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binntho

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Re: Arctic energy balance
« Reply #50 on: June 03, 2020, 02:32:05 PM »
While trying to get my head around the radiative thermal transfer thing, I was reminded that when we say that a body emits 500 W/m2 of thermal energy, that translates into 500 Joules/second.

So a typical westerner at 2 m2 and 500 W/m2 would lose 60*60*24*500 Joules per day, or 43.200 kJ, or 10.000 Calories. Through radiative thermal transfer alone. Not counting heat loss through conduction or convection, not counting movement and metabolism and brain activity.

Edit: Not much brain activity here, the numbers should of course have been doubled since the well-fed westerner comes in at 2 m2. So 20.000 Calories lost daily to thermal radiation.
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P-maker

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Re: Arctic energy balance
« Reply #51 on: June 03, 2020, 02:51:05 PM »
Binntho,

I have actually felt radiant heat from another human being (who has now taken up extreme winter ice swimming). I also have difficulties these days with ambient temperatures above 15C (warm days) and above 25C (hot days). I am not claiming that the physics have changed, just that our perceptions of heat are different.

i do like your strict adherence to basic physics, but I also kindly ask you to acknowledge that the difference between a hot&humid air mass and a cold&dry air mass in the Arctic may sometimes be difficult to grasp, when you are not living in the Arctic and in the Tropics every second day.
« Last Edit: June 03, 2020, 02:56:44 PM by P-maker »

Aluminium

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Re: Arctic energy balance
« Reply #52 on: June 03, 2020, 03:01:18 PM »
Humans are powerful lamps. But they also are getting thermal radiation from environment. In addition, skin temperature may be lower if necessary. Any insulation like clothes will help if it absorbs or reflects longwave radiation.

Phoenix

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Re: Arctic energy balance
« Reply #53 on: June 04, 2020, 09:46:21 AM »
Here is another peer reviewed paper which adds on to the conclusions from the earlier paper and is based on the same field study.

https://journals.ametsoc.org/doi/full/10.1175/JCLI-D-18-0216.1?mobileUi=0

From the conclusion...

Surface temperature inversions over sea ice during ACSE occurred 33% of the time and occurred in two categories, moist and dry....

In moist inversions, consistent presence of optically thick warm fog or low clouds combined with stable stratification led to consistently larger net downward heat flux to the surface by 10–25 W m−2

binntho

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Re: Arctic energy balance
« Reply #54 on: June 04, 2020, 02:11:36 PM »
This whole discussion, from my point of view, has revolved around whether a large airmass coming in from Siberia (specifically on June 10th 2019) could cause the melt claimed by Phoenix, i.e. 200km3 of ice.

I've made a few attempts at calculating this, and others have kindly pointed our my errors, but my conclusion after all that is as follows:

1) Direct heat from the air itself could melt perhaps 1% of  the 200km3.
2) Assuming 50% humidity and 100% condension of water vapour could perhaps add another 1%

I've seen repeated attempts and comments about how much difference the humidity could make, but in reality it is of very little direct consequence, simply because air is not able to hold that much water vapour (100% humidity at 15 degrees C is only 10g water per 1kg air, or 1% per weight).

The main assumption in 1) has resolved around heat transfer. I have totally ignored thermal radiation from the airmass, concentrating solely on conduction combined with some convection, and estimated that the lowest 5 m of air was involved. Which I think is generous.

Following this, some wild claims have been made about thermal radiation, but they simply do not make sense. If a moderately warm air mass was able to lose energy by thermal radiation in anything approaching significant numbers per day, then all the air on the planet would cool down to ice-age conditions in a week or two.

I honestly don't know how to calculate thermal radiation of a mass of air. Aluminium came up with a number of 391 W/m2 for a black body at 15 degrees C, which is equivalent to the daily average insolation in the tropics which obviously doesn't add up.

And extrapolating to a human body means that we lose some 20.000 Calories per day through thermal radiation!

Not to say that Aluminium's calculations are wrong. But obviously, these bodies (airmass or human) are not losing heat in anything resembling these numbers.

So a few reality checks: Insulation, including using several layers of window panes, is geared exclusively towards blocking conduction and convection. Thermal radiation is not even considered. Insulation works by blocking convection and minimizing conduction, but normal insulation methods do not consider thermal radiation (and I'm talking weather and human temperatures now, not excessive temperatures).

Another thing that just came to mind: In the Arctic itself, at a depth of just a few tens of meters, is a huge mass of warm water with enough energy to melt the ice many times over. The only thing that stops this from happening is the low conductivity of water and the absence of convection. Thermal radiation is not even considered.

So my conclusion is still unchanged: The direct melting effects of this massive WAA on the 10th of June 2019 could perhaps at absolut maximum have melted some 2% of the 200km3 of excess melt recorded that day, i.e. an insignficant amount.

Indirect effects are of course possible, and Phoenix linked to a paper from another similar event where they never made any claims as for direct melt from the WAA, but considered that the WAA may have had secondary effects that significantly increased the melting strength of the solar radiation on Arctic at the time.
because a thing is eloquently expressed it should not be taken to be as necessarily true
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binntho

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Re: Arctic energy balance
« Reply #55 on: June 04, 2020, 02:13:43 PM »
Here is another peer reviewed paper which adds on to the conclusions from the earlier paper and is based on the same field study.

https://journals.ametsoc.org/doi/full/10.1175/JCLI-D-18-0216.1?mobileUi=0

From the conclusion...

Surface temperature inversions over sea ice during ACSE occurred 33% of the time and occurred in two categories, moist and dry....

In moist inversions, consistent presence of optically thick warm fog or low clouds combined with stable stratification led to consistently larger net downward heat flux to the surface by 10–25 W m−2

Absolutely in line with what I have been saying. The secondary effects incrased the insolation effect by a realisty 10-25 W/m2 (and compare this to the earlier indicated thermal radiation of 391 W/m2 from a 15 degree warm air mass)
because a thing is eloquently expressed it should not be taken to be as necessarily true
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binntho

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Re: Arctic energy balance
« Reply #56 on: June 04, 2020, 02:19:07 PM »
Just a small addendum: If the WAA of the 10th of June 2019 managed to melt 2 - 4 cubic kilometers of ice directly in one day is actually very good going, and in line with anectdotal experience of the melting power of e.g. foehn winds.

But remember that ther Arctic is huge, and a flow of warm air loses it's melting strength very quickly This particular WAA helped the melt of the EES and Laptev by quite a significant amount.
because a thing is eloquently expressed it should not be taken to be as necessarily true
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SteveMDFP

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Re: Arctic energy balance
« Reply #57 on: June 04, 2020, 02:31:00 PM »
This whole discussion, from my point of view, has revolved around whether a large airmass coming in from Siberia (specifically on June 10th 2019) could cause the melt claimed by Phoenix, i.e. 200km3 of ice.

I've made a few attempts at calculating this, and others have kindly pointed our my errors, but my conclusion after all that is as follows:

1) Direct heat from the air itself could melt perhaps 1% of  the 200km3.
2) Assuming 50% humidity and 100% condension of water vapour could perhaps add another 1%

I've seen repeated attempts and comments about how much difference the humidity could make, but in reality it is of very little direct consequence, simply because air is not able to hold that much water vapour (100% humidity at 15 degrees C is only 10g water per 1kg air, or 1% per weight).

The main assumption in 1) has resolved around heat transfer. I have totally ignored thermal radiation from the airmass, concentrating solely on conduction combined with some convection, and estimated that the lowest 5 m of air was involved. Which I think is generous.

Following this, some wild claims have been made about thermal radiation, but they simply do not make sense. If a moderately warm air mass was able to lose energy by thermal radiation in anything approaching significant numbers per day, then all the air on the planet would cool down to ice-age conditions in a week or two.

I honestly don't know how to calculate thermal radiation of a mass of air. Aluminium came up with a number of 391 W/m2 for a black body at 15 degrees C, which is equivalent to the daily average insolation in the tropics which obviously doesn't add up.

And extrapolating to a human body means that we lose some 20.000 Calories per day through thermal radiation!

Not to say that Aluminium's calculations are wrong. But obviously, these bodies (airmass or human) are not losing heat in anything resembling these numbers.

So a few reality checks: Insulation, including using several layers of window panes, is geared exclusively towards blocking conduction and convection. Thermal radiation is not even considered. Insulation works by blocking convection and minimizing conduction, but normal insulation methods do not consider thermal radiation (and I'm talking weather and human temperatures now, not excessive temperatures).

Another thing that just came to mind: In the Arctic itself, at a depth of just a few tens of meters, is a huge mass of warm water with enough energy to melt the ice many times over. The only thing that stops this from happening is the low conductivity of water and the absence of convection. Thermal radiation is not even considered.

So my conclusion is still unchanged: The direct melting effects of this massive WAA on the 10th of June 2019 could perhaps at absolut maximum have melted some 2% of the 200km3 of excess melt recorded that day, i.e. an insignficant amount.

Indirect effects are of course possible, and Phoenix linked to a paper from another similar event where they never made any claims as for direct melt from the WAA, but considered that the WAA may have had secondary effects that significantly increased the melting strength of the solar radiation on Arctic at the time.

Air is not remotely a black body.  It infrared wavelengths, snow, ice, and water approximately are, though not at all for visible wavelengths.  IR just doesn't get very far within water, maybe a millimetre.  I believe several of the conundrums posed here can be resolved with this understanding.

Overall, I concur that large amounts of melting of arctic ice directly by warm air advection seems  unlikely to be born out by calculations, even including humidity.  However, the local greenhouse effect should be very substantially increased by humid air versus dry air.  Amplification of effects of solar insolation by this route may be worth considering.

binntho

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Re: Arctic energy balance
« Reply #58 on: June 04, 2020, 03:19:56 PM »
Air is not remotely a black body.  It infrared wavelengths, snow, ice, and water approximately are, though not at all for visible wavelengths.  IR just doesn't get very far within water, maybe a millimetre.  I believe several of the conundrums posed here can be resolved with this understanding.

You put your finger on it! I was thinking along the same lines but couldn't quite put words to it.

Overall, I concur that large amounts of melting of arctic ice directly by warm air advection seems  unlikely to be born out by calculations, even including humidity.  However, the local greenhouse effect should be very substantially increased by humid air versus dry air.  Amplification of effects of solar insolation by this route may be worth considering.

The local greenhouse effect of water vapor is significant, consider the cold nights in the Sahara compared to e.g. Sicily during summer. Sahara may be at freezing point in the mornings, in Sicily your are lucky to get below 20 in the middle of the summer.

But I'm not at all sure that this would make much difference in our hypothetical case. The Arctic is closer to the Sahara when it comes to water vapour generally, and most of the WAA from the mainlands (specially Siberia) doesn't hold that much humidity, having  travelled a long way from the nearest large body of water and over several mountainranges.
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Aluminium

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Re: Arctic energy balance
« Reply #59 on: June 04, 2020, 04:47:59 PM »
Air is not too distinct from a black body, considering whole atmosphere. Globally infrared radiation from air is 340 W/m2 downward and 200 W/m2 upward.

interstitial

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Re: Arctic energy balance
« Reply #60 on: June 05, 2020, 02:49:24 PM »
i have often read on this site that the arctic recieves 4 watts/m2 solar radiation at the surface. As I recall it was given as the reason why it is hard to pin down exactly what was important and what was and wasnt important. because it is a small amount.
near the tropics it is near 400 watts/meter2
if 340 w/m2 were the amount of radiation from air summer would have a neglible effect on melting. :o



I suspect 340 w/m2 is the average global solar radiation at the surface and not the average global radiation of air.

Aluminium

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Re: Arctic energy balance
« Reply #61 on: June 05, 2020, 03:39:34 PM »
Air is much cooler and drier in winter. Ice radiate about 315 W/m2 at the melting point.

Interesting. Absorbed by air solar radiation is 77 W/m2 globally. Given high surface albedo and low altitude of the Sun in the Arctic, air should absorb more solar radiation than ice.