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Neville R. Smith

Abstract

A two-dimensional primitive equation model is developed to study the thermohaline circulation of the Southern Ocean. The primary objectives are to identify those elements of the ocean climate model important for the thermohaline balance, and to assess the capability of the numerical formulations. The simplified configuration adopted here permits extended runs from rest to equilibrium for a variety of configurations and parametric conditions.

The model is driven by surface flux of momentum, heat and salt, and is implemented with and without the dynamic component in order to delineate important thermodynamic interactions. Additional experiments analyze the effects of seasonal forcing versus annual mean conditions, the eddy coefficient parameterizations, resolution, and convective adjustment schemes.

Reasonable qualitative agreement is found between the model and observations. The fundamental climatic balance is characterized by downward and poleward diffusion of heat, predominantly by diffusive processes, and subsequent convection at high latitudes. The balance is sensitive to seasonal effects, particularly salt-forced convection in winter, and the details of the parameterizations. The convection and diffusion representations are critical for Antarctic water mass formation and frontogenesis as they not only determine the large-scale climatic environment, but also the seasonal production rates of various water masses.

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Neville R. Smith

Abstract

This study demonstrates techniques that lead to improved use of ocean thermal information and more useful and informative products for monitoring variability in the tropical oceans. The method is based on statistical interpolation and is illustrated using analyses for the 20°C isotherm depth over the Pacific and Indian Oceans. A new monthly climatology is derived by exploiting the statistical interpolation method to provide an improved weighted estimate. The new climatology is shown to better represent key aspects of the tropical ocean thermal structure.

A statistical forecast based on the previous analysis and climatology significantly improves the analysis product, both in a qualitative sense and as judged by quantitative measures of the skill of the forecast and of the estimated error of the analysis. Both the new climatology and the statistical forecasting scheme are interpreted as strategies for delivering enhanced information to the analysis system.

A series of 10-day analyses are presented. It is shown that these analyses retain all the information contained in longer period analyses, at least when used with statistical forecasts, and that in addition they resolve higher-frequency events in the equatorial waveguide. The 10-day analyses have around the same absolute estimated error as the longer period analyses but substantially higher accuracy due to the larger variance of the 10-day field. Some implications of these results are discussed.

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Klaus Fraedrich and Neville R. Smith

Abstract

The linear combination of two statistical forecast schemes of a single observable provides, in the average, a more accurate prediction than the individual forecasts alone. This method is applied to long-range forecasting of the monthly mean tropical Pacific sea surface temperatures.

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Neville R. Smith and G. Dale Hess

Abstract

The vertical eddy mixing formulations employed in the K-theory model of Pacanowski and Philander and in second-moment closure models are compared for an equatorial Pacific Ocean simulation. The Pacanowski and Philander model is found to be mainly driven by changes in the stratification rather than shear-generated instabilities, and the position and width of the mixing transition zone between high and low mixing values is found to be sensitive to the parameters of the model. In the second-moment closure models the master length scale limit effectively determines the threshold of the mixing zone, while the inclusion of storage, advection, and diffusion terms in the turbulent kinetic energy equation affects both the position and extent of the transition zone. Viscous mixing is more intense than diffusive mixing in the Pacanowski and Philander scheme, but in the second-moment closure models the reverse tends to be true. As expected, there is no simple functional relationship between the gradient Richardson number and the intensity of mixing in the second-moment closure schemes.

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Andreas Schiller, Gary Meyers, and Neville R. Smith

Abstract

No abstract available.

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Neville R. Smith and C. B. Fandry

Abstract

A simple, frictional, linear model is used to study the motion of the Gull Stream over the continental shelf. It is found that the combination of frictional and topographic effects may provide a further mechanism by which the observed separation of the Gulf Stream may be achieved.

The model predicts separation in the form of a classical separated boundary layer and interrelates the slope of the bottom with the position of separation. Counter-circulations northwest of the stream and increased northward transport of the current are also predicted.

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Richard Kleeman, Andrew M. Moore, and Neville R. Smith

Abstract

An adjoint variational assimilation technique is used to assimilate observations of both the oceanic state and wind stress data into an intermediate coupled ENSO prediction model. This method of initialization is contrasted with the more usual method, which uses only wind stress data to establish the initial state of the ocean. It is shown that ocean temperature data has a positive impact on the prediction skill in such models. On the basis of hindcasts for the period 1982–91, it is shown that NIN03 SST anomaly correlations greater than 0.7 can be obtained for hindcasts of duration up to 13 months and greater than 0.6 up to 16 months. There are also clear indications of skill at two years.

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Guomin Wang, Richard Kleeman, Neville Smith, and Faina Tseitkin

Abstract

An El Niño–Southern Oscillation (ENSO) prediction system with a coupled general circulation model and an ocean data assimilation scheme has been developed at the Australian Bureau of Meteorology Research Centre (BMRC). The coupled model consists of an R21L9 version of the BMRC climate model and a global version of the Geophysical Fluid Dynamics Laboratory modular ocean general circulation model with resolution focused in the tropical region and 25 vertical levels. A univariate statistical interpolation method, with 10-day data ingestion windows, is used to assimilate ocean temperature data and initialize the coupled model. The coupling procedure does not use any flux corrections. Hindcasts have been carried out for the period 1981–95 for each season (60 in all), for up to a lead time of 12 months. This paper will describe these initial experiments and show that the skill of sea surface temperature (SST) hindcasts in the tropical Pacific is comparable to other published coupled models. The skill of the model is strongest in the central Pacific. SST skill tends to be lower during the earlier 1990s than during 1980s in the eastern Pacific but not in the central Pacific. Since the ENSO SST anomaly in the central Pacific is the most important forcing of regional and global climate anomalies, the high SST prediction skill and its insensitivity over the hindcast period in this region in this model give grounds for optimism in the use of coupled general circulation models.

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Worth D. Nowlin Jr., Melbourne Briscoe, Neville Smith, Michael J. McPhaden, Dean Roemmich, Piers Chapman, and J. Frederick Grassle

The Global Ocean Observing System (GOOS) was initiated in the early 1990s with sponsorship by the Intergovernmental Oceanographic Commission, the International Council for Science, the United Nations Environment Programme, and the World Meteorological Organization. Its objective is to design and assist with the implementation of a sustained, integrated, multidisciplinary ocean observing system focused on the production and delivery of data and products to a wide variety of users. The initial design for the GOOS is nearing completion, and implementation has begun.

The initial task in developing a sustained observing system is to identify the requirements of users for sustained data and products. Once such needs are known, the next task is to examine observing system elements that already exist; many necessary elements will be found to exist. The next tasks are to identify and integrate the useful elements into an efficient and effective system, while removing the unneeded elements, and to develop and implement effective data management activities. Moreover, the system must be augmented with new elements because some requirements cannot be met with existing elements and because of technological advances.

Our key objective is to discuss the mechanism whereby new candidate observing system elements are transformed from development status into elements of the sustained system. Candidate systems normally will pass through many different phases on the path from idea and concept to a mature, robust technique. These stages are discussed and examples are given:

  1. Development of an observational/analysis technique within the ocean community.

  2. Community acceptance of the methodology gained through experience within pilot projects to demonstrate the utility of the methods and data.

  3. Pre-operational use of the methods and data by researchers, application groups, and other end users, to ensure proper integration within the global system and to ensure that the intended augmentation (and perhaps phased withdrawal of an old technique) does not have any negative impact on the integrity of the GOOS data set and its dependent products.

  4. Incorporation of the methods and data into an operational framework with sustained support and sustained use to meet societal objectives.

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Worth D. Nowlin Jr., Neville Smith, George Needler, Peter K. Taylor, Robert Weller, Ray Schmitt, Liliane Merlivat, Alain Vézina, Arthur Alexiou, Michael McPhaden, and Massaaki Wakatsuchi

Designs and implementation are proceeding for a Global Ocean Observing System (GOOS) and a Global Climate Observing System (GCOS). The initial design for the ocean component of the GCOS, which is also the climate module of the GOOS, was completed in 1995 by the Ocean Observing System Development Panel (OOSDP). This design for an ocean observing system for climate aims to provide ocean observations leading to gridded products, analyses, forecasts, indexes, assessments, and other items needed to detect, monitor, understand, and predict climate variations and change. A summary of the OOSDP report is presented here, beginning with the rationale for such a system and the series of specific goals and subgoals used to focus the design. The instruments, platforms, transmission systems, or processing required to observe the climate variables or quantifiable aspects of the climate system to meet these subgoals are identified. These observing system elements are divided into three categories: 1) elements of existing operational systems, 2) those that should be added now to complete the initial observing system, or 3) elements perhaps not now readily attainable but that should be added to the system at the earliest feasible time. Future research and development likely needed for further development of the system are also identified in the report. The elements needed for each subgoal are ranked as to feasibility (i.e., routine, systematic, timely, and cost-effective characteristics) versus their impact on attaining the subgoal. Priorities among the various subgoals are presented based on the panel's perception of where the immediate and important issues lie. This then provides the basis for an incremental approach to implementation, leading to a coherent conceptual design.

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