Messages

1

Arctic sea ice / Re: The Cause of the Muted Melt of 2013

« on: August 09, 2013, 12:10:32 PM »

Muted melt?

Other than the late melting of Kara and Beaufort, both of which will achieve the same (0) area as last year if trends continue, the other regions seem to be following almost exactly the same area pattern as last year ..

( from http://forum.arctic-sea-ice.net/index.php/topic,382.0.html)

2

Arctic sea ice / Re: Home brew AMSR2 extent & area calculation

« on: July 29, 2013, 09:33:42 AM »

For the region of the day it cannot be helped, but we keep coming back to the Beaufort. This is not just action, this is flash melting!

(now log in to see the image)

how does this description of "flash melting" match with the large area increase? (+53k)

3

Arctic sea ice / Re: Home brew AMSR2 extent & area calculation

« on: July 26, 2013, 11:45:21 AM »

how much does ice-free water warm up? -- ie, could punting the ice over water which melted out a week ago cause significant melting to offset the cooling effect from above?

4

Arctic sea ice / Re: Melt Ponds

« on: July 25, 2013, 01:29:57 PM »

The melt pond is starting to break through the sea ice now to the ocean beneath (see attached image, left-side of buoy).

I was waiting for that to begin happening -- to keep 1m of ice submerged requires about 9kN/m2 due to a density difference is about 125kg/m3(which is about 20% of the fracture force of the ice, which is about 50kN/m2 at large scale according to http://link.springer.com/article/10.1023%2FA%3A1021134128038#page-1)

5

Arctic sea ice / Re: What the Buoys are telling

« on: July 25, 2013, 08:09:38 AM »

between the last 2 posts, it looks like the water level has risen. (water at the level of the cable connecting to the depth sensor vs water almost at transducer level)

Where is the water coming from for that?

Also, i wouldn't expect this situation to persist, eventually the ice would have to crack somewhere and drain as the forces involved in keeping 1m of ice submerged would be "significant" over a large area.

Seawater is about 1025kg/m3, sea ice (1st year) is about 900.  the density difference would result in around 9kN of force/m2 from submerging 1m thick ice. This means that the buoyancy forces alone could be around 20% of the fracture strength of the ice.

(The fracture toughness of ice is in the range of 50–150 kPa m1/2, with larger pieces having lower strength due to being more liekly to include a weakness -  from   http://link.springer.com/article/10.1023%2FA%3A1021134128038#page-2 )

6

Consequences / Re: Melting Arctic an "economic time bomb"

« on: July 25, 2013, 07:42:54 AM »

" Methane is a wildcard on the end of an already very bad hand we've dealt ourselves."

It should be noted that we were also peeking at the deck quite heavily towards the end of the deal.

7

Arctic sea ice / Re: What the Buoys are telling

« on: July 23, 2013, 01:13:31 AM »

does anyone know how a single "thickness" is calculated when you have 75% 1.7m, 25% 0m? and a moderately large proportion of the ice somewhere in between?

8

Arctic sea ice / Re: Short to Medium Term Arctic Sea Ice Conditions Discussion

« on: July 21, 2013, 06:27:25 AM »

.. the term 'flash-melting' to describe what happens when a large region of sea ice at 20-odd % concentration all goes below the 15% SIE threshold over a single day.

And this is the problem with using any specific threshold -- you can get a nice uniform linear loss of 5%/week from top/bottom melting, then on some specific day you cross a threshold and it looks like "lots" of melt happens on that specific day.

Would it be possible to create a set of graphs with extent vs time, with plots of extent with a threshold of 5,10,15,25,33,50,75,90,95% ?

9

Arctic sea ice / Re: Home brew AMSR2 extent & area calculation

« on: July 20, 2013, 01:46:10 AM »

given that there are issues with costal pixels anyway, would there be a significant downside to producing numbers at the high resolution with the low resolution ground mask? ie; just ignore that extra area when computing some of the numbers, for the purpose of comparing the 2 datasets?

10

Arctic sea ice / Re: Cryosphere Today 2013 Arctic SIA daily minimum: July poll

« on: July 10, 2013, 09:42:24 AM »

I estimate 2.5, almost all in the arctic basin. This assumes that the arctic basin loses about 10% more area than it lost last year, because the thickness is 8% less, and assuming that regions which melted out for more than a month will melt out this year also.


Furthermore i estimate that at the end of this month we will still be above the 2012 value, but i would place less certainty on that prediction than the final number.

All numbes done by eyeball estimate based on regional trends from http://forum.arctic-sea-ice.net/index.php/topic,382.0.html


Direct regional trends

	2012 now	2012 1st aug	2012 min	2013 now	2013 1st aug   minimum
Total	7.15	5.15	3	7.4	5.35	2.5
arctic basin	4.2	3.9	2.8	4.2	3.9	2.4
Greenalnd Sea	0.3	0.2	0.1	0.18	0.1	0.05
Hudson Bay	0.15	0.05	0	0.15	0.05	0.05
East Siberian Sea	0.8	0.5	0	0.8	0.5	0
LapTev Sea	0.4	0.1	0	0.4	0.1	0
kara Sea	0.15	0	0	0.3	0.1	0
Barents Sea	0	0	0	0	0	0
Baffin/Newfoundland Bay	0.15	0	0	0.17	0	0
St Lawrence	0	0	0	0	0	0
Canadian Archipelago	0.5	0.2	0.1	0.55	0.25	0
Beaufort Sea	0.2	0	0	0.4	0.2	0
Chukchi Sea	0.3	0.2	0	0.25	0.15	0
Bearing Sea	0	0	0	0	0	0
Sea of Okhotsk	0	0	0	0	0	0

11

Arctic sea ice / Re: Home brew AMSR2 extent & area calculation

« on: July 07, 2013, 02:52:52 PM »

Every area which is going to melt will melt out at some stage will have a maximum contribution of exactly the same as last year -- 100% of the current ice. Estimating what happens this year is determined by the ice left over.

Last year the following areas melted out: (from the area graph in the first post)
East Siberian Sea
Laptev Sea
Chukchi Sea
- Kara Sea
- Beaufort Sea
= Baffin/Newfoundland Bay
= Hudson Bay
* Barerits Sea
* Bearing Sea
* St Lawrence
* Sea of Okhotsk
 ( - = melting slower than last year)
 ( = = major melt pattern underway, complete melt highly probable)
 ( * = already melted out this year)
---
Other Regions
Arctic Basin
Greenland Sea
Canadian Archipelago

---
In estimating the final minimum extent i think 2 questions should be asked:
a) will the areas which melted out last year melt out this year?
  a1) the East Siberian Sea and the Beaufort sea have the furthest to go, but melting is only just starting.
b) what will be the extent of the surviving ice areas be?
  b1) the majority of this is the arctic basin, and that is running about the same as last year
  b2) could the greenland sea almost completely melt out, as we are below last year by more than the minimum ice area from last year.

if every area that was 100% melted for more than a month last year melts out this year, and the greenland Sea area is worse, the final "do we set a record extent" is almost completely determined by the arctic basin.

I don't know enough ice dynamics/ have enough forecasting ability/... to even make a guess at this, but i can see that keeping exact track of areas which we already know will have 0 contribution at the final minimum could just be adding noise to the system.

12

Arctic sea ice / Re: Short to Medium Term Arctic Sea Ice Conditions Discussion

« on: July 06, 2013, 09:39:31 AM »

Does anyone know how accurate volume calcs are for fragmented ice?

Solid blocks of ice over several square km i can understand getting a good measurement, but what about the rubble type ice we're seeing in some places?

13

Arctic sea ice / Re: What the Buoys are telling

« on: June 24, 2013, 11:27:25 AM »

wanderer,
The video linked previously by Jim Hunt has been updated until the 21st, so i imagine that it'll contain todays shots in a day or 2.

14

Arctic sea ice / Re: Short to Medium Term Arctic Sea Ice Conditions Discussion

« on: June 18, 2013, 10:32:50 AM »

25 w/m2 isn't that much when you're melting ice
25 w/m2 * 3600s/hr*24hr/day / 1000j/kj
=2,160 kj/day/m2

ice :
density - 0.917 g/cm3   
 =917 kg/m3
heat of fusion - 334 kj/kg
 = 306,178 kj/m3

Dividing the heat of fusion by the energy flow = 7.05 mm/day melted.

A surface at about 88.5' inclination to a heat source of 1000 w/m2 will recieve 25 w/m2. (or 87' if you wish to take into account a day/night cycle)

15

Arctic sea ice / Re: Short to Medium Term Arctic Sea Ice Conditions Discussion

« on: June 06, 2013, 08:44:28 AM »

It occurs to me, with the massive fracturing and re-fracturing of the ice, that we are dramatically increasing the area exposed to sea water.

From some of the papers I posted earlier, as I recall once you get below 100M in diameter, lateral melting begins to make a noticeable and increasing contribution to reducing floes.  Certainly not all the ice is being reduced to this size, but I expect *enough* of it; perhaps enough to make up for reduced expanse of clear water.  Add the "stirring" effect of the storms mixing sea water, and I think we will see there is a lot more energy available than in the past.

Given the broken-up nature of the ice, and the reduced volume, the longer the surface area stays up, the less effort per unit area it will actually take to melt it all. If the area was already falling off i would be less woried about a crash than the current situation where we have large amounts of broken ice somehow maintaining (or only slowly decreasing) area under conditions which have been shown to decrease area when solid ice is present.