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\section{Forward sensitivity experiments} |
\section{Forward sensitivity experiments} |
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\label{sec:forward} |
\label{sec:forward} |
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This section presents results from global and regional coupled ocean and sea |
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ice simulations that exercise various capabilities of the MITgcm sea ice |
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model. The first set of results is from a global, eddy-permitting, ocean and |
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sea ice configuration. The second set of results is from a regional Arctic |
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configuration, which is used to compare the B-grid and C-grid dynamic solvers |
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and various other capabilities of the MITgcm sea ice model. The third set of |
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results is from a yet smaller regional domain, which is used to illustrate |
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treatment of sea ice open boundary condition sin the MITgcm. |
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\subsection{Global Ocean and Sea Ice Simulation} |
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\label{sec:global} |
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The global ocean and sea ice results presented below were carried out as part |
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of the Estimating the Circulation and Climate of the Ocean, Phase II (ECCO2) |
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project. ECCO2 aims to produce increasingly accurate syntheses of all |
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available global-scale ocean and sea-ice data at resolutions that start to |
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resolve ocean eddies and other narrow current systems, which transport heat, |
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carbon, and other properties within the ocean \citep{menemenlis05}. The |
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particular ECCO2 simulation discussed next is a baseline 28-year (1979-2006) |
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integration, labeled cube76, which has not yet been constrained by oceanic and |
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by sea ice data. A cube-sphere grid projection is employed, which permits |
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relatively even grid spacing throughout the domain and which avoids polar |
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singularities \citep{adcroft04:_cubed_sphere}. Each face of the cube comprises |
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510 by 510 grid cells for a mean horizontal grid spacing of 18 km. There are |
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50 vertical levels ranging in thickness from 10 m near the surface to |
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approximately 450 m at a maximum model depth of 6150 m. Bathymetry is from the |
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National Geophysical Data Center (NGDC) 2-minute gridded global relief data |
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(ETOPO2) and the model employs the partial-cell formulation of |
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\citet{adcroft97:_shaved_cells}, which permits accurate representation of the |
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bathymetry. The model is integrated in a volume-conserving configuration using |
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a finite volume discretization with C-grid staggering of the prognostic |
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variables. In the ocean, the non-linear equation of state of \citet{jac95} is |
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used. |
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The ocean model is coupled to the sea-ice model discussed in |
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Section~\ref{sec:model} with the following specific options. The |
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zero-heat-capacity thermodynamics formulation of \citet{hib80} is used to |
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compute sea ice thickness and concentration. Snow cover and sea ice salinity |
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are prognostic. Open water, dry ice, wet ice, dry snow, and wet snow albedo |
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are, respectively, 0.15, 0.88, 0.79, 0.97, and 0.83. Ice mechanics follow the |
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viscous plastic rheology of \citet{hibler79} and the ice momentum equation is |
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solved numerically using the C-grid implementation of the \citet{zhang97} LSR |
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dynamics model discussed hereinabove. |
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This particular ECCO2 simulation is initialized from temperature and salinity |
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fields derived from the |
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\subsection{Arctic Domain with Open Boundaries} |
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\label{sec:arctic} |
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A second series of forward sensitivity experiments have been carried out on an |
A second series of forward sensitivity experiments have been carried out on an |
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Arctic Ocean domain with open boundaries. Once again the objective is to |
Arctic Ocean domain with open boundaries. Once again the objective is to |
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compare the old B-grid LSR dynamic solver with the new C-grid LSR and EVP |
compare the old B-grid LSR dynamic solver with the new C-grid LSR and EVP |
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solvers. One additional experiment is carried out to illustrate the |
solvers. One additional experiment is carried out to illustrate the |
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differences between the two main options for sea ice thermodynamics in the MITgcm. |
differences between the two main options for sea ice thermodynamics in the MITgcm. |
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\subsection{Arctic Domain with Open Boundaries} |
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\label{sec:arctic} |
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The Arctic domain of integration is illustrated in Fig.~\ref{fig:arctic1}. It |
The Arctic domain of integration is illustrated in Fig.~\ref{fig:arctic1}. It |
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is carved out from, and obtains open boundary conditions from, the |
is carved out from, and obtains open boundary conditions from, the |
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global cubed-sphere configuration of the Estimating the Circulation |
global cubed-sphere configuration of the Estimating the Circulation |
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