Eric, regarding a comment you made a couple of posts ago, IIRC the expectation is that after the initial summer sea ice loss it will reform in the winter because winter air temps will remain damned cold. That reformed ice will be thin stuff and very prone to disappearing quickly the following summer, but still will be thick enough to allow the Arctic Ocean to retain much of the heat gained via the summer open water.
----- Original Message ----- From: "Eric Swanson" <[EMAIL PROTECTED]> To: "globalchange" <[email protected]> Sent: Saturday, August 11, 2007 7:54 PM Subject: [Global Change: 2040] Re: Rapid loss of sea-ice this summer > > > William M Connolley wrote: >> On Sat, 11 Aug 2007, Eric Swanson wrote: >> > Having been educated as a mechanical engineer, I learned a bit about >> > structures and stresses. I've also done a small bit of work with >> > fatigue failure. That said, I think it's obvious that ice does >> > exhibit tensile strength, all thought how that applies to sea-ice, I >> > can't yet say. >> >> Ice certainly has a tensile strength. Where it gets confusing (in terms >> of large >> scales, model or reality) is that you shouldn't think of it as one floe; >> its >> always an assembly of floes. Thats where both the "viscous" bit comes >> from, and >> the zero tensile strength (actually I think you'd find that a homogenous >> solid >> piece of ice 1m think has almost no tensile strength (measured by the >> wind >> whether it had leads or not; the same ice, on scales of 1m, would be >> strong). >> >> -W. > > Thanks. With a bit of googling, I found some reports on the subject, > including Hunke and Dukowicz, (1997), which I think you pointed to. > They do mention that the viscous approach includes the thickness of > the sea-ice in the calculations. Others have pointed out the low > tensile strength of ice, but that wasn't what I was trying to deal > with as much as the possible difference between first year and multi- > year ice in terms of motion. Using the viscous model, it would appear > obvious that the first year ice should tend to move about much more > easily than multi-year ice . > > Other reading brought out the scale problem which Michael discussed. > The physical strength of the ice is a factor at micron levels, yet the > movement and stresses are evident over hundreds of kilometers. One > example given showed fractures in the ice cap which produced features > evident over nearly the whole extent of the ice field. Ice rafting > and pressure ridges change the character of the ice as well and are > more likely to be seen in multi-year ice compared with first year > ice. Michael should know that the scale of the model in terms of the > resolution (or grid spacing) would change the level of detail that > would be appropriate for the sea-ice model as well, since the > treatment of the sea-ice as an aggregate of individual floes probably > will not be appropriate when the average floe size is near that of the > grid size. I doubt that's yet a problem, BTW. > > However, if the sea-ice becomes thinner as time goes on, the likely > result might be smaller floes, as storms and waves would tend to break > up the larger floes. That would make motion easier and might be > represented as a reduced viscosity. As it is, the model by Hibler is > said to use a viscosity that varied with the stress tensor. I do not > yet know whether that variation also includes ice thickness, but I > think it should. As noted by Hunke and Dukowicz, the viscosity used > in the VP models extend over several orders of magnitude, which is > part of their motivation in offering their improved model, since their > use of an elastic response speeds the computations considerably, > especially for short term transient situations. > > Perhaps we will witness another strong storm moving across the Arctic > sea-ice this season, while the ice is near minimum. Such an event > could prove extremely interesting to the curious, since we wouldn't > need a model to see changes. > > E. S. > > > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups Global Change ("globalchange") newsgroup. Global Change is a public, moderated venue for discussion of science, technology, economics and policy dimensions of global environmental change. Posts will be admitted to the list if and only if any moderator finds the submission to be constructive and/or interesting, on topic, and not gratuitously rude. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/globalchange -~----------~----~----~----~------~----~------~--~---
