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Antarctica / Re: Antarctic Tectonics
« Last post by gerontocrat on Today at 01:55:11 PM »

Is not the rebound a see-saw effect, wherein a bit of the Earth's crust rises as another part sinks?


The Article I read about this used an analogy. Imagine a big lump of dough on your table top. Plonk a heavy weight in the middle. The middle sinks and the periphery outside the weight rises. Remove the weight - the centre rises and the periphery sinks - slowly.

But I am a "wish I had been" geologist
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Arctic sea ice / Re: Northwest Passage thread
« Last post by Peter Ellis on Today at 01:36:24 PM »
I suspect the categorisation is only nominally based on age and in fact depends more on thickness.  This is irrelevant during the freeze-up, when thickness depends on age (new ice being thin, older ice being thicker), etc.  However, during the melt season it's perfectly plausible to have "old" ice that is only 20cm thick because most of it has melted.  Note that there is no category for thin old ice, and even the categories for thinner first-year ice are structured around the formation process.
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Antarctica / Re: Antarctic Tectonics
« Last post by Adam Ash on Today at 01:17:32 PM »
...clearly, this rebound could contribute meaningfully to sea level rise in the future.

Is not the rebound a see-saw effect, wherein a bit of the Earth's crust rises as another part sinks?

Does not the rebound require the rebounding slab to have some latent buoyancy due to loading of the crust somewhere not too far away?  When the load on the depressed slab is reduced, then must not there be a corresponding settlement of the nearby loading mass, which would simply neutralise to some degree the impact of the rebound on sea levels. 

The effect of the rebound is also constrained by the shapes of the rising and falling crustal slabs, and their position relative to the ocean surface.  In an extreme case consider a very narrow skyscraper as the load - mostly above the existing ocean level, and a broad 'table' as the currently-depressed crust slab below sea level.  As the load comes off the slab it rises displacing water as it rises from the ocean floor approaching the water's surface. The falling load tower has minimal positive displacement as it moves down, so the net change is an increase in the displaced volume, and thus some sea level rise.  But as soon as any element of the rising slab breaches the sea surface, then no matter how much higher it goes, that column of the slab does not contribute any more to displacement.  So the slab (aka Antarctica) can rise to a considerable height without displacing any more ocean beyond that displaced at the stage where it pierces the sea surface.   

There are some funny games to be played in how this all works, but it certainly does not appear obvious that isostatic rebound in a given location will automatically lead to displacement of sea water and hence to SLR.

Which reminds me of a recent paper (mentioned somewhere in this forum) which indicated that when Greenland is completing its rebound, then Iceland will have sunk to several hundred metres below sea level as its mass provides the downward moment which is used to shove Greenland up as the ice cap is removed.  I don't know if that paper calculated the planet-wide net impact of that rise+fall event.

Not as simple as it sounds, but of course I guess nature will contrive to ensure that all feedbacks are net 'bad' for us just to keep us in our intellectual place!
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Arctic sea ice / Re: The 2017 melting season
« Last post by Glenn Tamblyn on Today at 01:09:39 PM »
WTF

Looking at the last few days of Uni Bremen concentration maps. How can it vary so much?

Is this the ice doing something weird? Is this a programming/algorithm issue. How can concentration variations sweep across the basin so radically?
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Arctic sea ice / Re: Northwest Passage thread
« Last post by numerobis on Today at 01:04:06 PM »
Oh, I've been misreading these charts! Good thing I'm not a captain.

Indeed, seems odd the ice got from mostly old ice to mostly thick new ice, just about overnight.
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The rest / Re: Global Sea Ice Extent According to NSIDC
« Last post by gerontocrat on Today at 01:01:17 PM »
A Confession:-

Two days ago I posted a table concerning Global Sea Ice Extent with the following warning.

JAXA data says that on average (2007-2016) remaining Arctic extent loss is 0.2 million km2 greater than Antarctic extent gain. However, the end dates of freezing and melting are unlikely to be the same. This complicates matters. So it is with some trepidation, misgivings and a BEWARE notice that I include the little table below of some possible end of season outcomes.

The table was arithmetically correct, but wrong. The methodology of just looking at remaining extent loss and extent gain misses further losses due to the timing of events.
The sequence of events over the next one to 5 weeks seems to be (on average) :-
- arctic extent loss exceeds antarctic extent gain up to the antarctic maximum. Global extent reduces.
- antarctic maximum is reached a few days before arctic minimum meaning further global extent reduction.
- for a few days after arctic minimum (until mid-September) arctic extent gain is still less than antarctic ice loss.
- Arctic freezing gets into high gear and exceeds antarctic extent loss until end-October/Mid-November, at which point Global Sea Ice Extent is at the maximum.
- Then the Antarctic Spring Summer ice extent loss far exceeds arctic winter gain. Global Sea Ice Extent drops.

However, the sequence of events is highly variable. The new table below shows that in the last 10 years the Autumn minimum of global sea ice has happened as early as 23 Aug and as late as the 20 September.

Methinks 'tis the Antarctic that will decide - if 2017 repeats the 2016 low maximum and early rapid extent that made it lowest in the satellite record by November 5th then........
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Arctic sea ice / Re: Home brew AMSR2 extent & area calculation
« Last post by Wipneus on Today at 12:59:56 PM »
Attached the regional area graph of the CAB. Black=2017 UH AMSR2, purple is 2017 Jaxa.

Large swings are not unusual for UH AMSR2, but not in every year in the same amount.

Further the Jaxa data is much smoother and tends to follow the tops of the UH data. I am inclined to think that those (the tops) are a more realistic area value.
Wipneus, do you have a chart of just the CAB JAXA area since 2012?
Even better, where can I download the regional JAXA area data? I couldn't find it on the web.

Data for the graphic above is here:
https://sites.google.com/site/arctischepinguin/home/amsr2/data/Jaxa_AMSR2_L3_10km_Area_Extent-v0.0.txt

Notes:

- normally updates 24 hours after the others;
- total extent and area are calculated over the 14 well-known regions. E.g. Baltic, Maine and Alaska are ignored;
- no two day averages like ADS's product;
- apart from the above my day-to-day extent data is not exactly the same as ADS/Jaxa's numbers. Why that is I do not know yet.
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The rest / Re: 2017 open thread
« Last post by johnm33 on Today at 12:59:37 PM »
Interesting paper on how the sun works, from an electric universe perspective, may give some insight into variability. http://www.journalcra.com/sites/default/files/23817.pdf
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Arctic sea ice / Re: Northern Sea Route thread
« Last post by Pavel on Today at 12:45:54 PM »
Russia is therefore using the old fashioned law "Power Gives The Right" to bully submission. And who can stop them ? No-one.
I'm a russian, and here in Russia I 100500 times per day hear that US is the country using the old fashioned law "Power Gives The Right" to bully submission. And who can stop them ? Only mr Putin lol. Sorry for OT
20
...
I am thinking also that ice dyking much of the through-flow channels of the CAA would be a big bonus in disabling the Garlic-press  and throttling down Halodecline by fresh surface water export here.

Rite, I will play 'your silly game'!  Attached image shows 'dykes' plugging all viable channels of the garlic press - each located at the narrowest point between bits of terra firma.  The total length of dyke required is 300 kilometres, with the longest span being about 100 km. 

Such a project would not be a 'bonus', it would be an engineering impossibility within the presently available resources and skills and likely a practical failure too, IMHO.  The environmental implications are poorly understood, and the potential unintended consequences (including the impact of the soot from the fossil fuel emissions of plant building the dykes on ice life) are likely to be too numerous to enumerate, with either forward- or hind-sight. 

Next!
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