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TerryM

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Re: Greenland 2019 Melt Season
« Reply #350 on: July 24, 2019, 02:39:56 PM »

And yes, there are many times I think of reducing posts to just one a week.


FWIW
I've come to look forward to your daily recaps.


Your labors are very much appreciated!
Terry

wili

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Re: Greenland 2019 Melt Season
« Reply #351 on: July 24, 2019, 02:41:22 PM »
Hear, hear!
"A force de chercher de bonnes raisons, on en trouve; on les dit; et après on y tient, non pas tant parce qu'elles sont bonnes que pour ne pas se démentir." Choderlos de Laclos "You struggle to come up with some valid reasons, then cling to them, not because they're good, but just to not back down."

oren

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Re: Greenland 2019 Melt Season
« Reply #352 on: July 24, 2019, 05:24:23 PM »
I appreciate the daily updates, but you might make the caveats/notes section a weekly occurrence?
Same here. Love the dailies, could do without the repeating text. Just put a few lines in, and post the rest every week for the trolls and occasional readers.

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Re: Greenland 2019 Melt Season
« Reply #353 on: July 24, 2019, 06:17:38 PM »
I agree with oren. Gerontocrat very thankful for your efforts, creativity and smartness. You are some kind of a 'pillar' on this forum I think.
"It is preoccupation with possessions, more than anything else, that prevents us from living freely and nobly" - Bertrand Russell
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grixm

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Re: Greenland 2019 Melt Season
« Reply #354 on: July 25, 2019, 08:18:10 AM »
If the 0z GFS verifies, Greenland will see an extreme melt event starting at +120h. At daytime 90% of the island will have above freezing surface air temperature and the coast will reach 20C+, all lasting several days!


gerontocrat

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Re: Greenland 2019 Melt Season
« Reply #355 on: July 25, 2019, 08:45:57 AM »
http://polarportal.dk/en/greenland/surface-conditions/ as at 24 July 2019

On this day

Melt High but down a bit. Still predominantly in the West. .

Precipitation minimal, and as a result SMB (Surface Mass Balance) loss substantially above average despite the slightly lower melt.
_______________________________________________
GFS Outlook

Precipitation 5 day outlook. Greenland North & West very dry for the next 5 days. Some precipitation in the south and on the east coast - partly rain?

Melt / Temperatures. Extreme warmth Monday 29 to Wed 31 July. Will it happen? If it does, melt % will likely be new maxima for the year.

High pressure has been, is, and will be stuck over Greenland until ....?
____________________________________________
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BornFromTheVoid

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Re: Greenland 2019 Melt Season
« Reply #356 on: July 26, 2019, 09:53:48 AM »
The heat from Europe is now beginning to make its way north west towards Greenland, via Iceland. You can track the movement on the 850hPa anomalies in the animation below.



By the time it arrives, as mentioned by grixm, surface temps are widely above 0C across the ice sheet, with plenty of very warm spots around the coastal fringes.


gerontocrat

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Re: Greenland 2019 Melt Season
« Reply #357 on: July 26, 2019, 12:46:11 PM »
http://polarportal.dk/en/greenland/surface-conditions/ as at 25 July 2019

Just when I think about reducing activity on this thread as nothing much is changing....

On this day

Melt Down to not much above average. Still predominantly in the West. .

Precipitation low, and as a result SMB (Surface Mass Balance) loss well above average despite the lower melt.
_______________________________________________
GFS Outlook

Precipitation 5 day outlook. Greenland North & West very dry for the next 5 days. Some precipitation pushing in from the south and towards especially the east coast - looking like rain at lower altitudes.

Melt / Temperatures. Today and Saturday looking average for the time of year but then..

For once a predicted major weather event looks likely to happen. Warmer starting on Sunday, reaching extreme highs on Tuesday, and staying much above average to perhaps Saturday.

If the Tuesday extreme happens, melt will likely be a new maximum for the year and cover most of Greenland.
 
High pressure has been, is, and will be stuck over Greenland until ....?
____________________________________________
« Last Edit: July 26, 2019, 01:27:35 PM by gerontocrat »
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grixm

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Re: Greenland 2019 Melt Season
« Reply #358 on: July 26, 2019, 07:54:31 PM »
I was surprised to see that the upcoming potential greenland melt event made the top of my national news site NRK.no: https://i.imgur.com/e4Y4doz.jpg

I thought keeping up with this stuff was a bit too niche for mainstream media

Stephan

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Re: Greenland 2019 Melt Season
« Reply #359 on: July 26, 2019, 09:24:33 PM »
gerontocrat,
thanks for your daily postings and analyses.
I recognize that surface melt on Grønland has been and very likely will be above average for at least five weeks in a row. Has that ever happened before or is this unprecendented?

gerontocrat

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Re: Greenland 2019 Melt Season
« Reply #360 on: July 26, 2019, 09:43:36 PM »
gerontocrat,
thanks for your daily postings and analyses.
I recognize that surface melt on Grønland has been and very likely will be above average for at least five weeks in a row. Has that ever happened before or is this unprecendented?
Don't know.
No nice ASCII or .csv files at DMI. Experts only,  think.

But a nice if oldish paper gives a clue (http://prudence.dmi.dk/data/temp/RUM/HIRHAM/GREENLAND/MottramEtAl2017.pdf)

Data to 2014 shows an increase in snow-melt - 2012 is still No.1 by far. Should get some comparisons late in the year from NSIDCs Greenland today and DMI do an annual report as well.



"Para a Causa do Povo a Luta Continua!"
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Rod

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Re: Greenland 2019 Melt Season
« Reply #361 on: July 27, 2019, 01:27:23 AM »
More bad news for the ice sheet.

gerontocrat

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Re: Greenland 2019 Melt Season
« Reply #362 on: July 27, 2019, 08:46:41 AM »
http://polarportal.dk/en/greenland/surface-conditions/ as at 26 July 2019

Just when I think about reducing activity on this thread as nothing much is changing....

On this day melt and SMB loss very much at average. The calm before the storm?

Melt Down to not much above average. Still predominantly in the West. .

Precipitation a bit higher, and as a result SMB (Surface Mass Balance) loss only just above average in line with the lower melt.
_______________________________________________
GFS Outlook

Precipitation 5 day outlook. Greenland North & West very dry for the next 5 days. Precipitation, that could be high, pushing in from the south and towards especially the east coast - looking like rain at lower altitudes.

Melt / Temperatures. Today and Saturday looking average for the time of year but then..

For once a predicted major weather event looks even more likely to happen. Warmer starting on Sunday, reaching extreme highs on Tuesday, and staying much above average to perhaps Saturday. The maximum temperatures for the next 5 days from GFS shows that nearly all of Greenland will get some melt at some time over the next 5 days - and in some low altitude places extreme melt for long periods. See post from Rod above.

High pressure has been, is, and will be stuck over Greenland until ....?
____________________________________________
"Para a Causa do Povo a Luta Continua!"
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gerontocrat

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Re: Greenland 2019 Melt Season
« Reply #363 on: July 27, 2019, 08:51:16 AM »
The post from Rod talks about albedo. Attached is the status as at 25 July. Red and yellow = darker
Also attached cumulative SMB anomaly map.

The end of season analyses from DMI and NSIDC's Greenland Today will be interesting.
« Last Edit: July 27, 2019, 08:58:02 AM by gerontocrat »
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grixm

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Re: Greenland 2019 Melt Season
« Reply #364 on: July 27, 2019, 09:51:38 PM »
NSIDC has a new interactive melt map where you can browse melt extent and temperature readings for different dates: https://greenland-measures.labs.nsidc.org/

gerontocrat

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Re: Greenland 2019 Melt Season
« Reply #365 on: July 27, 2019, 10:46:24 PM »
 GRACE-FO is producing new mass loss data that I can read. Also posted on what's new.

We will get a much better handle on what's going on from now on.
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Ktb

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Re: Greenland 2019 Melt Season
« Reply #366 on: July 28, 2019, 07:32:59 AM »
GRACE-FO is producing new mass loss data that I can read. Also posted on what's new.

We will get a much better handle on what's going on from now on.

Best news I've heard in quite a while!!!
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oren

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Re: Greenland 2019 Melt Season
« Reply #367 on: July 28, 2019, 07:40:37 AM »
Thank you Gerontocrat. At last!
The good news: mass loss was much below average in the last two years.
The not so good news: SMB data gave hope for no mass loss, but it turns out calving and ocean melting were greater (or that SMB modelling is imperfect).

gerontocrat

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Re: Greenland 2019 Melt Season
« Reply #368 on: July 28, 2019, 09:00:14 AM »
http://polarportal.dk/en/greenland/surface-conditions/ as at 26 July 2019


On this day melt and SMB loss very much at average. The calm before the storm?

Melt Down to not much above average. Still predominantly in the West. .

Precipitation a bit higher, and as a result SMB (Surface Mass Balance) loss only just above average in line with the lower melt.
_______________________________________________
GFS Outlook

Precipitation 5 day outlook. Greenland North & West very dry for the next 5 days. Precipitation, that could be high, pushing in from the Atlantic towards the east coast - looking like rain at lower altitudes.

Melt / Temperatures.
For once a predicted major weather event looks even more likely to happen. Warmer starting today (Sunday), reaching extreme highs on Tuesday/Wednesday, and staying much above average to perhaps Saturday. Nearly all of Greenland will get some melt at some time over the next 5 days - and in some low altitude places extreme melt for long periods.

It will be interesting to see how much the higher precipitation offsets the higher melt in the SMB gain / loss equation.
____________________________________________
High pressure has been, is, and will be stuck over Greenland until ....?
Part of a major weather change in the whole Arctic Basin?
"Para a Causa do Povo a Luta Continua!"
"And that's all I'm going to say about that". Forrest Gump
"Damn, I wanted to see what happened next" (Epitaph)

gerontocrat

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Re: Greenland 2019 Melt Season
« Reply #369 on: July 28, 2019, 01:36:53 PM »
There are times when one would like to shoot a scientist or two. This is one of them.

GRACE-FO
I have had a good look at the new GRACE-FO ice loss data.  The technical notes say

"The definition of 25 major drainage basins for the AIS and 7 drainage basins for the GIS, as well as the inversion procedure based on a forward modelling approach follows Sasgen et al. (2013) and Sasgen et al. (2012), respectively. "

Next stage, find a map. So after hitting a paywall a few times, bingo.....

https://www.researchgate.net/publication/233811055_Timing_and_origin_of_recent_regional_ice-mass_loss_in_Greenland

Attached is the map- Basins A to G.
There is a table of mass loss 2003-2009 by 7 basins A to G

The data file has Basins 301 to 308.  Yes, eight. Graph attached

8 vs 7. In the same order? Don't know.
But there is a table of mass loss 2003-2009.

NASA - IceSat
While hunting for the definitive map of the 7 drainage basins I come across

https://icesat4.gsfc.nasa.gov/cryo_data/ant_grn_drainage_systems.php

and what do I find - Greenland's  8 - eight - Drainage Basins. (map attached).
If you can handle this stuff (I can't) the lat longs of the drainage basisn are in this file.
https://icesat4.gsfc.nasa.gov/cryo_data/drainage_divides/GrnDrainageSystems_Ekholm.txt

 and a quote:-
Quote
Drainage Systems and Divides
Ice sheet drainage systems were delineated to identify regions broadly homogeneous regarding surface slope orientation relative to atmospheric advection, and additionally in the case of Antarctica, denoting the ice sheet areas feeding large ice shelves. Systems and sub-systems include one or more primary basins, each identifiable with a particular outlet glacier or ice stream that drains the interior of an ice sheet, plus secondary basins that complete the periphery of an ice sheet and are normally ignored in net mass budget estimates based on input-minus-output methods. The drainage system schemes for Antarctica and Greenland cover the entire area within the coterminous coastline.

Both GRACE and IceSat are NASA projects.
My guess is that the 2012 analysis by Sasgen et al has been changed to add an extra basin, but they have not noted that in the documentation

But what do I know?


I am not looking at Antarctica yet, frightened of losing the will to live.
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gerontocrat

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Re: Greenland 2019 Melt Season
« Reply #370 on: July 29, 2019, 12:34:06 PM »
http://polarportal.dk/en/greenland/surface-conditions/ as at 28 July 2019

On this day...

Melt up a bit
Precipitation much higher, all in the SE quadrant, overwhelming slightly higher melt and as a result
SMB (Surface Mass Balance) much below average.
_______________________________________________
GFS Outlook

Precipitation 5 day outlook. Greenland North & West very dry for the next 5 days. Precipitation, that could be high, pushing in from the Atlantic towards the east coast - looking like rain at lower altitudes.

Melt / Temperatures.
For once a predicted major weather event looks inevitable. Spike in temperatures starting today (Monday), reaching extreme highs on Tuesday & Wednesday, and staying much above average to perhaps Saturday. Nearly all of Greenland will get some melt at some time over the next 5 days - and in some low altitude places extreme melt for long periods.

It will be interesting to see how much the higher precipitation offsets the higher melt in the SMB gain / loss equation. And how does the DMI model deal with precipitation falling as rain in lower altitudes?
_______________________________________________
The Accumulated SMB Anomaly map shows the extreme contrast between the SE coast and the West coast. In theory, the DMI model should show the SMB gains and losses by drainage basins. GRACE-FO data is also by drainage basins.

If the drainage basins used are the same (!?), and if IceSat drainage basins are the same (!?), measurements of mass loss / gain from calving, melt and precipitation and consequential topographical change by Greenland's individual drainage basins would be possible.
____________________________________________
High pressure has been, is, and will be stuck over Greenland until ....?
Part of a major weather change in the whole Arctic Basin?
"Para a Causa do Povo a Luta Continua!"
"And that's all I'm going to say about that". Forrest Gump
"Damn, I wanted to see what happened next" (Epitaph)

Klondike Kat

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Re: Greenland 2019 Melt Season
« Reply #371 on: July 29, 2019, 04:25:43 PM »
A slight change from your regular post.  Thank you for your continuing updates.

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Re: Greenland 2019 Melt Season
« Reply #372 on: July 29, 2019, 11:32:08 PM »
All of that precip over SE Greenland has to be rain the freeze level is close to 3000M.

I hope that DMI model doesn't record it as snow.  There is no way.
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philopek

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Re: Greenland 2019 Melt Season
« Reply #373 on: July 30, 2019, 12:53:04 AM »
All of that precip over SE Greenland has to be rain the freeze level is close to 3000M.

I hope that DMI model doesn't record it as snow.  There is no way.

If the freeze level is around 3000m it can snow down to 2500m (approx) because it can snow up to 4C and usually does till 2C.

Depending on the slope / gradient this can be a huge are, hence the "ALL" term can in fact be around "half"

Csnavywx

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Re: Greenland 2019 Melt Season
« Reply #374 on: July 30, 2019, 01:26:38 AM »
500m is usually the maximum freeze level for snow. To get it with surface temperatures at 2-4C, you need drier sub-cloud air, for evaporational cooling to do its work on keeping hydrometeors frozen to the surface. That's a bit of a special case. With this kind of setup, the low level warm wedge (driven by advection) is likely to be pretty stout. It only takes 10 J/kg of excess heat (above freezing) to prevent snow from reaching the ground.

We'll find out for sure on the DMI figures since almost nowhere will be getting snow starting tonight/tomorrow. Even the summit looks to get above freezing.

Funny, I seem to remember a recent paper about rain events on a future Greenland ice sheet wrt mass loss/gain.

philopek

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Re: Greenland 2019 Melt Season
« Reply #375 on: July 30, 2019, 01:39:14 AM »
500m is usually the maximum freeze level for snow. To get it with surface temperatures at 2-4C, you need drier sub-cloud air, for evaporational cooling to do its work on keeping hydrometeors frozen to the surface. That's a bit of a special case. With this kind of setup, the low level warm wedge (driven by advection) is likely to be pretty stout. It only takes 10 J/kg of excess heat (above freezing) to prevent snow from reaching the ground.

We'll find out for sure on the DMI figures since almost nowhere will be getting snow starting tonight/tomorrow. Even the summit looks to get above freezing.

Funny, I seem to remember a recent paper about rain events on a future Greenland ice sheet wrt mass loss/gain.

To be honest, in this case I don't care much about theories because i spent 50 years in places where the temperatures hovered often if not mostly between zero and 5C once westerly winds braught precipitation.

During this entire period I carefully studied the temperatures related to the kind of precipitation
and in case of snowfall it's quality, flake-size etc.

Result is what I wrote above, it mostly snows till 2C and can snow till 4C. Or in other words, I don't remember snowfall above 5C but I do remember snowfall between 2-4C.

Why does it matter?

Because roughly 100m account for 1C (roughly and generally speaking) and if the freezing temps are around 3000m that makes it snowing down to 2500m if conditions are right but certainly down to 2750m and considering the average slop at such altitudes in greenland those 250m can cover a huge area for sure and the 500m would cover an even larger area that could account for almost half the area where it is snowing.


gerontocrat

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Re: Greenland 2019 Melt Season
« Reply #376 on: July 30, 2019, 05:34:25 AM »
http://polarportal.dk/en/greenland/surface-conditions/ as at 29 July 2019

On this day...

Melt up a bit
Precipitation**high, all in the SE quadrant, overwhelming slightly higher melt and as a result
SMB (Surface Mass Balance) LOSS"" much below average.

""EDIT - added the missing word "LOSS"

**GFS showing most precipitation as snow.
_______________________________________________
See next post for next 3 days
« Last Edit: July 30, 2019, 06:43:29 PM by gerontocrat »
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gerontocrat

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Re: Greenland 2019 Melt Season
« Reply #377 on: July 30, 2019, 05:42:49 AM »
http://polarportal.dk/en/greenland/surface-conditions/ Prospects 29 July to Aug 01 2019

GFS Outlook

Precipitation 3 day outlook. Greenland North & West very dry. Precipitation, that could be high, pushing in from the Atlantic towards the east coast - looking like rain at lower altitudes. But still shown as mostly snow.

After 3 days precipitation in the SE quadrant reduces.

Does GFS take high temperatures into account sufficiently ?

Melt / Temperatures.
Spike in temperatures reaching extreme highs on Tuesday (i.e. today) & still very strong Wednesday.
Much above average Thursday and then moderating day by day. Nearly all of Greenland will get some melt at some time over the next 3 days - and in some low altitude places extreme melt for long periods.

It will be interesting to see how much the higher precipitation offsets the higher melt in the SMB gain / loss equation. And how does the DMI model deal with precipitation falling as rain in lower altitudes?
_______________________________________________

High pressure has been, is, and will be stuck over Greenland until ....("sticky weather")?
Part of a major weather change in the whole Arctic Basin?
"Para a Causa do Povo a Luta Continua!"
"And that's all I'm going to say about that". Forrest Gump
"Damn, I wanted to see what happened next" (Epitaph)

HapHazard

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Re: Greenland 2019 Melt Season
« Reply #378 on: July 30, 2019, 08:30:45 AM »
To be honest, in this case I don't care much about theories because i spent 50 years in places where the temperatures hovered often if not mostly between zero and 5C once westerly winds braught precipitation.

During this entire period I carefully studied the temperatures related to the kind of precipitation
and in case of snowfall it's quality, flake-size etc.

Result is what I wrote above, it mostly snows till 2C and can snow till 4C. Or in other words, I don't remember snowfall above 5C but I do remember snowfall between 2-4C.

Why does it matter?

Because roughly 100m account for 1C (roughly and generally speaking) and if the freezing temps are around 3000m that makes it snowing down to 2500m if conditions are right but certainly down to 2750m and considering the average slop at such altitudes in Greenland those 250m can cover a huge area for sure and the 500m would cover an even larger area that could account for almost half the area where it is snowing.
All of this correlates with my experience living in the mountains, but I feel like I should throw this out there as an addendum (and to be scrutinized either way)... such precipitation does indeed fall as snow in these conditions, but it doesn't necessarily accumulate. More often than not (IME) it melts as it hits the ground, or very shortly thereafter.

?

DrTskoul

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Re: Greenland 2019 Melt Season
« Reply #379 on: July 30, 2019, 10:48:44 AM »
In this case however the ground is ice...

HapHazard

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Re: Greenland 2019 Melt Season
« Reply #380 on: July 30, 2019, 05:51:18 PM »
Yep, that's just it. I've seen it go both ways and normally it's more dependent on wind.

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Re: Greenland 2019 Melt Season
« Reply #381 on: July 30, 2019, 05:59:08 PM »
The summit on the 12Z sounding was -0.7C.

Might go above freezing today.
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Re: Greenland 2019 Melt Season
« Reply #382 on: July 30, 2019, 06:06:55 PM »
The surface of GIS being rocked.

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Re: Greenland 2019 Melt Season
« Reply #383 on: July 30, 2019, 09:30:34 PM »
To be honest, in this case I don't care much about theories because i spent 50 years in places where the temperatures hovered often if not mostly between zero and 5C once westerly winds braught precipitation.

During this entire period I carefully studied the temperatures related to the kind of precipitation
and in case of snowfall it's quality, flake-size etc.

Result is what I wrote above, it mostly snows till 2C and can snow till 4C. Or in other words, I don't remember snowfall above 5C but I do remember snowfall between 2-4C.

Why does it matter?

Because roughly 100m account for 1C (roughly and generally speaking) and if the freezing temps are around 3000m that makes it snowing down to 2500m if conditions are right but certainly down to 2750m and considering the average slop at such altitudes in Greenland those 250m can cover a huge area for sure and the 500m would cover an even larger area that could account for almost half the area where it is snowing.
All of this correlates with my experience living in the mountains, but I feel like I should throw this out there as an addendum (and to be scrutinized either way)... such precipitation does indeed fall as snow in these conditions, but it doesn't necessarily accumulate. More often than not (IME) it melts as it hits the ground, or very shortly thereafter.

?

Sure, but probably not when it snows on ice ?

I share your observation on streets and on already growing grass in spring but not on snow and over frozen ground with flat brown grass.

Whatever the details, I think we were looking at the exactly same thing. Where I was living altitude was between 500 and 900m above sea-level. In lower areas where the bottom is less deep or not at all frozen, that may differ again.

grixm

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Re: Greenland 2019 Melt Season
« Reply #384 on: July 30, 2019, 09:59:39 PM »
More melt ponds than any other day in the season so far at the Freya glacier webcam. 13.6C
 
https://www.foto-webcam.eu/webcam/freya1/

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Re: Greenland 2019 Melt Season
« Reply #386 on: July 31, 2019, 03:01:43 AM »
Sure, but probably not when it snows on ice ?

I share your observation on streets and on already growing grass in spring but not on snow and over frozen ground with flat brown grass.

Whatever the details, I think we were looking at the exactly same thing. Where I was living altitude was between 500 and 900m above sea-level. In lower areas where the bottom is less deep or not at all frozen, that may differ again.

I'm just musing, mostly. I've lived at 1400m above sea level for 12 years now, and although I often enough observe snowfall melting on ice during above-freezing days, this ain't Greenland.

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Re: Greenland 2019 Melt Season
« Reply #387 on: July 31, 2019, 08:55:05 AM »
http://polarportal.dk/en/greenland/surface-conditions/ as at 30 July 2019

On this day...

Melt a new maximum for the year by a substantial anount- but not quite as high as I thought it would be.

Precipitation high again, all in the SE quadrant, partially counteracting very high melt and as a result
SMB (Surface Mass Balance) LOSS"" much above average, but not spectacularly so.
______________________________________________________
GFS Outlook

Melt / Temperatures.
Spike in temperatures reaching another extreme high today (Wenesday 31 July)

Much above average Thursday and then moderating day by day.

Precipitation 3 day outlook.
Today (Wednesday)  another day of significant precipitation confined to the SE quadrant.

But after that all of Greenland looking very dry or bone dry for at least a week. This could mean that SMB loss will be higher than July 30 & July 31 as lower melt more than offset by no precipitation.

It will be interesting to see how much the higher precipitation offsets the higher melt in the SMB gain / loss equation on this day.

And how does the DMI model deal with precipitation falling as rain in lower altitudes? How much does the model see it as being retained, and how much as runoff to the ocean?
_______________________________________________

High pressure has been, is, and will be stuck over Greenland until ....
« Last Edit: July 31, 2019, 09:05:17 AM by gerontocrat »
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Re: Greenland 2019 Melt Season
« Reply #388 on: July 31, 2019, 09:04:29 AM »
Albedo and accumulated SMB anomaly maps attached.

It has been definitely a melting season..
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Re: Greenland 2019 Melt Season
« Reply #389 on: July 31, 2019, 12:47:09 PM »
The model showed snow over SE GIS where a promice Station reported temperatures of 5.42C.


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Re: Greenland 2019 Melt Season
« Reply #390 on: July 31, 2019, 05:57:45 PM »
Regardless of moderating temperatures, the recent widespread melt should have lowered albedo across much of the ice sheet. If it stays sunny we should continue to see high melt.

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Re: Greenland 2019 Melt Season
« Reply #391 on: July 31, 2019, 06:02:26 PM »
"On the northwestern Greenland ice sheet, 2019 melt to-date is 1.2x that of the previous record melt in 2012." - Jason Box.
-- Programme for monitoring of the Greenland ice sheet - Promice.

https://www.facebook.com/PromiceGL/posts/2375372692725444

http://promice.org/home.html?fbclid=IwAR2fIm4hPSZvZtD7yiGkw0dsaS3mUMetWoBBSPpBm4z0PNQJ0qAGLMNdvjk

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Re: Greenland 2019 Melt Season
« Reply #392 on: July 31, 2019, 06:09:42 PM »
"On the northwestern Greenland ice sheet, 2019 melt to-date is 1.2x that of the previous record melt in 2012." - Jason Box.
-- Programme for monitoring of the Greenland ice sheet - Promice.

https://www.facebook.com/PromiceGL/posts/2375372692725444

http://promice.org/home.html?fbclid=IwAR2fIm4hPSZvZtD7yiGkw0dsaS3mUMetWoBBSPpBm4z0PNQJ0qAGLMNdvjk

Thank you for that information!!!

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Re: Greenland 2019 Melt Season
« Reply #393 on: July 31, 2019, 06:11:33 PM »
Webcam at Freya Gletscher (alt. 1053 m above sea level) shows 15.2°C today. Of course I do not know whether this T measurement can stand quality standards of meteorology, but it must be pretty warm up there - also visible in even more melt ponds.
https://www.foto-webcam.eu/webcam/freya1/

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Re: Greenland 2019 Melt Season
« Reply #394 on: July 31, 2019, 06:51:38 PM »
The summit on the 12Z sounding was -0.7C.

Might go above freezing today.

Willing to bet, after looking at Bufkit and other soundings, that there was no snow anywhere on the sheet yesterday. 700mb temps shot above 0C, up to +5 in the east. Hence the very high surface temps even with melting ice and snow. Any mass gain is due to rain and meltwater percolating into the firn. Firn storage isn't infinite though. Several bad melt years are enough to saturate it and cause increasing ponding and runoff. Not to mention the deleterious effect on albedo. Summit never used to reach freezing except once in a lifetime. Now it does so every other year, sometimes more.

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Re: Greenland 2019 Melt Season
« Reply #395 on: July 31, 2019, 07:37:35 PM »
10 hour loop, band M8.
Click to run

Wow.  Just 10 hours?  A huge fraction of all Greenland showing new melt before our eyes.

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Re: Greenland 2019 Melt Season
« Reply #396 on: July 31, 2019, 08:11:44 PM »
To be honest, in this case I don't care much about theories because i spent 50 years in places where the temperatures hovered often if not mostly between zero and 5C once westerly winds braught precipitation.

During this entire period I carefully studied the temperatures related to the kind of precipitation
and in case of snowfall it's quality, flake-size etc.

Result is what I wrote above, it mostly snows till 2C and can snow till 4C. Or in other words, I don't remember snowfall above 5C but I do remember snowfall between 2-4C.

Why does it matter?

Because roughly 100m account for 1C (roughly and generally speaking) and if the freezing temps are around 3000m that makes it snowing down to 2500m if conditions are right but certainly down to 2750m and considering the average slop at such altitudes in Greenland those 250m can cover a huge area for sure and the 500m would cover an even larger area that could account for almost half the area where it is snowing.
All of this correlates with my experience living in the mountains, but I feel like I should throw this out there as an addendum (and to be scrutinized either way)... such precipitation does indeed fall as snow in these conditions, but it doesn't necessarily accumulate. More often than not (IME) it melts as it hits the ground, or very shortly thereafter.

?

Sure, but probably not when it snows on ice ?

I share your observation on streets and on already growing grass in spring but not on snow and over frozen ground with flat brown grass.

Whatever the details, I think we were looking at the exactly same thing. Where I was living altitude was between 500 and 900m above sea-level. In lower areas where the bottom is less deep or not at all frozen, that may differ again.
`

Again, the situation he describes is diabatically-driven localized cooling in the boundary layer. It requires colder air aloft and steep lapse rates in the boundary layer (near dry adiabatic) with a dry sub-cloud layer. In that situation, precipitation can fall through an above freezing layer and survive via evaporational cooling as it falls to the ground. That doesn't happen in a saturated warm layer aloft once the max T in the layer exceeds ~1C and an aggregate depth past about 400m (depending somewhat on precip rates).

On an ice surface, once the temperature rises above freezing due to advection of a warm air mass over the area, a near surface inversion begins to set up due to melting, which it did, across almost the entire ice sheet. This causes a warm "wedge" to form aloft. Using surface temps to determine precip type then is not advisable:




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Re: Greenland 2019 Melt Season
« Reply #397 on: July 31, 2019, 08:20:14 PM »
New high for the season in NSIDC melt extent too.

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Re: Greenland 2019 Melt Season
« Reply #398 on: July 31, 2019, 08:21:29 PM »
That sounding was from the southeast coast during the precip event there last night.

As you can see, despite the surface temperature being ~3C, the air aloft is *much* warmer and lapse rates are very weak due to advection driven processes (in fact, nearly isothermal to 800mb). The freezing level is up around 750-700mb with a deep warm layer below that.

This was while precip was falling, so I can virtually guarantee almost none of that precip that hit the ice sheet was snow, even with adiabatic cooling from upslope flow and diabatic cooling from precip. melting. There's too much warm advection here. You'd have to go up above 2500m to get it and that might be generous since this was the coolest sounding I could find.

While I do appreciate long personal observational experience, I'm an operational meteorologist by both trade and hobby, so my earlier comments weren't made solely from theory.

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Re: Greenland 2019 Melt Season
« Reply #399 on: July 31, 2019, 08:32:49 PM »
Than you very much for the professional input Csnavywx