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Messages - slow wing

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551
Consequences / Re: Sea Level Rise by 2100 (POLL)
« on: April 29, 2013, 08:22:35 AM »
I don't like to take the end bin but, since you asked for the maximum, I have to go with >3m.

James Hansen might be wrong, but I don't think we can rule out that he is right.

For the maximum, we have to consider high end forcings. And the best candidate for providing most of that rise is the unpinning of those areas of the West Antarctic ice sheet that are below sea level. There is always going to be enough heat available in that scenario because if the ice floats then it can always float around until it finds enough heat somewhere in the Southern Ocean.

See http://en.wikipedia.org/wiki/West_Antarctic_Ice_Sheet for a non-technical overview.


If someone can provide a simple dynamical explanation for why that is not possible, whether from Pfeffer 2008 or elsewhere, then I would be willing to revise my answer.

I would be genuinely interested to hear any such explanation if it can be made, and I'm sure others here would also.



552
Arctic sea ice / Re: North Pole Web Cam 2013
« on: April 24, 2013, 02:32:44 AM »
Thanks, Espen.



553
Arctic sea ice / Re: Year-round ice-free Arctic
« on: April 17, 2013, 10:00:07 AM »

That is an excellent video! Thanks for posting it, FrankenDoodle.

554
Arctic sea ice / Re: Ice Export through Bering Strait?
« on: April 15, 2013, 12:00:15 AM »
There is some ice transport out through the Bering Strait at the moment...




The rate is some tens of cm/s, which is some tens of km/day, and such patterns tend to only last for days, not weeks, so the ice only travels of order 100 km before going back the other way when the pattern reverses. For comparison, the image shows the latitude lines at 60N and 70N bracketing the strait and the distance between those lines is 1111 km. So it is up to you whether you choose to describe much shorter outwards drift distances as "export". Personally, I wouldn't.

555
Arctic sea ice / Re: Arctic sea ice free (extent)
« on: April 14, 2013, 12:08:12 PM »
Hi Lodger

  Thanks for the information. Yes, the simple model is too optimistic in assuming that the ice is evenly spread throughout the Arctic Ocean as a mish mash of ice chunks and water gaps. In reality this Summer, there are going to be areas of thicker and thinner ice and also large areas of exposed water where the ice has melted out completely.

That is why the CAPIE value is too optimistic for this prediction. In regions where there is no ice nearby, the sun's energy cannot melt ice even if it is absorbed and heating up the water. And where the ice is thickest, it won't melt out by the end of July even if 25% of the insolation in that region goes into melting the ice.

  Stepping away from the July question for a moment, it is noted that the ice cover this year is more even than it was last year. Although the volume is the same for March according to PIOMAS, there is less ice thicker than 3 metres and on the other hand the ice is not so thin as last year on the Russian side. That more even spread appears to favour more melting this year than last as it is closer to the situation in the simple model.



556
Arctic sea ice / Re: When will we see open ocean at the north pole?
« on: April 13, 2013, 12:22:14 PM »
slow wing

Read a little about the Beaufort Gyre and Transpolar Drift. These are the primary currents effecting the Arctic Ocean.


Today's thinner more diffuse ice pack is generally thought to be more mobile than in the past & also more susceptible to wind while the recent Arctic dipole patterns alter the old +AO, -AO regime.


I personally don't put much faith in the Navy graphics posted - even to check against themselves. The drift buoy maps & data from the ASI daily graphics page are totally reliable.


Terry
...
Hi Terry

  The movement of the ice over the past 2 months can now be seen from A-team's outstanding graphic that he posted on  Neven's blog site:


Lines at the end of the animation show how far the ice in various places has moved in a little over two months. If the currents stay similar (a big 'if') then the ice might have moved around 2.5 times as far again by mid-September, which is about 5 months away.

So it looks like some ice that is currently around the middle of the East Siberian Sea might arrive at the North Pole in September, or else possibly have melted out while heading there.

The ice all around that region was seen to be between 1.6-2.0 metres thick in March from this graph by Wipneus of the gridded PIOMAS data (that you might believe more, Terry?)...


(If image doesn't show then look here.)


So the question of whether we will see open ocean this year at the North Pole becomes whether any of the ice in that region that is heading towards the pole will melt out on the way.

It's not obvious to me one way or the other whether that will happen or not, so I still think it is a toss-up. What do others think?



557
Arctic sea ice / Re: Arctic sea ice free (extent)
« on: April 13, 2013, 05:29:08 AM »
...
Slow Wing,
...Vergent's figures for insolation are for top of atmosphere insolation, due to the low angle of incidence figures hitting the surface are lower, and due to low angle of incidence albedo is higher due to reflection of oblique rays off the surface...
Hi Chris,

Thanks for your comments and particularly the point quoted above.

It makes sense to look up the actual Summer insolation at the North Pole in Summer.
The appropriate insolation values can be obtained from https://eosweb.larc.nasa.gov/:

Monthly Averaged Insolation Incident On A Horizontal Surface (kWh/m2/day)
Lat 90
Lon 0   
22-year Average   
Jan 0.00
Feb 0.00
Mar 0.17
Apr 2.93
May 6.78, x 3.6 MJ/kWh = 24.4  MJ/(day.m^2)
Jun 7.49, x 3.6 MJ/kWh = 27.0  MJ/(day.m^2)
Jul 6.70, x 3.6 MJ/kWh = 24.1  MJ/(day.m^2)
Aug 4.03
Sep 0.82
Oct 0.00
Nov 0.00
Dec 0.00


In my first hand-waving post I simply guessed mid-Summer insolation of 20 MJ/(day.m^2),  x 1 kWh/3.6 MJ = 5.6  kWh/(day.m^2). This is seen to be a bit less than the measured value at the North Pole, but actually fairly close when averaged over the Arctic Ocean - try out a few different latitudes and longitudes on that website above. So it was a reasonable guess.



 In the second post I doubled the value based on Vergent's number, which turned out to be for the top of the atmosphere. That was a mistake and too optimistic. Going back to my original guess of 20 MJ/(day.m^2) gives...


critical absorbtion fraction to just melt the ice =

300 MJ/tonne x 1 tonne/m^2 / (20 MJ/(day.m^2) x 60 days) = 1/4

So, in this simple model and neglecting other heat sources and sinks...

 If 1/4 of the direct solar energy goes into melting the ice then the Arctic Ocean could be ice free by the end of this July.


That much is now pushing it but the scenario is still at least plausible imo if the ice has already broken up some more - which is all that I was trying to address.


558
Arctic sea ice / Re: PIOMAS Maximum
« on: April 11, 2013, 01:22:18 PM »
Attached plot of the ice thickness differences between March 2013 and March 2012.
Thanks Wipneus, that is very interesting indeed.

Just to make the general comment that the quality of data presentation from you and some of the others on the forum and blog is incredible! It really helps to get a handle on what is happening and so is much appreciated.




559
Arctic sea ice / Re: Arctic sea ice free (extent)
« on: April 10, 2013, 09:48:45 AM »
Slow wing, great. Let me throw in data from buoy 2006C, showing bottom melting of ~1m per month happened in summer 2007.
Wow! That's a lot!

Am I right that the general consensus was that about twice the normal amount of heat to melt the ice flowed in through the Bering Strait that year? It could be carnage if it happens again this year.

560
Arctic sea ice / Re: Arctic sea ice free (extent)
« on: April 10, 2013, 09:44:56 AM »
Hi Vergent and Dodger,

  Yes Vergent, the state of the ice in that photo should do the trick.

Dodger, thanks for information in the references. It was just a plausibility argument so I didn't worry too much about 10-20% effects. That factor of 2 in the insolation needed to be fixed though.

So, re-running the argument with the factors rounded to 1 significant figure:

Ice is all broken up by the end of May: could it melt out by the end of July? Assume:

1 tonne/m^2 of ice left at end of May (this is about 15,500 km^3 at a density of 0.9 tonnes/m^3)
300 J/g = 300 MJ/tonne = heat of fusion
Insolation is 40 MJ/(day.m^2) (question: does that allow for clouds?)
60 days (OK, is 61)

critical absorbtion fraction to just melt the ice =

300 MJ/tonne x 1 tonne/m^2 / (40 MJ/(day.m^2) x 60 days) = 1/8

So, in this simple model and neglecting other heat sources and sinks...

 If only 1/8th of the solar energy goes into melting the ice then the Arctic Ocean could be ice free by the end of this July.

So the scenario is at least plausible imo.











561
Arctic sea ice / Re: Arctic sea ice free (extent)
« on: April 10, 2013, 03:14:58 AM »
 Cheers, Vergent. Wow, that's nearly a factor of 2 higher than I had assumed!  So the scenario becomes less implausible so far as I can tell.

  A question though to people who know about sea ice: is it plausible that it might continue to break up throughout much of the Arctic until it reaches small chunks of typically only a metre, or a few metres, on a side?

562
Arctic sea ice / Re: Arctic sea ice free (extent)
« on: April 10, 2013, 02:27:32 AM »
Hi Arcticio,

If you only need plausible then, sure, I will wave my hands...  ;D

The area of the Arctic Ocean is 14 million km^2.

Let's suppose the ice volume is 14,000 km^3 at the start of July, but it is all broken up into chunks and spread throughout the Arctic Ocean, with gaps everywhere exposing water to the sun.

Let's define the effective critical albedo as the fraction of the incident sunlight required to melt all the ice in the month of July.

In mid-summer, the sun shines 24 hours/day at the pole. I seem to recall that the incident sunlight energy/day there is more than at any other place in the world. I don't remember exactly, but lets assume 20 MJ/(day.m^2) x 31 days in July ~ 600 MJ/m^2 in July.

We know the average ice thickness is 14,000 km^3 / 14,000,000 km^2 = 1m. Therefore, we need to melt 1 tonne of ice per m^2.

The latent heat of fusion for ice is 334 J/g = 334 MJ/tonne.

Putting it altogether,

effective critical albedo ~  334 MJ/tonne x 1 tonne/m^2 / 600 MJ/m^2 ~ 0.56.


So, given the roughness of the calculation, it seems that about half the incident sunlight in July  would have to go towards melting the ice in order to melt it all that month.


But then we could move to a more plausible model than that - where the ice has all broken up by the beginning of June and then has both June and July to all melt out. The effective critical albedo in that case might only be about 0.3 - which doesn't look crazy to me if there is a lot of water exposed.

Then we could look at where the ice has all broken up by the beginning of May, where maybe we are down to an effective critical albedo of 0.2...

Then we can wave our hands a bit more about the currents, the wind and layer mixing bringing in extra heat as well, and maybe some extra export through the straits...


So I say the scenario is unlikely but it is not physically impossible for the ice to all melt out by the end of this July, due to it all breaking up into small chunks.





563
Arctic sea ice / Arctic sea ice conditions in coming days and weeks
« on: April 07, 2013, 03:13:46 AM »
This is a very interesting discussion, thanks BornFromTheVoid. Could I suggest a more specific thread title, such as the heading for this post?

564
Greenland and Arctic Circle / Re: The Cold Pole?
« on: April 04, 2013, 11:10:58 AM »
Jim, thanks, that's an amazing plot!


Newbie questions and apologies if everyone else is already up-to-speed, but is the following all true?
  o high pressure has moved from typically being centred close to the North Pole to instead being more centred over Greenland
  o that will make the predominant wind direction in the Arctic ocean more along the line from 180 degrees long. to 0 degrees long. than it used to be, where before it used to swirl more clockwise around the Pole
  o that aids the currents and ice flow from the direction of the Bering Strait towards, and through, the Fram Strait?


Also, is it just an empirical observation, or are there known or hypothesised physical reasons?

Thanks.

565
Greenland and Arctic Circle / Re: Greenland Melt Impacts 2012
« on: April 04, 2013, 10:59:26 AM »
Crandles, the image isn't showing for me.

566
This is a difficult poll! There could be some bounce back from last year. Or the more fractured ice could in one way or another lead to a record.

I agree with everything Juan said. 1-2 million km^2 being such a big bin makes it the most likely bin to contain the outcome imo. Even if the bins are split up like Juan suggests then I will still agree with his guess of 1.8-2.0 million  km^2.*

*EDIT: with the re-binning, I ended up picking 1.50-1.75 million km^2 as the sea ice had meanwhile continued to fracture.

567
Arctic sea ice / Re: When will we see open ocean at the north pole?
« on: April 01, 2013, 11:25:43 AM »
...
As for slow wing & Richard Rathbone, I agree that prevailing currents go from the North Pacific to the North Atlantic. ...
Cheers, Frankendoodle. For my post above, I had read that the prevailing winds were more important than the currents, but maybe that has changed?

The ice drift map I posted was from a while back - data from 1978-2003. It shows the ice direction at the pole back then averaged 1-2 cm/s and the direction was from around 130E. But perhaps that has changed? Or there is a lot of year-to-year or seasonal variation?

This reconstruction of the past 365 days gives a good indication of ice movement towards the pole in the last melt season...


It can be seen that the ice region that ends up at the Pole in September 2012 starts at around (185W,82.5N) at this time of year last year - the beginning of April 2012. It is the ice at about half way in between two convenient markers: the red dash of thicker ice that starts at (183W,80N) and the point of a green strip that starts at (183W,85N) at the beginning of April 2012.

So the ice last year that travelled over the Pole in September came from almost the direction of Bering Strait, as you said. And it came from around 7.5 degrees South = 7.5*10,000/90 ~ 800 km away from the Pole at the beginning of April 2012.

The strange thing is that the red dash marker then completely changes direction after September, then heading roughly downwards in the direction ~110W. It does jerk around a bit too.


So the upshot is that I no longer believe that the September ice over the Pole in September will necessarily have come from the Russian side - that old pattern didn't apply last year.


IF the ice transport this year will turn out to be the same as last year then the ice currently at (185W,82.5N) will end up over the Pole in September. This is seen to be thicker ice, currently more than 3m thick:



...and so less likely to melt out than the thinner ice on the Eastern side. In that case, we probably won't get open ocean over the Pole this year.

Also, I note that the ice now even on the Russian side is thicker than it was at the same time last year. (Someone just posted that pictorial comparison on one of the other threads - thanks.)

Given the new uncertainties, I can no longer sustain a 70% probability of an ice free North Pole this year. I'm going to drop it to a 50% probability. (And that is even factoring in the recent fracturing that could favour quicker transport than last year.)


In order that I might better understand things, some general questions for those more knowledgeable than I:
1) does average ice drift direction depend on the season? For example, is the average Summer drift direction the same as in the Winter?
2) has the average ice drift direction changed over the years?
3) how much stochastic variability is in the ice drift direction? For example, how accurately can it be predicted where the region of ice is now that will be over the North Pole this September?

If you know the answer to any of these questions, what is the physics behind the answer?

Thanks,
slow wing


568
Arctic sea ice / Re: When will we see open ocean at the north pole?
« on: March 29, 2013, 03:21:21 AM »
Good question, Frankendoodle. It would even be interesting if you added a poll for the year.


Consider that the ice is going to move around in bulk throughout the melt season, and also that the thinner ice in the Arctic is going to melt out, as usual. So a useful construction is to try to identify where the ice is now that will be over the North Pole around the peak of the melt season, and then to ask whether or not that patch of ice is thick enough to survive the melt season.

Concerning ice direction, we know that the ice drifting over the Pole tends to have come from the Russian side...


Arctic Ocean circulation.
—Image courtesy of Arctic Monitoring and Assessment Programme (AMAP), Figure 3.29, AMAP (1998).


Plot showing mean (average) Arctic ice motion from 1978 to 2003. Arrows show the direction and velocity of the ice, with longer arrows representing higher velocities.
—Image courtesy of the National Snow and Ice Data Center, University of Colorado, Boulder, CO
http://nsidc.org/cryosphere/seaice/processes/circulation.html

These drift patterns are determined mostly by the prevailing winds in the Arctic Ocean - particularly the prevalence of high atmospheric pressure regions resulting in clockwise wind circulation around the ocean.


As the other part of the question, the ice thickness maps are showing not much ice left over 2-2.5m anywhere in the Russian half of the Arctic (currently; this image will update)...





Therefore, I'm picking a 75% chance of an ice-free North Pole this year, with the ice clearing from the Russian side and perhaps biased towards the Atlantic side due to currents from the Atlantic.






569
Arctic sea ice / Re: Arctic sea ice free (extent)
« on: March 18, 2013, 09:51:07 PM »
Jim Hunt,

  Thanks for going to that conference and reporting back. It was very interesting to read that.

  Did any of those scientists happen to say how they reconcile their predictions stated above with what is observed for year-on-year ice volume loss? What are they thinking might be physical reasons for the volume loss to pull up before volume reaches zero? Thanks.

570
That's a very interesting idea, thanks for presenting it. A couple of questions to start with:

1) where does the 2c/kWh estimate come from? Is there a source for it in a paper?

2) How would net CO2 be used up in making concrete? Making cement gives off CO2 rather than absorbing it. Heated calcium carbonate sheds CO2 to become the calcium oxide that is combined with silicates in portland cement. The hydration of the cement forms the concrete. See
http://matse1.matse.illinois.edu/concrete/prin.html .



Thanks.

571
Arctic sea ice / Re: Arctic sea ice free (extent)
« on: March 14, 2013, 12:15:50 PM »
Long time lurker on Neven's Arctic sea ice blog but this is my first post. I would like to express my appreciation to Neven and the other posters for the outstanding standard of the information and analysis provided there and here.

I voted 2013-16 because firstly the ice volume trend when naively extrapolated shows only a few years left anyway, with an end-point perhaps around 2016 +/- 3. Secondly, it appears likely that the deviation from a naive extrapolation should likely be in the direction of a quicker melt-out. The FYI that now predominates is more saline and should melt more easily than the MYI used to, volume-for-volume. And there have been reports documented on the blog that at least some of the MYI is 'rotten', with little mechanical strength. Thirdly, the ice is already observed to be breaking up on a scale that is unusual and perhaps unprecedented in the satellite record for this time of year. I am largely convinced by Artful Dodger's analysis from the 'Fragmentation event' thread that this should allow all the MYI ice in particular to be transported around to areas where it can more easily melt. Additionally, broken up ice can more efficiently absorb the local heat and salt content. The large scale break-up may be a prelude to break-up into smaller pieces that can melt out quickly.




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