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Andrew Xnn

The FrankD graph (melt season area/extent) shows us that the last 3 years are exceptional in that the minimum was reached in late August while the previous 4 years were consistently reaching minimums in late July.

It is also interesting to see how consistent 2002 thru 2006 were during most of the melt season. The most significant anomaly among those years was 2004 which was high during May to June.

2010 is also something of a standout in how erratic it has been between late June thru July.


Thanks again for all the great work!!

FrankD

Andrew - That shift is interesting; it suggests more open water between floes at a moderately fine scale - a looser pack, in essence - since the bad years of 2006 & 2007. I'm watching to see if this year repeats the downwards kick through the middle of August that we have seen for the last three.

The 2004 line through April-June is quite odd, and I double-checked it to make sure I hadn't muffed a formula somewhere. But it does make sense when you look at the graphs side-by-side. While 2004 April area was low, 2004 April extent was the lowest of the nine years charted. Over the next two months both measures rose to the highest in the nine years, but with area always leading by a little. Since both were declining, obviously, we can say that the decline in area was relatively slower than the decline in extent. So the area:extent ratio was always high, even though both were varying.

I haven't gone back to look at the pictures, I expect that extent declined because of melt at the fringes, but the pack remained comparatively well consolidated. CT's historical maps seem to be offline, but I'll have a poke through the archive when I stop getting 404 errors at see if thats what their maps show.

Neven - thanks again for running this great blog. I totally sympathise with IJIS's position, and I hasten to add that I always thought what I was doing was fairly crude and non-definitive. However it seems an interesting indicator of pack health, so I'll update it from time-to-time over the remainder of the season, and post links here.

Larry's long span graph is very interesting, though I must concede I don't have the patience for two data points per year - I want see where the August line is going to be in five years NOW, dammit!

Artful Dodger

FrandD, the NSIDC data is month means for Area and Extend, from 1979 to present.

Artful Dodger

Neven, good work on the graph. Smoothing the curves is a nice touch. I would prefer to see at least a full season's data (preferably 6 mths) on the graph. The way it is drawn now with only a few days of 2010 data we can not compare this year to others. As long as you continue to update the spreadsheet, I don't think that a coarser resolution on the time axis matters.

With respect to the 'data hole' at the north pole, CT does add in the area to their daily posted Area numbers, so I believe 'ignoring' worked well here.

Neven

Thanks, AD. I tried to make a graph for the whole year, but somehow OpenOffice didn't accept something I did and made all the trend lines appear in red. I'll try making a 6 month graph this weekend.

I believe 'ignoring' worked well here.

I know. It is one of the best methods around. The whole pseudoskeptic community is using it on a continuous basis.

L. Hamilton

July NSIDC means just came out, so I drew an updated "area as % of extent" graph. To highlight July I (and give Frank more than 2 data points/year to look at!) I added a third line for that month.

The result was a surprise: July or August, not September, comprise all of the low points in the area/extent curves (except for an odd double-dip in 1995). FWIW, in the past 3 years August has been the low point.

July 2010 looks similar to July 2007, by this metric.

http://img.photobucket.com/albums/v224/Chiloe/Climate/area_vs_extent2.png

Neven

Larry, you're making it difficult to keep up with you. Thanks for the great graphs.

Neven

AD, I've added two more graphs, for half-year and full-year.

The half-year one looks nice for the SIE updates, I think.

Artful Dodger

Neven, top shelf. This story needs to be put up front, how about adding the 6-mth graph to the the Arctic Sea Ice Graphs page? Well done!

siili

Indeed, very interesting graphs! And now we are ready to answer Dodgers original question, if we can use this to forecast extent? I'm still sorely missing my old favourite plottingprogram SM, so i am only at the point at plotting CT area although i fint that interesting in itself, but maybe you could start to put the three graphs: area, extent and area/extent together and see if something emerges from that.

Artful Dodger

My original question was, does a significant drop in the Area/Extent ratio precede a dramatic drop in total Extent? It seems to me that, in the case where the pack is melting in from the edges, A/R will not change significantly in advance of the drop in Extent.

In the case where the pack is breaking up / collapsing by being inundated with warmer water, then A/R must go up just before the drop in Extent.

Again, without per basin data, there may be so much noise in Area & Ext. measurements that a significant signal may be drowned out (though CT clearly has per basin data...)

Neven

AD, in the previous Area vs Extent post Axel/IceMan says that the area/extent ratio is called 'compactness' and gives as an example a paper by Lindsay and Zhang.

I've updated the Arctic sea ice graphs page with the webcam image from Healy. If I knew how to make a script that collects all data and automatically adjusts the ice compactness graph I would add it to the page as well. To do it manually though (OpenOffice won't let me export the graph, so I have to do it with PrintScrn and Photoshop).

I will be using the 6 month-graph for tomorrow's SIE update.

siili

Guys, it's really easy to suggest work for others to do, but i really think that we should do a bit more of the process ourselfs and hence have much better controll of the outcome.

Over at the other side in a more than usually stupid thread Julienne from NSIDC has advertized their gridded daily data with concentration per pixel given. With that we can define own areas of interest and determine area, extent, compactness whatever we like.

It's a very simple dataformat, that in principle only has to be read into a matrix, together with the areatransformation matrix, and then we just start adding things up.

I can try it myself, but since the same ole was dicussed at the other place on the other side some years age, i'm sure there must be plentifull of code arround.

Neven

siili, count me out! :-)

Artful Dodger

Neven, there's no overwhelming need to automate the 'Compactness' (A/E ration) graph on the Arctic Sea Ice Extent page (although AJAX could do it). I suggest it's fine to simply link there to a static URL for the graph as updated every 3 days or so in your regular updates.

Two suggestions for the graph: 1. perhaps provide a table (or at least a label) equating Day of the Year (x-axis) to Date. 2. a format other than jpeg would be more appropriate, perhaps .png or even .gif

Finally, it should be fairly straightforward to code a javascript that gets the current GMT time and and converts it into the image URL for the current Healy AloftCam. If you request, I could provide some support with that. Cheers!

Artful Dodger

Johann, can you provide a link to the NSIDC gridded data?

siili

Getting exited are we?
You could try theese to start with
http://nsidc.org/data/polar_stereo/ps_grids.html
http://nsidc.org/data/docs/noaa/g02135_seaice_index/index.html#doc_info
http://nsidc.org/data/polar_stereo/ps_grids.html

siili

and the data: ftp://sidads.colorado.edu/pub/DATASETS/seaice/polar-stereo/nasateam/near-real-time/north/
and the tools: ftp://sidads.colorado.edu/pub/DATASETS/seaice/polar-stereo/tools/

Neven

If you request, I could provide some support with that. Cheers!

AD, thanks, I'll keep that in mind. I'm really busy at the moment, so this is low on my priority list for now.

FrankD

New version of the IJIS Area/Extent graph to 10th August can be found at:
http://img808.imageshack.us/img808/4606/areaoverextent100810.png

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