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ENSO Simulation in CGCMs and the Associated Errors in Atmospheric Response

Description: Tropical Pacific variability, and specifically the simulation of ENSO in coupled ocean-atmosphere general circulation models (CGCMs) has previously been assessed in many studies (McCreary and Anderson [1991], Neelin et al. [1992], Mechoso et al. [1995], Latif et al. [2000], and Davey et al. [2000]). These studies have concentrated on SST variations in the tropical Pacific, and discussions of the atmospheric response have been limited to east-west movements of the convergence zone. In this paper we discuss the large-scale atmospheric response to simulated ENSO events. Control simulations from 17 global CGCMs from CMIP (Meehl et al. [2000]) are studied. The web site http:// www-pcmdi.llnl.gov/cmip/modeldoc provides documentation of the configurations of the models.
Date: September 11, 2000
Creator: AchutaRao, K. & Sperber, K.R.
Partner: UNT Libraries Government Documents Department

Parameterizations in high resolution isopycnal wind-driven ocean models. Final report, August 1, 1992--January 31, 1996

Description: Development of a general quasi-isopycnal code suitable for numerical experimentation and test of parameterizations was the main goal of the proposed research. A versatile ocean modeling system, which the authors refer to as the Thermodynamic Ocean Modeling System (TOMS) is the result of this effort. TOMS is based on an Arbitrary Lagrangian Eulerian (ALE) vertical coordinate and is a hybrid between isopycnal and z-coordinate models. The modeling system is designed for oceanic and coastal flows where the aspect ratio is small. As part of the development effort, the authors also proposed to implement and test new numerical schemes, parameterizations of boundary layer flow and development and implementation of mixed layer physics in this model. The addition objectives for the proposed research were: (1) incorporate various mixed layer parameterizations; (2) implement and test the positive definite Arakawa and Hsu, (1990) scheme; (3) recode a version of the model for a highly parallel architecture; (4) determine effects of various parameterizations of islands, and; (5) determine the correct lateral boundary condition for boundary layer currents, as for instance the Gulf Stream, and other western boundary currents.
Date: March 1, 1996
Creator: Jensen, T.G. & Randall, D.A.
Partner: UNT Libraries Government Documents Department

Deep convection in the Arctic: The evaluation of results from an OGCM with a new convection parameterization

Description: The current generation of ocean general circulation models (OGCMS) uses a convective adjustment scheme to remove static instabilities and to parameterize shallow and deep convection. In simulations used to examine climate-related scenarios, investigators found that in the Arctic regions, the OGCM simulations did not produce a realistic vertical density structure, did not create the correct quantity of deep water, and did not use a time-scale of adjustment that is in agreement with tracer ages or observations. A possible weakness of the models is that the convective adjustment scheme does not represent the process of deep convection adequately. Consequently, a penetrative plume mixing scheme has been developed to parameterize the process of deep open-ocean convection in OGCMS. This new deep convection parameterization was incorporated into the Semtner and Chervin (1988) OGCM. The modified model (with the new parameterization) was run in a simplified Nordic Seas test basin: under a cyclonic wind stress and cooling, stratification of the basin-scale gyre is eroded and deep mixing occurs in the center of the gyre. In contrast, in the OGCM experiment that uses the standard convective adjustment algorithm, mixing is delayed and is wide-spread over the gyre.
Date: January 1, 1995
Creator: Paluszkiewicz, T.; Hibler, L.F. & Romea, R.D.
Partner: UNT Libraries Government Documents Department

A hierarchy of thermohaline circulation models. Final report

Description: 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.
Date: April 1, 1998
Creator: Cessi, P. & Young, W.R.
Partner: UNT Libraries Government Documents Department

Thermohaline circulations and global climate change. Final report

Description: This report discusses results from the project entitled Thermohaline Circulations and Global Climate Change. Results are discussed in three sections related to the development of the Miami Isopycnic Coordinate Ocean Model (MICOM), surface forcing of the ocean by the atmosphere, and experiments with the MICOM related to the problem of the ocean`s response to global climate change. It will require the use of a global, coupled ocean-atmospheric climate model to quantify the feedbacks between ocean and atmosphere associated with climate changes. The results presented here do provide guidance for such studies in the future.
Date: October 1, 1996
Creator: Hanson, H.P.
Partner: UNT Libraries Government Documents Department

Final Technical Report: Ocean CO{sub 2} Measurements for the WOCE Hydrographic Survey in the Pacific Ocean, 1992-1995 Field Years: Shore Based Analysis of Dissolved Inorganic Carbon January 1, 1993-April 15, 1998

Description: Participation in the hydrographic survey of the world ocean circulation experiment (WOCE) began in December 1990 with a two year grant from DOE for shore related analyses of inorganic carbon in sea water. These analyses were intended to assure that the measurements carried out under difficult laboratory conditions on board ships were consistent with measurements made under more carefully controlled shore laboratory conditions.
Date: April 15, 1998
Creator: Keeling, Charles D.
Partner: UNT Libraries Government Documents Department

Toward an extended-geostrophic Euler-Poincare model for mesoscale oceanographic flow

Description: The authors consider the motion of a rotating, continuously stratified fluid governed by the hydrostatic primitive equations (PE). An approximate Hamiltonian (L1) model for small Rossby number {var_epsilon} is derived for application to mesoscale oceanographic flow problems. Numerical experiments involving a baroclinically unstable oceanic jet are utilized to assess the accuracy of the L1 model compared to the PE and to other approximate models, such as the quasigeostrophic (QG) and the geostrophic momentum (GM) equations. The results of the numerical experiments for moderate Rossby number flow show that the L1 model gives accurate solutions with errors substantially smaller than QG or GM.
Date: July 1998
Creator: Allen, J. S.; Newberger, P. A. & Holm, D. D.
Partner: UNT Libraries Government Documents Department

Circulation and particle fluxes in the southern California Bight. Final report

Description: Work funded by the grant consisted of a series of experiments designed to elucidate scales and forcing mechanisms of the circulation and water properties within Santa Monica/San Pedro basin. Each experiment consisted of a moored array of roughly 30 current meters, CTD surveys (usually upon deployment and retrieval of the moored array), and satellite imagery. The CROSS moored array was designed primarily to obtain information on cross-shelf and cross-basin coherence scales, vertical coherence scales and the principal forcing mechanisms for the circulation. Several papers are referenced.
Date: July 26, 1993
Creator: Hickey, Barbara M.
Partner: UNT Libraries Government Documents Department

Dispersive internal long wave models

Description: This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). This work is a joint analytical and numerical study of internal dispersive water wave propagation in a stratified two-layer fluid, a problem that has important geophysical fluid dynamics applications. Two-layer models can capture the main density-dependent effects because they can support, unlike homogeneous fluid models, the observed large amplitude internal wave motion at the interface between layers. The authors have derived new model equations using multiscale asymptotics in combination with the method they have developed for vertically averaging velocity and vorticity fields across fluid layers within the original Euler equations. The authors have found new exact conservation laws for layer-mean vorticity that have exact counterparts in the models. With this approach, they have derived a class of equations that retain the full nonlinearity of the original Euler equations while preserving the simplicity of known weakly nonlinear models, thus providing the theoretical foundation for experimental results so far unexplained.
Date: November 1, 1998
Creator: Camassa, R.; Choi, W.; Holm, D.D.; Levermore, C.D. & Lvov, Y.
Partner: UNT Libraries Government Documents Department

Abstracts of oral and poster sessions

Description: The climate model of the Goddard Institute for Space Studies (GISS GCM) has been used to project the influence of increasing concentrations of greenhouse gases on the future global climate. New parameterizations for the GISS GCM are being developed to improve its depiction of current climate scenarios and to make it more sensitive to the variability of external forcing mechanisms such as sea-surface temperatures (SST), atmospheric aerosols and constituent trace gases. The new moist convection scheme makes cumulus fluxes proportional to vertical thermal instability and computes convective-scale downdrafts whose effect is to prevent excessive drying of the boundary layer by compensating subsidence. The physically-based ground hydrology component improves the land surface sensible and latent heat calculations by explicitly considering transpiration, evaporation from intercepted precipitation, evaporation from bare soil, infiltration, soil water flow and runoff. The revised planetary boundary layer uses a more valid physical model than previously to obtain more realistic near-surface winds and energy budgets. Preliminary results with newer versions of the GCM include a better seasonal migration of the ITCZ and more realistic tropical winds. One of our approaches to model validation is the evaluation of runs forced by globally observed sea-surface temperatures. The presentation will show how model improvements increase the quality of simulated interannual variations in global circulation and tropical rainfall.
Date: December 31, 1994
Creator: Druyan, L.M.
Partner: UNT Libraries Government Documents Department

Computational physical oceanography -- A comprehensive approach based on generalized CFD/grid techniques for planetary scale simulations of oceanic flows. Final report, September 1, 1995--August 31, 1996

Description: The original intention for this work was to impart the technology that was developed in the field of computational aeronautics to the field of computational physical oceanography. This technology transfer involved grid generation techniques and solution procedures to solve the governing equations over the grids thus generated. Specifically, boundary fitting non-orthogonal grids would be generated over a sphere taking into account the topography of the ocean floor and the topography of the continents. The solution methodology to be employed involved the application of an upwind, finite volume discretization procedure that uses higher order numerical fluxes at the cell faces to discretize the governing equations and an implicit Newton relaxation technique to solve the discretized equations. This report summarizes the efforts put forth during the past three years to achieve these goals and indicates the future direction of this work as it is still an ongoing effort.
Date: February 20, 1997
Creator: Beddhu, M.; Jiang, M.Y.; Whitfield, D.L.; Taylor, L.K. & Arabshahi, A.
Partner: UNT Libraries Government Documents Department

Benchmarking ocean circulation models on massively parallel computers

Description: 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.
Date: August 1, 1997
Creator: Poling, D.A.
Partner: UNT Libraries Government Documents Department

Evidence of systematic biases in ocean surface heat fluxes simulated by AGCMs

Description: The Atmospheric Model Intercomparison Project has provided a unique opportunity to evaluate atmospheric general circulation model (AGCM) simulations made with realistic boundary forcing. Here we report on some results from AMIP Subproject No. 5, making use of a suite of observationally-based estimates of ocean surface heat fluxes to evaluate the seasonal cycle of surface heating as simulated by AGCMs.
Date: January 1, 1995
Creator: Gleckler, P.J. & Randall, D.A.
Partner: UNT Libraries Government Documents Department

Model-based inversion for a shallow ocean application

Description: A model-based approach to invert or estimate the sound speed profile (SSP) from noisy pressure-field measurements is discussed. The resulting model-based processor (MBP) is based on the state-space representation of the normal-mode propagation model. Using data obtained from the well-known Hudson Canyon experiment, a noisy shallow water ocean environment, the processor is designed and the results compared to those predicted using various propagation models and data. It is shown that the MBP not only predicts the sound speed quite well, but also is able to simultaneously provide enhanced estimates of both modal and pressure-field measurements which are useful for localization and rapid ocean environmental characterization.
Date: March 1, 1994
Creator: Candy, J. V. & Sullivan, E. J.
Partner: UNT Libraries Government Documents Department

Ocean current observations near McMurdo Station, Antarctica from 1991 to 1993: Relation to wastewater discharge dispersal

Description: Analyses of ocean currents in the vicinity of McMurdo Station, Antarctica, are relevant to the transport and dispersal of wastewater from the McMurdo Station sewage outfall pipe. Observations of ocean currents during the initial phases of this study have been presented by Howington and McFeters. These studies, using coliform bacterial counts as an indicator of dispersion of the wastewater plume and current meters to measure flow patterns, indicated that dispersal of the plume by local currents does not effectively remove the plume from the vicinity of McMurdo Sound, under the present outfall pipe location. Moreover, these studies suggest that, although the flow pattern is generally consistent with transport of the plume away from McMurdo Station, episodes of current reversal are sufficient to transport the wastewater plume along the shore toward the southeast, eventually overlapping the seawater intake area near the McMurdo jetty. Several concerns included (a) impacts of wastewater inputs to nearshore benthic and pelagic habitats adjacent to McMurdo Station, (b) effects of wastewater input to the McMurdo Station fresh water intake source, and (c) reduction in human impacts on the McMurdo Sound ecosystem. These concerns motivated studies to characterize nearshore currents more extensively in relation to dispersal of the wastewater plume. This report discusses analysis results of current observations from November 1992 to November 1993.
Date: August 1, 1994
Creator: Barry, J. P.
Partner: UNT Libraries Government Documents Department

Simulations of the global carbon cycle and anthropogenic CO{sub 2} transient. Final report, September 15, 1993--September 14, 1997

Description: The primary accomplishment of this research was the development of an ocean biogeochemistry model for the carbon cycle, and the application of this model to studies of anthropogenic CO{sub 2} uptake and the global carbon cycle. The model has been used to study the oceanic uptake that would occur if future atmospheric CO{sub 2} were to be stabilized with the ocean circulation remaining constant. The authors also modeled how oceanic uptake would be affected by changes in ocean circulation that are predicted to occur due to global warming. The research resulted in 21 publications, and an additional 5 papers either in press or in preparation. The accomplishments of this research served as the foundation on which the Carbon Modeling Consortium was built. The CMC is a NOAA funded collaborative program involving principal investigators from various NOAA laboratories and universities. It has the goal of developing techniques to monitor the global carbon cycle on land as well as the ocean, and to predict its future course.
Date: June 1998
Creator: Sarmiento, J. L. & Pacala, S. W.
Partner: UNT Libraries Government Documents Department


Description: This paper is about the parallel implementation of a high-resolution, spectral element, primitive equation model of a homogeneous equatorial ocean. The present work shows that the high-order domain decomposition methods can be efficiently implemented in a massively parallel computing environment to solve large-scale CFD problems, such as the general circulation of the ocean.
Date: November 1997
Creator: Ma, H.; McCaffrey, J. & Piacsek, S.
Partner: UNT Libraries Government Documents Department

Studies of Ocean Predictability at Decade to Century Time Scales Using a Global Ocean General Circulation Model in a Parallel Computing Environment

Description: The objectives of this report are to determine the structure of oceanic natural variability at time scales of decades to centuries, characterize the physical mechanisms responsible for the variability; determine the relative importance of heat, fresh water, and moment fluxes on the variability; determine the predictability of the variability on these times scales. (B204)
Date: November 30, 1998
Creator: Barnett, T.P.
Partner: UNT Libraries Government Documents Department


Description: The present work is about the algorithms and parallel constructs of a spectral element equatorial ocean model. It shows that high order domain decomposition ocean models can be efficiently implemented on massively parallel architectures, such as the Connection Machine Model CM5. The optimized computational efficiency of the parallel spectral element ocean model comes not only from the exponential convergence of the numerical solution, but also from the work-intensive, medium-grained, geometry-based data parallelism. The data parallelism is created to efficiently implement the spectral element ocean model on the distributed-memory massively parallel computer, which minimizes communication among processing nodes. Computational complexity analysis is given for the parallel algorithm of the spectral element ocean model, and the model's parallel performance on the CM5 is evaluated. Lastly, results from a simulation of wind-driven circulation in low-latitude Atlantic ocean are described.
Date: July 15, 1998
Partner: UNT Libraries Government Documents Department

Ocean predictability studies in a parallel computing environment. Final report

Description: The goal of the SDSC effort described here is to evaluate the performance potential of the Oberhuber isopycnal (OPYC) ocean global circulation model on the 64-node iPSC/860 parallel computer at SDSC and its near term successor, the Intel Paragon, relative to that of a single vector processor of a CRAY Y-MP and its near term successor, the CRAY C90. This effort is in support of a larger joint project with researchers at Scripps Institution of Oceanography to study the properties of long (10 to 100-year scale), computationally intensive integrations of ocean global circulation models. Generally, performance of the OPYC model on the iPSC/860 has proved quite disappointing, with a simplified version of the entire model running at approximately 1.4 Mflops on a single i860 node in its original form and after extensive optimization, including coding in assembler, at 3.2 Mflops. The author estimates overall performance to be limited to 75 Mflops or less on the 64-node machine, as compared to 180 Mflops for a single CRAY Y-MP processor and 500 Mflops for a single CRAY C90 processor. Similarly, he believes an implementation on an Intel Paragon, even with several hundred nodes, will not be competitive with a single processor C90 implementation. Additionally, the Hamburg Large Scale Geostrophic (LSG) model has been implemented on high-performance workstations and evaluated for its computational potential as an alternative to OPYC for the long term integrations.
Date: November 1, 1992
Creator: Leary, R.H.
Partner: UNT Libraries Government Documents Department