transport from glaciers, run off and snow will be estimated. Results are based on 5 years simulation (2005-2010) This work was partially performed in the frame of the projects GAME (DEC-2012/04/A/NZ8/00661) and AWAKE2 (Pol-Nor/198675/17/2013)

  5. 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.

  6. Integrated cumulus ensemble and turbulence (ICET): An integrated parameterization system for general circulation models (GCMs)

    SciTech Connect

    Evans, J.L.; Frank, W.M.; Young, G.S.

    1996-04-01

    Successful simulations of the global circulation and climate require accurate representation of the properties of shallow and deep convective clouds, stable-layer clouds, and the interactions between various cloud types, the boundary layer, and the radiative fluxes. Each of these phenomena play an important role in the global energy balance, and each must be parameterized in a global climate model. These processes are highly interactive. One major problem limiting the accuracy of parameterizations of clouds and other processes in general circulation models (GCMs) is that most of the parameterization packages are not linked with a common physical basis. Further, these schemes have not, in general, been rigorously verified against observations adequate to the task of resolving subgrid-scale effects. To address these problems, we are designing a new Integrated Cumulus Ensemble and Turbulence (ICET) parameterization scheme, installing it in a climate model (CCM2), and evaluating the performance of the new scheme using data from Atmospheric Radiation Measurement (ARM) Program Cloud and Radiation Testbed (CART) sites.

  7. 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

  8. Adjoint Data Assimilative Model Study of the Gulf of Maine Coastal Circulation

    NASA Astrophysics Data System (ADS)

    He, R.; McGillicuddy, D. J.; Lynch, D. R.

    2004-12-01

    Data assimilation (DA) in the coastal ocean can be divided into category of either sequential estimation or variational adjoint. Sequential estimation techniques blend models with observations directly, using a variety of algorithms with which the relative weights of data and model are calculated. Variational adjoint techniques infer model control variables (e.g. parameters, forcing functions, boundary conditions, etc.) that minimize the misfit between observations and predictions. The advantage of the latter techniques over the former is that the resulting model solutions obey model dynamics. In this study, the Gulf of Maine coastal circulation and the material property transport are investigated with the Dartmouth variational adjoint DA modeling system, which assimilates in-situ data via inversion for the unknown sea level elevation at open boundaries. In-situ observations include ADCP currents and coastal sea levels. The adjoint DA model skill is evaluated by the inter-comparisons between modeled and observed drifter trajectories. Excellent model skill is found, demonstrating the utility and effectiveness of the adjoint DA modeling system in bridging in-situ observations with coastal ocean model simulations. Implications of the adjoint DA strategy on the emergent coastal ocean observing systems are discussed.

  9. Multidecadal North Atlantic sea surface temperature and Atlantic meridional overturning circulation variability in CMIP5 historical simulations

    NASA Astrophysics Data System (ADS)

    Zhang, Liping; Wang, Chunzai

    2013-10-01

    In this paper, simulated variability of the Atlantic Multidecadal Oscillation (AMO) and the Atlantic Meridional Overturning Circulation (AMOC) and their relationship has been investigated. For the first time, climate models of the Coupled Model Intercomparison Project phase 5 (CMIP5) provided to the Intergovernmental Panel on Climate Change Fifth Assessment Report (IPCC-AR5) in historical simulations have been used for this purpose. The models show the most energetic variability on the multidecadal timescale band both with respect to the AMO and AMOC, but with a large model spread in both amplitude and frequency. The relationship between the AMO and AMOC in most of the models resembles the delayed advective oscillation proposed for the AMOC on multidecadal timescales. A speed up (slow down) of the AMOC is in favor of generating a warm (cold) phase of the AMO by the anomalous northward (southward) heat transport in the upper ocean, which reversely leads to a weakening (strengthening) of the AMOC through changes in the meridional density gradient after a delayed time of ocean adjustment. This suggests that on multidecadal timescales the AMO and AMOC are related and interact with each other.

  10. Electricity Portfolio Simulation Model

    Energy Science and Technology Software Center (ESTSC)

    2005-09-01

    Stakeholders often have competing interests when selecting or planning new power plants. The purpose of developing this preliminary Electricity Portfolio Simulation Model (EPSim) is to provide a first cut, dynamic methodology and approach to this problem, that can subsequently be refined and validated, that may help energy planners, policy makers, and energy students better understand the tradeoffs associated with competing electricity portfolios. EPSim allows the user to explore competing electricity portfolios annually from 2002 tomore » 2025 in terms of five different criteria: cost, environmental impacts, energy dependence, health and safety, and sustainability. Four additional criteria (infrastructure vulnerability, service limitations, policy needs and science and technology needs) may be added in future versions of the model. Using an analytic hierarchy process (AHP) approach, users or groups of users apply weights to each of the criteria. The default energy assumptions of the model mimic Department of Energy’s (DOE) electricity portfolio to 2025 (EIA, 2005). At any time, the user can compare alternative portfolios to this reference case portfolio.« less

  11. SSPX simulation model