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Martin Losch and Patrick Heimbach

1. Introduction Numerical ocean general circulation models (OGCMs) consist of a set of discretized partial differential equations for a set of prognostic variables (the numerical ocean state ), which are solved subject to initial conditions and boundary conditions (lateral and surface boundary conditions, surface forcing); the solution also depends on a number of model parameters (e.g., diffusivity and viscosity parameters). These quantities are referred to as independent parameters, or

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A. J. Meijers, N. L. Bindoff, and J. L. Roberts

topography. The model was integrated for 20 yr, using asynchronous time stepping (6 min for velocities and 30 min for tracers). Velocities were initialized to zero, and initial temperatures and salinities were taken from the World Ocean Circulation Experiment (WOCE) Hydrographic Programme–Special Analysis Centre (WHP–SAC) atlas ( Gouretski and Janke 1998 ) supplemented by Levitus (1982) data in the Arctic Ocean. Restoring boundary conditions loosely constrain the sea surface temperature and salinity

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A. Köhl, D. Stammer, and B. Cornuelle

–XBT discrepancies in most regions by changing the initial conditions or surface forcing fields. However, the enhanced (relative to other geographical locations) total model–XBT misfit remains in the North Atlantic, which presumably results from erroneous northern boundary conditions: as will be discussed below, problems in the vertical mixing/convection, and especially those associated with the Denmark Straight overflow, cause the model to deviate from the observed temperature distributions in those regions. A

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Claudia Pasquero and Eli Tziperman

–sea heat fluxes, when restoring temperature boundary conditions are used. The heat fluxes from the standard convective adjustment and the statistical convection parameterization are very similar ( Figs. 3b and 3c ). During summertime the surface layers are very stable, so that the air–sea heat fluxes are not affected by the convective parameterization chosen (no convection takes place). In the winter months, the heat loss to the atmosphere is larger (by about 25%) in the case of the standard convective

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Reiner Schlitzer

below). Surface boundary conditions for all tracers except radiocarbon and CFC are formulated as flux boundary conditions, and the respective air–sea tracer fluxes (if applicable) are contained in q . c. Radiocarbon For radiocarbon (and CFC; see below) surface concentration boundary conditions are used instead of flux conditions, because 14 C and CFC concentrations are better known than fluxes. Consequently, the distributions of these two tracers are simulated only for model layers 2 and deeper

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Peter Huybers, Geoffrey Gebbie, and Olivier Marchal

sampled. a. Circulation model The model generally follows LW95 , except that we use a more idealized basin. The hypothetical ocean basin has a flat bottom and vertical walls and extends from 10° to 50°N in latitude, from 0° to 35° in longitude, and from 1 to 4 km in depth. The domain is divided into 10° × 10° × 1 km boxes except along the western boundary where boxes are 5° in longitude, giving 48 boxes in total. Boundary transport is only allowed through the north, south, and top surfaces of the

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Rui M. Ponte and Sergey V. Vinogradov

the surface to 500 m at the bottom. The bathymetry is based on the 2′ Gridded Earth Topography (ETOPO2) dataset provided by the National Geophysical Data Center (information online at http://www.ngdc.noaa.gov/mgg/fliers/01mgg04.html ), which has been modified to improve the coarse-grid representation of coastlines, islands, and straits ( Köhl et al. 2003 ). Free-slip bottom and no-slip lateral wall boundary conditions are imposed. Laplacian viscosity is used with horizontal and vertical

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Dimitris Menemenlis, Ichiro Fukumori, and Tong Lee

km zonal by 3.7 km meridional. Grid spacing gradually increases to approximately 4° near the poles and in the Pacific Ocean. This grid configuration avoids having to make arbitrary decisions about where and what open boundary conditions to impose, it provides high horizontal resolution in the study region, and yet it results in a manageable 440 × 266 horizontal grid dimension. Bathymetry is from the National Geophysical Data Center (NGDC) 2-min gridded global relief data (2′ Gridded Earth

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Walter Munk and Bruce Bills

. Loder and Garrett (1978) related the nodal tide to an 18.6-yr variability of SST in coastal waters, using a simple diffusion equation for guidance. They chose a quadratic nonlinearity, κ ∼ 〈 u 2 〉, based on boundary layer turbulence in nonstratified fluids. These processes are not applicable to tidally produced turbulence in the pelagic oceans. (But we end up using the same κ ∼ 〈 u 2 〉 proxy: it is traditional and simple, and does not offend any presently known evidence.) We associate the

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