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revision 1.18 by mlosch, Thu Jul 3 18:16:22 2008 UTC revision 1.19 by mlosch, Fri Jul 4 11:51:09 2008 UTC
# Line 45  It has 420 by 384 grid boxes and is carv Line 45  It has 420 by 384 grid boxes and is carv
45  boundary conditions from, a global cubed-sphere configuration  boundary conditions from, a global cubed-sphere configuration
46  similar to that described in \citet{menemenlis05}.  similar to that described in \citet{menemenlis05}.
47    
48    \ml{[Some of this could be part of the introduction?]}%
49  The global ocean and sea ice results presented in \citet{menemenlis05}  The global ocean and sea ice results presented in \citet{menemenlis05}
50  were carried out as part  were carried out as part
51  of the Estimating the Circulation and Climate of the Ocean, Phase II (ECCO2)  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
116  albedos of open water, dry ice, wet ice, dry snow, and wet snow, which  albedos of open water, dry ice, wet ice, dry snow, and wet snow, which
117  are now, respectively, 0.15, 0.85, 0.76, 0.94, and 0.8.  are now, respectively, 0.15, 0.85, 0.76, 0.94, and 0.8.
118    
119  The model is integrated from Jan~01, 1992 to Mar~31, 2000  The model is integrated from Jan~01, 1992 to Mar~31, 2000.
120  \reftab{experiments} gives an overview over the experiments discussed  \reftab{experiments} gives an overview over the experiments discussed
121  in \refsec{arcticresults}.  in \refsec{arcticresults}.
122  \begin{table}  \begin{table}
# Line 188  steps for the EVP solutions: \citet{hunk Line 189  steps for the EVP solutions: \citet{hunk
189  for the EVP solution. We use two interpretations of this choice where  for the EVP solution. We use two interpretations of this choice where
190  the EVP model is subcycled 120 times within a (short) model timestep  the EVP model is subcycled 120 times within a (short) model timestep
191  of 1200\,s resulting in a very long and expensive integration  of 1200\,s resulting in a very long and expensive integration
192  ($\Delta{t}_\mathrm{evp}=10\text{\,s}$) and 120 times within the  ($\Delta{t}_\mathrm{evp}=10\text{\,s}$) and 144 times within the
193  forcing timescale of 6\,h ($\Delta{t}_\mathrm{evp}=150\text{\,s}$).  forcing timescale of 6\,h ($\Delta{t}_\mathrm{evp}=150\text{\,s}$).
194    
195  \subsection{Results}  \subsection{Results}
# Line 207  model solutions can be interpreted as cu Line 208  model solutions can be interpreted as cu
208    
209  \reffig{iceveloc} shows ice velocities averaged over Janunary,  \reffig{iceveloc} shows ice velocities averaged over Janunary,
210  February, and March (JFM) of 1992 for the C-LSR-ns solution; also  February, and March (JFM) of 1992 for the C-LSR-ns solution; also
211  shown are the differences between B-grid and C-grid, LSR and EVP, and  shown are the differences between this reference solution and various
212  no-slip and free-slip solution. The velocity field of the C-LSR-ns  sensitivity experiments. The velocity field of the C-LSR-ns
213  solution (\reffig{iceveloc}a) roughly resembles the drift velocities  solution (\reffig{iceveloc}a) roughly resembles the drift velocities
214  of some of the AOMIP (Arctic Ocean Model Intercomparison Project)  of some of the AOMIP (Arctic Ocean Model Intercomparison Project)
215  models in a cyclonic circulation regime (CCR) \citep[their  models in a cyclonic circulation regime (CCR) \citep[their
# Line 268  differs most between B and C-grids: On a Line 269  differs most between B and C-grids: On a
269  velocity lies on the boundary (and is thus zero through the no-slip  velocity lies on the boundary (and is thus zero through the no-slip
270  boundary conditions), whereas on the C-grid it is half a cell width  boundary conditions), whereas on the C-grid it is half a cell width
271  away from the boundary, thus allowing more flow. The B-LSR-ns solution  away from the boundary, thus allowing more flow. The B-LSR-ns solution
272  has less ice drift through the Fram Strait and especially the along  has less ice drift through the Fram Strait and along
273  Greenland's east coast; also, the flow through Baffin Bay and Davis  Greenland's east coast; also, the flow through Baffin Bay and Davis
274  Strait into the Labrador Sea is reduced with respect the C-LSR-ns  Strait into the Labrador Sea is reduced with respect the C-LSR-ns
275  solution.  \ml{[Do we expect this? Say something about that]}  solution.  \ml{[Do we expect this? Say something about that]}
# Line 300  EVP solutions. Line 301  EVP solutions.
301  %\end{figure}  %\end{figure}
302    
303  Compared to the other parameters, the ice rheology TEM  Compared to the other parameters, the ice rheology TEM
304  (\reffig{iceveloc}(e)) has a very small effect on the solution. In  (\reffig{iceveloc}e) has a very small effect on the solution. In
305  general the ice drift tends to be increased, because there is no  general the ice drift tends to be increased, because there is no
306  tensile stress and ice can be ``pulled appart'' at no cost.  tensile stress and ice can be ``pulled appart'' at no cost.
307  Consequently, the largest effect on drift velocity can be observed  Consequently, the largest effect on drift velocity can be observed
308  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
309  the ice-ocean stress formulation of \citet{hibler87},  stronger almost everywhere in the computational domain in the run with
310  \reffig{iceveloc}(f) the drift is stronger almost everywhere in the  the ice-ocean stress formulation of \citet{hibler87}
311  computational domain. The increase is mostly aligned with the general  (\reffig{iceveloc}f). The increase is mostly aligned with the general
312  direction of the flow, implying that the different stress formulation  direction of the flow, implying that the different stress formulation
313  reduces the deceleration of drift by the ocean.  reduces the deceleration of drift by the ocean.
314    
# Line 321  are very different, because the ice exte Line 322  are very different, because the ice exte
322  \mbox{C-LSR-ns~WTD}; inward from the ice egde, this run has smaller  \mbox{C-LSR-ns~WTD}; inward from the ice egde, this run has smaller
323  drift velocities, because the ice motion is more contrained by a  drift velocities, because the ice motion is more contrained by a
324  larger ice extent than in \mbox{C-LSR-ns}, where the ice at the same  larger ice extent than in \mbox{C-LSR-ns}, where the ice at the same
325  place is drifting nearly freely.  geographical position is nearly in free drift.
326    
327  A more sophisticated advection scheme (\mbox{C-LSR-ns DST3FL},  A more sophisticated advection scheme (\mbox{C-LSR-ns DST3FL},
328  \reffig{iceveloc}(h)) has its largest effect along the ice edge, where  \reffig{iceveloc}h) has its largest effect along the ice edge, where
329  the gradients of thickness and concentration are largest. Everywhere  the gradients of thickness and concentration are largest. Everywhere
330  else the effect is very small and can mostly be attributed to smaller  else the effect is very small and can mostly be attributed to smaller
331  numerical diffusion (and to the absense of explicitly diffusion for  numerical diffusion (and to the absense of explicit diffusion for
332  numerical stability).  numerical stability).
333    
334  \subsubsection{Ice volume during JFM 2000}  \subsubsection{Ice volume during JFM 2000}
# Line 336  numerical stability). Line 337  numerical stability).
337  area) of the C-LSR-ns solution, averaged over January, February, March  area) of the C-LSR-ns solution, averaged over January, February, March
338  of year 2000. By this time of the integration, the differences in the  of year 2000. By this time of the integration, the differences in the
339  ice drift velocities have led to the evolution of very different ice  ice drift velocities have led to the evolution of very different ice
340  thickness distributions, which are shown in \reffig{icethick}b--d, and  thickness distributions, which are shown in \reffig{icethick}b--h, and
341  concentrations (not shown).  concentrations (not shown).
342  \begin{figure}[tp]  \begin{figure}[tp]
343    \centering    \centering
# Line 387  Severnaya Semlya\ml{/or Nordland?}, Line 388  Severnaya Semlya\ml{/or Nordland?},
388  because ice tends to flow along coasts less easily in the B-LSR-ns  because ice tends to flow along coasts less easily in the B-LSR-ns
389  solution.  solution.
390    
391  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
392  smaller differences to C-LSR-ns in the central Arctic than the  smaller differences to C-LSR-ns in the central Arctic than the
393  transition from the B-grid to the C-grid (\reffig{icethick}c), except  transition from the B-grid to the C-grid (\reffig{icethick}c), except
394  in the Canadian Archipelago. There it reduces the effective ice  in the Canadian Archipelago. There it reduces the effective ice
# Line 410  time step and the ice is still thinner b Line 411  time step and the ice is still thinner b
411  solution with $\Delta{t}_\mathrm{evp}=150\text{\,s}$.  solution with $\Delta{t}_\mathrm{evp}=150\text{\,s}$.
412    
413  In year 2000, there is more ice everywhere in the domain in  In year 2000, there is more ice everywhere in the domain in
414  \mbox{C-LSR-ns WTD}, \reffig{icethick}(g). This difference, which is  C-LSR-ns~WTD (\reffig{icethick}g). This difference, which is
415  even more pronounced in summer (not shown), can be attributed to  even more pronounced in summer (not shown), can be attributed to
416  direct effects of the different thermodynamics in this run. The  direct effects of the different thermodynamics in this run. The
417  remaining runs have the largest differences in effective ice thickness  remaining runs have the largest differences in effective ice thickness
# Line 418  long the north coasts of Greenland and E Line 419  long the north coasts of Greenland and E
419  effects of TEM and \citet{hibler87}'s ice-ocean stress formulation are  effects of TEM and \citet{hibler87}'s ice-ocean stress formulation are
420  so different on the initial ice velocities, both runs have similarly  so different on the initial ice velocities, both runs have similarly
421  reduced ice thicknesses in this area. The 3rd-order advection scheme  reduced ice thicknesses in this area. The 3rd-order advection scheme
422  has an opposite effect of similar magnitude, point towards more  has an opposite effect of similar magnitude, pointing towards more
423  implicit lateral stress with this numerical scheme.  implicit lateral stress with this numerical scheme.
424    
425  The observed difference of order 2\,m and less are smaller than the  The observed difference of order 2\,m and less are smaller than the
# Line 458  leads to generally thicker ice (\reffig{ Line 459  leads to generally thicker ice (\reffig{
459    \label{tab:icevolume}    \label{tab:icevolume}
460  \end{table}  \end{table}
461    
462    \subsubsection{Ice transports}
463    
464  The difference in ice volume and ice drift velocities between the  The difference in ice volume and ice drift velocities between the
465  different experiments has consequences for the ice transport out of  different experiments has consequences for the ice transport out of
466  the Arctic. Although by far the most exported ice drifts through the  the Arctic. Although by far the most exported ice drifts through the
# Line 469  with large uncertainties; also note that Line 472  with large uncertainties; also note that
472  ice-ocean model to reproduce observations is not our goal, but we use  ice-ocean model to reproduce observations is not our goal, but we use
473  the published numbers as an orientation.  the published numbers as an orientation.
474    
 \subsubsection{Ice transports}  
   
475  \reffig{archipelago} shows an excerpt of a time series of daily  \reffig{archipelago} shows an excerpt of a time series of daily
476  averaged, smoothed with monthly running means, ice transports through  averaged ice transports, smoothed with a monthly running mean, through
477  various straits in the Canadian Archipelago and the Fram Strait for  various straits in the Canadian Archipelago and the Fram Strait for
478  the different model solutions and \reftab{icevolume} summarizes the  the different model solutions; \reftab{icevolume} summarizes the
479  time series.  time series.
480  \begin{figure}  \begin{figure}
481  %\centerline{{\includegraphics*[width=0.6\linewidth]{\fpath/Jan1992xport}}}  %\centerline{{\includegraphics*[width=0.6\linewidth]{\fpath/Jan1992xport}}}
482  %\centerline{{\includegraphics*[width=0.6\linewidth]{\fpath/ice_export}}}  %\centerline{{\includegraphics*[width=0.6\linewidth]{\fpath/ice_export}}}
# Line 549  thus leading to different solutions for Line 550  thus leading to different solutions for
550  this were true, this tantalizing circumstance would have a dramatic  this were true, this tantalizing circumstance would have a dramatic
551  impact on sea-ice modeling in general, and we would need to improve  impact on sea-ice modeling in general, and we would need to improve
552  the solution techniques for dynamic sea ice models, most likely at a very  the solution techniques for dynamic sea ice models, most likely at a very
553  high compuational cost (Bruno Tremblay, personal communication). Further,  high compuational cost (Bruno Tremblay, personal communication).
554  we observe that the EVP solutions tends to produce effectively  
555  ``weaker'' ice that yields more easily to stress. The fast response to  Further, we observe that the EVP solutions tends to produce
556  changing wind was also observed by \citet{hunke99}, their Fig.\,10--12,  effectively ``weaker'' ice that yields more easily to stress. This was
557  where the EVP model adjusts quickly to a cyclonic wind pattern, while  also observed by \citet{hunke99} in a fast response to changing winds,
558  the LSOR solution does not. This property of the EVP solutions allows  their Figures\,10--12, where the EVP model adjusts quickly to a
559  larger ice transports through narrow straits, where the implicit  cyclonic wind pattern, while the LSOR solution lags in time. This
560  solver LSOR forms rigid ice. The underlying reasons for this striking  property of the EVP solutions allows larger ice transports through
561  difference need further exploration.  narrow straits, where the implicit solver LSOR forms rigid ice. The
562    underlying reasons for this striking difference need further
563    exploration.
564    
565  % THIS is now almost all in the text:  % THIS is now almost all in the text:
566  %\begin{itemize}  %\begin{itemize}
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