tag:blogger.com,1999:blog-5337555368793819627.post4227361305072798850..comments2023-06-07T09:04:36.390-04:00Comments on More Grumbine Science: Sea Ice EstimationsRobert Grumbinehttp://www.blogger.com/profile/10783453972811796911noreply@blogger.comBlogger11125tag:blogger.com,1999:blog-5337555368793819627.post-73744529955654413732010-07-02T06:40:46.757-04:002010-07-02T06:40:46.757-04:00http://farm5.static.flickr.com/4075/4754564774_c92...http://farm5.static.flickr.com/4075/4754564774_c9243458a9_b.jpg<br /><br />A few things I have been wrestling with about this graph:<br /><br />The heat transfer in is maximum at soltice (subject to weather variation). The peak melt rate is always later which is not too suprising - the later in the melt season the thinner the ice. <br /><br />After the peak melting rate, the downward trend in rate is suprisingly linear. (OK 2008 does not look linear but then 2009 has a big jog in the other direction.) The heat transfer in is not linear, so what pattern of increasing areas of just above 15% ice cover occurs to make the trends in ice melt rate look linear?<br /><br />If the volume is particularly low this year, presumably this pattern of increasing areas with low ice cover may be more important this year so leading to a more curved in 2008 direction shape.<br /><br /><br />The date of peak melting rate seems more variable than the date when net melting ends:<br />2010 <br />2009 26/07/2009 103069<br />2008 26/07/2008 89910<br />2007 13/07/2007 118850<br />2006 06/07/2006 93259<br />2005 31/07/2005 91239<br />2004 09/08/2004 88393<br />2003 25/07/2003 88002<br /><br />peak rate 35 day range<br /><br />1st positive 15/09/2004 <br />last negative 27/09/2003 <br /><br />zero rate 13 day range<br /><br />If 13 days reflects weather variability, are the other 22 days of peak rate variability predictable from factors other than weather?crandleshttps://www.blogger.com/profile/15181530527401007161noreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-62916786669468031452010-06-05T07:39:18.799-04:002010-06-05T07:39:18.799-04:00Good thought provoking piece. In your predictive ...Good thought provoking piece. In your predictive model output as with most of the others the current rate of ice cover loss is seen as at or a close to the maximum rate, what about the potential for a steepening trend, what is it that seems to limit a faster sea ice extent loss?Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-26827566656230045132010-06-03T19:53:57.293-04:002010-06-03T19:53:57.293-04:00Anon:
Always a good thing to know about more thin...Anon: <br />Always a good thing to know about more things. As you see from Eli's answer, there's a different good example that I could also be drawing on. But I'm more familiar with logistic curve than hysteresis, so went with that.<br /><br />Something you can do, though, is start working on applying the argument I did in <a href="http://moregrumbinescience.blogspot.com/2010/06/when-will-arctic-ice-be-gone.html" rel="nofollow">when will arctic ice be gone</a>. Except you'd use a criterion of the 2007 average instead of 0. By eye, I agree that it looks likely that the new record will be set before 2017.<br /><br />thomas:<br />You see/show the weakness of heuristic curves. It looks good to me, but 'looks good' doesn't have much persuasive value. The wave-induced breakup process is something already being observed, though, so to the extent that the logistic curve is appropriate, it won't be surprised by waves. <br /><br />Your point about extrapolation is good. That's why other reason for the logistic curve is that the data we already have don't look linear.<br /><br />Hank:<br />Good example. That's also why multiyear ice is thick. In general, it is not because of freezing. Thicker ice insulates itself so as to not freeze much. But being slammed against the Canadian Archipelago or Greenland suffices to pile it up impressively.<br /><br />crandles:<br />I haven't run the numbers, but yes, I do think area is probably going to be equally logistic to extent. <br /><br />Volume, on the other hand, it is not so intuitively clear to me. Maybe.<br /><br />Something that bodes well for me playing with the volume numbers from PIOMAS is that I've recently been talking to Ron Lindsay (one of the folks involved in that model). We have some overlapping work interests. I'll be late July before I can really do anything about it, but it'll be an interesting thing to pursue.<br /><br />Methods of reconciliation would depend on how different the different methods were. If they made similar estimates, with similar uncertainties (or at least that we had similar confidence in them), then the right thing to do is fairly straightforward. I'll illustrate this next week, when I turn to how Wu and I came up with our model estimate. On the other hand, if we really don't know what confidence we can have -- as happened between the model and the statistical method -- the most honest and meaningful thing to do is simply report the different estimates.<br /><br />Greg:<br />I'm sometimes distressingly literal :-)<br /><br />If you could tell me how to get the 'most recent comments' box to be a little narrower, so as to display next to, rather than below, the index terms, that would help a lot. I haven't had time to fool around to get it going myself.Robert Grumbinehttps://www.blogger.com/profile/10783453972811796911noreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-60465296176491595232010-06-03T18:51:00.887-04:002010-06-03T18:51:00.887-04:00Never mind "where's the poll". You ...Never mind "where's the poll". You weren't kidding when you said the bottom of the blog. (scroll, scroll, ...)Greghttps://www.blogger.com/profile/07116646136992710754noreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-26410059038125991032010-06-03T18:43:46.728-04:002010-06-03T18:43:46.728-04:00Where's the poll?Where's the poll?Greghttps://www.blogger.com/profile/07116646136992710754noreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-71026743894869549162010-06-03T17:32:46.531-04:002010-06-03T17:32:46.531-04:00Do you also expect a logistic curves for sea ice v...Do you also expect a logistic curves for sea ice volume (and area)?<br /><br />Have you considered trying to also fit a logistic curve to volume?<br /><br />http://psc.apl.washington.edu/ArcticSeaiceVolume/images/BPIOMASIceVolumeAnomalyCurrent.png<br /><br />What probabilities would that come out with using just a logistic fit to ice volume?<br /><br />How would you then reconcile differences in the probabilities from two or three such methods into one believable probability?crandleshttps://www.blogger.com/profile/15181530527401007161noreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-629261125516188882010-06-03T10:00:42.783-04:002010-06-03T10:00:42.783-04:00Remember ice can stack up as well as crumble. Exa...Remember ice can stack up as well as crumble. Example:<br />http://www.mms.gov/alaska/reports/1990rpts/91_0073APPEND.pdf<br /><br />"… ice conditions changed drastically when a tremendous wind storm swept across the North Slope for three days. Visibility dropped to just a few feet. The wind gusted to over 102 mph and sustained winds of 50 to 70 mph were common …. The worst factor of this storm was the powerful wind which drove ice crashing onto the shore…. the ice stacked up along the shore to a height of 20 feet …."Hank Robertshttps://www.blogger.com/profile/07521410755553979665noreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-50548605637792230842010-06-02T11:31:53.991-04:002010-06-02T11:31:53.991-04:00Thomas, think land-fast ice shelves, such as those...Thomas, think land-fast ice shelves, such as those along the north shore of Ellesmere Island and in the longer northern fjords of Ellesmere, Baffin, and Greenland. Being more massive, some of that floating ice will take much longer to melt than free-floating multi-year pack ice.Jim Eagernoreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-47939237966666578762010-06-02T09:11:16.417-04:002010-06-02T09:11:16.417-04:00Not that I know much about ice dynamics, but the l...Not that I know much about ice dynamics, but the logistic curve just looks wrong to me. Once ice cover is sufficiently small I think it would be unstable. There is nothing to keep the water at freezing and larger waves in the open water will crush the remaining ice or push it south where it will melt.<br /><br />I don't understand why you are bothered by a linear extrapolation reaching negative values. It's common that extrapolations break down at some, hopefully physically obvious, point. Drop a ball and you can extrapolate its path as a parabola, but only until it hits the floor.<br /><br />My very unphysical estimate is that ice cover will be very low this September, based on how many contrarians that are usually wrong started talking about a cooling trend this winter :-)Thomas Palmhttps://www.blogger.com/profile/12135033271970754087noreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-64824640858553105462010-06-01T22:20:28.981-04:002010-06-01T22:20:28.981-04:00For quite some time I've been thinking about t...For quite some time I've been thinking about the sea ice curve as a process with a lot of hysteresis, which looks very much like the upside down logistic curve. The lag is the need to rebuild multiyear ice when there is significant melting.EliRabetthttps://www.blogger.com/profile/07957002964638398767noreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-83112689082451360642010-06-01T17:12:51.663-04:002010-06-01T17:12:51.663-04:00Interesting - I don't think I've come acro...Interesting - I don't think I've come across the logistic curve before, it looks like a useful tool (I plan on doing a modelling course next year). A nice explanation, and I thank you for it.<br /><br />I had kind of hoped that 2007 would hold the record for a similar amount of time as 1995 did (about a decade) - but your curve makes that look very unlikely. <br /><br />S2Anonymousnoreply@blogger.com