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Gray-Wolf

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Re: The 2017 melting season
« Reply #1150 on: May 08, 2017, 07:09:37 PM »
So the forecasts start to look a little High pressure dominated?

Some long range forecasts appear to want this to continue right through their runs ( end of June) . If they verify then melt ponds will explode across the ice and set in motion a period of heavy ice loss ( as long as the sun keeps beating down?)

If we have 'cycles' in the basin then we also seem to be poorly positioned? After 07' we were told to expect another 'perfect Melt storm from 10 to 20 years later with the caveat that the two prior to 07' had 10 year spacing's). We then have recent history with 07' and 2012 showing a 5 year gap between record low years?

I worried over an average melt year bringing us issues this time. I never considered a full sun high insolation event across the Basin.

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seaicesailor

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Re: The 2017 melting season
« Reply #1151 on: May 09, 2017, 08:02:23 AM »
I think I am going to move this to a separate thread, but it is interesting to consider how much extra energy is required to bottom-melt MYI in the Arctic Ocean because it has strong implications in this melting season:
- Out of spring, water right underneath the ice is at -1.8C in thermodynamic equilibrium  with the freezing bottom.
- Let's say bottom melting starts in June/July depending on the location (year/round near Atlantic currents).
- For MYI, after a while of bottom-melting the half a meter or so of last season bottom-freezing, the temperature of the water has to raise from -1.8C to 0C in order to continue melting. In contrast, for the more saline FYI, melting proceeds at or slightly above -1.8C.
- This raise of temperature to continue bottom-melting MYI must happen for the whole water column of the mixed layer. In other words, the mixing that happens in this layer will take care of keeping its temperature homogeneous, with a turnover time of the order of the day or a few days.
- Assume the mixing layer is 20 to 40 m depending on location. Let's take 30 m in average.
- The energy for raising 1.8 degrees 30 m of water is equivalent to that needed for bottom-melting approximately 0.75 m of ice!!!! (since raising 1C of a 80m-deep extent of water requires the same energy to melt 1m of the same extent of ice)

So what happens this summer? In parts of the pacific half of the Arctic, and, especially, along Eurasia, we find typically 25-100 cm thinner ice than any previous year.

https://forum.arctic-sea-ice.net/index.php/topic,119.msg112166.html#msg112166

 On top of that, most of it is FYI, which will require "75 cm-equivalent less energy" to start bottom-melting than MYI. The MYI is mostly accumulated in a region that is gradually melting out no matter what due to its proximity with Atlantic water.

So as in 2013 (or even more than 2013), we will have to ask ourselves, in case it is an uneventful season, why there was no record or even <1m km2 ice in September. Something must happen in the melting season to prevent so (negative feedback due to snow cover, a cold PAC to prevent insolation and WAAs,...). Otherwise I have little doubt we can get a record low in September.
« Last Edit: May 09, 2017, 09:38:16 AM by seaicesailor »


Sterks

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Re: The 2017 melting season
« Reply #1153 on: May 09, 2017, 09:57:19 AM »
I think I am going to move this to a separate thread, but it is interesting to consider how much extra energy is required to bottom-melt MYI in the Arctic Ocean because it has strong implications in this melting season:
- Out of spring, water right underneath the ice is at -1.8C in thermodynamic equilibrium  with the freezing bottom.
- Let's say bottom melting starts in June/July depending on the location (year/round near Atlantic currents).
- For MYI, after a while of bottom-melting the half a meter or so of last season bottom-freezing, the temperature of the water has to raise from -1.8C to 0C in order to continue melting. In contrast, for the more saline FYI, melting proceeds at or slightly above -1.8C.
- This raise of temperature to continue bottom-melting MYI must happen for the whole water column of the mixed layer. In other words, the mixing that happens in this layer will take care of keeping its temperature homogeneous, with a turnover time of the order of the day or a few days.
- Assume the mixing layer is 20 to 40 m depending on location. Let's take 30 m in average.
- The energy for raising 1.8 degrees 30 m of water is equivalent to that needed for bottom-melting approximately 0.75 m of ice!!!! (since raising 1C of a 80m-deep extent of water requires the same energy to melt 1m of the same extent of ice)

So what happens this summer? In parts of the pacific half of the Arctic, and, especially, along Eurasia, we find typically 25-100 cm thinner ice than any previous year.

https://forum.arctic-sea-ice.net/index.php/topic,119.msg112166.html#msg112166

 On top of that, most of it is FYI, which will require "75 cm-equivalent less energy" to start bottom-melting than MYI. The MYI is mostly accumulated in a region that is gradually melting out no matter what due to its proximity with Atlantic water.

So as in 2013 (or even more than 2013), we will have to ask ourselves, in case it is an uneventful season, why there was no record or even <1m km2 ice in September. Something must happen in the melting season to prevent so (negative feedback due to snow cover, a cold PAC to prevent insolation and WAAs,...). Otherwise I have little doubt we can get a record low in September.

Good exercise. However, we must not forget that there are ocean currents in the Arctic that help spread that energy. And those streams end abruptly in certain areas of the Central Arctic as a result of the oceanographic topography. In other words, the ice can melt a lot from this distribution of energy, but upon reaching a certain high latitude, the flow is off. Coincidentally, the albedo feedback too. Note that we are talking about the central Arctic, which will be frozen and cold until August.

Only two mechanisms I can imagine. One is powerful export of ice toward the Atlantic Ocean during the summer, but does not seem likely at all, and very heavy storms in August as well as last summer.

If Neven thinks so yes, we can move this discussion elsewhere.

Pmt111500

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Re: The 2017 melting season
« Reply #1154 on: May 09, 2017, 10:51:11 AM »
Now as the spring has warmed the ice up some, it came to mind to ask if there has been many Double Century (loss) days in previous years? 150000Km2/day losses are regularly seen these days. Some sort of breakdown (ha-ha) on these numbers would be nice.
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seaicesailor

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Re: The 2017 melting season
« Reply #1155 on: May 09, 2017, 11:11:33 AM »
Good exercise. However, we must not forget that there are ocean currents in the Arctic that help spread that energy. And those streams end abruptly in certain areas of the Central Arctic as a result of the oceanographic topography. ...
If Neven thinks so yes, we can move this discussion elsewhere.
https://forum.arctic-sea-ice.net/index.php/topic,2030.0.html
« Last Edit: May 09, 2017, 12:43:58 PM by seaicesailor »

Bill Fothergill

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Re: The 2017 melting season
« Reply #1156 on: May 09, 2017, 12:47:01 PM »
...
I think I am going to move this to a separate thread
...
- The energy for raising 1.8 degrees 30 m of water is equivalent to that needed for bottom-melting approximately 0.75 m of ice!!!! (since raising 1C of a 80m-deep extent of water requires the same energy to melt 1m of the same extent of ice)
...

NB I will move my comment over to the appropriate thread once you have set it up.

I was going to mention that the density of ice is less than that of water, but you appear to have already included that in order to get to the 0.75 metre value.

(30/80) * 1.8 would just give 0.675 metres, but if the (relative) density was taken as ~ 0.9, that would give your figure of 0.75 metres.

I think your x80 multiplier would only be appropriate for fresh water. The SH of sea water varies somewhat with salinity, but is roughly 3.985 kJ.kg-1.K-1, as opposed to the 4.186 kJ.kg-1.K-1 value for pure water. {I am assuming you are using a value of around 333.5 kJ.kg-1 as the enthalpy of fusion?}

However, that only represents a difference of ~ 5%, so it doesn't really help much in answering the question you raised.


seaicesailor

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Re: The 2017 melting season
« Reply #1157 on: May 09, 2017, 01:34:54 PM »
...
I think I am going to move this to a separate thread
...
- The energy for raising 1.8 degrees 30 m of water is equivalent to that needed for bottom-melting approximately 0.75 m of ice!!!! (since raising 1C of a 80m-deep extent of water requires the same energy to melt 1m of the same extent of ice)
...

NB I will move my comment over to the appropriate thread once you have set it up.

I was going to mention that the density of ice is less than that of water, but you appear to have already included that in order to get to the 0.75 metre value.

(30/80) * 1.8 would just give 0.675 metres, but if the (relative) density was taken as ~ 0.9, that would give your figure of 0.75 metres.

I think your x80 multiplier would only be appropriate for fresh water. The SH of sea water varies somewhat with salinity, but is roughly 3.985 kJ.kg-1.K-1, as opposed to the 4.186 kJ.kg-1.K-1 value for pure water. {I am assuming you are using a value of around 333.5 kJ.kg-1 as the enthalpy of fusion?}
...

Bill thank you very much for the correction. Yes, there is a new thread
https://forum.arctic-sea-ice.net/index.php/topic,2030.0.html
And it has drifted unexpectedly to another physical problem, perhaps you have a say in that too. :-)
« Last Edit: May 09, 2017, 03:26:55 PM by seaicesailor »

gerontocrat

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Re: The 2017 melting season
« Reply #1158 on: May 09, 2017, 02:26:01 PM »
DMI 80N+ has woken up. Very average temp increase May 2 to to May 9.




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Re: The 2017 melting season
« Reply #1159 on: May 09, 2017, 03:06:41 PM »
This is a week out, so we can wait and see whether it verifies.  Rain smack in the middle of the Arctic seems unusual for mid-May.
     Note that the band of rainfall is forecast to track just poleward of a likely large area of melt ponding (less cloudy part toward left of image).

Lord M Vader

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Re: The 2017 melting season
« Reply #1160 on: May 09, 2017, 05:51:53 PM »
Just have to ask: How many here have seen "SITHs map"? :P E.g "Sea Ice THickness map" ;D

Sorry, OT, I know! But here is the deal, ESS is forecasted to see temps above zero in a few days. And Beaufort might see temps above zero by early next week. How early would such melt ponding be?

In addition, despite cold conditions in Kara Sea the ice there is on the verge to break up. The forecast calls for another week with cold conditions. Once a heat pulse will move into that area, the melting will be rather quick with a fast extent loss, presumably by early June, like it was back in 2012.

The very big lack of sea ice in Berings Strait will allow for a very, very long period with heat absorbed by the ocean which most likely will make refreezing difficult later this year.

jai mitchell

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Re: The 2017 melting season
« Reply #1161 on: May 09, 2017, 06:00:42 PM »
This is a week out, so we can wait and see whether it verifies.  Rain smack in the middle of the Arctic seems unusual for mid-May.
     Note that the band of rainfall is forecast to track just poleward of a likely large area of melt ponding (less cloudy part toward left of image).

if you look at the normal >80'N DMI temperature trend, having a large portion of the CAB at above freezing surface temperatures would be, well, shocking to say the least.  I am pretty skeptical about this long-range forecast, though it does indeed fit the projections of GHG forcing and atmospheric circulation changes produced by global warming.

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StopTheApocalypse

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Re: The 2017 melting season
« Reply #1162 on: May 09, 2017, 06:11:50 PM »
This is a week out, so we can wait and see whether it verifies.  Rain smack in the middle of the Arctic seems unusual for mid-May.
     Note that the band of rainfall is forecast to track just poleward of a likely large area of melt ponding (less cloudy part toward left of image).

if you look at the normal >80'N DMI temperature trend, having a large portion of the CAB at above freezing surface temperatures would be, well, shocking to say the least.  I am pretty skeptical about this long-range forecast, though it does indeed fit the projections of GHG forcing and atmospheric circulation changes produced by global warming.



Just for reference's sake, here's what the forecast says for 168 hr. It's the second intrusion of warm air towards the pole.

Hyperion

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Re: The 2017 melting season
« Reply #1163 on: May 09, 2017, 07:49:15 PM »
The 250hpa jet activity has been looking interesting to put it mildly. There's a mutant wave 8ish. Tangled from Pole to pole with about fifty mixing vortexes embedded like the knots in Birdseye maple.
https://earth.nullschool.net/#current/wind/isobaric/250hPa/overlay=off/patterson=-119.27,0.42,105/loc=-92.752,-10.117
 Folks. Full tropospheric mixing is in the house. We've even had cyclone Donna team up with the seas of New Calidonia and Columbia to put 100% humidity over Greenland at 6 to twelve km altitude. And the stratosphere is looking interesting with several weather systems extending to over 20 km altitude, eg low in the nth Atlantic.
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Ninebelowzero

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Re: The 2017 melting season
« Reply #1164 on: May 09, 2017, 08:08:36 PM »
....Folks. Full tropospheric mixing is in the house. .


Also, looking down at the Pole at the 10 hpa level a large hexagonal shaped pattern is forming. Is that something to concerned about?

Hyperion

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Re: The 2017 melting season
« Reply #1165 on: May 09, 2017, 10:23:33 PM »
https://earth.nullschool.net/#2017/04/07/0000Z/wind/isobaric/10hPa/overlay=total_precipitable_water/stereographic=49.67,76.71,198/loc=-19.495,63.053

....Folks. Full tropospheric mixing is in the house. .


Also, looking down at the Pole at the 10 hpa level a large hexagonal shaped pattern is forming. Is that something to concerned about?
Man. The infinite hypothesis theorem is in control. The more you know the more you know you don't know. At 10hpa we have a solidly established pattern for several months now of a spiral of air peeling back off the faster than planetry rotation equatorial belt and spiraling into the nth pole where it it descendes to fuel these uberpressure high pressure systems that keep emerging. But there is a tendancy towards increasing complexity. And reducing relative humidity at equatorial lattitudes and increasing polar in recent years. And that potentiates accelerated polar gw amplification.
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seaicesailor

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Re: The 2017 melting season
« Reply #1166 on: May 10, 2017, 12:21:25 AM »
The heat wave in Eastern Siberia is going to be memorable in a week and for a week, if the CFSv2 and GFS and ensembles realize, (and the CFSv2 has been working really well,  and btw has been predicting this for weeks).
Alaska and parts of Canada/CAA too. Wall-to-wall

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Re: The 2017 melting season
« Reply #1167 on: May 10, 2017, 03:49:43 AM »
The heat wave in Eastern Siberia is going to be memorable in a week and for a week, if the CFSv2 and GFS and ensembles realize, (and the CFSv2 has been working really well,  and btw has been predicting this for weeks).
Alaska and parts of Canada/CAA too. Wall-to-wall

It will be interesting, to say the least to see what unfolds around the area of open water in the ESS in this worldview image from May 9. GFS is already showing that small area remaining at or just above freezing dispite colder temps all around and the heat is about to start today.

Each wave of heat over the next week in the forecast sends  a band of rain right into the heart of the basin - and at the end of tuesday 12Z run there's suggestions of a third

slow wing

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Re: The 2017 melting season
« Reply #1168 on: May 10, 2017, 05:19:10 AM »
... Each wave of heat over the next week in the forecast sends  a band of rain right into the heart of the basin - and at the end of tuesday 12Z run there's suggestions of a third


At this time of year is the essential threat of rain more that:

A) it ruins the insulating effect of any snow cover on the ice pack?

&/or

B) it acts like melt ponds in raising the absorption of solar radiation?


(I'm guessing still A, because it is probably going to freeze quickly?)
« Last Edit: May 10, 2017, 05:25:12 AM by slow wing »

Lord M Vader

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Re: The 2017 melting season
« Reply #1169 on: May 10, 2017, 07:54:11 AM »
GFS op 00z run in fantasyland:


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Re: The 2017 melting season
« Reply #1170 on: May 10, 2017, 08:51:48 AM »
Aren't above zero temperatures at 2m not highly unlikely when there is still a lot of ice, because the ice will 'absorb' the heat?

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Re: The 2017 melting season
« Reply #1171 on: May 10, 2017, 09:03:00 AM »
GFS op 00z run in fantasyland:


May 22 (this image) looks also scary. And May 16, 17, 18, 19, 20, 21, 24, 25, 26 ... Image: trobicaltidbits.com.

F.Tnioli

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Re: The 2017 melting season
« Reply #1172 on: May 10, 2017, 09:19:11 AM »
Coldest Victory day in Moscow (and much of central Russia) in 70+ years (since Victory itself, pretty much). Some snow May 8th, but snowcover didn't last more than few hours. Plenty sun yesterday, and seems it'll be more sunshine today, too. Arctic really sends unprecedented amounts of cold air south, and it warms up. Fast.

cesium62

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Re: The 2017 melting season
« Reply #1173 on: May 10, 2017, 09:46:50 AM »
Looks like the MacKenzie River is starting to flow.  What are the best links, pictures, anecdotes to view to watch the flow over the next week or two?

F.Tnioli

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Re: The 2017 melting season
« Reply #1174 on: May 10, 2017, 11:16:53 AM »
Greenland starts to get blue:
 


+3% in a day. At this pace, whole thing would be wet early June, eh. Possible? I guess not (yet), give it another decade 1st, then may be. Still, this is already quite special event even as it is, me thinks.

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Re: The 2017 melting season
« Reply #1175 on: May 10, 2017, 11:53:28 AM »
... Each wave of heat over the next week in the forecast sends  a band of rain right into the heart of the basin - and at the end of tuesday 12Z run there's suggestions of a third


At this time of year is the essential threat of rain more that:

A) it ruins the insulating effect of any snow cover on the ice pack?

&/or

B) it acts like melt ponds in raising the absorption of solar radiation?


(I'm guessing still A, because it is probably going to freeze quickly?)

There's also:

C) Heat transfer by conduction from above-freezing raindrops to below freezing ice (effectively transferring the warmth from the warm air the rainclouds are carried in on more effectively)

And also:

D) Kinetic energy transferred from the raindrops to the ice, wearing it away + partly being converted to heat.

I suspect the second effect is smaller than some of the others, but what do I know?

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Re: The 2017 melting season
« Reply #1176 on: May 10, 2017, 12:24:58 PM »
Paddy,

D is several orders of magnitude lower. You can pretty much discount it.
C is the biggie directly.
A & B are large follow-on effects depending on weather.

Lord M Vader

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Re: The 2017 melting season
« Reply #1177 on: May 10, 2017, 12:36:11 PM »
Here are the earliest dates for melt onset according to Polarportal:

http://polarportal.dk/en/nyheder/arkiv/nyheder/the-true-start-of-the-greenland-melt-season/

1996 is numero uno (4/29) followed by 2010 (5/2), 1990 (5/6), 2006 (5/7) and 2016/1999 sharing the fifth place with the date May 10.

2015 has the latest date for melt onset which didn't occur until June 12.

UPDATE: according to a new and improved model these dates have been altered! In the new version 2016 tops the list with melt onset date estimated to April 11. Read more at: http://polarportal.dk/en/nyheder/arkiv/nyheder/update-to-melt-and-ablation-season-onsets/

JayW

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Re: The 2017 melting season
« Reply #1178 on: May 10, 2017, 01:16:25 PM »
First attachment: 76hr Chukchi Sea loop, May 6-9. Suomi VIIRS Day night bands from Colorado State University.

http://rammb.cira.colostate.edu/ramsdis/online/npp_viirs_arctic.asp


Second attachment: NCEP polar ice drift 7 day forecast.

http://mag.ncep.noaa.gov/model-guidance-model-parameter.php?group=Model%20Guidance&model=POLAR&area=POLAR&ps=model#
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Re: The 2017 melting season
« Reply #1179 on: May 10, 2017, 01:17:14 PM »
Excellent reading there, Vader; thank you. What i meant though wasn't how early it is, but the pace of the process. Mean 1981-2010 curve is starting slow, but this year, it doesn't, this kinda freaked me out.

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Re: The 2017 melting season
« Reply #1180 on: May 10, 2017, 01:39:16 PM »
Paddy,

D is several orders of magnitude lower. You can pretty much discount it.
C is the biggie directly.
A & B are large follow-on effects depending on weather.
Agree on D.

C is still tiny though. Specific heat of water is 4.2 J/(g.K); heat of fusion is 334 J/g (assumed salt-free). So 4 mm of rain at 2 degrees C will only melt 0.1 mm of ice before cooling to freezing point.
(And the resulting 5 mm puddle of water might still then freeze anyway.)

iceman

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Re: The 2017 melting season
« Reply #1181 on: May 10, 2017, 02:20:41 PM »
Paddy,

D is several orders of magnitude lower. You can pretty much discount it.
C is the biggie directly.
A & B are large follow-on effects depending on weather.
Agree on D.

C is still tiny though. Specific heat of water is 4.2 J/(g.K); heat of fusion is 334 J/g (assumed salt-free). So 4 mm of rain at 2 degrees C will only melt 0.1 mm of ice before cooling to freezing point.
(And the resulting 5 mm puddle of water might still then freeze anyway.)

My impression is that at this time of year, A has the greatest knock-on effects, especially:
  - if followed by a sunny spell (downwelling long-wave radiation matters less as we approach the solstice);
  - over relatively smooth areas of first-year ice that are susceptible to melt ponding;
  - at more southerly latitudes or near the ice edge, where the albedo effect will advance to open water as the melt season progresses.

It doesn't seem like rainfall is an unusually large factor so far this year, though: no big spring storms sweeping in on either the Atlantic or Pacific side.
 

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Re: The 2017 melting season
« Reply #1182 on: May 10, 2017, 02:36:11 PM »
Paddy,

D is several orders of magnitude lower. You can pretty much discount it.
C is the biggie directly.
A & B are large follow-on effects depending on weather.
Agree on D.

C is still tiny though. Specific heat of water is 4.2 J/(g.K); heat of fusion is 334 J/g (assumed salt-free). So 4 mm of rain at 2 degrees C will only melt 0.1 mm of ice before cooling to freezing point.
(And the resulting 5 mm puddle of water might still then freeze anyway.)
Ain't no "anyway" about freezing, i think. That 334 J/g works both ways. Not only when melting ice, but also when water freezes, too (just reverted energy flow, but same amount basically). I.e. to freeze that water into solid, thick layer of ice below it would have its temperature increased to zero (if it was 2 degrees below melting point i mean, if to use same idea reverted). Something like 390mm layer of ice (yep, not even 200 (5mm x40) - because ice specific heat is almost half of water's). But if that ice was already at its melting point? Then there will be no freezing happening, given strictly 0C air at the surface (since we don't talk how air temperature affects it, right now). When everything's 0C, ice will be sending exactly same amount of heat into water layer as water layer will be sending into the ice, basically - so nothing melts and nothing freezes. Things get real fancy when one starts to consider air temperature influence, evaporation's cooling, thermal conductivities vs thicknesses and wind effects, though.

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Re: The 2017 melting season
« Reply #1183 on: May 10, 2017, 03:17:58 PM »
Wouldn't rain and the dramatic change in the crystal structure of snow that it falls on have a dramatic effect on the albedo of the snow. In studies of Greenland, even minor surface melt of snow increases the absorption IIRC.

Csnavywx

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Re: The 2017 melting season
« Reply #1184 on: May 10, 2017, 03:28:14 PM »
Rain on snow or ice lowers albedo significantly -- which is the important part. It can kick-start ponding if timed correctly.

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Re: The 2017 melting season
« Reply #1185 on: May 10, 2017, 03:38:16 PM »
Meanwhile, Jaxa May 9 2017 sea ice extent is 600,000 km2 more than May 9 2016, (that is 9 days behind). 600,000 km2 of ocean is reflecting most solar radiation as opposed to absorbing most solar radiation than at this day last year. The positive feedback from increased insolation is, therefore, as of today, somewhat less than last year.

Given that the insolation season is well underway, and is of little import after August, to equal last year's increased positive feedback from insolation would require a daily sea-ice extent loss well above that of last year. Since the last week of April, daily sea extent loss is far below that of 2016.


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Re: The 2017 melting season
« Reply #1186 on: May 10, 2017, 03:56:51 PM »
Ah, but from PIOMAS, volume is way down. At low thickness levels the light can go though the ice and warm the water underneath, causing both top and bottom melt at the same time.

And don't forget those pesky leads.

So many variables, so little space in my head to fit them all in.

gerontocrat

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Re: The 2017 melting season
« Reply #1187 on: May 10, 2017, 04:07:25 PM »
Ah, but from PIOMAS, volume is way down. At low thickness levels the light can go though the ice and warm the water underneath, causing both top and bottom melt at the same time.

And don't forget those pesky leads.

So many variables, so little space in my head to fit them all in.

I restricted my comment to one variable only as of today and an indication of required melt from today simply because there is so much else going on that would suggest the ice cap is liable to fall apart, but on this variable so far hasn't.
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Re: The 2017 melting season
« Reply #1188 on: May 10, 2017, 04:10:31 PM »
In 2012 and 2017 extent recovered greatly during spring and then hit a cliff in June that made  those years record low extent years.

2016 was different. 2016 suffered an early dip in spring (which I attribute to el niƱo) and then the freezing season resumed as "normal" (for current climate change state).

The first attachment is NSIDC Sea ice extent for years 2007,2012,2016,2017


2017 is unique in that there is no precedent for such a warm arctic winter, that produced such a low volume of sea ice.  I do think that a cliff in extent is very near, probably by the end of the week.  The second image is a nullschool screenshot for 5/13. There will be compaction and melting in the CS and more separation on the BS.  It may be somewhat offset by the ice being pushed into the Atlantic.
« Last Edit: May 10, 2017, 04:18:57 PM by Archimid »
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Re: The 2017 melting season
« Reply #1189 on: May 10, 2017, 06:59:45 PM »
SST and SSTAs seem pretty high in Chukchi sea.
How will this impact that area as the season progresses?
« Last Edit: May 11, 2017, 12:26:39 AM by Thomas Barlow »

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Re: The 2017 melting season
« Reply #1190 on: May 10, 2017, 07:31:57 PM »
SSA and SSTAs seem pretty high in Chukchi sea.
How will this impact that area as the season progresses?
Earlier melt of Pac/Asian peripheral sea ice than ever before, enhanced transport of ATL ice out of FRAM, enhanced CAA garlic press -- we very well may see a Blue Arctic this autumn.

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Re: The 2017 melting season
« Reply #1191 on: May 10, 2017, 07:51:58 PM »
Algal growth on and in underside of floes is a very large effect that will very likely kick like a mule this year. They bloom and grow through the porous ice when its under 2.5m and in adition to absorbing more heat through albedo their metabolic heat and antifreeze compounds they produce can cause bottom melt at -10c air temps. The fragmented pack and mobility will have given them a big head start. May be  significantly more nutrient spread into the cab too.
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Re: The 2017 melting season
« Reply #1192 on: May 10, 2017, 08:26:56 PM »
(Let's try that again)

This is new...

Lincoln Sea. Yesterday an unbroken sheet. Today, cracked-up all the way down to Nares. Don't think We've ever seen it do that before, least of all in early May.

magnamentis

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Re: The 2017 melting season
« Reply #1193 on: May 10, 2017, 09:09:28 PM »
(Let's try that again)

This is new...

Lincoln Sea. Yesterday an unbroken sheet. Today, cracked-up all the way down to Nares. Don't think We've ever seen it do that before, least of all in early May.

yesterday's image was either inaccurate and/or photoshopped. howerer cracks are around for quite some time and they were certainly not gone on leave for a day ;)

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Re: The 2017 melting season
« Reply #1194 on: May 10, 2017, 10:44:47 PM »

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Re: The 2017 melting season
« Reply #1195 on: May 10, 2017, 11:37:07 PM »
Second attachment: NCEP polar ice drift 7 day forecast.

http://mag.ncep.noaa.gov/model-guidance-model-parameter.php?group=Model%20Guidance&model=POLAR&area=POLAR&ps=model#
To complement this, according to ACNFS there are still three or four days of localized but strong drift out of the Amundsen Gulf, also two days of strong drift northwards over Bering strait and Chukchi sea. It isn't over yet


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Re: The 2017 melting season
« Reply #1197 on: May 11, 2017, 12:20:21 AM »
Aaand sorry for overposting but couldn't restraint myself.
Nice dipole, staying for about a week with more or less strength, our prime suspect of dragging the heat and pushing things around...

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Re: The 2017 melting season
« Reply #1198 on: May 11, 2017, 07:06:17 AM »
Aren't above zero temperatures at 2m not highly unlikely when there is still a lot of ice, because the ice will 'absorb' the heat?
at surface yes, but at two meters the tenperatures can already be a bit above zero. By how much depends on winds/humidity
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Re: The 2017 melting season
« Reply #1199 on: May 11, 2017, 09:39:47 AM »
Yes, the temperature gets "stuck" at 0 all throughout the melting season.
Gross and misleading oversimplification IMO.

1st, salinity lowers the melting point to some -2C, which is where temps get "stuck" for bottom melt. This page says it's about -1.8C, but things differ a bit further both directions depending on how much salt is in involved in each particular layer of ice, whether it's multi-year or not, etc.

2nd, as mentioned few posts above, algae is a factor and can lower melting point to some -10C (give or take a lot; personally i'm complete noob in this and have no idea how true that figure would be at any significant scale).

3rd, on the "positive" side, temps can and will get higher than 0C in melt ponds when surface air temps are much above zero (with or without sunny weather, though sun obviously pushes things even warmer), with near-melting-point temperature in the thin layer of water right next to ice, but warmer temps in the upper water layers of melt ponds (which does a bit of extra melt through IR radiation downwards into the ice). This only happens with warm enough air masses though, so only in some locations / days, basically it gotta be enough gradient to overcome vertical mixing in melt ponds caused by water's density anomaly at +4C;

4th, above 0C temps can and will happen at the bottom edge of ice in some locations, large-scale, whenever warm enough water current enters under some ice field. If that wouldn't be the case, then we'd never hear "bottom melt" term - but we do and it's quite very important for the melting season, you know;

5th, melting seasons these days produce lots and lots of open water in Arctic - areas with no ice whatsoever. Those can and will have their surface temperatures much higher than 0C whenever it's sunny and/or warm surface air masses come in. For example, i remember reading about sea surface temperature (open water) near Svalbard being some 17C early July 2016. Such areas will of course transport some of such heat to nearby areas with remaining ice whenever winds and water currents are going "right" way, creating situations described above.