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kassy

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Re: "Stupid" Questions :o
« Reply #2650 on: September 26, 2019, 07:59:28 PM »
Does extracting oil and gas from underground cause subsidence?
It does. That is why we are stopping the gas production in the Groningen area. Quakes (very minor ones) are damaging houses.

If the millimeter or two is the actual number it is not that relevant compared to sea level rise.
That is at 0,3 cm per year (and bound to go up).

Is the area around the Persian Gulf sinking a millimeter or two a year, exacerbating SLR?

Land sinking does not make SLR worse but it makes the area effected more vulnerable to flooding.
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gerontocrat

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Re: "Stupid" Questions :o
« Reply #2651 on: September 26, 2019, 08:42:17 PM »
Here's one I could have put in the Oil & Gas thread, but just in case it's stupid, I'll put it here.
Does extracting oil and gas from underground cause subsidence? For example, is the area around the Persian Gulf sinking a millimeter or two a year, exacerbating SLR?
Yes, it did belong in the Oil & Gas thread, but, 

Forget SLR, minimal impact.

But... (not only Oil & Gas - over-extraction of groundwater causing big problems in some megacities, e.g. Tehran, Mexico City).  Not talking about a millimetre or two per year, but can be tens of centimetres of ground slump per year in the most vulnerable places. 

Count the ways mankind is screwing up the joint, they are legion.

Also happened in California during the unregulated 30's and 40's - the Trump Vision for the future.

Earthquakes in Oklahoma since fracking started.

https://www.forbes.com/sites/trevornace/2018/03/28/massive-oil-fields-in-texas-are-heaving-and-sinking-at-alarming-rates/#32c0a536c8b3

From a 2006 Paper.
https://www.researchgate.net/publication/242757170_SUBSIDENCE_PREDICTION_CAUSED_BY_THE_OIL_AND_GAS_DEVELOPMENT
Quote
Abstract:
Oil and gas development from underground reservoirs disturbs original rock mass balance. The tending of the rock mass to achieve a new, even only temporary balance is manifested in the movements of the ground surface. Movements can affect ground infrastructure like offshore platforms, pipelines and buildings.

1.  Introduction
Surface subsidence of areas where oil, gas and water are exploited are a serious problem in various parts of the World. In the coastal regions, vertical movements of the surface may result in flooding or generate extra costs for securing the banks.

Such problems were encountered, e.g. in the area of Maracaibo Lake in Venezuela (ca. 3.5 m – maximum subsidence), Mexican Gulf, in California (ca. 10 m – maximum subsidence) and in Japan. The subsidence troughs may be huge in size and the damage to the objects standing on them is comparable to those in the mining areas. Considerable deformations of surface usually can be found in the places where thick fluid reservoirs occur and the host rocks have compaction qualities.
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Richard Rathbone

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Re: "Stupid" Questions :o
« Reply #2652 on: September 27, 2019, 09:45:00 PM »
It depends on the reservoir, some are a lot more dependent on the pressure of the fluid in them than others, but if they are sensitive, subsidence can be pretty fast. I don't know about the Persian Gulf, but 10s of cm per year has happened as a result of oil and gas extraction as well as groundwater extraction.


ajouis

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Re: "Stupid" Questions :o
« Reply #2653 on: October 02, 2019, 02:57:07 AM »
When i worked on a glacier, the black ash that was on it actually insulated the ice, do you know if it still hold up at macro level or if the type of matter (volcanic ash) is important? Would be interested to hear of other phenomenas in the arctic where something doesn t work out as usual.

wallen

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Re: "Stupid" Questions :o
« Reply #2654 on: October 02, 2019, 07:15:58 AM »
When you look at Worldview and see the "Blackout " area extending daily, is this the extending limit of 24 hour darkness or a visual limitation of the satellite as the Arctic progresses toward winter.

nanning

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Re: "Stupid" Questions :o
« Reply #2655 on: October 02, 2019, 10:19:02 AM »
When i worked on a glacier, the black ash that was on it actually insulated the ice, do you know if it still hold up at macro level or if the type of matter (volcanic ash) is important? Would be interested to hear of other phenomenas in the arctic where something doesn t work out as usual.

What do you mean by "insulated the ice"?
Was there direct sunshine on the black ash? I expect it would heat up.
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ajouis

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Re: "Stupid" Questions :o
« Reply #2656 on: October 02, 2019, 11:44:47 AM »
When i worked on a glacier, the black ash that was on it actually insulated the ice, do you know if it still hold up at macro level or if the type of matter (volcanic ash) is important? Would be interested to hear of other phenomenas in the arctic where something doesn t work out as usual.

What do you mean by "insulated the ice"?
Was there direct sunshine on the black ash? I expect it would heat up.
Funnily enough the part with the ash thawed slower than the rest, as far as I understand because while the ash heated up, it reduced much of the radiation and convection heat towards the ice by sheltering it, leaving only very inefficient conduction to transmit the extra energy from the ash to the ice, which transmits less energy than the heat tranports on normal ice.

nanning

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Re: "Stupid" Questions :o
« Reply #2657 on: October 02, 2019, 05:13:53 PM »
<snip>
Funnily enough the part with the ash thawed slower than the rest, as far as I understand because while the ash heated up, it reduced much of the radiation and convection heat towards the ice by sheltering it, leaving only very inefficient conduction to transmit the extra energy from the ash to the ice, which transmits less energy than the heat tranports on normal ice.

Thank you very much for this information ajouis! I thought that the, by the radiation, heated black ash would melt down into the ice.
Your observation makes sense to me. Of course convection is a much stronger effect than thermal conduction. I understand better now :) .
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dnem

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Re: "Stupid" Questions :o
« Reply #2658 on: October 02, 2019, 06:13:04 PM »
I'm pretty sure the standard view of this is that atmospheric deposition of dark particles on clean ice reduces albedo and increases melt.

https://insideclimatenews.org/news/19042018/greenland-ice-sheet-melting-climate-change-arctic-pollution-sea-level-rise-algae-black-carbon

In areas near the edge of the ice sheet, things get even more interesting: a carpet of microbes and algae mixed with dust and soot, a short-lived climate pollutant, is darkening the ice sheet, absorbing the sun's rays and accelerating the melting of the ice.

New research shows this dark zone is growing.

binntho

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Re: "Stupid" Questions :o
« Reply #2659 on: October 02, 2019, 08:26:08 PM »
When i worked on a glacier, the black ash that was on it actually insulated the ice, do you know if it still hold up at macro level or if the type of matter (volcanic ash) is important? Would be interested to hear of other phenomenas in the arctic where something doesn t work out as usual.

This sounds right and can easily be observed on Icelandic glaciers. Apparently a layer of a few mm is enough to insulate the ice  causing black ridges and bumps. The ash is volcanic with fairly large grainsize.
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Tor Bejnar

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Re: "Stupid" Questions :o
« Reply #2660 on: October 02, 2019, 10:43:38 PM »
Layers of rock debris (e.g., from landslides falling onto the ice) on top of a glacier are well know to protect the ice from melting. Exceptional example from dreamstime.com

Obviously, this picture shows that not all rock debris actually protects the ice!
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dnem

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Re: "Stupid" Questions :o
« Reply #2661 on: October 03, 2019, 12:06:59 AM »
Jason Box Dark Snow Project:
https://www.darksnow.org

Wikipedia Dark Snow Project
https://en.wikipedia.org/wiki/Dark_Snow_Project
Background
"Soot darkens snow and ice, increasing solar energy absorption, hastening the melt of the cryosphere."[1] The soot comes in part from wildfires, of which there were many in 2012. Also in 2012, almost all of the surface of Greenland was observed to be melting.[9] The increase in size of the wildfires may itself be a result of global warming.[5] Jason Box has been studying Greenland for 20 years.

binntho

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Re: "Stupid" Questions :o
« Reply #2662 on: October 03, 2019, 09:01:56 AM »
Jason Box Dark Snow Project:
https://www.darksnow.org

Wikipedia Dark Snow Project
https://en.wikipedia.org/wiki/Dark_Snow_Project
Background
"Soot darkens snow and ice, increasing solar energy absorption, hastening the melt of the cryosphere."[1] The soot comes in part from wildfires, of which there were many in 2012. Also in 2012, almost all of the surface of Greenland was observed to be melting.[9] The increase in size of the wildfires may itself be a result of global warming.[5] Jason Box has been studying Greenland for 20 years.

We are talking about different things here. Soot from wildfires (and other sources) often called black carbon are never in sufficient amounts to create a thick blanket on ice. So their effect will always be to hasten melt.

Volcanic ash on the other hand can easily form layers several cm thick, and pumice is very insulating. Seeing black ridges of pumice-protected ice is very common in Iceland, and from personal experience I know that 1 or 2 mm of pumice is enough to slow down melt.
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Peter Ellis

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Re: "Stupid" Questions :o
« Reply #2663 on: October 04, 2019, 12:15:38 AM »
Pumice is also foamy with a lot of trapped air, which makes it an excellent insulator.

dnem

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Re: "Stupid" Questions :o
« Reply #2664 on: October 04, 2019, 01:06:29 PM »
For sure. The original post that started this used the phrase "black ash" which to me sounded like soot or black carbon.

binntho

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Re: "Stupid" Questions :o
« Reply #2665 on: October 05, 2019, 01:14:00 PM »
For sure. The original post that started this used the phrase "black ash" which to me sounded like soot or black carbon.
A very natural mistake to make since in Icelandic volcanic ash is normally black and looks more like sand than pumice. Even so it still has good insulation properties since the individual grains are very rough and even at times frothy, unlike sand which is smooth-grained.
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Thomas Barlow

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Re: "Stupid" Questions :o
« Reply #2666 on: October 07, 2019, 12:03:40 AM »
Is there a mean for yearly sea ice extent comparing year to year?
Not sure how you would do that, but maybe there is a general method?  Maybe adding monthly averages up for each year? Or weekly?


« Last Edit: October 07, 2019, 02:31:06 PM by Thomas Barlow »

dnem

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Re: "Stupid" Questions :o
« Reply #2667 on: October 07, 2019, 02:42:11 PM »
gerontocrat frequently posts a running 365 day average on the Area and Extent thread that somewhat captures what you're looking for.

Niall Dollard

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Re: "Stupid" Questions :o
« Reply #2668 on: October 14, 2019, 11:55:24 PM »
I posted this originally in the Mike Horn expedition thread :

But here is a question. Mike mentions he was about 87 N. Should the sun be below the horizon by this date ? I plugged this lattitude into a couple of online solar angle calculators and they are saying max angle is circa -4 degrees ie below the horizon.

https://keisan.casio.com/exec/system/1224682277

To still see the sun you would need to be near 82 N (according to the online calculations).

Or maybe the calculations are not taking into account the flattening at the poles ? 


binntho

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Re: "Stupid" Questions :o
« Reply #2669 on: October 15, 2019, 07:21:48 AM »
Good question Niall. Over on the Mosaic thread A-Team posted a picture of two ships meeting in the polar "night" on Oktober 3rd, presumably around 85N, and it certainly looks a lot more like "early twilight" to me. But less than two weeks after equinox I guess it makes sense for that location, even if the sun doesn't tecnnically rise.

The image above is apparently from Oktober 13th, some three weeks after equinox, and according to my favourite solar altitude calculator, the sun should not rise at all on that date at 87N.

Judging by the picture, the sun is at perhaps 0.2 degrees, which would place the location at no further north than ~82N for that date as far as I can work out.
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slow wing

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Re: "Stupid" Questions :o
« Reply #2670 on: October 15, 2019, 11:10:14 AM »
I posted this originally in the Mike Horn expedition thread :

But here is a question. Mike mentions he was about 87 N. Should the sun be below the horizon by this date ? I plugged this lattitude into a couple of online solar angle calculators and they are saying max angle is circa -4 degrees ie below the horizon.

https://keisan.casio.com/exec/system/1224682277

To still see the sun you would need to be near 82 N (according to the online calculations).

Or maybe the calculations are not taking into account the flattening at the poles ?

Agree it is puzzling. However, there is some refraction of sunlight in the atmosphere. Wikipedia says that at sunset it is 35.4' -- so more than half a degree. So that accounts for a small part of the discrepancy.

This website, which includes refraction, says there is no direct sunlight but still 4h19 minutes of "civil twilight" at 87N, even now on 15th October, which is two days after the photo.


binntho

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Re: "Stupid" Questions :o
« Reply #2671 on: October 15, 2019, 11:12:35 AM »
Wonder what "uncivil twilight" looks like ...  :o
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Tor Bejnar

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Re: "Stupid" Questions :o
« Reply #2672 on: October 15, 2019, 02:58:48 PM »
Aren't search engines wonderful?
Quote
title: an uncivil twilight summary: Is everyone here make-believe? — Baelfire/Wendy/Peter. —..... Neverland was nothing like Bae had thought it would be like. He'd thought there'd be no responsibilities, no rules—but of course, that had been a delusion brought on by Peter Pan's flute.
and, less cherry:
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In The Colder Case Series,  Uncivil Twilight is the 1925 case about the trial of S.C. Stone …
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Phil.

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Re: "Stupid" Questions :o
« Reply #2673 on: October 15, 2019, 04:36:45 PM »
Good question Niall. Over on the Mosaic thread A-Team posted a picture of two ships meeting in the polar "night" on Oktober 3rd, presumably around 85N, and it certainly looks a lot more like "early twilight" to me. But less than two weeks after equinox I guess it makes sense for that location, even if the sun doesn't tecnnically rise.

The image above is apparently from Oktober 13th, some three weeks after equinox, and according to my favourite solar altitude calculator, the sun should not rise at all on that date at 87N.

Judging by the picture, the sun is at perhaps 0.2 degrees, which would place the location at no further north than ~82N for that date as far as I can work out.

Wayne who frequently posts here, studies the effect of refraction of sunlight and how it effects sunrise and sunset viewed from near the pole, can be found at:
https://eh2r.blogspot.com

binntho

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Re: "Stupid" Questions :o
« Reply #2674 on: October 16, 2019, 06:56:47 AM »
Good question Niall. Over on the Mosaic thread A-Team posted a picture of two ships meeting in the polar "night" on Oktober 3rd, presumably around 85N, and it certainly looks a lot more like "early twilight" to me. But less than two weeks after equinox I guess it makes sense for that location, even if the sun doesn't tecnnically rise.

The image above is apparently from Oktober 13th, some three weeks after equinox, and according to my favourite solar altitude calculator, the sun should not rise at all on that date at 87N.

Judging by the picture, the sun is at perhaps 0.2 degrees, which would place the location at no further north than ~82N for that date as far as I can work out.

Wayne who frequently posts here, studies the effect of refraction of sunlight and how it effects sunrise and sunset viewed from near the pole, can be found at:
https://eh2r.blogspot.com
I'm familiar with his site but I wasn't aware that he "studies the effect of refraction of sunlight and how it effects sunrise and sunset viewed from near the pole" ... I don't recall him ever posting on that subject, although of course he may well have (I'm not claiming to have read all his posts!)

But Phil, are you indicating that the strange sun-in-the-sky image from above is actually showing a natural phenomenon that Wayne is there to study, and is not just a mistake in either date or latitude?
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kassy

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Re: "Stupid" Questions :o
« Reply #2675 on: October 16, 2019, 09:49:13 AM »
It was a while back. May 2015 has some articles about it and most of his posts on that are earlier then that.
https://eh2r.blogspot.com/2015/05/
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binntho

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Re: "Stupid" Questions :o
« Reply #2676 on: October 16, 2019, 10:00:12 AM »
It was a while back. May 2015 has some articles about it and most of his posts on that are earlier then that.
https://eh2r.blogspot.com/2015/05/
I remember it now! Fantastic work, based on comparing the apparent horizon with the astronomical horizon and working out a temperature inversion over the ice from the difference between the two. I joined in early 2016 and the topic was still being discussed then.

But I doubt if temperature inversion can explain the sun in the image above.
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Niall Dollard

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Re: "Stupid" Questions :o
« Reply #2677 on: October 17, 2019, 01:13:00 AM »
Thanks for all the contributions/replies so far to my question.

So what explanations do we have to explain the visible sun at 87N on Oct 13th, in summary (in no particular order) :

1) The online solar elevation calculations available are incorrect. The sun is not at 4 degs below the horizon. The calculations are not accounting for the flattening at the poles.

2) The calculations are correct and the what they saw at 87N was a refracted image of the sun (above the horizon) and changed horizon heights due to thermal fluxes. 

3) Mike Horn is lost ! And has drifted considerably south and in fact is not at 87N but more like 82N.   

I agree with Binntho though that 5 degrees is quite an extreme amount of bending/horizon height changes necessary to make the sun visible at 87N on Oct 13th. 

 

KiwiGriff

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Re: "Stupid" Questions :o
« Reply #2678 on: October 17, 2019, 04:35:22 AM »
you can clearly see the effect of refraction  in the photo.
The sun should be a round disk in that photo it is an oblong shape suggesting light bending from refraction.
Quote
Endurance expedition, Sir Ernest Shackleton recorded refraction of 2°37′:[7]

“The sun which had made ‘positively his last appearance’ seven days earlier surprised us by lifting more than half its disk above the horizon on May 8. A glow on the northern horizon resolved itself into the sun at 11 am that day. A quarter of an hour later the unreasonable visitor disappeared again, only to rise again at 11:40 am, set at 1 pm, rise at 1:10 pm and set lingeringly at 1:20 pm. These curious phenomena were due to refraction which amounted to 2° 37′ at 1:20 pm. The temperature was 15° below 0° Fahr., and we calculated that the refraction was 2° above normal.”
https://en.wikipedia.org/wiki/Atmospheric_refraction

P-maker

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Re: "Stupid" Questions :o
« Reply #2679 on: October 17, 2019, 07:20:16 AM »
Niall,

You seem to have forgotten one fourth option: The photo has been manipulated after it was taken.

If you just enlarge the "Sun" part a little bit, you will easily see that it is a square. To my knowledge, this is the first time the sun has been depicted as a square. I will admit that there is a tiny light bulp on the right hand side of the "square" which may have provided some of the square content.

Who done it?

IDK, but sometimes these long winter nights bring out the best in some creative souls...

binntho

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Re: "Stupid" Questions :o
« Reply #2680 on: October 17, 2019, 07:24:55 AM »
you can clearly see the effect of refraction  in the photo.
The sun should be a round disk in that photo it is an oblong shape suggesting light bending from refraction.
Quote
Endurance expedition, Sir Ernest Shackleton recorded refraction of 2°37′:[7]

“The sun which had made ‘positively his last appearance’ seven days earlier surprised us by lifting more than half its disk above the horizon on May 8. A glow on the northern horizon resolved itself into the sun at 11 am that day. A quarter of an hour later the unreasonable visitor disappeared again, only to rise again at 11:40 am, set at 1 pm, rise at 1:10 pm and set lingeringly at 1:20 pm. These curious phenomena were due to refraction which amounted to 2° 37′ at 1:20 pm. The temperature was 15° below 0° Fahr., and we calculated that the refraction was 2° above normal.”
https://en.wikipedia.org/wiki/Atmospheric_refraction
I think we need clarification from Mike before we can conclude that his image is showing the same phenomenon - which would be truly fantastic. I can see from the same Wikipedia arcticle (just above the Shackleton piece) that a 4 degree refraction has been measured in Athens.
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binntho

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Re: "Stupid" Questions :o
« Reply #2681 on: October 17, 2019, 07:30:25 AM »
Niall,

You seem to have forgotten one fourth option: The photo has been manipulated after it was taken.

If you just enlarge the "Sun" part a little bit, you will easily see that it is a square. To my knowledge, this is the first time the sun has been depicted as a square. I will admit that there is a tiny light bulp on the right hand side of the "square" which may have provided some of the square content.

Who done it?

IDK, but sometimes these long winter nights bring out the best in some creative souls...

Looking closely as you suggested, the sun seems diffracted at various rates at various heights, giving it a "hamburger" appearance i.e. squarish and layered. So no doctoring needed.

But it made me think - who took the picture? And using what equipment? Details on the sled would have been obscured in black shadow against the glare of the sun with "normal" equipment  at standard settings. I'm no photography expert but I do know that getting both the sun and the details of the sled (and ice features) that should be in shadow in the same image is not easy.
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Tealight

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Re: "Stupid" Questions :o
« Reply #2682 on: October 17, 2019, 11:43:31 AM »
you can clearly see the effect of refraction  in the photo.
The sun should be a round disk in that photo it is an oblong shape suggesting light bending from refraction.

I agree the photo shows just a refraction. If the sun would be above the horizon the ice would also be very bright, but it is dark. You must keep in mind that at 87N you are only surrounded by extremly flat and highly reflective sea ice. No mountains, trees or buildings to block sunlight. If direct sunshine hits the ice at 82N at an angle of 1-2 degrees it gets reflected and travels a few hundred kilometer further through the atmosphere. Clouds can then reflect this reflection back again towards the surface.

I so happen to have webcam footage from McMurdo Station in Antarctica from the 9th August when the sun was equally 4 degrees below the horizon and the phenomena looks the same to me.

binntho

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Re: "Stupid" Questions :o
« Reply #2683 on: October 17, 2019, 12:25:07 PM »
It's certainly an eyeopener for me to learn that near-daylight can at times penetrate this far over the astsronomical horizon. But I'd still like to get confirmation of whether or not that picture of Mike's is showing such a phenomenon.

The pictures from Antartica are very interesting, but the do not show a recognizable sun disc (whether or not that's because of the quality of the camera) and is therefore not directly comparable.

I agree the photo shows just a refraction. If the sun would be above the horizon the ice would also be very bright, but it is dark.

So are you saying that the refracted sunlight is only a small fraction of the sunlight that would have fallen directly without refraction? Not unreasonable, although the pictures from McMurdo Station seem to be showing typical non-refractionary polar daylight just around sunset or sunrise.

So I'm not at all convinced that you can tell the difference between "real" sunlight and "refracted" sunlight based on photographs.
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Niall Dollard

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Re: "Stupid" Questions :o
« Reply #2684 on: October 18, 2019, 01:23:24 AM »
So here's another image posted on Mike's instagram account. It is attached to a later update than the last one so likely taken a couple of days ago Oct 15th ? at almost 88N.

slow wing

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Re: "Stupid" Questions :o
« Reply #2685 on: October 22, 2019, 09:19:09 AM »
From the Freezing Season thread...

.... Nevertheless, it would appear that accumulated heat in the Arctic Ocean/system is an important factor.

It seems to be THE most important factor


Wondering if the record late refreeze may be due, at least in part, to the Arctic basin having been stormy since the extent minimum?


Reason: the thermal conductivity of water is terrible, as I illustrated earlier on this Stupid Questions thread.

So I'm guessing that, to a good approximation, it will only be the action of wind & waves stirring up the water that makes the accumulated sub-surface heat available to retard the refreeze.

Also, ice can't easily form in wind & waves.

Fair?
« Last Edit: October 22, 2019, 09:24:59 AM by slow wing »

binntho

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Re: "Stupid" Questions :o
« Reply #2686 on: October 22, 2019, 11:10:22 AM »
From the Freezing Season thread...

.... Nevertheless, it would appear that accumulated heat in the Arctic Ocean/system is an important factor.

It seems to be THE most important factor


Wondering if the record late refreeze may be due, at least in part, to the Arctic basin having been stormy since the extent minimum?


Reason: the thermal conductivity of water is terrible, as I illustrated earlier on this Stupid Questions thread.

So I'm guessing that, to a good approximation, it will only be the action of wind & waves stirring up the water that makes the accumulated sub-surface heat available to retard the refreeze.

Also, ice can't easily form in wind & waves.

Fair?
Sounds eminently fair.
because a thing is eloquently expressed it should not be taken to be as necessarily true
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El Cid

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Re: "Stupid" Questions :o
« Reply #2687 on: October 22, 2019, 11:42:01 AM »
Considering the GAC of 2012 and what you have said above, it seems quite true. The more "stirring" we get, the slower the refreeze

be cause

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Re: "Stupid" Questions :o
« Reply #2688 on: October 22, 2019, 12:04:35 PM »
I thought this was a remarkably storm free autumn/fall in the Arctic basin compared to recent years . b.c.
2007 + 5 = 2012 + 4 = 2016 + 3 = 2019 ...

binntho

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Re: "Stupid" Questions :o
« Reply #2689 on: October 22, 2019, 12:25:17 PM »
I thought this was a remarkably storm free autumn/fall in the Arctic basin compared to recent years . b.c.
Well nobody has been making any noises much about there being storms (or not storms) in the eastern and Pacific sides of the Arctic. But there have been a decent run of low pressure areas over those areas in the last couple of weeks, whether it's any more or less than other years I wouldn't know!

But I did mention somewhere else that the currently rapid refreeze shoreside in the Laptev might be due to pretty strong off-shore winds over the last few days, bringing low temps from the interior.

So, has it been windy or not, and what difference does it make? A truly stupid question.
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slow wing

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Re: "Stupid" Questions :o
« Reply #2690 on: October 22, 2019, 12:52:31 PM »
It's certainly relevant to the discussion whether or not it has been windy lately in the Arctic basin.

I do have the impression it has been unusually windy over the past month compared to previous years, but nothing quantitative and based only on looking at the weather maps which appeared to show lots of isobar lines in the basin, indicating strong pressure gradients and therefore strong winds. I might be wrong in this.

macid

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Re: "Stupid" Questions :o
« Reply #2691 on: October 22, 2019, 01:29:05 PM »
From the Freezing Season thread...

.... Nevertheless, it would appear that accumulated heat in the Arctic Ocean/system is an important factor.

It seems to be THE most important factor


Wondering if the record late refreeze may be due, at least in part, to the Arctic basin having been stormy since the extent minimum?


Reason: the thermal conductivity of water is terrible, as I illustrated earlier on this Stupid Questions thread.

So I'm guessing that, to a good approximation, it will only be the action of wind & waves stirring up the water that makes the accumulated sub-surface heat available to retard the refreeze.

Also, ice can't easily form in wind & waves.

Fair?

1.2e-2 W/m² seems quite insignificant to the fluxes we see at the surface indeed, the ESRL physics forecasts show upward longwave fluxes of over 300+ W/m² in the open arctic waters, net fluxes of -40 to -60 now that the sun is gone. 
https://www.esrl.noaa.gov/psd/forecasts/seaice/  <- Coupled <- Surface Fluxes

You only look at Joules that reach the ice from 50 meters down. What about all the other depths? And what about the joules that get stuck in higher layers? What's the top layer warming effect of those and how does that in turn reflect in the ice?

Unless i'm being stupid here, and I could very well be which is why I reply here, this calculation is far from complete and cannot conclude that warmer ocean temperatures, deeper down has little to no effect.


slow wing

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Re: "Stupid" Questions :o
« Reply #2692 on: October 22, 2019, 02:01:04 PM »
Good questions, thank you Macid.


Answering your last question first, my thermal conductivity calculation was for an illustrative 'toy model' that might approximate the true situation in some circumstances. The whole point is to get the magnitude of the heat flux for the process of thermal conduction -- which was found to be of order 1/100 W/m^2.

As you point out, this is negligible compared to the other thermal processes effecting the melting or freezing of the ice, which was what the toy model was intended to illustrate.


The background to my post above has been the common narrative on this forum that excess heat gets stored in the water column over the course of the melt season, together with the assertion that the refreeze cannot proceed to any great extent until that excess heat has first been removed by extraction to the atmosphere.


I've never been comfortable with that explanation because, given the situation of relatively calm water, I can't see how that trapped heat -- which I presumed to extend down by at least several meters and probably tens of meters or more, depending on whether it was sourced from ocean currents or direct sunlight -- can get to the surface to influence the refreeze.


So yes, as you point out, in calm conditions then the long-wave radiation to the cold sky should start the refreeze without noticing how much excess heat has been trapped below. Then, once the ice has formed and grown thick enough, there is no chance for wind and waves to start bringing the excess heat up to the surface. So the re-freeze continues and the trapped excess heat below becomes essentially irrelevant.


My suggestion above concerns the converse situation, where there is wind and waves. I'm suggesting that could mix some of the excess heat up to the surface to replace the heat lost to long-wave radiation and so to retard the start of the re-freeze.




slow wing

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Re: "Stupid" Questions :o
« Reply #2693 on: October 22, 2019, 02:11:21 PM »
The above discussion suggests a third mechanism whereby incoming storms can retard the start of the refreeze: introducing water vapour to the atmosphere which raises the 'effective temperature' of the sky for long-wave radiation. This lowers the rate of net heat loss from the water and so retards refreeze.

(This 'effective temperature' of the sky is a description I am familiar with from solar water heating applications, and I've also seen it used before in this forum.)

binntho

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Re: "Stupid" Questions :o
« Reply #2694 on: October 22, 2019, 02:26:17 PM »
But but but ... if what you are saying was true, slow-wing, then calm ocean surface should start freezing at less than -2 degrees Centigrade. And it doesn't.

The reason being that as the surface layers cool, they start sinking and warmer waters start rising from below. So even in calm weather, there will be quite a lot of vertical movement of water due to turbulence caused by heat loss at the surface.

Anecdotal evidence (which has been repeatedly discussed in this forum) indicates that calm ocean surface starts freezing at an air temperature of around -11C, indicating that this is the level at which sinking of cooled-down waters at surface is not fast enough to avoid freezing.
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macid

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Re: "Stupid" Questions :o
« Reply #2695 on: October 22, 2019, 05:58:25 PM »
Good questions, thank you Macid.


Answering your last question first, my thermal conductivity calculation was for an illustrative 'toy model' that might approximate the true situation in some circumstances. The whole point is to get the magnitude of the heat flux for the process of thermal conduction -- which was found to be of order 1/100 W/m^2.

..
I still don't understand, how can you use a very thin slice of a full model to approximate the true situation? I think I found a better approximation in this article: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6114986/

Quote
Before the 2000s, typical BG halocline heat content per unit area was around 2 × 108 J m−2 (Fig. 2A). Since that time, there has been a sustained increase in heat content per unit area (local values reach beyond 4 × 108 J m−2 in the 2014–2017 time period), with maximal values centered over the Canada Basin coincident with the climatological BG center (Fig. 2) (1). Over the period 1987–2017, total warm halocline heat content integrated horizontally over a region encompassing the BG has nearly doubled (Fig. 3A). It is instructive to set the resulting heat content increases in context alongside sea ice. The capacity for sea ice melt of the additional heat content (the increase of ~2 × 108 J m−2 over 30 years) equates to a change of about 0.8 m in thickness, taking the latent heat of melting to be 2.67 × 105 J kg−1 and the density of sea ice to be 900 kg m−3.

RoxTheGeologist

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Re: "Stupid" Questions :o
« Reply #2696 on: October 22, 2019, 06:46:10 PM »
Good questions, thank you Macid.

...

The background to my post above has been the common narrative on this forum that excess heat gets stored in the water column over the course of the melt season, together with the assertion that the refreeze cannot proceed to any great extent until that excess heat has first been removed by extraction to the atmosphere.

I've never been comfortable with that explanation because, given the situation of relatively calm water, I can't see how that trapped heat -- which I presumed to extend down by at least several meters and probably tens of meters or more, depending on whether it was sourced from ocean currents or direct sunlight -- can get to the surface to influence the refreeze.
....


As ice forms the ice is fresher than the seawater, the salts partitioning into the water. The denser cold, salty water sinks, creating convection. This causes the upper mixed layer to, well, mix, and deepen.  My guess is that it slows down the ice formation, but the mechanism needs ice to be growing before heat starts to move up from deeper layers.

I hope that the current expedition will show how this happens in real time! It's a really interesting theory.. lets see if the real world works that way.




binntho

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Re: "Stupid" Questions :o
« Reply #2697 on: October 22, 2019, 07:03:29 PM »
Have you all forgot the basics of sea ice formation? RoxTheGeologids, macid, slow wing?

Sea ice is densest at freezing point, and thus does not freeze in the same way that lake ice does. So slow wings "model" is patently wrong, and the increased density of surface waters as they cool and sink create enough convection to stir up the top tens of meters of ocean, getting all that heat to the surface.

Which is not to say that wave action will also create turbulence.

The current ice-free areas have a fair amount of wind according to NullSchool, but more importantly, the air temps are nowhere near low enough to start freezing.
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gandul

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Re: "Stupid" Questions :o
« Reply #2698 on: October 22, 2019, 09:15:59 PM »
The above discussion suggests a third mechanism whereby incoming storms can retard the start of the refreeze: introducing water vapour to the atmosphere which raises the 'effective temperature' of the sky for long-wave radiation. This lowers the rate of net heat loss from the water and so retards refreeze.

(This 'effective temperature' of the sky is a description I am familiar with from solar water heating applications, and I've also seen it used before in this forum.)
I think it goes hand in hand. The negative feedback of extra heat being able to vent out with the increase in humidity which helps to trap that heat. Eventually the effect overall is not much in either direction (unless we get a train of storms ala 2016/2017 season).
How 2020 Spring comes (early snow melt as in 07/12/19 or late as in 13/14/17) will make up for any of the difference or more.
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Re: "Stupid" Questions :o
« Reply #2699 on: October 22, 2019, 11:10:42 PM »
the increased density of surface waters as they cool and sink create enough convection to stir up the top tens of meters of ocean, getting all that heat to the surface.
Are you sure about that? itp103 microcats at 5m and 6m in the Beaufort recently, temperatures only occasionally peaking at the entrance to the amundsen gulf.