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Messages - Iain

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Arctic sea ice / Re: The 2019/2020 freezing season
« on: September 24, 2019, 08:36:16 AM »
Oe last look at the meltig seaso just past - I've posted a bunch of regional animations over on the test space thread , but here's one of the whole arctic drawn from Terra Modis on NASA worldview

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Arctic sea ice / Re: The 2019 melting season
« on: September 16, 2019, 03:31:20 PM »
Hey folks, sorry I've been away for a bit. Unfortunately, discussing the CAA ice here is necessarily low on my list of obligations. There's been some question about how the current ice regime will interact with the traditional "garlic press" process of the CAA. Short story: there's not much garlic left to press.

The way the garlic press is supposed to work, thick MYI at the southern boundary of the CAB gets forced into the steep channels of the CAA resulting in additional ridging and compaction. Over a number of years, that ice is eventually delivered south into melt-accessible areas. All of this works because the average prevailing wind pattern in the region forces that ice into the archipelago and then south (and, to some extent, southeast). This process is the primary reason why the ice in the CAA has traditionally behaved very differently from fast ice elsewhere (although the channel size and bathymetry of the archipelago would otherwise suggest that CAA ice is comparatively uninteresting fast ice).

This melting season did a lot of damage to these assumptions. Most of the season was spent with an atypical wind pattern that forced ice from the CAA/CAB boundary north against the CAB and west into the Beaufort. Thus, the Crack was born. Additionally, while this wasn't a record-setting year for CAA melt, it was pretty devastating nevertheless. Massey Sound was a killing field for ice. The Peary and Sverdrup Channels have some ice only by dint of latitude. In the Perry Channel, the surviving ice (primarily associated with the Viscount Melville Sound) has been forced by late storms to the southwest into areas that are frequent melt-out traps. The region that has been the temperature "cold core" of the archipelago in historical data wasn't actually very cold; ice in the PGAS is badly fragmented and exceptionally mobile, and even the sheltered ice in Wilkins Strait looks more than a little roughed up.

More importantly, what remains of the MYI -- the tiny, thin line of red on the age maps -- has been displaced north into the CAB, away from the CAA boundary. The Crack has filled as the wind patterns return to their expected directions, but the ice that filled the Crack is not that MYI stopgap, but an assemblage of broken bits transported in from elsewhere, including no small part of relatively young ice from the Lincoln Sea area. This is not robust garlic for the press. It's reasonable -- one hopes -- to assume that wind flow will indeed push ice south into the CAA. But this ice has demonstrated considerable structural weakness. So I expect floe disintegration rather than ridging as the disparate floes are forced together. Winter's cold will mitigate some of this, and the whole mess will freeze into a matrix of FYI (effectively fast) ice.

The overall trend for the Arctic is, of course, hotter with more melt. But as we've seen this year and the past couple, that melt is not always distributed in the same pattern year over year. If we get a year or two where the melt focus turns away from the CAA, and we don't see Crack 2 in 2020, the garlic press will likely crank back up for awhile anyway. Otherwise, within a couple of years, we may very well see what happens when the CAA explores a new modality (as we're already seeing with Bering/Chucki mechanics).

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Greenland and Arctic Circle / Old ice moving through Nares Strait
« on: March 01, 2019, 05:04:30 PM »
Floes entering Nares Strait take between a week and two month (plus?) to go the 500 km to Baffin Bay (when the Strait is open).  The arch around the Lincoln Sea Polynya has been stable for a couple of weeks, basically, so (basically) all the mobile thick ice ("old") in the Lincoln Sea has now flushed into Nares Strait.  The last bits are circled in the image below (DMI image dated 2019-02-27). 

So, will the 'old' ice that recently entered Nares Strait get to Baffin Bay before new 'old' ice enters the Strait?

"Yes" will be correct if the current Lincoln Polynya arch holds on long enough (How long will be enough?) or a bridge forms in the Kennedy Channel above these circled bits of 'old' ice before more recently mobilized thick ice gets to the Strait during March or April 2019 [edit: and no southern bridge forms …].

"No" is split. 
  • Either the Lincoln Polynya arch breaks soon enough so that at least one floe of thick ice (much older than the two-week old ice currently in the polynya) enters Nares S. before the circled bits pass beyond Smith Sound or
  • these circled bits get stuck in Nares Strait for the rest of the winter due to the formation of an ice bridge (arch) downstream (at which point all the ice in Lincoln Sea will be 'old' enough to count as 'old'
"Maybe so" will be correct if a southern bridge holds the circled bits for 50 days or more, but a northern bridge holds back all Lincoln Sea ice until after the southern bridge breaks and all the circled bits flow into Baffin Bay.

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Arctic sea ice / Re: The 2018/2019 freezing season
« on: October 24, 2018, 10:46:15 PM »
NSIDC puts the (at least 15%) ice extent below 2012...

https://nsidc.org/arcticseaicenews/

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Arctic sea ice / Re: The 2018/2019 freezing season
« on: October 24, 2018, 02:08:14 AM »
In the summer, we'd have called such temp anomalies a blow torch and I don't remember a one... Now we have a month long blow torch.  2016 was jaw dropping as it was

Eco-author: surface temperatures in the arctic have an upper limit very near to 0C as long as there is ice to melt.  You can see this in the DMI 80N temperature anomaly charts.  Even though 80N looks at such a small area, it is generally true of the Arctic as a whole.

2018 is joining a group of catastrophic years in the Arctic, 2007, 2012, 2016, although I fear it will be overshadowed by 2019 with this setup.

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Arctic sea ice / Re: The 2018 melting season
« on: July 01, 2018, 11:00:06 PM »
Yearly comparison of HYCOM CICE thickness for July 1st (June 30th on 2017 for the nearest date with data). Click to animate.

The main remarkable feature continues to be the thickness of ice along the Barents sea into the basin proper. The lack of transpolar drift associated with this also appears to be showing up as thicker ice along the Siberian side of the CAB as well. It appears that 2016 shows similar behavior but is less extreme both in terms of where thickness is lost and gained.

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