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Messages - Tealight

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1
Greenland and Arctic Circle / Re: What's new in Greenland?
« on: October 14, 2017, 11:25:46 PM »
The new BedMachine v3 is really great for marine terminating glaciers. Finally the bedrock map is not cropped anymore in the important terminus region.

For Petermann and Zachariae not much has changed since version 2, but Jakobshavn looks quite different. I wonder if a slower flow speed influenced the mass conversion calculations.

The bedrock beneath the wedged part of Spaltegletscher is modeled as above sea level, which obviously can't be right. One of the weak spots of the mass conversion model.

click on images to animate

2
Arctic sea ice / Re: NSIDC 2017 Arctic SIE September average: August poll
« on: October 02, 2017, 01:43:00 AM »
September is over and I calculated 4.871 million km2 as the monthly September extent. Just a small increase of 150k since the 23rd September.

3
Arctic sea ice / Re: NSIDC 2017 Arctic SIE September average: August poll
« on: September 23, 2017, 09:20:24 PM »
Update for the provisional monthly extent until 22nd September.

Not much happened in the last few days. The monthly extent is at 4.722 million km2, a mere 10k km2 increase from the 11th. This means the icepack wasn't very mobile and any refreezing  happened in the low concentration areas which already counted towards extent.

Edit: 4.594 million km2 is guaranteed

4
Arctic sea ice / Re: NSIDC 2017 Arctic SIE September average: August poll
« on: September 13, 2017, 02:33:04 AM »
For the monthly extent the NSIDC calculates the average sea ice concentration for every pixel and if the concentration is over 15% for the entire month the pixel is counted as ice covered. This is completely independent from daily values.

If high concentration areas move around by wind/currents then the monthly extent can also be higher than any daily value.

Using this method I calculated that the monthly extent until 11th September is 4.712 million km2.

Edit: Even if an asteroid would smash into the North Pole and wipe out the entire ice pack, the monthly September extent won't go below 4.029

5
Arctic sea ice / Re: The 2017 freezing season
« on: September 06, 2017, 11:24:48 AM »
By now over 95% of this years solar energy was either absorbed or reflected by the Arctic Ocean and I can finally post my refreeze-forecast.

When thinking about refreezing, the lowest sea minimum should also correlate with a low sea ice area / extent during the freezing season because a lot of open water has to refreeze. But the September minimum isn't quite as good as my AWP anomaly calculation, which considers absorbed heat by the oceans as well. For the last 11 years I compared the sea ice area minimum, the sea ice extent minimum and the cumulative AWP anomaly against the average sea ice area and extent anomaly during the October-December refreeze.

An Overview about individual years can be found here:
https://sites.google.com/site/cryospherecomputing/warming-potential


The AWP correlation is negative, because a higher solar energy absorption results in a slower refreeze, hence a negative area anomaly. See the attached graph for all 11 years.(the zero line is not the same for both axis and the secondary axis is inverted due to the negative correlation)

Correlation with Oct-Dec Extent anomaly
Minimum Area   0.779236221
Minimum Extent   0.699103822
Cumu AWP anomaly   -0.84296024
   
Correlation with Oct-Dec Area anomaly
Minimum Area   0.748245297
Minimum Extent   0.637113296
Cumu AWP anomaly   -0.784477392

Surprisingly for me all forecast methods correlate better with the sea ice extent anomaly and not the sea ice area anomaly. The ranking however always stays the same. The best is my cumulative AWP anomaly, followed by the sea ice area minimum and least skillful is the sea ice extent minimum.

For 2017 with a "cumu AWP" of +15.8 MJ/m2 we should expect an average extent anomaly of -0.22 million km2

Edit: without 2009 the AWP anomaly would correlate to 94% with sea ice extent and 93% with sea ice area

6
Greenland and Arctic Circle / Re: Glacier Lake 66N, 50W / West Greenland
« on: September 04, 2017, 10:55:29 PM »
I am afraid there is an anti western (danish) atmosphere in Greenland, so anything that rhimes with danish is a no-go.

I don't think Greenland will develop well with only Greenlandic as a language. With only 50-60 thousand speakers it is far too uncommon and under developed for modern life and new high-tech technologies. Even Danish with 5 million native speakers is quite small.

As a free economic advise I encourage them to accept English and attract more foreign investors  ;)

7
Greenland and Arctic Circle / Re: Glacier Lake 66N, 50W / West Greenland
« on: September 03, 2017, 10:24:21 PM »
Where exactly did you find "Sø 860"? I also couldn't find a name on GEUSs maps / website and if it is nowhere mentioned than aren't we are free to propose a name?

How about "Lake Espen"  ;D

In honor of his continuous year-long coverage of Greenland's glaciers. It's fitting for the lake with the biggest icebergs in the world. We are legitimate explorers and document our observation for other people to use.

8
Greenland and Arctic Circle / Glacier Lake 66N, 50W / West Greenland
« on: September 01, 2017, 01:08:59 PM »
Near the icecaps in West Greenland is a glacier lake without any visible surface outflow.

This lake has one of the biggest icebergs of any lake in the world. The biggest I have measured calved in 2016 and was 1km long, 200m wide and 120m in height. The height is estimated from an image in 2017 after the iceberg turned over. Other icebergs in the lake are similar in size, several reaching 300-600m in length. The whole front of the glacier retreated over 100m from August 2016 until August 2017.

The lake itself is 15 km W-E, 10.5 km N-S and at least 120m deep (otherwise the icebergs can't turn over). According to Google Earth and Greenland Bedrock Map the lake is at 800m above sea level. Maybe it has an outflow beneath a glacier, but I can't say under which one, the bedrock data isn't accurate enough. It should be a good place to study non-ocean terminating glaciers. If the ice sheet retreats further inland it might expose more lakes, which don't have warm ocean water to melt the glaciers from beneath and can't transport icebergs away.

On Google Earth/Maps this lake doesn't even exist and just shows as white snow unless you zoom really close. I'm not sure if it has a name, but feel free to reference it or any of the glaciers terminating in it.

The actual center of the lake is 66N, 55.15W, but in a few years it will melt the ice sheet and reach 50W.

9
Glaciers / Re: Barnes Ice Cap / Penney Ice Cap
« on: August 10, 2017, 01:52:30 AM »
This year melting on Barnes Ice Cap occurs all the way to the top. Some blue meltwater channels actually connect over the top, which looks very unusual (at least to me). The average width of a channel is 50m and the distance between them is 500m. Like in last years image all channels are very uniform, in parallel at the top and combine towards the bottom.


Sentinel-Playground Link:
http://apps.sentinel-hub.com/sentinel-playground/?lat=70.12379581564234&lng=-73.81233215332031&zoom=11&preset=1_NATURAL_COL0R&layers=B04,B03,B02&maxcc=74&gain=0.5&gamma=1&time=2015-01-01|2017-08-08&cloudCorrection=none&atmFilter=&showDates=false&evalscript=

10
Antarctica / Re: Thwaites Glacier Discussion
« on: August 02, 2017, 12:07:51 AM »
A close-up of Iceberg B42 & B43 which calved in March and traveled almost 100km north past the old iceberg tongue (north is on the left). It seems they won't get stuck and can travel freely into the open ocean to melt out over the coming years.

11
The iceberg has broken into two main pieces and leaves towards Nares Straight.

12
Arctic sea ice / Re: The 2017 melting season
« on: June 19, 2017, 01:22:19 AM »
I believe melt ponds will become less important in the Arctic. The increased mobility of sea ice and lower thickness allows sea ice to just break away from the coast and leave big open ocean areas behind. If the wind is right then waves increase the energy transfer from the warm water to the cold ice. Thankfully the compaction ratio is influenced by melt ponds and ice dispersion. This way we can look at one variable over a long period of time for changing melt mechanisms.

In the Antarctic we can already see that sea ice melts just fine in stormy conditions and on Worldview its hard to spot any melt ponds at all. But sheltered areas like the Weddell Sea still struggle to melt significantly.

13
These numbers suggest that the standard deviation over the residuals in your method are about 550-600 k km^2. Is that correct ?
If so, your method has little 'skill', since a simple linear trend has 550 k km^2 SD.
With 460 k km^2 SD, my method has little 'skill' too, and neither do most of SIPN projections.

Maybe May is just too early for skillful predictions of September SIE.

I never really calculated the standard deviation for extent. My model is albedo based and it can only calculate how much ice melts, but not how it is distributed over the month of September. The conversion from my area numbers into extent is more of a guessing game.

What I found out is that the compaction ratio alone influences the NSIDC September extent at least as much as the remaining melt conditions.

Normal variation for me due to compaction ratio is +-200k, but last year was extreme with +900k. Because of the very mobile ice pack I increased my forecast range this year to hopefully catch the final NSIDC extent number.

14
@Rob

Maybe you can develop a new or modified formula which includes PIOMAS volume. It is definitely a useful metric to describe the state of the sea ice .


My model prediction is 4.1 million km2, but I have an interdecile range of 3.2 - 5.1. The high snow cover slows down melt in my model as well, but due to the record low sea ice volume it still predicts a second place with a slight chance of a new record low.

If my model is correct then there is a 10% change we get below 3.2 million and 10% change above 5.1 million.

For the daily sea ice area minimum I get 2.513 million km2
Range:   1.964 - 3.112



15
Arctic sea ice / Re: Arctic Image of the Day
« on: May 29, 2017, 08:56:10 AM »
Arctic Poodles are real. I found definitive proof:
https://arcticpoodle.wordpress.com/author/finnfinn1/

On Worldview I found one lake east of James Bay which is still ice covered, but a river flowing through it has carved an ice free channel. Is this 100% natural or do Canadians use icebreakers in these remote parts?

16
Because of the popularity I made a close-up comparison of the northern branch between the record low conditions in 2015(August or September) and May 2017.

Despite the recent advancement on all sides Jakobshavn is still thinning. I spotted new exposed bedrock 2.5 km upstream. It is clearly distinguishable from the blue melt/rain water. Let's see if the glacier can retreat all the way to previous years in just one melting season.

1st image needs a click to start the animation

17
Greenland and Arctic Circle / Re: What's new in Greenland?
« on: May 03, 2017, 10:02:38 AM »
.... and it's a little early for the sun to have much warming power that far north.  Is it some unusual cloud condition causing increased downwelling ILR?
   If the forecast verifies, attendant surface melt will be quite early for that location.

Yes it is early, but solar radiation is equal to early August and with the right atmospheric conditions mentioned by AbruptSLR widespread melt can happen. It typically takes until June because the sun first has to melt all the snow and generally heat the land to freezing temperature.

18
Very nice pictures.  Are they draining off the edge as in the Bell paper ? doi:10.1038/nature22048
...

Most of the lakes are on the part that is about to calve and probably don't have and any effect on stability.


I've been thinking about that new crevasse (rift, crack) that appears to 'start' at the longitudinal trough (river bed, "feature") that runs down the middle of Petermann Glacier. (screen shot from the 2nd link above) 
... Brunt points out that the rift currently appears to end at a feature running down the center of the glacier. “That’s pretty typical,” she said, citing similar occurrences on ice shelves in Antarctica. ...
I'm surprised this is "typical"! Why would ice shelves have a mid-glacial river bed at which rifts start or end? (I'm confused, unless she's referring to chevron cracks that form semi-parallel relatively short cracks when a somewhat brittle material [like a glacier or ice shelf or cheese or clay] is stretched.) 

I'm not sure there is something as typical rifts/cracks. If something is typical then a glacier flows fasted in the middle, where the ocean is deepest and the lowest friction occurs. Because of the higher speed, the centre of the glacier detaches (cracks) from the main glacier before the sides do. But Petermann Gletscher is squeezed through a small fjord and the edges constantly grind along the rock. If the ice gets struck then cracks develop from the sides.

By the way the centre crack already cut through the main drainage channel. Not good for any rafting fan.

19
For a change here are some non-cracking news.

The terminus of Petermann Glacier is mostly blown snow free and left behind blue ice. It looks like several melt lakes survived the winter and appear in a deeper blue. I would really like to know how deep they are and how thick the ice cover is.

20
Great spotting Espen!

To celebrate the occasion I add a full 10m resolution image in true colour of Trekanten.

All you need to do now is get a ship, sail to the island and plant your flag ;D

21
The bedrock in the fjord is quite irregular varying between 400-600m below sea level and the deepest parts are under 1200m below sea level. Additionally the bedrock is only known to a 100-200m resolution so no one can tell you exactly where the grounding line is. It is probably not a real line and more a few sections where the ice floats and a few where the ice is grounded.

The thickest icebergs I have measured are close to 900m thick and likely drag along the bedrock. 

22
Jakobshavn Isbrae calved again!

Judging from NASA Worldview it was probably on the 19th April, but we only have high resolution Sentinel 2A images from the 15th and 20th. On the 15th the front position was close to the one in 2004/2005 and almost extended beyond the division between north and south branch. After the calving, the front moved 1.8 km inland to the 2006 level.



The first images is from the 15th April and the second from the 20th April. Click for full resolution.




23
Scientists just found a strange and worrying crack in one of Greenland’s biggest glaciers https://www.washingtonpost.com/news/energy-environment/wp/2017/04/14/scientists-just-found-a-strange-and-worrying-crack-in-one-of-greenlands-biggest-glaciers

This crack was already known in December last year. I posted an image of it in Reply #438 on: December 01, 2016, 09:39:09 PM »
S1B_20161201_Petermann.jpg (1840.12 kB, 2260x1624 - viewed 79 times.)

24
Antarctica / Re: Thwaites Glacier Discussion
« on: April 10, 2017, 10:04:11 PM »
The calved iceberg(1) is now visually detached on MODIS. The slightly smaller iceberg(2) right next to it moved a lot further out.
https://go.nasa.gov/2orQycz

The US National Ice Center tracks both icebergs as Iceberg B42 and Iceberg B43. The positions can also be seen on Polarview (select icebergs at the bottom)
http://www.polarview.aq//antarctic

25
Arctic sea ice / Re: The 2017 melting season
« on: April 08, 2017, 11:35:27 PM »
Tealight, maybe a short explanation would be interesting for people who lurk. I'm guessing you calculate Albedo-Warming Potential by combining sea ice concentration with how much energy is soaked up by open water?

Hang on, it's all there on your website:

Thank you Neven. That's of course important to explain. I just spend too much time on it and know it by heart.

AWP also considers melt ponds mainly in May/June/July.

26
Arctic sea ice / Re: The 2017 melting season
« on: April 08, 2017, 10:48:18 PM »
Everyone who believes in patterns can expect another strong melting season. In my pan-Arctic AWP graphs the cumulative value follows the pattern: 2 strong melting seasons followed by 2 weak melting season and one average melting season before the cycle repeats. However the regional breakdown is very important for the minimum in September. A record high pan-Arctic value doesn't guarantee a new record minimum like 2016 has shown. At least 2017 seems to follow the pattern with a record high AWP to date.

Over longer periods all years shift towards a higher energy absorption. When I did the calculation for 1988 and 1992 they ended up at -50 kWh/m2 and make 2009(-20kWh/m2) or 2013(-13kWh/m2) look like strong melting seasons.

The Pattern
2007   strong
2008   weak
2009   weak
2010   average
2011   strong
2012   strong
2013   weak
2014   weak
2015   average
2016   strong
2017   (strong)

27
Arctic sea ice / Re: Albedo-Warming Potential
« on: March 25, 2017, 09:04:48 AM »
It tells me that permission is required to view the graphs updated for 2017.

Ah sorry I forgot to make the images public. It should be fixed now.

28
Arctic sea ice / Re: Albedo-Warming Potential
« on: March 24, 2017, 11:25:44 PM »
I prepared the daily updates of my AWP model for this melting season. In April I have some more time for polishing and might update all regional graphs as well. Until then you can follow the bright colour spectacle on:

https://sites.google.com/site/cryospherecomputing/warming-potential/graphs


29
Spectacular imagery! BTW SNAP-toolbox can be used to track glacier-speed but I think the parameters take some experimenting.
I played a bit around with the offset tracking tool, but couldn't get it to work for S2A images without orbit data. It's not surprising since it is designed for S1A/B with an orbital file and other metadata.

The calving inactivity makes it easier to roughly calculate the ice volume that is pushed out of the ice sheet. The comparison is again against the 2015 record retreat.

area increase: 26.77 km2
thickness: 800m-900m

volume: 21-24 km3
mass: 19.2-21.6 Gt

If the DMI Surface Mass Budget model is correct then in the blue area fit 4% of the annual snowfall over all of Greenland.
http://beta.dmi.dk/en/groenland/maalinger/greenland-ice-sheet-surface-mass-budget/

30
Jakobshavn shows a very interesting calving inactivity. Between the 15th February and 11th March the icebergs just in front of the calving front moved 22-25m per day and the front itself moved 28m per day. Now they are all stuck together and it's very hard to see a distinct front position. If the calving inactivity continues the southern branch will fill the main fjord again and cut the northern branch off. The current front position is about 6.7 km away from the record retreat in 2015.

Click on images for full resolution or to start the gif animation

31
Arctic sea ice / Re: Albedo-Warming Potential
« on: March 01, 2017, 07:19:43 PM »
September sea-ice extent predicted by June reflected solar radiation

For some of the more "scientifically inclined"....I have a question:

What is PRECISELY meant by "top of the atmosphere reflected solar radiation (RSR)?"

Is it:

A)  Amount of solar radiation MEASURED AT the "top of the atmosphere"?
B)  Amount of solar radiation FROM the top of the atmosphere?
C)  Other...

A non-scientific inquiring mind would like to know.... :)

C)  Amount of reflected solar radiation MEASURED AT the "top of the atmosphere" (measured by satellites)

This is affected by many metrics like snow cover, sea ice, melt ponds and cloud cover. The more solar radiation is reflected from the earth the less energy is absorbed.

32
Arctic sea ice / Re: Stupid Questions :o
« on: March 01, 2017, 06:38:31 PM »
I think for photosynthesis or toxicity to humans ppm is a good unit, but for climate analysis it doesn't mean anything without an atmospheric mass/pressure.

I am sure the ppm of CO2 are in volume. The local concentration of CO2 dictates its absorbance and emissivity of IR. You cannot do any calculations or modeling based on the integral amount above your head. And it would vary based on the local pressure.

CO2 concentration alone is a useless unit to do calculations of absorbance and emissivity. 10 CO2 molecules per cm3 at 100% CO2 concentration absorb far less infrared radiation then 50 molecules at 10% CO2 concentration. If another other gas is released into the atmosphere it decreases the CO2 concentration, but the amount of CO2 and its warming effects stay the same.

If you feel funny then you can just release a few trillion tons of whatever gas into the atmosphere and the CO2 concentration will fall by definition to pre-industrial levels. It doesn't stop global warming, but it's enough to fulfill the goals of some lawmakers to bring the CO2 concentration down.

33
Arctic sea ice / Re: Stupid Questions :o
« on: February 28, 2017, 09:22:50 PM »
Why is CO2 measured in parts per million and not in kg/m2 ? Wouldn't this give us a better comparison to other greenhouse gases like water vapour? When looking at Mars & Venus we can see that it is not the concentration that matters, but the total mass. Both planets have around 96% CO2 concentration, but only Venus is hot because it has a very thick atmosphere. Mars on the other hand has a thin atmosphere and is very cold.

Using a standard atmosphere I get the following conversion:
Pressure   1013.25   hPa
Pressure   101325   N/m2 (kg⋅m⋅s−2/m2)
accelaration:   9.81   m/s2
Atmosphere mass:   10328.74618   kg /m2
      
CO2 concentration:   405   ppm      
CO2 mass:   4.183   kg/m2

34
Antarctica / Re: Melt water in Antarctica
« on: February 27, 2017, 09:21:34 PM »
All of the melt lakes on the Amery Ice Shelf have frozen over, but blue water is still visible through the thin ice cover. Maybe some of them won't drain over the winter and will appear again next year.

35
Alternatively you can use Amazon Web Services. They recently integrated Landsat 8 images into their Sentinel 2 image search. You can even look at the images in your browser without downloading them or using a special software.

http://sentinel-pds.s3-website.eu-central-1.amazonaws.com/image-browser/#lat=62.556021746271504/lng=-49.88067626953125/zoom=10

36
A Sentinel 2A image from the 16th February is available. The solar zenith angle is just 81 degrees. (9 degrees above the horizon.) This creates long shadows and reveals steep parts which are normally not visible.

The ice sheet edge is mostly blown snow-free from katabatic winds.

Click on the image for full resolution.

37
Antarctica / Re: Sea Ice Extent around Antarctica
« on: February 19, 2017, 09:48:18 PM »

Extent
1 2017-02-02 2.220714

18 Feb 2017 I assume.

Yes 18th Feb, thanks for spotting.

38
Antarctica / Re: Sea Ice Extent around Antarctica
« on: February 19, 2017, 09:21:09 PM »
Wipneus replacement post.

SH "NSIDC extent": -49.6k
SH "NSIDC area": -35.04k

This causes 2017 to move to 6th place in annual minimum SH area, skipping one place:

Extent
1 2017-02-18 2.220714
2 1997-02-27 2.264152
3 1993-02-19 2.280783
4 2011-02-22 2.318847

Area
1 1993-02-26 1.248163
2 1984-02-27 1.509585
3 1996-02-25 1.535481
4 2000-02-18 1.561033
5 2006-03-04 1.565059
6 2017-02-18 1.565366
7 1999-02-26 1.577058

39
Seems fast. Can we get a speed calculated from these images?
That's A-teams speciality, but i can give you a rough estimate from the front position.

My time frame is from the last calving on the 12th October to the 9th February (120 days)
In that time the front advanced 105 pixel which is 4200m at 40m resolution. That's 35 meter per day, pretty fast for winter.


40
Very enlightening animation. ZI never sleeps, although calving seems to be on hold (for the moment).

I know there is no consensus on this, but I could swear the animation shows how the immobile sea ice in the enclosed bay slows down the glacier somewhat (and perhaps stabilizes the front a little bit as well). The debris and icebergs can be seen to be pushed before the advancing glacier, and over time the movement propagates further into the bay.

I am one of them, the sea ice , icebergs, and debris etc. in the bay is just piece of cake, considering the forces coming from behind the glacier!
There must be other reasons for the break in calvings at Zachariae?

As far as I understand glaciers, there are two main forces at play.

The first are the millions of tons of ice pushing the front forwards. This pushing force is very strong but also slow. It can't create calvings because it only pushes the ice. However it can move sea ice out of the way.

The second force are winds/currents attacking the ice from below and above. They a lot weaker than the pusing force of ice, but also quicker and can transport loosely connected ice away from the glacier. It's what we call calving. I think sea ice can be strong enough in winter to withstand this second force.

41
Antarctica / Re: Sea Ice Extent around Antarctica
« on: February 13, 2017, 12:02:17 PM »
Wipneus & Co: do you have any idea about the "big block" that's is floating freely in the Ross Sea (Univ. of Bremens map) and has done so for more than a month now.

That is a huge Iceberg. Iceberg B30 to be exact.

On Polarview you can check radar images and track all big icebergs:
http://www.polarview.aq/antarctic

42
Antarctica / Re: Rift in Larsen C
« on: February 09, 2017, 02:31:24 PM »
First cloud free S2A image is in. I marked the end of the rift with GCP1 (Ground Control Point)

Link to Sentinel Playground
http://apps.sentinel-hub.com/sentinel-playground/#lat=-67.38663858288848/lng=-61.14372253417969/zoom=11/preset=1_NATURAL_COLOR/layers=B04,B03,B02/maxcc=22/gain=0.3/time=2015-01-01|2017-02-09/cloudCorrection=none/colCor=/evalscript=

43
Antarctica / Re: Melt water in Antarctica
« on: February 07, 2017, 08:34:12 PM »
These folks have some historic data on this looking at daily melt but nothing for last year and this.

http://lgge.osug.fr/personnels/PICARD_Ghislain/melting/

I did create two graphs from their cumulative data, one for corrected data and one for uncorrected data. Both datasets show very high annual variability and the uncorrected data shows a very small downward trend.

The Cumulative Melting Surface (CMS) for the different regions have been corrected from changes in acquisition hours due to satellite replacements with the method developed by Picard and Fily, 2006... To our opinion, the correction efficiently reduces errors for some regions (Peninsula, DML, Amery, Wilkes, MBL), but is less efficient or may add new errors for other regions (Filchner, Ross). In the latter regions, we recommend to use both the corrected and uncorrected CMS.

44
Antarctica / Re: Melt water in Antarctica
« on: February 04, 2017, 02:09:52 PM »
Regarding plumes in the water.

I think a mechanism related to wind-blown snow coming off the shelf edge is more likely. Remember, Coriolis force is reversed in the Southern Hemisphere. The rapid disappearance of the sea ice in the top of the image also points to strong winds blowing off-shore.

I agree the plumes look wind-borne.  They move far faster than the floes.  In the very first image of these posted here, you can see that there's clearing of the mist on the leeward side of the floes.  I'd favor fog.  Cold air coming off the ice shelf, flowing over slightly warmer ocean.

Have you guys looked at the 3rd image in full resolution? It can't be snow because the ice sheet surface is too clear to indicate any kind of snow drift. The fine pattern in the water (meter scale) also can't be created by winds blowing over a smooth and uniform surface like the ocean. The coriolis force is on the scale of a few hundred kilometer. I must admit the contrast isn't great and the patterns could be invisible on TN monitors at a bad viewing angle.

The plume is right at the edge of the ice shelf and very locally restrained, just 5km wide. The crevassed surface right at the plume shows that there is a weak point in the ice shelf where meltwater can exit.

Winds blow over the whole ice shelf which is 200km wide. If they were responsible for the plumes we would see them over a wider area.

How do we know it's on the water?

The plume is influenced by icebergs.

45
Developers Corner / Re: Mapping GeoCoded Data Sets
« on: February 04, 2017, 12:28:25 PM »

You may wish to take a look at:

ftp://ftp.cdc.noaa.gov/Datasets/ncep.reanalysis/surface/

Perhaps we should take this conversation over to the Developer's Corner?

I had a look at the NOAA reanalysis map and think it's terrible to create a FDD map for the Arctic. You would need transform the mercator projection into a polar sterographic projection. There probably are some libaries which help you to do it, but it will be extra work.

For all of my work I use Python 3 with the Anaconda distribution. It includes essential libaries like numpy and matplotlib to create maps/graphs. I learned the basics of Python in around one month and the rest is googling your needs because 90% of your problems were already solved by someone else.

46
Antarctica / Re: Melt water in Antarctica
« on: February 03, 2017, 11:38:09 PM »
Looking at the Amery ice sheet again.. I noticed these persistent plumes.

Could these be melt water, fresh water, flowing along under the ice shelf and then coming to the open ocean? The ocean at the edge of the ice shelf is probably cold enough to freeze some of the fresh water, hence the plume.

http://go.nasa.gov/2kamy2m is the EODIS link.

It fits in with the model of eroding the ice sheet that has been proposed: that fresh melt water flows along under the sheet and cause warm salty water to be drawn under the sheet by convection.

All that blue has to go somewhere, right?

Great observation! These plumes look nothing like sea ice or calved ice debri. They are also quite beautiful on Sentinel 2 images.

Very far inland I found two possible locations where meltwater goes beneath the ice. The first image shows a medium sized river (100m wide) ending apruptly. At the end are a few dark spots which should be holes draining all of the water.

The second image shows a mostly dried up meltwater lake featuring three big dark spots. They appear to be 30-40 meters wide, but it's hard to tell with a 10m resolution. To me 30-40m holes sound resonable compared to observations in Greeland.

Note: The red band (B4) is too sensitive on the Amery ice shelf and screws the colours in an RGB image. 

The third image is the plume Rox mentioned at 10m resolution.

47
Antarctica / Re: Sea Ice Extent around Antarctica
« on: January 31, 2017, 10:51:38 AM »
/Those figures from Wipneus are intriguing. If extent falls another 10% it will be a new satellite-era low and most contributors seem to expect that will happen. Yet apply a 10% fall to the current area figure and this year would only be in around 15th spot. Another oddity is the 1993 area which is hugely lower than any other year. Any suggestions as to what is/has been going on?

I think in 1993 strong foehn winds moved over the Antarctic Peninsula and reduced the Weddel Sea to rubble. The whole east coast of the Peninsula was ice free. Maybe this was a preconditioning for the Larsen A breakup.

On my website the AWP daily animations show the whole 1992/93 melting season.
https://sites.google.com/site/cryospherecomputing/warming-potential/Albedo-Warming-Overview/1992-3


48
Antarctica / Re: Melt water in Antarctica
« on: January 30, 2017, 12:35:43 AM »
P-maker, thanks for clarifiying these surface types. Could you re-post an image with your interpretation? Like most here this is my first season looking at high resolution images of Antarctica. It's time for us to learn the different melt features and your expert knowledge from being in these enviroments is invaluable. 10m resolution isn't always enough and a top down view makes it even harder to identify the correct surface type.

PS: You list three types a,b and c, but two sentences later you mention four surface types.

49
Antarctica / Re: Melt water in Antarctica
« on: January 29, 2017, 07:20:38 PM »
Tealight,

your image 2 shows wind shadow and scour.  The wind shadow effect occurs where air blowing over an obstruction induces turbulence to leeward which picks up the snow and carries it away leaving the blue ice surface showing.

The same effect occurs where the wind blows around an obstruction and becomes turbulent.

Generally speaking, in satellite images, pale blue is water, dark blue is ice.

Actually melt lakes are dark blue and blue ice is pale. The parts you have labeled melt ponds are just some melt/rain water channels, probably dried out and left light blue ice behind. The big deep blue area has almost the same shade as true melt ponds on the amery ice shelf or the partially melted lake Vida. For a simple wind shadow it is also too finely structured. There has to be some presence of liquid water even if it's not a real melt lake. Perhaps it is some frozen rain that fell on the glacier and the ice free slopes and just accumulated in this area.


50
Arctic sea ice / Re: Albedo-Warming Potential
« on: January 29, 2017, 02:14:24 AM »
This paper on the impact of an ice free Arctic in September got mentioned in the Scribbler comments section. It assumes a worst case of 2040 as the date for an ice-free September, with no deterioration after that, which leads to a 50% cut in the global carbon budget for a 2 degree temperature rise (including overshoot and negative emissions).

http://onlinelibrary.wiley.com/doi/10.1002/2016EF000429/full

I am not a climate scientist, but their assumptions of (i) 2040 as the earliest possible date for an ice-free September; (ii) no worsening due to feedback - e.g. August becoming ice free; and (iii) the heat imbalance assumptions seem to be a tad conservative. If I understand the paper correctly, less conservative assumptions could more than wipe out the carbon budget. Comments from more qualified individuals would be welcome.

I do have training as an economist, and their assumptions of the ability to ramp up a fossil fuel replacement infrastructure with no bottlenecks or delays as the timeframe shrinks and scale increases means that they very significantly underestimate the costs involved. Such "frictionless" models are the standard unfortunately for the Integrated Climate Models.

Any paper that only considers carbon emmisions will fail to predict the current Arctic warming trend. Especially this and last years warming is driven by heat and moisture import from lower latitudes. Combined with low albedo in spring these effects have far more influence than CO2.

Regarding the CO2 emissions scenario projecting a decline by mid-century. This is wishful thinking even if we eliminate all fossil fuel burning. Humans have been emitting CO2 and CH4 for over 8000 years due to agriculture. The increased land use (at least in Australia and America) and intensity of agriculture since the industrial revolution should at least keep the CO2 levels at a constant high level.

I'd suggest this presentation from the American Geophysical Union (AGU) for a more detailed view on past emissions:

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