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-revision 1.18 by mlosch,
Thu Jul  3 18:16:22 2008 UTC
+revision 1.21 by mlosch,
Mon Jul 28 07:38:27 2008 UTC
 Line 45 
 It has 420 by 384 grid boxes and is carv
  boundary conditions from, a global cubed-sphere configuration
  similar to that described in \citet{menemenlis05}.
+ \ml{[Some of this could be part of the introduction?]}%
  The global ocean and sea ice results presented in \citet{menemenlis05}
  were carried out as part
  of the Estimating the Circulation and Climate of the Ocean, Phase II (ECCO2)
-Line 115 
 free surface that are not supported by t
+Line 116 
 free surface that are not supported by t
  albedos of open water, dry ice, wet ice, dry snow, and wet snow, which
  are now, respectively, 0.15, 0.85, 0.76, 0.94, and 0.8.
- The model is integrated from Jan~01, 1992 to Mar~31, 2000
+ The model is integrated from Jan~01, 1992 to Mar~31, 2000.
  \reftab{experiments} gives an overview over the experiments discussed
  in \refsec{arcticresults}.
  \begin{table}
-Line 188 
 steps for the EVP solutions: \citet{hunk
+Line 189 
 steps for the EVP solutions: \citet{hunk
  for the EVP solution. We use two interpretations of this choice where
  the EVP model is subcycled 120 times within a (short) model timestep
  of 1200\,s resulting in a very long and expensive integration
- ($\Delta{t}_\mathrm{evp}=10\text{\,s}$) and 120 times within the
+ ($\Delta{t}_\mathrm{evp}=10\text{\,s}$) and 144 times within the
  forcing timescale of 6\,h ($\Delta{t}_\mathrm{evp}=150\text{\,s}$).
  \subsection{Results}
-Line 207 
 model solutions can be interpreted as cu
+Line 208 
 model solutions can be interpreted as cu
  \reffig{iceveloc} shows ice velocities averaged over Janunary,
  February, and March (JFM) of 1992 for the C-LSR-ns solution; also
- shown are the differences between B-grid and C-grid, LSR and EVP, and
+ shown are the differences between this reference solution and various
- no-slip and free-slip solution. The velocity field of the C-LSR-ns
+ sensitivity experiments. The velocity field of the C-LSR-ns
  solution (\reffig{iceveloc}a) roughly resembles the drift velocities
  of some of the AOMIP (Arctic Ocean Model Intercomparison Project)
  models in a cyclonic circulation regime (CCR) \citep[their
  Figure\,6]{martin07} with a Beaufort Gyre and a transpolar drift
  shifted eastwards towards Alaska.
+ %
- \newcommand{\subplotwidth}{0.44\textwidth}
+ \newcommand{\subplotwidth}{0.47\textwidth}
  %\newcommand{\subplotwidth}{0.3\textwidth}
  \begin{figure}[tp]
    \centering
    \subfigure[{\footnotesize C-LSR-ns}]
-   {\includegraphics[width=\subplotwidth]{\fpath/JFMuv_C-LSR-ns}}
+   {\includegraphics[width=\subplotwidth]{\fpath/JFMuv1992_C-LSR-ns}}
    \subfigure[{\footnotesize B-LSR-ns $-$ C-LSR-ns}]
-   {\includegraphics[width=\subplotwidth]{\fpath/JFMuv_B-LSR-ns-C-LSR-ns}}
+   {\includegraphics[width=\subplotwidth]{\fpath/JFMuv1992_B-LSR-ns-C-LSR-ns}}
    \\
    \subfigure[{\footnotesize C-LSR-fs $-$ C-LSR-ns}]
-   {\includegraphics[width=\subplotwidth]{\fpath/JFMuv_C-LSR-fs-C-LSR-ns}}
+   {\includegraphics[width=\subplotwidth]{\fpath/JFMuv1992_C-LSR-fs-C-LSR-ns}}
    \subfigure[{\footnotesize C-EVP-ns $-$ C-LSR-ns}]
-   {\includegraphics[width=\subplotwidth]{\fpath/JFMuv_C-EVP-ns150-C-LSR-ns}}
+   {\includegraphics[width=\subplotwidth]{\fpath/JFMuv1992_C-EVP-ns150-C-LSR-ns}}
  %  \\
  %  \subfigure[{\footnotesize C-LSR-ns TEM $-$ C-LSR-ns}]
- %  {\includegraphics[width=\subplotwidth]{\fpath/JFMuv_TEM-C-LSR-ns}}
+ %  {\includegraphics[width=\subplotwidth]{\fpath/JFMuv1992_TEM-C-LSR-ns}}
  %  \subfigure[{\footnotesize C-LSR-ns HB87 $-$ C-LSR-ns}]
- %  {\includegraphics[width=\subplotwidth]{\fpath/JFMuv_HB87-C-LSR-ns}}
+ %  {\includegraphics[width=\subplotwidth]{\fpath/JFMuv1992_HB87-C-LSR-ns}}
  %  \\
  %  \subfigure[{\footnotesize  C-LSR-ns WTD $-$ C-LSR-ns}]
- %  {\includegraphics[width=\subplotwidth]{\fpath/JFMuv_ThSIce-C-LSR-ns}}
+ %  {\includegraphics[width=\subplotwidth]{\fpath/JFMuv1992_ThSIce-C-LSR-ns}}
  %  \subfigure[{\footnotesize C-LSR-ns DST3FL $-$ C-LSR-ns}]
- %  {\includegraphics[width=\subplotwidth]{\fpath/JFMuv_adv33-C-LSR-ns}}
+ %  {\includegraphics[width=\subplotwidth]{\fpath/JFMuv1992_adv33-C-LSR-ns}}
    \caption{(a) Ice drift velocity of the C-LSR-ns solution averaged
      over the first 3 months of integration [cm/s]; (b)-(h) difference
      between solutions with B-grid, free lateral slip, EVP-solver,
-Line 250 
 shifted eastwards towards Alaska.
+Line 251 
 shifted eastwards towards Alaska.
  \end{figure}
  \addtocounter{figure}{-1}
  \setcounter{subfigure}{4}
- \begin{figure}[t]
+ \begin{figure}[tp]
    \subfigure[{\footnotesize C-LSR-ns TEM $-$ C-LSR-ns}]
-   {\includegraphics[width=\subplotwidth]{\fpath/JFMuv_TEM-C-LSR-ns}}
+   {\includegraphics[width=\subplotwidth]{\fpath/JFMuv1992_TEM-C-LSR-ns}}
    \subfigure[{\footnotesize C-LSR-ns HB87 $-$ C-LSR-ns}]
-   {\includegraphics[width=\subplotwidth]{\fpath/JFMuv_HB87-C-LSR-ns}}
+   {\includegraphics[width=\subplotwidth]{\fpath/JFMuv1992_HB87-C-LSR-ns}}
    \\
    \subfigure[{\footnotesize  C-LSR-ns WTD $-$ C-LSR-ns}]
-   {\includegraphics[width=\subplotwidth]{\fpath/JFMuv_ThSIce-C-LSR-ns}}
+   {\includegraphics[width=\subplotwidth]{\fpath/JFMuv1992_ThSIce-C-LSR-ns}}
    \subfigure[{\footnotesize C-LSR-ns DST3FL $-$ C-LSR-ns}]
-   {\includegraphics[width=\subplotwidth]{\fpath/JFMuv_adv33-C-LSR-ns}}
+   {\includegraphics[width=\subplotwidth]{\fpath/JFMuv1992_adv33-C-LSR-ns}}
    \caption{continued}
  \end{figure}
  The difference beween runs C-LSR-ns and B-LSR-ns (\reffig{iceveloc}b)
  is most pronounced along the coastlines, where the discretization
  differs most between B and C-grids: On a B-grid the tangential
  velocity lies on the boundary (and is thus zero through the no-slip
  boundary conditions), whereas on the C-grid it is half a cell width
  away from the boundary, thus allowing more flow. The B-LSR-ns solution
- has less ice drift through the Fram Strait and especially the along
+ has less ice drift through the Fram Strait and along
  Greenland's east coast; also, the flow through Baffin Bay and Davis
  Strait into the Labrador Sea is reduced with respect the C-LSR-ns
  solution.  \ml{[Do we expect this? Say something about that]}
-Line 283 
 Island.
+Line 285 
 Island.
  The C-EVP-ns solution with $\Delta{t}_\mathrm{evp}=150\text{\,s}$ is
  very different from the C-LSR-ns solution (\reffig{iceveloc}d). The
- EVP-approximation of the VP-dynamics allows for increased drift by
+ EVP-approximation of the VP-dynamics allows for increased drift by up
- over 2\,cm/s in the Beaufort Gyre and the transarctic drift.
+ to 8\,cm/s in the Beaufort Gyre and the transarctic drift.  In
- %\ml{Also the Beaufort Gyre is moved towards Alaska in the C-EVP-ns
+ general, drift velocities are strongly biased towards higher values in
- %solution. [Really?, No]}
+ the EVP solutions.
- In general, drift velocities are biased towards higher values in the
- EVP solutions.
- % as can be seen from a histogram of the differences in
- %\reffig{drifthist}.
- %\begin{figure}[htbp]
- %  \centering
- %  \includegraphics[width=\textwidth]{\fpath/drifthist_C-EVP-ns-C-LSR-ns}
- %  \caption{Histogram of drift velocity differences for C-LSR-ns and
- %    C-EVP-ns solution [cm/s].}
- %  \label{fig:drifthist}
- %\end{figure}
  Compared to the other parameters, the ice rheology TEM
- (\reffig{iceveloc}(e)) has a very small effect on the solution. In
+ (\reffig{iceveloc}e) has a very small effect on the solution. In
  general the ice drift tends to be increased, because there is no
  tensile stress and ice can be ``pulled appart'' at no cost.
  Consequently, the largest effect on drift velocity can be observed
- near the ice edge in the Labrador Sea. In contrast, in the run with
+ near the ice edge in the Labrador Sea. In contrast, the drift is
- the ice-ocean stress formulation of \citet{hibler87},
+ stronger almost everywhere in the computational domain in the run with
- \reffig{iceveloc}(f) the drift is stronger almost everywhere in the
+ the ice-ocean stress formulation of \citet{hibler87}
- computational domain. The increase is mostly aligned with the general
+ (\reffig{iceveloc}f). The increase is mostly aligned with the general
  direction of the flow, implying that the different stress formulation
  reduces the deceleration of drift by the ocean.
-Line 321 
 are very different, because the ice exte
+Line 312 
 are very different, because the ice exte
  \mbox{C-LSR-ns~WTD}; inward from the ice egde, this run has smaller
  drift velocities, because the ice motion is more contrained by a
  larger ice extent than in \mbox{C-LSR-ns}, where the ice at the same
- place is drifting nearly freely.
+ geographical position is nearly in free drift.
  A more sophisticated advection scheme (\mbox{C-LSR-ns DST3FL},
- \reffig{iceveloc}(h)) has its largest effect along the ice edge, where
+ \reffig{iceveloc}h) has some effect along the ice edge, where
  the gradients of thickness and concentration are largest. Everywhere
  else the effect is very small and can mostly be attributed to smaller
- numerical diffusion (and to the absense of explicitly diffusion for
+ numerical diffusion (and to the absense of explicit diffusion that is
- numerical stability).
+ requird for numerical stability in a simple second order central
+ differences scheme).
  \subsubsection{Ice volume during JFM 2000}
-Line 336 
 numerical stability).
+Line 328 
 numerical stability).
  area) of the C-LSR-ns solution, averaged over January, February, March
  of year 2000. By this time of the integration, the differences in the
  ice drift velocities have led to the evolution of very different ice
- thickness distributions, which are shown in \reffig{icethick}b--d, and
+ thickness distributions, which are shown in \reffig{icethick}b--h, and
  concentrations (not shown).
  \begin{figure}[tp]
    \centering
-Line 360 
 concentrations (not shown).
+Line 352 
 concentrations (not shown).
  \end{figure}
  \addtocounter{figure}{-1}
  \setcounter{subfigure}{4}
- \begin{figure}[t]
+ \begin{figure}[tp]
    \subfigure[{\footnotesize C-LSR-ns TEM $-$ C-LSR-ns}]
    {\includegraphics[width=\subplotwidth]{\fpath/JFMheff2000_TEM-C-LSR-ns}}
    \subfigure[{\footnotesize C-EVP-ns HB87 $-$ C-LSR-ns}]
-Line 374 
 concentrations (not shown).
+Line 366 
 concentrations (not shown).
  \end{figure}
  The generally weaker ice drift velocities in the B-LSR-ns solution,
  when compared to the C-LSR-ns solution, in particular through the
- narrow passages in the Canadian Archipelago, lead to a larger build-up
+ narrow passages in the Canadian Arctic Archipelago, lead to a larger build-up
  of ice north of Greenland and the Archipelago by 2\,m effective
  thickness and more in the B-grid solution (\reffig{icethick}b). But
  the ice volume in not larger everywhere: further west, there are
-Line 387 
 Severnaya Semlya\ml{/or Nordland?},
+Line 379 
 Severnaya Semlya\ml{/or Nordland?},
  because ice tends to flow along coasts less easily in the B-LSR-ns
  solution.
- Imposing a free-slip boundary condition in C-LSR-fs leads to a much
+ Imposing a free-slip boundary condition in C-LSR-fs leads to much
  smaller differences to C-LSR-ns in the central Arctic than the
  transition from the B-grid to the C-grid (\reffig{icethick}c), except
- in the Canadian Archipelago. There it reduces the effective ice
+ in the Canadian Arctic Archipelago. There it reduces the effective ice
  thickness by 2\,m and more where the ice is thick and the straits are
  narrow.  Dipoles of ice thickness differences can also be observed
  around islands, because the free-slip solution allows more flow around
  islands than the no-slip solution. Everywhere else the ice volume is
  affected only slightly by the different boundary condition.
  %
- The C-EVP-ns solution has generally stronger drift velocities than the
+ The C-EVP-ns solution has much thicker ice in the central Arctic Ocean
- C-LSR-ns solution. Consequently, more ice can be moved from the
+ than the C-LSR-ns solution (\reffig{icethick}d, note the color scale).
- eastern part of the Arctic, where ice volumes are smaller, to the
+ Within the Canadian Arctic Archipelago, more drift leads to faster ice export
- western Arctic (\reffig{icethick}d). Within the Canadian Archipelago,
+ and reduced effective ice thickness. With a shorter time step of
- more drift leads to faster ice export and reduced effective ice
+ $\Delta{t}_\mathrm{evp}=10\text{\,s}$ the EVP solution converges to
- thickness. With a shorter time step of
+ the LSOR solution (not shown). Only in the narrow straits in the
- $\Delta{t}_\mathrm{evp}=10\text{\,s}$ the EVP solution seems to
+ Archipelago the ice thickness is not affected by the shorter time step
- converge to the LSOR solution (not shown). Only in the narrow straits
+ and the ice is still thinner by 2\,m and more, as in the EVP solution
- in the Archipelago the ice thickness is not affected by the shorter
+ with $\Delta{t}_\mathrm{evp}=150\text{\,s}$.
- time step and the ice is still thinner by 2\,m and more, as in the EVP
- solution with $\Delta{t}_\mathrm{evp}=150\text{\,s}$.
  In year 2000, there is more ice everywhere in the domain in
- \mbox{C-LSR-ns WTD}, \reffig{icethick}(g). This difference, which is
+ C-LSR-ns~WTD (\reffig{icethick}g, note the color scale).
- even more pronounced in summer (not shown), can be attributed to
+ This difference, which is even more pronounced in summer (not shown),
- direct effects of the different thermodynamics in this run. The
+ can be attributed to direct effects of the different thermodynamics in
- remaining runs have the largest differences in effective ice thickness
+ this run. The remaining runs have the largest differences in effective
- long the north coasts of Greenland and Ellesmere Island. Although the
+ ice thickness long the north coasts of Greenland and Ellesmere Island.
- effects of TEM and \citet{hibler87}'s ice-ocean stress formulation are
+ Although the effects of TEM and \citet{hibler87}'s ice-ocean stress
- so different on the initial ice velocities, both runs have similarly
+ formulation are so different on the initial ice velocities, both runs
- reduced ice thicknesses in this area. The 3rd-order advection scheme
+ have similarly reduced ice thicknesses in this area. The 3rd-order
- has an opposite effect of similar magnitude, point towards more
+ advection scheme has an opposite effect of similar magnitude, pointing
- implicit lateral stress with this numerical scheme.
+ towards more implicit lateral stress with this numerical scheme.
  The observed difference of order 2\,m and less are smaller than the
  differences that were observed between different hindcast models and climate
-Line 431 
 averaging period) is smaller than $4,000
+Line 421 
 averaging period) is smaller than $4,000
  the run \mbox{C-LSR-ns~WTD} where the more complicated thermodynamics
  leads to generally thicker ice (\reffig{icethick} and
  \reftab{icevolume}).
- \begin{table}[htbp]
+ \begin{table}[t]
    \begin{tabular}{lr@{\hspace{5ex}}r@{$\pm$}rr@{$\pm$}rr@{$\pm$}r}
      model run & ice volume
      & \multicolumn{6}{c}{ice transport [$\text{flux$\pm$ std.,
-Line 453 
 leads to generally thicker ice (\reffig{
+Line 443 
 leads to generally thicker ice (\reffig{
    \caption{Arctic ice volume averaged over Jan--Mar 2000, in
      $\text{km$^{3}$}$. Mean ice transport and standard deviation for the
      period Jan 1992 -- Dec 1999 through the Fram Strait (FS), the
-     total northern inflow into the Canadian Archipelago (NI), and the
+     total northern inflow into the Canadian Arctic Archipelago (NI), and the
-     export through Lancaster Sound (LS), in $\text{km$^{3}$\,y$^{-1}$}$.}
+     export through Lancaster Sound (LS), in $\text{km$^{3}$\,y$^{-1}$}$.
-   \label{tab:icevolume}
+   \label{tab:icevolume}}
  \end{table}
+ \subsubsection{Ice transports}
  The difference in ice volume and ice drift velocities between the
  different experiments has consequences for the ice transport out of
  the Arctic. Although by far the most exported ice drifts through the
  Fram Strait (approximately $2300\pm610\text{\,km$^3$\,y$^{-1}$}$), a
  considerable amount (order $160\text{\,km$^3$\,y$^{-1}$}$) ice is
- exported through the Canadian Archipelago \citep[and references
+ exported through the Canadian Arctic Archipelago \citep[and references
  therein]{serreze06}. Note, that ice transport estimates are associated
  with large uncertainties; also note that tuning an Arctic sea
  ice-ocean model to reproduce observations is not our goal, but we use
  the published numbers as an orientation.
- \subsubsection{Ice transports}
  \reffig{archipelago} shows an excerpt of a time series of daily
- averaged, smoothed with monthly running means, ice transports through
+ averaged ice transports, smoothed with a monthly running mean, through
- various straits in the Canadian Archipelago and the Fram Strait for
+ various straits in the Canadian Arctic Archipelago and the Fram Strait for
- the different model solutions and \reftab{icevolume} summarizes the
+ the different model solutions; \reftab{icevolume} summarizes the
  time series.
  \begin{figure}
  %\centerline{{\includegraphics*[width=0.6\linewidth]{\fpath/Jan1992xport}}}
  %\centerline{{\includegraphics*[width=0.6\linewidth]{\fpath/ice_export}}}
  %\centerline{{\includegraphics[width=\linewidth]{\fpath/ice_export}}}
  \centerline{{\includegraphics[width=\linewidth]{\fpath/ice_export1996}}}
- \caption{Transport through Canadian Archipelago for different solver
+ \caption{Transport through Canadian Arctic Archipelago for different solver
    flavors. The letters refer to the labels of the sections in
    \reffig{arctic_topog}; positive values are flux out of the Arctic;
    legend abbreviations are explained in \reftab{experiments}. The mean
-Line 494 
 model solutions (annual averages range f
+Line 484 
 model solutions (annual averages range f
  $2300\text{\,km$^3$\,y$^{-1}$}$, except for \mbox{C-LSR-ns~WTD} with
  $2760\text{\,km$^3$\,y$^{-1}$}$ and the EVP solution with the long
  time step of 150\,s with nearly $3000\text{\,km$^3$\,y$^{-1}$}$),
- while the export through the Candian Archipelago is smaller than
+ while the export through the Candian Arctic Archipelago is smaller than
  generally thought. For example, the ice transport through Lancaster
  Sound is lower (annual averages are $43$ to
  $256\text{\,km$^3$\,y$^{-1}$}$) than in \citet{dey81} who estimates an
-Line 509 
 configuration, both B- and C-grid LSOR s
+Line 499 
 configuration, both B- and C-grid LSOR s
  ice transport, while the C-EVP solutions allow up to
  $600\text{\,km$^3$\,y$^{-1}$}$ in summer (not shown); \citet{tang04}
  report $300$ to $350\text{\,km$^3$\,y$^{-1}$}$.  As as consequence,
- the import into the Candian Archipelago is larger in all EVP solutions
+ the import into the Candian Arctic Archipelago is larger in all EVP solutions
  %(range: $539$ to $773\text{\,km$^3$\,y$^{-1}$}$)
  than in the LSOR solutions.
  %get the order of magnitude right (range: $132$ to
-Line 533 
 considerably smaller (the difference for
+Line 523 
 considerably smaller (the difference for
  but similar to that for the LSOR solver). Albeit smaller, the
  differences between free and no-slip solutions in ice drift can lead
  to equally large differences in ice volume, especially in the Canadian
- Archipelago over the integration time. At first, this observation
+ Arctic Archipelago over the integration time. At first, this observation
  seems counterintuitive, as we expect that the solution
  \emph{technique} should not affect the \emph{solution} to a higher
  degree than actually modifying the equations. A more detailed study on
-Line 549 
 thus leading to different solutions for
+Line 539 
 thus leading to different solutions for
  this were true, this tantalizing circumstance would have a dramatic
  impact on sea-ice modeling in general, and we would need to improve
  the solution techniques for dynamic sea ice models, most likely at a very
- high compuational cost (Bruno Tremblay, personal communication). Further,
+ high compuational cost (Bruno Tremblay, personal communication).
- we observe that the EVP solutions tends to produce effectively
- ``weaker'' ice that yields more easily to stress. The fast response to
+ Further, we observe that the EVP solutions tends to produce
- changing wind was also observed by \citet{hunke99}, their Fig.\,10--12,
+ effectively ``weaker'' ice that yields more easily to stress. This was
- where the EVP model adjusts quickly to a cyclonic wind pattern, while
+ also observed by \citet{hunke99} in a fast response to changing winds,
- the LSOR solution does not. This property of the EVP solutions allows
+ their Figures\,10--12, where the EVP model adjusts quickly to a
- larger ice transports through narrow straits, where the implicit
+ cyclonic wind pattern, while the LSOR solution lags in time. This
- solver LSOR forms rigid ice. The underlying reasons for this striking
+ property of the EVP solutions allows larger ice transports through
- difference need further exploration.
+ narrow straits, where the implicit solver LSOR forms rigid ice. The
+ underlying reasons for this striking difference need further
+ exploration.
  % THIS is now almost all in the text:
  %\begin{itemize}

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