Support the Arctic Sea Ice Forum and Blog

Author Topic: "Stupid" Questions :o  (Read 511433 times)

nanning

  • Grease ice
  • Posts: 613
    • View Profile
  • Liked: 86
  • Likes Given: 3868
Re: "Stupid" Questions :o
« Reply #2100 on: July 02, 2019, 09:54:51 AM »
"It is preoccupation with possessions, more than anything else, that prevents us from living freely and nobly" - Bertrand Russell

BenB

  • Frazil ice
  • Posts: 282
    • View Profile
  • Liked: 50
  • Likes Given: 13
Re: "Stupid" Questions :o
« Reply #2101 on: July 02, 2019, 10:34:30 AM »
In terms of the pack splitting in two, this sort of happened in 2012, but it was really an arm extending on the Pacific side that became detached from the main pack and then completely melted out.


Rich

  • Guest
Re: "Stupid" Questions :o
« Reply #2102 on: July 02, 2019, 12:25:32 PM »
Interested in tapping into the experience of veteran ice watchers.

Looking at the installed base of heat on the Pacific side, there is a lot of ocean heat along the coast in relatively shallow water. The atmospheric heat in the coming days is greatest in the regions of warm water.

The ice is already melted out in the areas where the heat is concentrated and it's not obvious how the heat moves laterally as the ocean gets much deeper.

Are there past years which serve as good examples of strong melt on the Pacific side? If so, what we're the keys that propelled the melt in those years?

crandles

  • Nilas ice
  • Posts: 2465
    • View Profile
  • Liked: 75
  • Likes Given: 46
Re: "Stupid" Questions :o
« Reply #2103 on: July 02, 2019, 12:49:16 PM »
Interested in tapping into the experience of veteran ice watchers.

Looking at the installed base of heat on the Pacific side, there is a lot of ocean heat along the coast in relatively shallow water. The atmospheric heat in the coming days is greatest in the regions of warm water.

The ice is already melted out in the areas where the heat is concentrated and it's not obvious how the heat moves laterally as the ocean gets much deeper.

Are there past years which serve as good examples of strong melt on the Pacific side? If so, what we're the keys that propelled the melt in those years?

What chart are you looking at? Is it just showing there is water there rather than ice this year?

Albedo is important. Water will absorb more of the heat rather than ice reflecting more.

Deeper water does seem to represent a barrier to melt with ice edge often seeming to show some relation to water depth shapes. Not sure if this is correct but I suspect:

In shallow water, the water is able to mix any salt fairly evenly and warm water is then least dense so tends to stay near surface where it can transfer heat to ice. In deeper water, any approaching warm salty water can sink beneath cold fresh water layer. Warmth and salt will slowly diffuse upwards but a small amount of melt can continue to replenish cold fresh layer.

Winds and water current will also have obvious roles in lateral spread of heat.

Rich

  • Guest
Re: "Stupid" Questions :o
« Reply #2104 on: July 02, 2019, 01:00:43 PM »

What chart are you looking at? Is it just showing there is water there rather than ice this year?


I use the climatereanalyzer.org site to get information about daily ocean and atmospheric temperature in various locations.

There are lots of charts posted here daily which show the boundaries of the open water.

Not sure if that answers your question.

crandles

  • Nilas ice
  • Posts: 2465
    • View Profile
  • Liked: 75
  • Likes Given: 46
Re: "Stupid" Questions :o
« Reply #2105 on: July 02, 2019, 01:27:07 PM »
What I was trying to get at was that sometimes

http://ocean.dmi.dk/arctic/satellite/plots/satanom.arc.d-02.png

looks dramatic. But you may need to look at

http://ocean.dmi.dk/arctic/satellite/plots/satsst.arc.d-02.png

but maybe it is still as dramatic looking at



Sebastian Jones

  • Frazil ice
  • Posts: 307
    • View Profile
  • Liked: 50
  • Likes Given: 35
Re: "Stupid" Questions :o
« Reply #2106 on: July 02, 2019, 07:31:38 PM »
Thanks @Nanning, your hypothesis could be valid. I'm not aware of any warm current that  enters Pang fiord. There could be a sub-sea hot spring too, but without evidence, it is a thin explanation.
I'm assuming it is a feature of bathymetry.
I doubt it is a sub-sea hot spring. Those are not seasonal and the fjord would be icefree year round.
Maybe there are maps of known currents? I also assume it is a feature of bathymetry, directing the flow.
Not knowing anything about this particular fjord, but having some experience of research into currents in long deep fjords elsewhere, the general rule seems to be that currents circulate. A fjord pointing east into a north-flowing current will have an inflowing current along its northern side, and an outgoing current along its southern side. These currents are surprisingly strong.

But I found this very good website apparently written by a local, about changes to the ice and how the ice is melting sooner, the sea is warmer etc.

Thanks for this! I really appreciate that people take the time to try to find answers on they forum.

So, perhaps the explanation is indeed the upwelling current that flows into Cumberland sound along the north shore.
I am surmising that this phenomenon is more evident in Cumberland Sound than in Frobisher Bay because the sound is wider, which better allows for the currents to be separated.

ajouis

  • New ice
  • Posts: 30
    • View Profile
  • Liked: 11
  • Likes Given: 18
Re: "Stupid" Questions :o
« Reply #2107 on: July 02, 2019, 07:48:33 PM »
Is there any map that combines concentration and thickness to get something like volume of ice per square meter?

Sterks

  • Guest
Re: "Stupid" Questions :o
« Reply #2108 on: July 02, 2019, 07:57:19 PM »
Is there any map that combines concentration and thickness to get something like volume of ice per square meter?
1. Vol / Area = effective thickness
2. Map of effective thicknesss =  PIOMAS thread

Am I missing something in what you're asking?...

kassy

  • Grease ice
  • Posts: 611
    • View Profile
  • Liked: 167
  • Likes Given: 262
Re: "Stupid" Questions :o
« Reply #2109 on: July 02, 2019, 08:51:44 PM »
Per square meter is very ambitious too. Would be nice to have but not realistic because the data input is to crude. This is not really a problem as the arctic is so big.
Þetta minnismerki er til vitnis um að við vitum hvað er að gerast og hvað þarf að gera. Aðeins þú veist hvort við gerðum eitthvað.

ajouis

  • New ice
  • Posts: 30
    • View Profile
  • Liked: 11
  • Likes Given: 18
Re: "Stupid" Questions :o
« Reply #2110 on: July 02, 2019, 09:18:15 PM »
Does the effective thickness accounts for concentration?

RoxTheGeologist

  • Frazil ice
  • Posts: 442
    • View Profile
  • Liked: 111
  • Likes Given: 87
Re: "Stupid" Questions :o
« Reply #2111 on: July 02, 2019, 09:33:57 PM »
Is there any reason that arctic sea ice loss should be linear?

I would expect it not to be given that there are feedbacks within the system (i.e. loss of albedo), but I'm wondering if there are arguments for why it should behave linearly?

Thanks

What is the linear relationship you are referring to?
 

Sterks

  • Guest
Re: "Stupid" Questions :o
« Reply #2112 on: July 02, 2019, 11:25:00 PM »
Does the effective thickness accounts for concentration?
Yes. For instance if there is increasing open water surrounding floes, the effective thickness is reduced even when the average thickness of floes remains constant

Klondike Kat

  • Grease ice
  • Posts: 681
    • View Profile
  • Liked: 32
  • Likes Given: 47
Re: "Stupid" Questions :o
« Reply #2113 on: July 03, 2019, 12:34:12 AM »
Is there any reason that arctic sea ice loss should be linear?

I would expect it not to be given that there are feedbacks within the system (i.e. loss of albedo), but I'm wondering if there are arguments for why it should behave linearly?

Thanks

Overall, no.  At times, it may display linear behavior, especially when focusing on ice atop large areas of ocean.  Even so, the largest losses have probably occurred already.  The ever-shrinking ice pack leaves less and less ice to melt.

wdmn

  • Frazil ice
  • Posts: 338
    • View Profile
  • Liked: 57
  • Likes Given: 38
Re: "Stupid" Questions :o
« Reply #2114 on: July 03, 2019, 12:41:25 AM »
@wdmn
There's this, for one:
https://forum.arctic-sea-ice.net/index.php/topic,933

Not really an argument for linearity, per se, but that positive feedbacks like decreased summer albedo might be cancelled out by negative feedbacks like increased winter ice growth.

Thanks!

Quote
What is the linear relationship you are referring to?

Whether the decline in summer area/extent should be linear... So I guess the relationship is superficially between time and area/extent, but more so between GMSTA and area and extent?

While there are negative feedbacks, I would suspect that at some point positive feedbacks overwhelm the system at which point it transitions rapidly to a new meta-stable state.

Michael Hauber

  • Grease ice
  • Posts: 838
    • View Profile
  • Liked: 46
  • Likes Given: 12
Re: "Stupid" Questions :o
« Reply #2115 on: July 03, 2019, 01:08:49 AM »
Why does the ocean appear black in MODIS images?
Climate change:  Prepare for the worst, hope for the best, expect the middle.

ajouis

  • New ice
  • Posts: 30
    • View Profile
  • Liked: 11
  • Likes Given: 18
Re: "Stupid" Questions :o
« Reply #2116 on: July 03, 2019, 01:22:50 AM »
Thanks sterks

Sterks

  • Guest
Re: "Stupid" Questions :o
« Reply #2117 on: July 03, 2019, 01:54:17 AM »
Why does the ocean appear black in MODIS images?
Is this a tricky question?
Shouldn't it appear black as it absorbs nearly all visible light (absortion depth varies with color... But anyways nothing comes back after a few tens of meters).
Now the question is why does it appear blue from Apollo XI?
Edit: apparently it should appear blueish as the high end of the spectrum penetrates less and is partially scattered and reflected. So.I don't know. MODIS visible is really a combination of filtered images, perhaps this treatment causes ocean look black.
« Last Edit: July 03, 2019, 02:03:09 AM by Sterks »

Michael Hauber

  • Grease ice
  • Posts: 838
    • View Profile
  • Liked: 46
  • Likes Given: 12
Re: "Stupid" Questions :o
« Reply #2118 on: July 03, 2019, 01:59:51 AM »
Ocean also appears blue from close up - i.e. from a boat or from land.
Climate change:  Prepare for the worst, hope for the best, expect the middle.

Sterks

  • Guest
Re: "Stupid" Questions :o
« Reply #2119 on: July 03, 2019, 02:04:47 AM »
Ocean also appears blue from close up - i.e. from a boat or from land.
Yes. See my edit above. I do not know for sure what happens to MODIS

Michael Hauber

  • Grease ice
  • Posts: 838
    • View Profile
  • Liked: 46
  • Likes Given: 12
Re: "Stupid" Questions :o
« Reply #2120 on: July 03, 2019, 02:23:42 AM »
Looking at some satellite images of the coast using google maps I'd say the ocean from directly above is quite transparent with shallow features such as sandbars very clearly visible, but deeper water gets dark, and with a grey shimmer of weak reflections on the surface.  Not perfectly black but relatively dark so depending on exposure sensitivity it could appear black.  Perhaps also the google map satellite views are much lower and so more variation from perfectly vertical whereas MODIS satellite(s) much higher so much closer to vertical.  However waves/roughness etc deviate from perfectly horizontal anyway so this shouldn't matter I'd think.  At any sort of angle blue reflection from the sky would dominate.
Climate change:  Prepare for the worst, hope for the best, expect the middle.

petm

  • Grease ice
  • Posts: 675
    • View Profile
  • Liked: 334
  • Likes Given: 27
Re: "Stupid" Questions :o
« Reply #2121 on: July 03, 2019, 03:57:13 AM »
Here's a stupid question: What thread does this belong in? Thanks.

Open access article describing a machine learning approach to ice concentration:



Remote Sens. 2019, 11(9), 1071; https://doi.org/10.3390/rs11091071

Article
Artificial Neural Network for the Short-Term Prediction of Arctic Sea Ice Concentration

Minjoo Choi 1, Liyanarachchi Waruna Arampath De Silva 2 and Hajime Yamaguchi 2
1 Mathematics and Cybernetics, SINTEF Digital, P.O. Box 124 Blindern, NO-0314 Oslo, Norway
2 Graduate School of Frontier Sciences, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa 277-8561, Japan
*Author to whom correspondence should be addressed.

Received: 15 March 2019 / Accepted: 3 May 2019 / Published: 6 May 2019

Abstract: In this paper, we applied an artificial neural network (ANN) to the short-term prediction of the Arctic sea ice concentration (SIC). The prediction was performed using encoding and decoding processes, in which a gated recurrent unit encodes sequential sea ice data, and a feed-forward neural network model decodes the encoded input data. Because of the large volume of Arctic sea ice data, the ANN predicts the future SIC of each cell individually. The limitation of these singular predictions is that they do not use information from other cells. This results in low accuracy, particularly when there are drastic changes during melting and freezing seasons. To address this issue, we present a new data scheme including global and local SIC information, where the global information is represented by sea ice statistics. We trained ANNs using different data schemes and network architectures, and then compared their performances quantitatively and visually. The results show that, compared with a data scheme that uses only local sea ice information, the newly proposed scheme leads to a significant improvement in prediction accuracy.

Keywords: artificial neural network; gated recurrent unit; Arctic sea ice prediction; short-term prediction

b_lumenkraft

  • Guest
Re: "Stupid" Questions :o
« Reply #2122 on: July 03, 2019, 09:10:31 AM »
Here's a stupid question: What thread does this belong in? Thanks.

I bet AbruptSLR wouldn't mind when you post this in "Ice Apocalypse - MULTIPLE METERS SEA..."

We have a vast variety of papers there, i think it would fit.

crandles

  • Nilas ice
  • Posts: 2465
    • View Profile
  • Liked: 75
  • Likes Given: 46
Re: "Stupid" Questions :o
« Reply #2123 on: July 03, 2019, 12:17:41 PM »

Whether the decline in summer area/extent should be linear... So I guess the relationship is superficially between time and area/extent, but more so between GMSTA and area and extent?

While there are negative feedbacks, I would suspect that at some point positive feedbacks overwhelm the system at which point it transitions rapidly to a new meta-stable state.

Not impossible for positive feedbacks to dominate. But why assume that? Have you adequately considered evidence for the other possibility?

The positive feedbacks (albedo) dominate in summer but the negative feedbacks (ice thickness/insulation) dominate in winter. As the ice dwindles, the further opportunities for added albedo effects dwindle so it seems to me that there is a good chance the negative feedbacks are more likely to slow the rate of change.

Is a more stable period after 2012 good evidence of this? Certainly not clear, but maybe slightly suggestive?

Archimid

  • Nilas ice
  • Posts: 2250
    • View Profile
  • Liked: 243
  • Likes Given: 174
Re: "Stupid" Questions :o
« Reply #2124 on: July 03, 2019, 01:19:45 PM »
Let's suppose that the thinner arctic ice combined with the hotter Arctic changes the way Arctic sea ice area decreases.  Let's suppose large swaths of contiguous ice area, sometimes not including peripheral ice, decrease in a day. On a map of the ice there should be a significant chunk of ice missing.  Let's call that event a poof.

How much contiguous daily area loss constitutes a "poof" event? 

 200k? 500k? More? Less?
I am an energy reservoir seemingly intent on lowering entropy for self preservation.

b_lumenkraft

  • Guest
Re: "Stupid" Questions :o
« Reply #2125 on: July 03, 2019, 01:41:48 PM »
How about poof for 200k and megapoof for 500k?

be cause

  • Grease ice
  • Posts: 826
  • Citizenship .. a Lurker gets asylum
    • View Profile
  • Liked: 203
  • Likes Given: 183
Re: "Stupid" Questions :o
« Reply #2126 on: July 03, 2019, 01:52:13 PM »
  .. and of course a minipoof would be allowed in confined spaces .. b.c.
2007 + 5 = 2012 + 4 = 2016 + 3 = 2019 ...

Shared Humanity

  • Young ice
  • Posts: 3906
    • View Profile
  • Liked: 389
  • Likes Given: 46
Re: "Stupid" Questions :o
« Reply #2127 on: July 03, 2019, 04:34:17 PM »

Whether the decline in summer area/extent should be linear... So I guess the relationship is superficially between time and area/extent, but more so between GMSTA and area and extent?

While there are negative feedbacks, I would suspect that at some point positive feedbacks overwhelm the system at which point it transitions rapidly to a new meta-stable state.

Not impossible for positive feedbacks to dominate. But why assume that? Have you adequately considered evidence for the other possibility?

The positive feedbacks (albedo) dominate in summer but the negative feedbacks (ice thickness/insulation) dominate in winter. As the ice dwindles, the further opportunities for added albedo effects dwindle so it seems to me that there is a good chance the negative feedbacks are more likely to slow the rate of change.

Is a more stable period after 2012 good evidence of this? Certainly not clear, but maybe slightly suggestive?

I've read all of your posts on the "Slow Transition" concept and am an absolute believer. I believe that the volume at minimum behavior and the "Volume Anomaly and Trend" chart demonstrates this. I'd have to go back and reread your analysis to explain it though.

As you have frequently pointed out, while 2012 reached an all time minimum in extent, the arctic ice was damaged far more severely in 2010 as the volume drop clearly shows. Since then, volume at minimum has bounced around.

This same behavior can be seen following the dramatic loss in volume in 2007. What is happening here is that severe melts destroy large amounts of thicker MYI. This lower baseline of MYI than establishes a range of the behavior of volume at minimum which will only be broken by another disastrous melt season with new lows of MYI.

Will we have another disastrous melt season this year? Certainly possible but, looking at the chart, I don't believe a disastrous melt season will result in a BOE. It could drop us below 2 thousand km3.

edit: What I have written here is a poor attempt of summarizing crandle's work. crandles: Could you direct people to the thread where this was discussed?
« Last Edit: July 03, 2019, 04:49:53 PM by Shared Humanity »

crandles

  • Nilas ice
  • Posts: 2465
    • View Profile
  • Liked: 75
  • Likes Given: 46
Re: "Stupid" Questions :o
« Reply #2128 on: July 03, 2019, 06:45:16 PM »

edit: What I have written here is a poor attempt of summarizing crandle's work. crandles: Could you direct people to the thread where this was discussed?

I think Chris Reynolds explained it well both on his blog
http://dosbat.blogspot.com/2015/05/the-slow-transition.html

and on the slow transition thread
https://forum.arctic-sea-ice.net/index.php/topic,933.0.html

wdmn

  • Frazil ice
  • Posts: 338
    • View Profile
  • Liked: 57
  • Likes Given: 38
Re: "Stupid" Questions :o
« Reply #2129 on: July 03, 2019, 07:10:31 PM »

Whether the decline in summer area/extent should be linear... So I guess the relationship is superficially between time and area/extent, but more so between GMSTA and area and extent?

While there are negative feedbacks, I would suspect that at some point positive feedbacks overwhelm the system at which point it transitions rapidly to a new meta-stable state.

Not impossible for positive feedbacks to dominate. But why assume that? Have you adequately considered evidence for the other possibility?

The positive feedbacks (albedo) dominate in summer but the negative feedbacks (ice thickness/insulation) dominate in winter. As the ice dwindles, the further opportunities for added albedo effects dwindle so it seems to me that there is a good chance the negative feedbacks are more likely to slow the rate of change.

Is a more stable period after 2012 good evidence of this? Certainly not clear, but maybe slightly suggestive?

My reasoning is roughly: assuming a state change (i.e. to an ice free arctic) is possible (and we know from the paleo records that it is), then at some point the negative feedbacks have to be overwhelmed. I would expect that would not unfold in a linear fashion.

As for the "stable" period after 2012, I would guess that it is a transitional phase... and also suggests that the changes occurring will not adhere to linearity.

None of this is based on any evidence related to the system itself (beyond that I've looked at both volume and extent graphs for min. and max). Now that reading has been provided I will do it.

Thank you!

RoxTheGeologist

  • Frazil ice
  • Posts: 442
    • View Profile
  • Liked: 111
  • Likes Given: 87
Re: "Stupid" Questions :o
« Reply #2130 on: July 03, 2019, 07:43:36 PM »
Why does the ocean appear black in MODIS images?

Ocean reflects very little light, even at low angles. It's albedo is 0.06. It's black because of this.

It loses heat by emitting long wave radiation, evaporation and through contact with air. None of which we can see.

If you observe from a very low angle, from a boat, then the color is down to refracted and reflected light. 

RoxTheGeologist

  • Frazil ice
  • Posts: 442
    • View Profile
  • Liked: 111
  • Likes Given: 87
Re: "Stupid" Questions :o
« Reply #2131 on: July 03, 2019, 07:54:51 PM »
Okay. Melt ponds. dumb questions?

Can melt ponds drain if the ocean at the ice/water contact is below the freezing point of freshwater (Say -0.5°C). If the ponds can't drain (because the water freezes) then, when ponds do drain, does it imply:

1) That the whole column of ice is at 0°C (warmed through by freezing freshwater)
2) That the ice itself is sitting on water at 0°C, or close to it.
3) Some bottom melt HAS to occur before a melt pond can drain, to warm and reduce the salinity of the ocean that the ice is sitting in.
4) Ice supporting melt ponds has to be thick enough and cold enough to support the pond, and therefore there will be a delay of a few weeks after the blue of the melt ponds disappears before ice melts out.
5)after the melt pond has drained all additional heat is going into melt rather than warming up the ice.
« Last Edit: July 03, 2019, 10:52:06 PM by RoxTheGeologist »

ArcticMelt2

  • Frazil ice
  • Posts: 428
    • View Profile
  • Liked: 40
  • Likes Given: 27
Re: "Stupid" Questions :o
« Reply #2132 on: July 03, 2019, 08:16:29 PM »
Why is the planet warmer in winter months faster than in summer? But the loss of snow and ice in the summer months is much more significant than in the winter.



Possible explanations:

1) Warming increases atmospheric circulation and clears all temperature gradients (diurnal, monthly, geographic).

2) When ice and snow melt, a lot of energy is expended, while when it freezes, energy is released on the contrary.

Which option is correct?

b_lumenkraft

  • Guest
Re: "Stupid" Questions :o
« Reply #2133 on: July 03, 2019, 08:19:19 PM »
Okay. Melt ponds. dumb questions?

I'm also very interested in the answers to these questions.

I would go for a 'yes' for 2) and 3).

The others are above my pay grade. I don't even understand 4).

Tor Bejnar

  • Young ice
  • Posts: 2932
    • View Profile
  • Liked: 279
  • Likes Given: 159
Re: "Stupid" Questions :o
« Reply #2134 on: July 03, 2019, 09:38:47 PM »
Sometimes, I'm sure, a floe with a melt pond 'cracks in two' and the pond drains 'over the new edge', with no regard to how cold the ocean is under the floe.  Besides this presumption, I like your questions, Rox.

AM,
Go to Skeptical Science for "winter warming faster than summer".  I've picked out a particular article here.
Arctic ice is healthy for children and other living things.

Stephan

  • Grease ice
  • Posts: 647
    • View Profile
  • Liked: 159
  • Likes Given: 97
Re: "Stupid" Questions :o
« Reply #2135 on: July 03, 2019, 10:15:46 PM »
Why is the planet warmer in winter months faster than in summer? But the loss of snow and ice in the summer months is much more significant than in the winter.

Possible explanations:

1) Warming increases atmospheric circulation and clears all temperature gradients (diurnal, monthly, geographic).

2) When ice and snow melt, a lot of energy is expended, while when it freezes, energy is released on the contrary.

Which option is correct?
At least for the Arctic 2) is correct. If you carefully look at the "DMI North of 80°N temperature graph" [on the Arctic Sea Ice Graphs web site] there is almost no change in the last decades when it comes to summer temperatures.
On the other hand winters have been much warmer, at least over some weeks, because the slower jet stream allowed more warm air intrusions into the high Arctic.

Please beware that the "DMI North of 80°N temperature graph" is not a result of real T measurements but results on models, and that it is "latitude weighted", i.e. the area N of 89° has the same relative weight than the area between 81° and 82°, although the latter is much larger.

___________

On the other side of the earth, warmer intrusions into Antarctica happen much more rarely in the Antarctic winter months - the jet stream around 60-70° south is much stronger and much more robust than its northern counterpart.
« Last Edit: July 03, 2019, 10:22:48 PM by Stephan »

RoxTheGeologist

  • Frazil ice
  • Posts: 442
    • View Profile
  • Liked: 111
  • Likes Given: 87
Re: "Stupid" Questions :o
« Reply #2136 on: July 03, 2019, 10:48:34 PM »
Okay. Melt ponds. dumb questions?

I'm also very interested in the answers to these questions.

I would go for a 'yes' for 2) and 3).

The others are above my pay grade. I don't even understand 4).

question 4....

My idea is that it might go something like this:

We see blue melt ponds, and I think that implies that the ice and water below is still cold enough to freeze the base of the freshwater pond to stop it draining. Once all the ice heats up to 0°C, then the pond can drain due to density and we don't see blue anymore. If that ice is still pretty white, then it's probably fairly thick and has to be warmed and thinned and finally melted. That process seems to take about 3-4 weeks (just observing).






crandles

  • Nilas ice
  • Posts: 2465
    • View Profile
  • Liked: 75
  • Likes Given: 46
Re: "Stupid" Questions :o
« Reply #2137 on: July 04, 2019, 12:32:10 AM »
Interesting questions and sorry I don't know the answers.

I think I have seen the suggestion that to some extent melt ponds can heal a hole as the fresh melt water can freeze. However: there is also possibility of v shaped crack fresh water at 0C enters crack is cooled and freezes but instead of healing the crack the ice has larger volume so it has the effect of opening up the crack.

Not sure but perhaps this means the answers to some of the questions are maybe?

b_lumenkraft

  • Guest
Re: "Stupid" Questions :o
« Reply #2138 on: July 04, 2019, 06:38:32 AM »
question 4....

My idea is that it might go something like this:

We see blue melt ponds, and I think that implies that the ice and water below is still cold enough to freeze the base of the freshwater pond to stop it draining. Once all the ice heats up to 0°C, then the pond can drain due to density and we don't see blue anymore. If that ice is still pretty white, then it's probably fairly thick and has to be warmed and thinned and finally melted. That process seems to take about 3-4 weeks (just observing).

OK. But ice floe temperature is not homogenous, or is it? When it starts to melt on its surface, it can still have a colder core. When bottom melt occurs also, you not only melt away the plug (the refrozen meltwater from the surface, which makes pond water able to drain) you also warm up the core, making refreeze of meltwater less likely.

I don't think your assumption white ice equals thick ice is correct. It becomes white again when the water has drained, that's not a function of thickness IMHO.

I provide a GIF showing the Inglefield Bredning fjord that had massive meltponding recently, then drained, then collapsed. In this GIF, pink is white. I think we see bottom melt here and indicates the ice was already fairly thin when it became white again before collapsing.

(Click to play)
« Last Edit: July 04, 2019, 06:58:32 AM by b_lumenkraft »

b_lumenkraft

  • Guest
Re: "Stupid" Questions :o
« Reply #2139 on: July 04, 2019, 06:51:31 AM »
Sometimes, I'm sure, a floe with a melt pond 'cracks in two' and the pond drains 'over the new edge', with no regard to how cold the ocean is under the floe.

As provided in this GIF.

Here we see cracks holding meltwater in it in the first frame. In the next frame, we see meltwater on top of the surface but in the crack and around them, it has already drained.

(also the Inglefield Bredning fjord)

BenB

  • Frazil ice
  • Posts: 282
    • View Profile
  • Liked: 50
  • Likes Given: 13
Re: "Stupid" Questions :o
« Reply #2140 on: July 04, 2019, 06:53:39 AM »
Interesting questions Rox. A couple of general points (based on my understanding, and I'm happy to be contradicted) before trying to answer some of your specific questions. Sea ice, particularly first-year ice, contains pockets of salty brine. This initially remains liquid when the sea ice freezes, as it has a lower melting point, and some of it then drains out, leaving air pockets. Some remains as trapped pockets of brine, which melt at a lower temperature than the surrounding ice. This, as well as other factors, mean that there are weaker and stronger points within the ice, including potential routes for the water to escape from the surface to the sea. When melt water refreezing blocks these cracks/passages, it doesn't necessarily block them at the base of the floe. If surface melt has started before the ice is all at 0C, the water will refreeze at some point on its way through the floe.

The water in melt ponds can reach temperatures above zero.

Fresh water coming into contact with subzero salt water won't necessarily freeze on contact. It may manage to mix sufficiently before losing enough energy to its surroundings to change state.

Now to your questions:

1. Yes, probably in general, but only at the column where the water drains. The whole floe won't be the same temperature. It is also possible that "warm"  (1 degree?) melt water is able to escape before refreezing through a larger crack produced by dynamic processes.
2. Usually, but not always, I think. From observation, sometimes you see melt ponds drain in areas where it is unlikely that the water has reached 0. The buoy temperature profiles could help with this.
3. Not sure, but I don't think so. See 2 and the point about losing energy to change state.
4. Yes, it must be thick and strong enough, but I think the depth implied by this varies a lot. Sometimes floes melt out very quickly after melt ponds drain, sometimes slowly.
5. Floes are massive, and they are constantly losing and gaining heat in different places, and heat is being transferred through them. The temperature won't be uniform when the pond drains. Either way, the energy needed for the change of state is much greater than the energy needed to raise the temperature a degree or two, so I don't think this has a huge impact on the subsequent rate of melt.

Overall, I think you're underestimating the dynamic nature of the process and the variation in conditions within avsing floe.

b_lumenkraft

  • Guest
Re: "Stupid" Questions :o
« Reply #2141 on: July 04, 2019, 07:09:14 AM »
Sea ice, particularly first-year ice, contains pockets of salty brine. This initially remains liquid when the sea ice freezes, as it has a lower melting point, and some of it then drains out, leaving air pockets. Some remains as trapped pockets of brine, which melt at a lower temperature than the surrounding ice. This, as well as other factors, mean that there are weaker and stronger points within the ice, including potential routes for the water to escape from the surface to the sea. When melt water refreezing blocks these cracks/passages, it doesn't necessarily block them at the base of the floe.

That makes so much sense. Thanks, Ben!

binntho

  • Grease ice
  • Posts: 974
    • View Profile
  • Liked: 240
  • Likes Given: 71
Re: "Stupid" Questions :o
« Reply #2142 on: July 04, 2019, 07:16:08 AM »
Just a quicky on why winters are warming faster than summers (and nights faster than days):

It's one of the hallmarks of insulation driven warming as opposed to insolation driven warming.

If the current warming was due to increased insolation (e.g. greater solar activity, less clouds) then the warming would be strongest between the tropics, in summer and during the day.

Since the current warming is due to increased insulation, the warming is seen to be stronger away from the tropics, in winter and during the nighttime.
because a thing is eloquently expressed it should not be taken to be as necessarily true
St. Augustine, Confessions V, 6

nanning

  • Grease ice
  • Posts: 613
    • View Profile
  • Liked: 86
  • Likes Given: 3868
Re: "Stupid" Questions :o
« Reply #2143 on: July 04, 2019, 08:09:46 AM »
I see blue plumes down the west coast of Greenland. What are they?
Worldview
"It is preoccupation with possessions, more than anything else, that prevents us from living freely and nobly" - Bertrand Russell

Wipneus

  • Citizen scientist
  • Young ice
  • Posts: 3969
    • View Profile
    • Arctische Pinguin
  • Liked: 536
  • Likes Given: 0
Re: "Stupid" Questions :o
« Reply #2144 on: July 04, 2019, 08:50:26 AM »

If the current warming was due to increased insolation (e.g. greater solar activity, less clouds) then the warming would be strongest between the tropics (...).

Sounds reasonable, but actually not true. Arctic Amplification would still make the warming stronger in the higher latitudes (Planck rules). Early 20th century warming is an example, paleo evidence another

binntho

  • Grease ice
  • Posts: 974
    • View Profile
  • Liked: 240
  • Likes Given: 71
Re: "Stupid" Questions :o
« Reply #2145 on: July 04, 2019, 08:58:55 AM »

If the current warming was due to increased insolation (e.g. greater solar activity, less clouds) then the warming would be strongest between the tropics (...).

Sounds reasonable, but actually not true. Arctic Amplification would still make the warming stronger in the higher latitudes (Planck rules). Early 20th century warming is an example, paleo evidence another

Yes, you are right, a good explanation is here https://www.mpimet.mpg.de/en/communication/news/focus-on-overview/arctic-amplification/

As for winters and nights, I still maintain that this is because of changes in insulation, while changes in insolation would have the opposite effect.
because a thing is eloquently expressed it should not be taken to be as necessarily true
St. Augustine, Confessions V, 6

BenB

  • Frazil ice
  • Posts: 282
    • View Profile
  • Liked: 50
  • Likes Given: 13
Re: "Stupid" Questions :o
« Reply #2146 on: July 04, 2019, 12:09:40 PM »
Another way of considering your question, Rox:

Imagine that melt ponds drained in the way that you suggest, with the fresh water freezing at the base of the floe as it hit the colder salt water, and that the ice in floes warmed evenly, tending towards a uniform temperature of 0C.

Water would flow down any crack that appeared, with the first drop of fresh water blocking the crack at the base of the floe and the rest of the crack filling up with "blocked" fresh water. This fresh water would refreeze. This would happen successively in any cracks/fissures in the ice. The floe would eventually become a perfectly consolidated rectangular block of ice, with all of its fissures filled.

Any further meltwater would have nowhere to go, so it would either stay on top of the floe or flow off its edges. Assuming a melt pond could form, it would only be able to drain once the bottom melt and top melt met, i.e. once the floe had totally melted out or, as Tor suggested, if the whole floe broke in two.

As this isn't what we observe, it suggests that the model needs adjusting.

Sterks

  • Guest
Re: "Stupid" Questions :o
« Reply #2147 on: July 04, 2019, 01:02:03 PM »
I see blue plumes down the west coast of Greenland. What are they?
Worldview
River/glacier melting from Greenland discharging in the sea?

BenB

  • Frazil ice
  • Posts: 282
    • View Profile
  • Liked: 50
  • Likes Given: 13
Re: "Stupid" Questions :o
« Reply #2148 on: July 04, 2019, 01:08:17 PM »
Serks, yes, I think so too. Technically called "sediment plumes", according to NASA, because it's the sediment in the meltwater (picked up at the base of glaciers as they grind the bedrock) that causes the colours:

https://earthobservatory.nasa.gov/images/84464/sediment-plumes-around-greenland

binntho

  • Grease ice
  • Posts: 974
    • View Profile
  • Liked: 240
  • Likes Given: 71
Re: "Stupid" Questions :o
« Reply #2149 on: July 04, 2019, 01:19:40 PM »
Another way of considering your question, Rox:

Imagine that melt ponds drained in the way that you suggest, with the fresh water freezing at the base of the floe as it hit the colder salt water, and that the ice in floes warmed evenly, tending towards a uniform temperature of 0C.

Water would flow down any crack that appeared, with the first drop of fresh water blocking the crack at the base of the floe and the rest of the crack filling up with "blocked" fresh water. This fresh water would refreeze. This would happen successively in any cracks/fissures in the ice. The floe would eventually become a perfectly consolidated rectangular block of ice, with all of its fissures filled.

Any further meltwater would have nowhere to go, so it would either stay on top of the floe or flow off its edges. Assuming a melt pond could form, it would only be able to drain once the bottom melt and top melt met, i.e. once the floe had totally melted out or, as Tor suggested, if the whole floe broke in two.

As this isn't what we observe, it suggests that the model needs adjusting.
Well what is it that we observe? I'd guess that structural instability will eventually open op channels between water in the meltponds and the underlying sea water.

The very large blue areas we see, that later change colors because of (presumably) draining are mostly very large landfast ice areas. When the water on the surface drains away, does the underlying ice float up? Is there a weight imbalance, where the surface water is pressing the ice downwards? I'm not really sure.

But I found a good image of meltponds and polynya and meltponds that have turned into polynya indicating that the whole process is not so clear after all.
because a thing is eloquently expressed it should not be taken to be as necessarily true
St. Augustine, Confessions V, 6