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Author Topic: The Nares Strait thread  (Read 445492 times)

Tor Bejnar

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Re: The Nares Strait thread
« Reply #900 on: January 16, 2017, 03:14:10 PM »
cross-posted... (Thanks A-Team for your high quality presentations!)
Storm analysis should marginally benchmark export through the Nares Strait. The focus usually is on the Fram and Svalbard-FJI front; for this storm, remarkable export out the Bering Strait is also anticipated by Hycom. (That will require clear weather on puffin-feeder imagery or low-res microwave as Sentinel-1AB rarely covers the Chukchi.)

Nares however proves quite astonishing -- the ice is cornering Ellesmere Island with a developing local coastal CAA current with a clear shear line peeling back ice to be exported from essentially stationary Lincoln Sea ice, the process seemingly accelerating in the last few days. DMI provides a daily series of Sentinel-1AB for the mouth of the Nares Strait, so an easily extensible storm monitoring template, so far for 01-14 Jan 17.

There has been clear weather recently and complimentary imagery with precision date stamps from NOAA AVHRR at DMI Lincoln in the full size image inset. These are not mosaics so subtracting UTC times then allows velocities as displacement in km / time between scenes in hours. However image geometry is slightly off co-registration.

The broader sweep along the CAA provided by DTU Saldo Sentinel-1AB mosaics shows the entire ice pack lifting off poleward, rather than garlic-pressing south. This process too seems to have picked up speed in the last 2-3 days. The gray wedges are gaps in mosaic coverage.

http://ocean.dmi.dk/arctic/nord.uk.php Lincoln series

Technical note: These are sub-optimal in contrast space, presented as RGB when in fact 7-bit grayscale (down from the original 16-bit). However they are correctly co-registered despite the land aspect flopping around with satellite viewing angle (being a mix of 1A and 1B). The interval between frames is not strictly 24 hours; timestamps are not provided.

After cropping to forum width, the 14 frames are tiled into 1 which is processed for adaptive contrast in ImageJ in one step and resliced back in gimp and saved with animation time delay of 140 ms. Unlike .mov a .gif  file can readily be downloaded and viewed locally for step-by-step analysis or run at a slower speed.

[Edit: go to the original A-Team post for images.]
« Last Edit: January 17, 2017, 04:07:10 PM by Tor Bejnar »
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Tor Bejnar

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Re: The Nares Strait thread
« Reply #901 on: January 17, 2017, 03:54:31 PM »
Floe breaking up on Hans Island. (Blue highlight should be on the island but isn't.  Purple 'circle' is the island.  (Purple dot is a mistake.)) Image from PolarView on 16-1-2017For scale, the island is 1.3 km2 (0.5 sq mi), 1,290 metres (0.80 mi) long and 1,199 metres (0.745 mi) wide.

« Last Edit: January 17, 2017, 04:04:45 PM by Tor Bejnar »
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bairgon

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Re: The Nares Strait thread
« Reply #902 on: January 18, 2017, 08:35:29 PM »
Floe breaking up on Hans Island.

That has suffered rather a lot in the GAC. Flow of the floes has reversed - compare 17th and 18th Jan pics from http://ocean.dmi.dk/arctic/kennedy.uk.php.

Current state of the floe:


logicmanPatrick

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Re: The Nares Strait thread
« Reply #903 on: January 19, 2017, 10:31:18 PM »
These images from some of my older blog posts may be of interest.

Image 1 shows, in red, locations where an ice bridge has formed in the past.  Please note that the arc often seen in the Lincoln Sea is not a true ice bridge, although it shows some of the same dynamic behaviour.
http://www.science20.com/chatter_box/arctic_tipping_points_4_broken_bridges_nares

Image 2 shows the formation of the Kane Basin ice bridge in February 2011.
http://www.science20.com/chatter_box/arctic_ice_april_2011-78127

This may also be of interest: Bridges that build themselves
http://www.science20.com/chatter_box/bridges_build_themselves
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solartim27

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Re: The Nares Strait thread
« Reply #904 on: January 24, 2017, 05:22:48 PM »
A bridge has formed in Kane, held together from the 21st to 23rd.  Doesn't look very strong to me.
FNORD

Tor Bejnar

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Re: The Nares Strait thread
« Reply #905 on: January 24, 2017, 09:23:08 PM »
Temporary bridge has broken - see today's DMI Kane Basin - Sentinel.  It "looked" good yesterday!  Winds next week, per Windtv, will be intense!
« Last Edit: January 24, 2017, 09:29:12 PM by Tor Bejnar »
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Tor Bejnar

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Re: The Nares Strait thread
« Reply #906 on: January 24, 2017, 09:35:06 PM »
Today starts a new chipping away at what looks like a bridge (but probably isn't) at the top of Nares Strait.
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oren

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Re: The Nares Strait thread
« Reply #907 on: January 24, 2017, 10:18:48 PM »
Thanks for the updates Tor.
This is basically on schedule. Last year the southern bridge first held on January 29th. Interesting if this year's warmer temps will cause a delay due to lower tensile strength of the ice, although the Lincoln Sea ice (being MYI) should be less affected by one season's conditions.

johnm33

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Re: The Nares Strait thread
« Reply #908 on: January 25, 2017, 12:57:34 AM »
With a new moon on saturday it'll be at least 10 days before it settles down again. I'm curious to see just how much the tides break up the Lincoln sea end.

Wipneus

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Re: The Nares Strait thread
« Reply #909 on: January 25, 2017, 06:42:43 PM »
The arch in the Kane basin did not hold. The one on the other side it is still there, it lost a peeling though.

bairgon

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Re: The Nares Strait thread
« Reply #910 on: January 25, 2017, 09:59:55 PM »
But here we go again. The wind is blowing from the SW again, and the peeling is being pushed back. A later picture is below.

Nullschool shows wind up the strait for the next few days. Maybe this time it will build a bridge?

Tor Bejnar

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Re: The Nares Strait thread
« Reply #911 on: January 26, 2017, 04:53:04 PM »
The largest part of the floe that crumbled when hitting Hans Island on the 16th, and then got blown back northwards, is now back beside Hans Island (on the other side of Hans O. and 'upside-down')!  (2nd image from Polar View.)
« Last Edit: January 26, 2017, 07:33:07 PM by Tor Bejnar »
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A-Team

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Re: The Nares Strait thread
« Reply #912 on: January 26, 2017, 06:27:36 PM »
Below are the Sentinel-1AB time series for the Nares for 01-25 Jan 2017. These were made the easy way using the ability of ImageJ to chase down and compile a stack of urls (provided those end in an image tag such as jpg, tif, png etc) ready for stack-level cropping, rotating, and exporting as forum-ready gif.

Nares comes as a 37º diagonal so it is best to rotate CW to make best use of the 700 pixel forum constraint while retaining full resolution. Sentinels benefit from an adaptive contrast improvement (CLAHE command set at 64 pixel boxes at 1.65 slope).

Note a layer of upper arch peeling away in the last two frames.

There is no need to understand anything about ImageJ. Simply acquire and open File --> Import --> Stack from List... and point it at your previously compiled plain text file of urls. These are named and stored systematically (though variantly) at most sites. After competing stack operations, save as 'Animated Gifs...' with looping and an appropriate time delay between frames. Exit ImageJ, file is now ready for upload to the forum (or more reprocessing in gimp).

The DMI Greenland case is shown below; here just the Sentinels were wanted. For just 1A or just 1B use the 11th character in the file name as a sort field.

For Sentinel etc we don't know whether or not there will be an image taken tomorrow or some day next week. However it doesn't matter to ImageJ: if the image isn't available, it simply inserts an all black layer in the stack. Thus a rolling request window solves the auto-updating problem.

Sites like AMSR2, ADS-Jaxa, SMOS,... work very similarly. There are some resources however that don't display the source url or don't allow access to the archive folder hierarchy.

http://ocean.dmi.dk/arctic/kennedy.uk.php entry to DMI database
http://ocean.dmi.dk/arctic/images/MODIS/Kennedy/ where the files are listed

Tabs and sort field need to be removed:

http://ocean.dmi.dk/arctic/images/MODIS/Kennedy/   20170120s01b.ASAR.jpg   b
http://ocean.dmi.dk/arctic/images/MODIS/Kennedy/   20170122s01a.ASAR.jpg   a
http://ocean.dmi.dk/arctic/images/MODIS/Kennedy/   20170122s01b.ASAR.jpg   b
http://ocean.dmi.dk/arctic/images/MODIS/Kennedy/   20170123s01a.ASAR.jpg   a
http://ocean.dmi.dk/arctic/images/MODIS/Kennedy/   20170123s01b.ASAR.jpg   b
http://ocean.dmi.dk/arctic/images/MODIS/Kennedy/   20170124s01a.ASAR.jpg   a
http://ocean.dmi.dk/arctic/images/MODIS/Kennedy/   20170124s01b.ASAR.jpg   b
http://ocean.dmi.dk/arctic/images/MODIS/Kennedy/   20170125s01a.ASAR.jpg   a
http://ocean.dmi.dk/arctic/images/MODIS/Kennedy/   20170125s01b.ASAR.jpg   b
« Last Edit: January 26, 2017, 06:37:48 PM by A-Team »

Wipneus

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Re: The Nares Strait thread
« Reply #913 on: January 30, 2017, 12:44:23 PM »
No, does not hold, go for a bigger arch?

bairgon

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Re: The Nares Strait thread
« Reply #914 on: January 30, 2017, 01:41:57 PM »
It's what is to be expected.

Nullschool shows winds helping the ice along for at least 4 days, so we could see a big area opening up in Lincoln Sea again.

I wonder if it's going to reach through to the line of moving ice across the top of Ellesmere and Greenland?

Wipneus

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Re: The Nares Strait thread
« Reply #915 on: February 02, 2017, 08:29:00 AM »
The arch keeps peeling off, each time leaving a bigger arch.

Adam Ash

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Re: The Nares Strait thread
« Reply #916 on: February 02, 2017, 09:06:25 AM »
To my eye, the 'arch' does not seem to have any structural integrity itself - its not resisting movement of anything towards the straight.

Rather the arch-shaped features seem to be created by a northbound push emanating from Nares Straight.  The loss of portions of the arch seem to be rebound events from a northbound swell or tidal race from the straight, rather than a collapse of a structurally-stressed arch. 

??

oren

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Re: The Nares Strait thread
« Reply #917 on: February 02, 2017, 12:18:23 PM »
To my eye, the 'arch' does not seem to have any structural integrity itself - its not resisting movement of anything towards the straight.

Rather the arch-shaped features seem to be created by a northbound push emanating from Nares Straight.  The loss of portions of the arch seem to be rebound events from a northbound swell or tidal race from the straight, rather than a collapse of a structurally-stressed arch. 

??
The ice seems to be weak indeed. However, I doubt that the push is northbound. The ice beyond the "arch" is stationary, while the ice peeling off is carried towards the strait.

logicmanPatrick

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Re: The Nares Strait thread
« Reply #918 on: February 02, 2017, 12:45:09 PM »
The arc (sic) in the Lincoln Sea is not an ice arch.  It is usual to see a Lincoln Sea polyna.  Less usual is an ice arch just inside the Nares Strait.

Although ice arches normally form by about April, I don't expect to see one form this year: the ice is too thin, weak, young and mobile.
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johnm33

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Re: The Nares Strait thread
« Reply #919 on: February 02, 2017, 12:55:34 PM »
Adam Ash
 "Rather the arch-shaped features seem to be created by a northbound push emanating from Nares Straight.  The loss of portions of the arch seem to be rebound events from a northbound swell or tidal race from the straight, rather than a collapse of a structurally-stressed arch.

??"
The tidal surge north seems to be hugging and undermining the ellesmere side but is inhibited by the opposing wind, the ebb tide however is accelerated. Looks to me like the ellesmere side will collapse in a day or two.

Tigertown

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Re: The Nares Strait thread
« Reply #920 on: February 02, 2017, 02:06:42 PM »
@johnm33
I Agree. 3 meter waves can be seen in the lower part of the Strait, where there is a clearing. Check
here https://earth.nullschool.net/#current/ocean/primary/waves/overlay=significant_wave_height/orthographic=-80.78,76.84,3000/loc=-73.403,76.412

Tor Bejnar

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Re: The Nares Strait thread
« Reply #921 on: February 02, 2017, 05:04:56 PM »
Ice in the upper Nares Strait is certainly moving right along.  Following images are from January 30 and 31 and February 1.  A readily identified floe has a purple dot added.  For scale: Petermann Fjord is 22 km wide (lower left on these screenshots). (Jan. 30 image is the lowest of 3 images; Feb. 1 image is 'on top' - they are mis-labeled - woops.)
« Last Edit: February 02, 2017, 05:11:24 PM by Tor Bejnar »
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ghoti

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Re: The Nares Strait thread
« Reply #922 on: February 02, 2017, 05:46:45 PM »
The consensus of the various ice thickness products seems to suggest the ice in the Lincoln Sea is 4m thick. Looking at the rate of breakup and flow rates south through the Nares makes that seem unlikely.

Can 4m thick ice really shatter so easily and flush out the strait?

DrTskoul

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Re: The Nares Strait thread
« Reply #923 on: February 02, 2017, 06:06:44 PM »
Yes if is chunks of 4 m I've glued by first and second year ice. Strength will be this compromised.
« Last Edit: February 05, 2017, 12:33:19 AM by DrTskoul »
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Re: The Nares Strait thread
« Reply #924 on: February 02, 2017, 07:38:32 PM »
There's a good series of images on polarview from about noon today showing almost the whole strait, this one http://www.polarview.aq/images/106_S1jpgsmall/201702/S1B_IW_GRDH_1SSH_20170202T120025_23E5_N_1.jpg from the southern end has the signature of internal waves caused by the full flood of the ebbing tide.

oren

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Re: The Nares Strait thread
« Reply #925 on: February 05, 2017, 12:27:19 AM »
For the last three days (2/2 - 4/2) the "arch" at the Lincoln Sea seems to be stationary. Will this stability prove to be long-lived? Past experience this month says no, the date says maybe yes.

oren

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Re: The Nares Strait thread
« Reply #926 on: February 05, 2017, 06:55:04 PM »
Candidate Lincoln arch proposed. Sentinel animation from Jan 29 to Feb 5.

DrTskoul

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Re: The Nares Strait thread
« Reply #927 on: February 05, 2017, 07:20:13 PM »
Candidate Lincoln arch proposed. Sentinel animation from Jan 29 to Feb 5.

That's no arch. A melangerie of ice chunks....
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Tor Bejnar

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Re: The Nares Strait thread
« Reply #928 on: February 08, 2017, 05:37:12 PM »
As best I can tell from DMI Sentinel images, there is virtually no Arctic Ocean ice in Nares Strait north of Kane Basin.  Nothing has peeled off of the Lincoln Sea 'bridge' since about February 1.  A floe that broke off on Jan. 30 or 31 is in southern Kane Basin.
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Tor Bejnar

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Re: The Nares Strait thread
« Reply #929 on: February 09, 2017, 04:15:02 AM »
"As best I can tell" (where did I just read that phrase?), comparing the DMI Sentinel images dated 7/2 and 6/2 (both showing part of the Lincoln Sea bridge), there is a tiny amount of movement on the southern (eastern) side of the Sea, but none in the middle part.  This might not be 'real' (only an artifact of the technologies used), but it bears watching.  The 'half-white' floe whose images I once marked with purple dots is about to exit Nares Strait, so about 10 days to go the whole way.
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Tor Bejnar

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Re: The Nares Strait thread
« Reply #930 on: February 09, 2017, 08:46:48 PM »
I'm pretty sure what I see is an artifact and not movement.

I don't think I've seen Nares Strait so free of floes!

This next week will see mostly winds out of the south, according to Windytv.  Next Thursday and Friday shows strong winds.

Will these southerly winds break the week-old arch in the Lincoln Sea?
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johnm33

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Re: The Nares Strait thread
« Reply #931 on: February 09, 2017, 11:23:57 PM »
I'm thinking the Ellesmere side won't last past sunday, after that it depends on the winds which are very changeable.

Tor Bejnar

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Re: The Nares Strait thread
« Reply #932 on: February 10, 2017, 05:43:55 PM »
The identified floe is now in Baffin Bay, as of February 9: 10 days to go 500 km (50 km/day or 0.6 m/s or 1.2 mph)
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Wipneus

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Re: The Nares Strait thread
« Reply #933 on: February 11, 2017, 06:01:37 PM »
Still there.

DrTskoul

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Re: The Nares Strait thread
« Reply #934 on: February 11, 2017, 06:22:55 PM »
Amazing....
“You can know the name of a bird in all the languages of the world, but when you're finished, you'll know absolutely nothing whatever about the bird... So let's look at the bird and see what it's doing -- that's what counts.”
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Tor Bejnar

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Re: The Nares Strait thread
« Reply #935 on: February 11, 2017, 06:52:37 PM »
Windytv forecasts strong southerly winds (> 30 kt) in the Lincoln Sea area most of Monday and on Thursday-Friday.  Those are the next 'make-it-or-break-it' times to watch.
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Tor Bejnar

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Re: The Nares Strait thread
« Reply #936 on: February 12, 2017, 02:05:35 AM »
At first glance it looks like the Lincoln Sea ice arch sloughed some ice, but it didn't happen.  Below are screenshots from Feb. 11 (suggesting the ice movement) and the 10th showing there wasn't any.
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Wipneus

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Re: The Nares Strait thread
« Reply #937 on: February 21, 2017, 08:22:24 AM »
Arch is holding, gets an inner arch from new formed ice.

Shared Humanity

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Re: The Nares Strait thread
« Reply #938 on: February 21, 2017, 03:22:12 PM »
Although that inner arch looks fragile.

Adam Ash

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Re: The Nares Strait thread
« Reply #939 on: February 23, 2017, 06:54:23 AM »
There is no sign of the main arc being pushed into / snuggled up to by the general pack ice at all over these animations.  The main pack is just sitting there.  So the arc is not resisting movement towards Nares, rather the clearer water between Nares and the main arc defining the edge of the pack ice is like a prop wash from Nares which peters out as it expands into the main pack area. 

Tor Bejnar

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Re: The Nares Strait thread
« Reply #940 on: February 28, 2017, 06:51:03 PM »
This DMI image shows the transverse fault [purple arrows] (remember, natural ice is a monomineralic rock) protecting the Lincoln Sea (plus some) ice from the tossed and turned (fractured) Arctic. Sometimes the equivalent fault line is further south, more nearly on the edge of the Lincoln Sea.  (And sometimes all the ice is fractured.)
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Shared Humanity

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Re: The Nares Strait thread
« Reply #941 on: March 01, 2017, 05:54:58 AM »
All of the ice looks like rubble.

bairgon

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Re: The Nares Strait thread
« Reply #942 on: March 01, 2017, 07:27:27 AM »
Although that inner arch looks fragile.

The inner arch has collapsed - see image below from 27/02/2017. This is also visible in Tor's image.

There was some ice to the north-west of the strait which has separated as well. Nullschool shows winds going up the strait for a while on 26/02, but not particularly strong. Very cold. https://earth.nullschool.net/#2017/02/26/1500Z/wind/surface/level/overlay=temp/orthographic=8.93,84.97,3000/loc=-61.715,81.906

Arch is holding, gets an inner arch from new formed ice.

Was there a foehn wind locally? There were winds up the strait from 12th to 17th, much stronger and warmer than the 26th, which seemed to have the effect of forming the inner arch (see message quoted above). Why should the relatively low winds on the 26th break the arch and also cause the ice to separate from the north of the strait?

Image link: http://ocean.dmi.dk/arctic/images/MODIS/Kennedy/20170227s01a.ASAR.jpg. See http://ocean.dmi.dk/arctic/kennedy.uk.php to browse images.




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Re: The Nares Strait thread
« Reply #943 on: March 01, 2017, 08:01:29 AM »
@bairgon
 There have been these terrible storms SE of Greenland that have made giant waves locally and stirred up smaller ones at greater distances. Add to that  the area where Baffin and Nares meet being susceptible to wave activity, it is not unreasonable to think that upwelling warmer water has eroded away at this arch area for a while now. But beyond that it seems that the ice is really breaking down all over the Arctic right now without any one outstanding event to blame.

johnm33

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Re: The Nares Strait thread
« Reply #944 on: March 01, 2017, 11:47:03 AM »
" Why should the relatively low winds on the 26th break the arch and also cause the ice to separate from the north of the strait?" Tides force a current north on the west/south side of the strait, these undermine the fast ice on the arctic coast of Ellesmere. When the tide turns a surge of water tends to flow down the Greenland side, the size of the new ice 'crescents' breaking off indicate the interuptions to the overwhelmingly southern flow. Given some of the powerful winds going up or down the strait, i'm a little surprised that the big arch has held out.

charles_oil

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Re: The Nares Strait thread
« Reply #945 on: March 01, 2017, 01:44:41 PM »
I could not help but think of the flimsy looking arch at Nares when I saw this one !  Amazingly its got greenery sprouting so has lasted a while.

DrTskoul

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Re: The Nares Strait thread
« Reply #946 on: March 01, 2017, 01:54:03 PM »
I could not help but think of the flimsy looking arch at Nares when I saw this one !  Amazingly its got greenery sprouting so has lasted a while.

While everything around it crumbled !!
“You can know the name of a bird in all the languages of the world, but when you're finished, you'll know absolutely nothing whatever about the bird... So let's look at the bird and see what it's doing -- that's what counts.”
― Richard P. Feynman

bairgon

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crandles

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Re: The Nares Strait thread
« Reply #948 on: March 05, 2017, 07:28:41 PM »
Not visible on Kennedy at dmi yet - http://ocean.dmi.dk/arctic/kennedy.uk.php

Looks visible on NOAA 14:45 5 Mar to me