Ocean general circulation from a global eddy‐resolving model

A concerted effort has been made to simulate the global ocean circulation with resolved eddies, using a highly optimized model on the best available supercomputer. An earlier 20-year spin-up has been extended for 12.5 additional years: the first 2.5 with continued annual mean forcing and the final 10.0 with climatological monthly forcing. Model output archived at 3-day intervals has been analyzed into mean fields, standard deviations, products, and covariances on monthly, annual, and multiyear time scales. The multiyear results are examined here in order to give insight into the general circulation of the world ocean. The three-dimensional flow fields of the model are quite realistic, even though resolution of eddies in high latitudes is marginal with a 0.5°, 20-level grid. The use of seasonal forcing improves the simulation, especially in the tropics and high northern latitudes. Mid-latitude gyre circulations, western boundary currents, zonal equatorial flows, and the Antarctic Circumpolar Current (ACC) all show mean and eddy characteristics similar to those observed. There is also some indication of eddy intensification of the mean flow of the ACC and of separated boundary jets. A global thermohaline circulation of North Atlantic Deep Water is identified in deep western boundary currents connected by the ACC. This deep circulation rises mainly in the equatorial Pacific. Several zonal jets are an integral part of this circulation near the equator. The deep flow rises toward the surface in a series of switchbacks. Much of the thermohaline return flow then follows an eddy-rich warm-water route through the Indonesian archipelago and around the southern tip of Africa. However, some intermediate level portions of the thermohaline circulation return south into the ACC and follow a cold water route through the Drake Passage. The representation of a global “conveyor belt” circulation with narrow and relatively high-speed currents along most of its path may be the most important result of this modeling study. Statistics of scalar fields such as transport stream function and surface height are exhibited, as are time series and frequency spectra of certain variables at selected points. These provide a baseline for comparison both with observations and with other model studies at higher resolution. Mean and eddy characteristics of the near-surface temperature and salinity fields are discussed, and surface forcing fields are examined. In particular, combined thermal and hydrological forcing effects are found to drive a conveyor belt circulation between the tropical Pacific and the high-latitude North Atlantic. The effect of weak restoring terms to observed temperature and salinity at great depth and in polar latitudes is found mainly to augment the model's convective processes, which are poorly resolved with 0.5° grid spacing. However, the deep restoring terms are insignificant in both the tropics and the mid-latitudes. The geographical distributions of eddy heat and salt transport are discussed. The eddies transport heat and salt down the gradients and along the mean flow in many regions of strong currents. Net meridional transports of heat and salt by both the total currents and the eddies are computed for the Atlantic, the Indo-Pacific, and the global ocean. The total currents provide for poleward heat transport (except near 40°S, where the contribution from ACC instabilities is rather weak) and, in particular, for that needed to sustain the conveyor belt transport. Meridional eddy transports are especially important for warming the Pacific upwelling branch of the thermohaline circulation and for transporting salt across the equator into the North Pacific. Planned improvements to the model include a free-surface treatment of the barotropic mode and additions of the Arctic Basin and sea ice. A fully prognostic extension of the existing integration is intended, with subsequent transitioning of the model onto a 0.25° grid having very realistic geometry. The 0.25° version of the model will run effectively on newly available supercomputers.

[1]  M. England.  On the Formation of Antarctic Intermediate and Bottom Water in Ocean General Circulation Models , 1992 .

[2]  Detlef Stammer,et al.  Mesoscale Variability in the Atlantic Ocean from Geosat Altimetry and WOCE High-Resolution Numerical Modeling , 1992 .

[3]  William D. Hibler,et al.  Modeling Pack Ice as a Cavitating Fluid , 1992 .

[4]  R. Schmitt,et al.  Transport of freshwater by the oceans , 1992 .

[5]  D. Webb,et al.  The Development of a Free-Surface Bryan–Cox–Semtner Ocean Model , 1991 .

[6]  R. Döscher,et al.  Seasonal Transport Variation in the Western Subtropical North Atlantic: Experiments with an Eddy-resolving Model , 1991 .

[7]  F. Schott,et al.  The WOCE model in the western equatorial Atlantic: Upper layer circulation , 1991 .

[8]  D. Hansen,et al.  Anticyclonic current rings in the eastern tropical Pacific Ocean , 1991 .

[9]  Harry L. Bryden,et al.  Ocean heat transport across 24゜ N in the Pacific , 1991 .

[10]  S. Rintoul.  South Atlantic interbasin exchange , 1991 .

[11]  Wallace Broeker,et al.  The Great Ocean Conveyor , 1991 .

[12]  B. Moore,et al.  Resolving the intermediate and deep advective flows in the Indian Ocean by using temperature, salinity, oxygen and phosphate data: the interplay of biogeochemical and geophysical tracers , 1990 .

[13]  R. Chervin,et al.  Environmental effects on acoustic measures of global ocean warming , 1990 .

[14]  E. Sarachik,et al.  On the Importance of Vertical Resolution in Certain Ocean General Circulation Models , 1990 .

[15]  A. Watson,et al.  Deep-water renewal in the northern North Atlantic , 1990, Nature.

[16]  Robert M. Chervin,et al.  An Ocean Modelling System for Supercomputer Architectures of the 1990s , 1990 .

[17]  David T. Sandwell,et al.  Global mesoscale variability from the Geosat Exact Repeat Mission - Correlation with ocean depth , 1989 .

[18]  R. Ponte,et al.  Analysis and Interpretation of Deep Equatorial Currents in the Central Pacific , 1989 .

[19]  Keith W. Dixon,et al.  Simulations of radiocarbon in a coarse-resolution world ocean model: 1. Steady state prebomb distributions , 1989 .

[20]  E. Firing.  Mean zonal currents below 1500 m near the equator, 159°W , 1989 .

[21]  H. Bryden,et al.  Eddy momentum and heat fluxes and their effects on the circulation of the equatorial Pacific Ocean , 1989 .

[22]  J. S. Godfrey.  A sverdrup model of the depth-integrated flow for the world ocean allowing for island circulations , 1989 .

[23]  R. Chervin,et al.  A simulation of the global ocean circulation with resolved eddies , 1988 .

[24]  Victor Zlotnicki,et al.  Satellite Altimetry: Observing Ocean Variability from Space , 2007 .

[25]  M. Kawase.  Establishment of Deep Ocean Circulation Driven by Deep-Water Production , 1987 .

[26]  K. Hasselmann,et al.  Transport and storage of CO2 in the ocean ——an inorganic ocean-circulation carbon cycle model , 1987 .

[27]  A. Semtner,et al.  A Numerical Study of Sea Ice and Ocean Circulation in the Arctic , 1987 .

[28]  Wallace S. Broecker,et al.  Unpleasant surprises in the greenhouse? , 1987, Nature.

[29]  W. Bettge.  An Ocean Model Processor for Climate Studies , 1987 .

[30]  K. Bryan.  Poleward Buoyancy Transport in the Ocean and Mesoscale Eddies , 1986 .

[31]  Arnold L. Gordon,et al.  Interocean Exchange of Thermocline Water , 1986 .

[32]  K. Bryan.  Accelerating the Convergence to Equilibrium of Ocean-Climate Models , 1984 .

[33]  Bernard Kilonsky,et al.  Mean Water and Current Structure during the Hawaii-to-Tahiti Shuttle Experiment , 1984 .

[34]  J. Reid,et al.  Abyssal characteristics of the World Ocean waters , 1983 .

[35]  Sol Hellerman,et al.  Normal Monthly Wind Stress Over the World Ocean with Error Estimates , 1983 .

[36]  S. Levitus.  Climatological Atlas of the World Ocean , 1982 .

[37]  G. Meehl,et al.  Experiments with a global ocean model driven by observed atmospheric forcing , 1982 .

[38]  Harry L. Bryden,et al.  Direct estimates and mechanisms of ocean heat transport , 1982 .

[39]  Jorge L. Sarmiento,et al.  An ocean transport model for the North Atlantic , 1982 .

[40]  R. Pacanowski,et al.  Parameterization of Vertical Mixing in Numerical Models of Tropical Oceans , 1981 .

[41]  S. Hastenrath.  Heat Budget of Tropical Ocean and Atmosphere , 1980 .

[42]  K. Trenberth.  Mean annual poleward energy transports by the oceans in the southern hemisphere , 1979 .

[43]  L. V. Worthington.  On the North Atlantic Circulation , 1977 .

[44]  R. Haney.  Surface Thermal Boundary Condition for Ocean Circulation Models , 1971 .

[45]  M. Cox,et al.  A mathematical model of the Indian Ocean , 1970 .

[46]  H. Stommel,et al.  On the abyssal circulation of the world ocean — II. An idealized model of the circulation pattern and amplitude in oceanic basins , 1959 .