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Messages - slow wing

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1
Arctic sea ice / Re: The 2018 melting season
« on: Today at 04:21:26 AM »
Hyperion, agree that's way too fast.

I'm a total amateur but use ezgif.com. Maybe use something of the order 1 second per frame and add an extra rest at the end.

The physics question is how well the SMOS display variable acts as a proxy for some useful definition of absorptance. It's definitely flagging some sort of surface change, and can be compared year-to-year.

Hopefully it's not too biased by e.g. the characteristics of the cloud cover on that day - these are more detailed questions.

The SMOS display this year looks qualitatively similar to on the corresponding date in the record melt year 2012. Yes, in the absence of a more rigorous comparison I would accept that as some sort of evidence that the surface absorptance considered over the Arctic Basin may be similar.

The absorptance of recent days was discussed about 2 pages back, e.g. #1487 by bbr2314 & #1497 A-Team; and the related topic of melt ponds at #1505 by A-Team.

2
Arctic sea ice / Re: The 2018 melting season
« on: June 21, 2018, 12:57:54 AM »
Based on the thickness maps above (HYCOM) & from Wipneus (PIOMAS), this melt season is reasonably likely to have open water extending closest to the North Pole for any year in the satellite record.

On the Atlantic side, open water is already at around 7-1/2 degrees from the Pole (e.g. at 35 or at 45 degrees E on AMSR2 map) & the current thickness maps show the ice inside that still only reaches around 1.3 metres thickness by 5 degrees from the Pole. From there, the ice thickens only to around 2 metres thick on approaching the North Pole itself.

On eye-balling Neven's map page https://sites.google.com/site/arcticseaicegraphs/concentration-maps/sic0901, the current record appears to be just inside 5 degrees from the Pole, for an indent from the Siberian side in 2014.

Depending on how the ice melts and moves around, that record could go this year.

3
Arctic sea ice / Re: The 2018 melting season
« on: June 20, 2018, 06:30:03 AM »
Today's AMSR2 map is out from U. Bremen & it's one of the dates on Neven's year-to-year AMSR2 graphic comparison that I like.

As already noted in #1473 above, melt is quite aggressive in two regions this year, as shown with white arrows:

1) North of Svalbard, where the ice front position looks almost like it's September. The retreat of the ice front has been particularly aggressive in recent days as Aluminium illustrated in post #1452 above; and

2) The hole in the Laptev sea.

The other regions of the Arctic Basin look fairly average for this time of year - that is to say, still mainly covered in ice.

The anomalous amount of heat north of Svalbard is the most interesting feature for me at the moment. It looks like it's being brought primarily by wind &/or water rather than direct sunlight. Will the ice edge come even closer to the North Pole? How much ice will be pushed into this region during the rest of the melt season & will that all just melt away?

Most of the melt season is still ahead of us and I think it is still premature to pick where this year will end in the yearly standings for minimum extent. For example, it could still be a record or end in second place, or it might not.

4
Arctic sea ice / Re: How soon could we go ice free?
« on: June 16, 2018, 06:11:27 AM »
... If the models show a slowdown in the rate of decline as zero ice is approached and also the data is tending to show this recently...

Which models are you referring to? I've never seen a physics-based model with good predictive ability on this trend. True, there are models that don't work well, e.g. for the IPCC studies. If the model can't find the recent trend then it's not much use for predicting future trends.

Why do you say the data is showing a slowdown recently? If I look back at the linear fit of #97 then the residuals are all over the place and I don't see that trend. Based on the second plot, I suspect a quadratic fit would also curve downwards rather than upwards.


  If we're looking for a physical reason for a slowdown then I would point to the existence of a 'sanctuary region' against the North side of the CAA and Greenland where the ice hasn't melted out in any year.

  The prevailing combination of winds and current tends to push the ice against the coast - it has every single season we've been observing. It's deep water so the warm salty Atlantic waters can't get to it - their higher salinity makes them denser so they dive down instead.

   That's where the remaining multi-year ice is, so that also makes it harder to melt through.

   It might even be that it's cloudier there in the Summer than over the rest of the Arctic basin, so it sees less sun? (True or false? I have that impression but may be wrong.)
 
   So the first year below 1 million square kilometres should be the first year where the ice sanctuary is no longer effective, for whatever reason. The ice gets pushed away from there and/or melts in situ.


   When will that happen? I don't know. But the presence of an identifiable ice sanctuary region provides an arguable physical reason for a potential future slowdown in the rate of the year-to-year decline in minimum sea ice extent.

5
How accurate should the predictions be?

By far the worst prediction was the first year, 2013, when the median was 3.32 and the melt season ended at 5.21 so off by 1.89.

Was the forum particularly alarmist in 2013? Or did it instead have something to do with the trend of preceding seasons, dropping from 4.56 in 2011 to 3.57 in 2012 - a drop of 0.99.

So the median prediction, after a drop of 0.99 in 2012, was to drop only a further 0.25 in 2013.

Imo that was not so unreasonable given the information available - and yet it was the worst prediction. Imo that was Nature's fault more than the fault of the participants in the poll.

If someone wants to make a counter-argument that it was the participants fault then they would do well to explain how the 5.21 result could have been known in advance in 2013, or at least a good approximation to that. Good luck!

So imo it's not a case of having been chastened out of alarmist tendencies. Instead, the main reason we didn't, this year, pick as low as in 2013 is the additional physical information available to us from the intervening years.

We still might anyway be off by a lot this year - Nature simply isn't that easy to predict here!

6
As I read Hyperion's post, s/he thinks I've gone too high with my prediction, not too low.

7
3.75-4.25.

I simply went one bin - 0.25 - above my prediction for the daily minimum that I explained here.

8
Voted 3.50-4.00 bin & so a second-lowest finish, behind only 2012.

The ice albedo now is in the middle compared to the years 2011-2017, as I just posted, with a gif, in the melt season thread.

What brings it down for me is that the Atlantic side is weak. The ice has retreated from in front of Svalbard and there seems to be a lot of heat there, perhaps related to the 'Atlanticization' of that region that people here discuss (maybe not using that exact word lol). It will likely be a 'kill zone' for any ice drifting in that direction.

The Bering-Chukchi region has also melted out fast. The Beaufort is better than in 2016 or 2017 for this date but there are still a lot of gaps in the ice there. The albedo on the Russian side has just recently reduced and there is already a big gap in the Laptev ice.

So we should be left with the usual ice sanctuary on the Canadian side, with ice pushed up against the CAA, and little or no ice remaining elsewhere.

9
Arctic sea ice / Re: The 2018 melting season
« on: June 11, 2018, 01:43:54 PM »
Albedo over half the Arctic has plumetted with vigorous 24/7 sunny skies.

Weather models say this will slowly grow this week

Courtesy of NASA worldview, here is a gif giving a year-to-year visual comparison for Terra true color on 11 June, up to this year and going back to 2011.

Speaking roughly, it's seen that the 'dirtiest ice' on average - presumably corresponding to lowest albedo - on this day was in the record-breaking year, 2012. There is some cloud cover obscuring the comparison but very roughly the order from 'dirtiest' to 'cleanest' might look something like:

1. 2012
2. 2016

3=. 2013
3=. 2015
3=. 2018 <==

6=. 2017
6=. 2011
6=. 2014

So this year we're somewhere in the middle of the pack.

The weather from here on in will of course have a big effect on the extent at the end of the melt season.

10
Arctic sea ice / Re: The 2018 melting season
« on: June 11, 2018, 11:20:22 AM »
My understanding is that the water from the Lena River can contain so much sediment that it can be denser than the sea water when it enters the Arctic Basin and so sink underneath it rather than floating on the surface.

Sorry, I did a web search but can't find a reference to support this. Anyone?

11
Arctic sea ice / Re: The 2018 melting season
« on: June 11, 2018, 04:53:53 AM »
 As I understand it, the Slater model isn't intended to produce an exact map where they stand by the prediction at each point on the map.

  Ice can move around, for instance, so a hole in the ice in one place now can move to a different place in 50 days time.

 I recall that in past years that map has shown, for example, a bar of remaining ice across the Hudson Bay that was obviously unphysical.

 In my opinion the Slater method is a powerful and helpful way to predict sea ice extent.

 It is a public service that they also provide the map for our benefit and we should be grateful for that rather than casting aspersions on it based on its detailed features.


... Hey, even I could do better than this! ...
::) This is really not that type of forum.

12
Arctic sea ice / Re: Svalbard
« on: June 08, 2018, 02:19:57 AM »
The polar bear made it out of that window?! No way!  ???

13
Arctic sea ice / Re: The 2018 melting season
« on: June 05, 2018, 11:44:14 PM »
Thanks A-Team, I love those Kevin Pluck graphics at #994!

That raises an obvious question about a related but simpler plot: has anyone done an extent vs. volume scatter plot for the yearly minima? Presumably! But I don't recall having seen one.

Presuming the plot has been done, would it be amenable to any sort of simple fit constrained to go through the origin & with a finite slope at the origin (corresponding to the average thickness of the remaining ice at the end of the melt season on approaching a blue ocean year)? (A quadratic going through the origin would be the obvious first form to try.) How much scatter would the yearly values have around the fit?

In trying to relate it to the complex physical reality, would it be expected to be predictive at all?

(Sorry for being slightly off-topic, Neven.)

14
Arctic sea ice / Re: The 2018 melting season
« on: May 23, 2018, 03:07:25 AM »
For the multi-year ice I tend to conceptualize the drift pattern - both this past year & previous several years - slightly differently from the canonical description of a Beaufort gyre +trans-polar drift (agree, the latter not much seen if at all these years).

Instead, I see it as a prevalent drift from the (central) Russian side to the (central) Canadian side that compresses the ice against the Canadian Arctic coastline but also with faster drifts on both the Atlantic & Alaskan sides - the former in a similar direction but the latter bringing the ice back in the opposite direction, towards Russia.

The fast Atlantic side drift sweeps that ice through the Fram Strait, unless it melts out first. This is in pretty much in the same direction as the prevalent central drift only faster because the ice isn't blocked.

The drift on the Alaskan side sweeps the ice fast in the opposite direction to the central & Atlantic-side drifts, in a direction parallel to the Alaskan Arctic coastline & in the direction of Russia.

The sum of the central+Alaskan-side drifts is re-describing the Beaufort gyre, obviously, but acknowledges that the drift back towards Russia is seen to be much faster because it isn't blocked by land, namely the Canadian Arctic coastline. (There is a small leak through the Nares Strait though.)


Is this a useful way now to broadly conceptualize the Arctic sea ice movement given that there is no longer significant a) trans-polar drift, or b) sea ice that survives multi-year cycles around the Beaufort gyre?

15
Arctic sea ice / Re: The 2018 melting season
« on: May 23, 2018, 02:25:21 AM »
Thanks A-team!

Your .mp4 "233 days of anti-transpolar drift 2017-2018" is probably going to become my go-to reference for where last year's remaining ice has drifted since.

I downloaded the movie and by dragging the cursor backwards & forwards through the time sequence can easily track features visually to see how the different parts of the ice pack have moved. Much appreciated!  :)

16
21 May. so we're one month before the summer solstice.

Maybe a good date to flag about when the amount of cloud cover in the Arctic Basin Proper has become really important?

I don't worry too much about the Arctic sea ice outside the central Basin because that is going to melt out anyway.

Roughly speaking, cloud cover insulates the ice from the sky. It's true you can have different types of cloud cover that might not do that well for the shorter wave insulation (direct sunlight coming down) or the longer wave thermal radiation coming up - but we won't make that distinction here.

In the Winter, cloud insulation traps the heat in from draining to the sky, so it works against the ice thickening. However, growth in ice thickness slows down anyway as the ice gets thicker and so itself better insulates heat from escaping from the water underneath to the sky above. So the eventual ice thickness at the end of the freezing season won't have been affected too much by how much cloud cover there has been in the winter.

In the (late) Spring, at the start of the melt season, it's more of a balance between cloud stopping the thermal radiation going up and the cloud stopping the increasing amounts of sunlight from reaching the ice.

But by now, that balance should be progressively tipping in favor of the latter. Less clouds will allow more sunlight down to heat up the ice. Also, as the snow & ice on top begins to melt and the sunlight can begin to shine on liquid water, the ice will just be beginning to become less reflective and instead absorb a greater fraction of the incident solar energy.

    So what I'm suggesting is it's starting to become important to watch, e.g. Worldview, to see the amount of cloud cover over the central Arctic Basin.

 Less clouds also tends to correlate with high pressure. So we can also watch the forecasts for more high pressure.

   Concerning other heat sources that can melt the ice - warm winds and water being carried into the Arctic - the Summer also heats up that air and water more, & it brings bigger heat engines to potentially blow it into the Arctic basin.


   So it's been interesting already, but I hereby proclaim that the really interesting part of the melt season officially begins today.  :P

17
Arctic sea ice / Re: The 2018 melting season
« on: May 08, 2018, 04:22:20 AM »
Thanks Oren, yes I took a closer look and agree it's probably strange clouds rather than melt ponds.

It was too cloudy on the day before, 2018-05-06, for all three satellites, and mostly too cloudy for the other satellites on the same day, 2018-05-07. (Already suggesting a lot of cloud about.)

But I was able to scan around the TERRA view and see a progression to other structures that tended to look more cloud-like.

Also, there was a small gap in the AQUA cloud cover showing white ice in the same identifiable ice position where the TERRA view showed those structures - at around 81.81N, 5.44E - compare the attached images.

So yes, the structure seems to be cloud &/or artifacts rather than melt ponds.

18
Arctic sea ice / Re: The 2018 melting season
« on: May 08, 2018, 02:31:57 AM »
Clouds or melt ponds?

Looking at Worldview visible, North of Svalbard (details in image names) & the ice looks qualitatively different than it was previously.

It could just be cloud formations but, if so, these would have to be strange given what I would describe as a 'grooves & angles' appearance.

It was above freezing in the region displayed, around approximately 83.63N, 4.17E, on 2018-05-06 at 1200 UTC. (It's colder there now, ~-10 degrees C.)

So could the Worldview experts comment on whether large scale melt ponds could be an alternative possible explanation, even early in May?

19
Arctic sea ice / Re: The 2018 melting season
« on: May 03, 2018, 12:57:08 PM »
Here are the 925 hPa temperature graphs for April...
Very interesting, thanks Neven! How many years are on this record?

20
Arctic sea ice / Re: The 2018 melting season
« on: April 25, 2018, 06:48:04 AM »
Neven is impressed by some research that shows melt ponds are the devil.

The argument is that if you have ponds of water forming on top of the ice, they can gather up a lot of heat and melt the ice from the top during the early summer (until the ice cracks and the ponds drain). That means more total solar heat absorbed over the summer, and conditions the remaining ice to melt faster.

And how do you make melt ponds? By shining the sun on the snow to melt it, but not breaking up the ice too early with a storm.

So that's why high pressure on the arctic, from the end of April to early June, seems bad.

 Yes, it is clear to me also that melt ponds can accelerate melt, for the physical reason given above and because liquid water absorbs shortwave solar energy so much better than ice or snow.

 I think it likely that a large part of the reason 2012 set the low extent record in September was the extraordinary fraction of Arctic sea ice covered in melt ponds during May & June - as was observable even from the satellite data.

 The part of your post where I haven't seen observational evidence is that the ice pack can be broken up by storms so much, over so much of the Arctic & as early as May or June, that melt ponds can't easily form.

 Has that been established? If so, could someone point out where please?

 In the central Arctic much of the ice will have a thickness in the range of roughly 1.5 to 2.5 meters and so a free board above the water level of a couple of tens of centimeters - say 20-30 cm. Can much of the 2 meter thick ice be broken up so small - presumably no more than meters across rather than tens of meters or larger - by storms in May or June?

 I would need to see some evidence for what runs counter to my mental picture that is based in part on photos of ice breakers & their trails, where the ice can look intact even when substantially thinner than that.

 Parenthetically, I also suspect that if sea ice is broken into transverse dimensions not much larger than its thickness - and so unable to form melt ponds - then it would melt out more quickly anyway due to all the exposed leads and to bobbing and rocking around. But I've only seen lake ice, not sea ice - so that is just a guess.

21
Arctic sea ice / Re: The 2018 melting season
« on: April 19, 2018, 01:16:20 PM »
A sea ice region to watch at the moment is North of Svalbard, with:
  • ~1000 km front of ice that can drift southwards;
  • 100+ km wide zone for ice to expand into before hitting Svalbard
  • ice already breaking up into large floes, as far north as 6 degrees ~700 km from the Pole (at 30 degrees E);
  • wind in that region predicted to tend northerly (i.e. from the Pole direction) over most of the next 5 days.

I looked on Worldview at previous years and this is already an unusual amount of this type of flaking for the date.

With the wind potentially opening up the leads wider, it will be interesting to see if there is even more flaking to follow, and also how much the flaking might compromise the survivability of the ice in this region over the course of the melt season.

Or, instead, is it early enough in the year that these leads might still freeze over?

22
Arctic sea ice / Re: First year PIOMAS volume below 1000km^3 poll 2018
« on: April 03, 2018, 12:58:42 AM »
Picked 2019-21.

Main contender for me was 2022-2024.

In my humble opinion we are already at the stage where an extreme year could do it.

Superimposed on that is the expectation that the situation is getting progressively worse. But it's problematic to quantify that for Arctic sea ice - the physics is far too complicated & poorly understood, & the constraining observations and measurements are far too few &/or too poor.

I think the year-to-year fluctuations are so big as to be more important than the progressive trend in choosing the first year below 1000 km^3.

It could possibly be this year. But it would take a very bad melt season. The 2018 bin is only 1 year wide so I think it less likely than the 3 year bin afterwards that I did choose.

Competing against the progressive trend, the bins 2022-24 and later are disadvantaged by the possibility that, even if the volume does fall below 1000 km^3, it might have already happened in a prior melt season. That's why I chose 2019-21.

This poll runs for a long time - was it for two months? People voting near the start have less information than those voting later on. Can the close date be made earlier? Also, my preference would be to change the poll settings so we can change our vote.

23
Arctic sea ice / Re: The 2018 melting season
« on: March 30, 2018, 03:09:09 AM »
  Concerning the discussion above, I really like the vectorized sea ice motion maps we see that are plotted for 1 day's motion if I recall correctly.

Question: does anyone do them for longer time periods? Weekly, or even monthly or for an 8 month melt season?

Would showing such ice vector displacement maps be instructive or not? For example, would they inform discussions on trends and tendencies in seasonal ice motion?

Technically I suspect they are doable, given that the daily maps exist and that the human eye can easily follow the ice motion in the plots above that A-team has kindly posted. (I realise that it is in 2 dimensions that humans have traditionally best out-performed computers.)

Sorry I don't have the skills or commitment to do them myself but I'm guessing they would be interesting  :D

24
Arctic sea ice / Re: What the Buoys are telling
« on: March 30, 2018, 02:56:00 AM »
Excellent! Thanks for the update Jim & thanks to those participating in this program.

25
Arctic sea ice / Re: The 2017/2018 freezing season
« on: March 15, 2018, 02:21:36 AM »
As a scenario for this year, suppose open water North of the Bering Strait & of Svalbard comprise an area of 10% of the Arctic basin by around the Summer solstice.

Can winds then fill up those regions with ice while - to conserve ice area - leaving leads throughout the Arctic basin?

Because open water absorbs sunlight much more efficiently than ice does, those leads could then seed wider gaps in the ice, reinforcing the effect.

Could the Arctic ice melt out that way rather than predominantly getting eaten away at the edges?

Could the ice go like that given sufficient open water to start with at the edges of the Arctic basin? Or is the wind movement too slow to spread the effect through the Arctic basin in a melt season. (Doubtful. I think it's fast enough.) Or, instead, does the ice mainly hold together and most of the open water areas remain at the periphery? Or, as a fourth model, does the ice spread out as it shifts around and any leads are more transitory?

Which of the four is the most appropriate mechanical model for the Arctic sea ice?

26
Arctic sea ice / Re: Updating the ASIG
« on: March 08, 2018, 12:51:13 AM »
Thanks Neven! The graphic comparison is very helpful for getting an impression of year-to-year variations.

27
Arctic sea ice / Re: AMSR2 Sea Ice Volume/Thickness
« on: March 05, 2018, 04:14:37 AM »
Very nice Tealight!

28
Arctic sea ice / Re: The 2017/2018 freezing season
« on: October 05, 2017, 05:19:34 AM »
...More buoys could be deployed, 1000x of what is planned for 2018, for a tiny fraction of submarine or surface ship charter costs.
Yes, true and important. The graphical display of the models is getting so much better but the models have insufficient calibration data from the water. A 1000x bigger deployment of buoys was discussed in last year's freezing season thread, 11 months ago - e.g. #481 - with links to further discussion. A major scale-up of buoy deployment really deserves a thread of its own.

29
Arctic sea ice / Re: The 2017/2018 freezing season
« on: September 28, 2017, 01:22:38 AM »
  A-Team, thanks for your (typically) wonderful graphics above #118 concerning the persistent hole observed this year in the ice north of the Laptev Sea.

  You conclude "Happenstance with no deeper meaning is the null hypothesis" and say there is no reason to reject it.

  Your graphics show, as you say "polynyas developed at a similar (but not identical) location in some but not all years" from 2012 onwards. In my view that would be surprising under the null hypothesis. The persistence of the 2017 hole was already surprising to me.

  While I agree the null hypothesis cannot yet be rejected, in my view there are other hypotheses that are reasonable and worth exploring further.

  In particular, the polynya was over the Gakkel Ridge - a prominent baryometric feature and with known geothermal vents.

  An issue that needs to be addressed here is that underwater volcanism has been abused by some as a counter to climate change concerns. Here is an example where a polynya was observed over the Gakkel Ridge and all sorts of non sequiturs were drawn from that: http://climatechangedispatch.com/heat-from-deep-ocean-fault-punches-hole-in-arctic-ice-sheet/.

  The intuition of some climate scientists has been that the volcanism probably doesn't have much affect on the sea ice: https://dotearth.blogs.nytimes.com/2008/07/01/whats-up-with-volcanoes-under-arctic-sea-ice/.

  However, that seems somewhat equivocal. The argument is that the heat certainly effects the local ocean depths but is diluted before it gets to the surface.

  The amount of volcanic heat averaged over the Arctic basin is said to be of order 0.1 W/m^2. As it takes around 334 kJ/ kg to melt ice, that is about enough to melt around 3 mm of ice over 4 months (10^7 seconds), averaged over the Arctic basin.

   But what if much of the heat from the Gakkel Ridge volcanoes effectively reaches the surface over the much smaller region where the polynya formed? That much heat over ~1/300th of the Arctic Basin (say 20,000 km^2 which, eye-balling, looks of order the size of the polynya) could melt of order an extra metre of ice rather than just 3 mm and so could punch a polynya in the ice.

  To me the polynya was a notable and recurring feature and some sort of mechanism for getting volcanic vent heat to the surface to cause that is not ruled out as far as I know.

   Are there measured temperature and salinity profiles in that region? (I seem to recall there being a string of Russian tethered buoys but that may be closer to shore.)

UPDATE: there is some instrumentation, see http://research.iarc.uaf.edu/NABOS2/technology.php:

30
Again imho, the best 1-parameter indicator of a 'weak freezing season' is the ice volume gain over the Arctic basin. We do have estimates for that from previous years.

What beyond that would make one characterize a freezing season as 'weak'? It could be said to be weak in some regions. An ice thickness gain map could therefore be of interest - up to and ignoring ice position displacements. A freezing season could be said to be weak if it left the Arctic vulnerable to a melt-out in the following melt season. Parameters such as the ice temperature and the quality of the ice (e.g. "rotten ice") could be considered.

But imo the ice volume gain captures much of what we might call a 'weak freezing season'.



31
There is no coverage of previous years so what best provides historical context for a 'weak freezing season'?
Imho a map over the Arctic Basin of freezing-degree-days should show which freezing seasons are relatively weak, and in which regions. That data exists for previous years as we have their temperature maps.

32
Arctic sea ice / Re: Latest PIOMAS update (mid July update)
« on: September 19, 2017, 12:01:35 AM »
Thanks Wipneus, always interesting!

So the current ice thickness contours are fairly simple in shape: nearly triangular at 1.75m, 1.50m, 1.25m and weighted to the Atlantic side; and with the Pacific side filled out to form more of a trapezoid at the 1.00m contour.

At this time of year, would we expect it to melt out to around the 1.25m triangular contour?

If so then the Pacific side is going to look very blue come September, as in the past years 2007, 2012 and 2016.

Just eye-balling it, call the 1.25m triangle as having a 2600 km base and 2000 km height, so half-base-times-height would be an end-of-melt-season extent of roughly 2.6 million square kilometers. That is somewhere close to the 2012 record of 3.18 in those units if we add in some extra bits e.g. in the CAA. (Very rough estimate only! It just says it's plausible we could have another low year - perhaps a record or close to a record. Whether that happens or not is still up to the weather and the ocean currents.)
Nope! Looking back 2 months, not the 1.25m contour but instead the 1.00m contour back then was a very good predictor of the melt region perimeter at minimum.

33
Thanks Wipneus, very interesting!

So this season must have had one of the lowest melt volumes for a while then?

Just eye-balling the graph, it appears that 2014 was the most recent year with a similarly small volume loss, then we need to go back to 2006 for another such year.

34
Arctic sea ice / Re: Home brew AMSR2 extent & area calculation
« on: September 10, 2017, 10:38:02 PM »
...The ice facing the Laptev looks a bit strange to me, it looks like two packs separated by a crack that opens and closes again. How can the cohesion be expalined?
Striking how closely the shape of the ice appears to match the bathymetry. The ice edge appears to correlate with the termination of the deep water.

Concerning the crack, the bathymetry map shows the deep water is split almost evenly into two basins - the Amundsen Basin on the Pacific side and the Nansen Basin on the Atlantic side - separated by the Nansen-Gakkol Ridge.

Could the edge of the ice be determined in large part by the edge of the deep water? Further, could the crack in the ice, along with its terminating lead (is that a manifestation of the frequently appearing "Laptev Bite"?), correlate with the Nansen-Gakkol Ridge?

Image source: https://nordpil.com/static/images/arctic_topographic_map_full.jpg

35
Arctic sea ice / Re: What the Buoys are telling
« on: August 14, 2017, 10:01:36 PM »
Fantastic movie! The action in the last 30 seconds reminds me of the climax to the old movie Straw Dogs, it's that dramatic  :o

Based on the movie I'm guessing that the edge of the ice floe has been progressively eaten away until it reached the buoy, which had hitherto faced away from the open water but was then released and swiveled around to view it.

36
I missed the close as wanted to see what the storm would do  :-\

Would have chosen 3.0-3.5 million square kilometres.

37
Arctic sea ice / Re: What the Buoys are telling
« on: August 10, 2017, 08:51:26 AM »
The halocline has all but collapsed.

Perhaps you could highlight on that ITP 95 T&S plot what you consider to be evidence for your assertion?
Had just been musing on the potential benefit of having a third profile contour plot to go with the temperature and salinity ones, namely, the water density profile. (Or could instead plot the gradient of the density.)

That should be easily derived from the information already in the other two and would show more directly where the density gradient was small i.e. 'halocline all but collapsed'.

Is that third profile contour ever plotted along with the other two?

38
Arctic sea ice / Re: The 2017 melting season
« on: August 08, 2017, 12:03:44 PM »
At tropicaltidbits.com, NAVGEM as well has the storm strengthening - down to 973 hPa in the 48h prediction.

With weaker ice than in 2012, we may well be looking at storm damage to the ice comparable to that from the 2012 GAC (Great Arctic Cyclone).

From memory, Neven records the GAC as bottoming out at 966 hPa and lasting 13 days. For comparison, NAVGEM records the current storm as having already dropped to 985 hPa at 12z back on 5 August, waxing and waning through the present and still at 986 hPa at their final, 180h prediction, 10 days later at 12z on 15 August.

While that final prediction is expected to be too far out to be reliable, the point is that the NAVGEM predictions show no sign of the storm dying out in the foreseeable future.

So for how much of August will it rotate around the Arctic Basin, sometimes weaker, sometimes stronger, but bringing significant winds all the while to potentially damage the ice pack?

39
Arctic sea ice / Re: IJIS
« on: August 08, 2017, 11:32:40 AM »
 ;D this discussion has already taken place.

The outcome was that Espen is mightier than the N word.  :P

40
Arctic sea ice / Re: The 2017 melting season
« on: August 08, 2017, 02:54:03 AM »
A-Team, I was thinking the 'Beaufort Finger' was this feature?

41
Arctic sea ice / Re: The 2017 melting season
« on: August 08, 2017, 01:31:24 AM »
Interesting sequence Thomas.

The thing that catches the eye about the 2017 plot is a 'channel' of thinner ice running from the Fram strait towards the Beaufort sea.

What is it?
If I recall correctly, it was a band of ice that piled up against the coast and then was blown out to sea.

42
Arctic sea ice / Re: Arctic Image of the Day
« on: August 06, 2017, 05:26:44 AM »
Adam, yes the ship is going backwards!

It is a double acting ship: https://en.wikipedia.org/wiki/Double_acting_ship

"The propulsion system of the new gas carrier consists of Azipod type propulsion units. They provide a very high degree of manoeuvrability, and allow use of the stern-first motion (Double Acting Tanker, DAT function) principle, which is necessary to overcome hummocks and heavy ice fields. Uniquely Christophe de Margerie has three Azipods – this is the first time so many of these propulsion units have been installed on an Arctic ice class vessel."
http://www.hellenicshippingnews.com/unique-ice-breaking-lng-carrier-christophe-de-margerie-ready-to-serve-yamal-lng-project/


In thick ice, it is faster when going backwards!

"The stern section is designed to enable navigation in severe ice conditions.
The double-acting tanker capability allows the vessel to break heavy ice in both bow and astern manuoevres.
The vessel proved her capability to move stern-first in 1.5 metres thick ice at a speed of 7.2 knots (target figure was 5 knots) and head-on at a speed of 2.5 knots (target figure was 2 knots)"
http://www.ship-technology.com/projects/christophe-de-margerie-class-icebreaking-lng-carriers/




43
Arctic sea ice / Re: The 2017 melting season
« on: August 06, 2017, 05:11:24 AM »
Adam, thanks for your comment.
That is true - the initial wave and wind damage will be largely on metre-scale floes - although it could also break up larger floes.
Even so, I still don't see any regions where more water is showing.
Q1. There will presumably be some regions composed of lots of metre-scale floes?
Q2. Wouldn't such regions darken in this gif if the small floes are decomposing?

44
Arctic sea ice / Re: The 2017 melting season
« on: August 06, 2017, 12:56:20 AM »
July 31-Aug 4, high speed loop to allow the eye to see through the clouds.

Wrangel island in lower left, Beaufort lower right.

http://feeder.gina.alaska.edu
Thanks Jay, this is very helpful to my understanding of what is going on under these storms.
Yes, the ice is moved around, but is there any melt or breaking up of the floes?
I just can't see any, even in the regions where the ice is already degraded.
This gif has caused me to think the storms are having less impact than I had previously thought.

45
Arctic sea ice / Re: The 2017 melting season
« on: August 04, 2017, 02:58:14 AM »
Sorry, if I'm interrupting the current discussion. Just posting an animation of the last two weeks with some slowmotion. In my opinion now you can see very well, what are clouds and what is SI. If the trend we see continues, the next two weeks could definitely wreck the ice.
Building on the last frame of TT's concentration map, I overlaid 48hrs of Euro forecasted surface winds via WindyTV. GFS is in good general agreement, although the euro has higher winds - up to 64KM.

Just loving these graphics, thank you! They provide excellent visual aids to understand what is going on with the ice.

(Probably way too much to even suggest but I would bookmark these if it happened they could be done daily and put on Neven's graphics page.)



46
Arctic sea ice / Re: Determining ocean heat content and salinity
« on: July 29, 2017, 03:40:54 AM »
Thanks Ice Shieldz, this is an important topic!

The Arctic sea ice is going to be blown around from now until the end of the melt season and how much melts out is going to be largely determined by how much heat in the water is available to it.

My impression is that we can't answer that question with any degree of accuracy because we don't have anywhere enough instrumentation in the water to tell us.

True or false?

If true then it's a travesty given the importance of the Arctic sea ice and given that deploying sufficient arrays of buoys should only cost in the ballpark of tens of millions of dollars - chickenfeed in today's global economy.


Is there a summary map somewhere showing locations of all the buoys in the Arctic basin with strings of temperature and salinity sensors?

47
Arctic sea ice / Re: Northwest Passage thread
« on: July 26, 2017, 10:18:55 PM »
Really nice pics! Thanks Jim.

48
Arctic sea ice / Re: The 2017 melting season
« on: July 22, 2017, 07:20:24 AM »
People keep hoping that all the clouds will preserve the ice. Its faster to boil a potato than to bake it. And faster to steam it than boil it. Water vapour at or below boiling point is a very effective heat transfer vehicle to colder objects.
  Hyperion, I read your analyses with great interest. Not so sure about your potato-cooking analogy of the bolded bit though.

  Baking a potato relies on thermal convection and conduction through the air in the oven. The Arctic ice melt process that best corresponds to is not to direct insolation but instead to the different heating mechanism of warm winds blowing across the ice.

  About the fastest way to cook a potato is to microwave it and that might provide the best analogy for direct solar insolation into the ice.

  With direct insolation, the sun's energy (which of course is ultimately responsible for the other heating processes you discuss as well) is deposited directly into the interior of the ice (or melt-pond water) - which is how microwave ovens work as well, just using a different part of the electromagnetic spectrum.

  So my gut feeling is that this heat transfer by vapour condensation must need a lot of vapour (as you point out, this is the situation at the moment) and be reasonably efficient in order to be comparably effective to direct solar insolation.

  I'm skeptical because to the extent that it's falling as rain at a few degrees C then that part of the 10 cubic kilometres per day of incoming total atmospheric water that you mention is only going to melt a fraction of one cubic kilometre of ice per day (compare water's 334 J/g heat of fusion with a few times 4.2 J/g-degrees C). The only really efficient mechanism will be direct contact of the water vapour with the ice.

  That also accords with experience from observing the melt season in past years: generally the best atmospheric conditions for melting ice near mid-Summer appears to have been clear skies.

  I do appreciate your point that there is an anomalously large amount of incoming water at the moment so it will anyway be interesting to see how much melt there has been on the Pacific side when the clouds clear.

49
Arctic sea ice / Re: Home brew AMSR2 extent & area calculation
« on: July 21, 2017, 03:30:45 AM »
Thanks again Wipneus for your amazingly informative plots - most recently the comparison between last year and this year of melting until the currrent date in the Beaufort Sea.

I agree, Shared Humanity, the large amount of dispersion last year in the Beaufort Sea was fatal for its sea ice. Indeed, it essentially melted out by the end of July! As far as I know this was earlier than any other year in the satellite record: see year comparison maps for Arctic sea ice at 1 August.

That won't happen this year but, as seaicesailor points out, there will still be a further month-and-a-half for the Beaufort ice to melt out and I expect that to happen.

50
Arctic sea ice / Re: Latest PIOMAS update (mid July update)
« on: July 18, 2017, 03:26:40 PM »
Thanks Wipneus, always interesting!

So the current ice thickness contours are fairly simple in shape: nearly triangular at 1.75m, 1.50m, 1.25m and weighted to the Atlantic side; and with the Pacific side filled out to form more of a trapezoid at the 1.00m contour.

At this time of year, would we expect it to melt out to around the 1.25m triangular contour?

If so then the Pacific side is going to look very blue come September, as in the past years 2007, 2012 and 2016.

Just eye-balling it, call the 1.25m triangle as having a 2600 km base and 2000 km height, so half-base-times-height would be an end-of-melt-season extent of roughly 2.6 million square kilometers. That is somewhere close to the 2012 record of 3.18 in those units if we add in some extra bits e.g. in the CAA. (Very rough estimate only! It just says it's plausible we could have another low year - perhaps a record or close to a record. Whether that happens or not is still up to the weather and the ocean currents.)

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