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Arctic sea ice / Re: When will the Arctic Go Ice Free?
« Last post by wdmn on Today at 07:09:51 AM »
This could be a stupid question...

Has anyone looked at the annual extent data by arctic region, found the lowest year's number, and calculated what the overall extent would be if all of the seas reached that lowest number simultaneously?

I'm not sure it would have any merit as an exercise, but it strikes me that once a sea has reached a minimum we have to accept the possibility of its reoccurring soon. Might give a kind of glimpse into what sort of abrupt declines might be possible...

Also, would have just done this myself, but can't find the relevant regional data.
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The rest / Re: Elections 2020 USA
« Last post by blumenkraft on Today at 07:05:06 AM »
Let's talk about the smartest Republican Senators...

3
Maybe he is sick and tired of the same old shit?

That's ridiculous.

He wants to be the fucking president but can't answer a legit question? He just can't handle the mildest criticism, this is a pattern with him.

He is ready for a retirement home, not a high office. Period!


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Arctic sea ice / Re: 2019 sea ice area and extent data
« Last post by Juan C. García on Today at 05:09:30 AM »
[ADS NIPR VISHOP (JAXA)] Arctic Sea Ice Extent.

December 7th, 2019:
     10,805,648 km2, a century increase of 153,383 km2.
     2019 is now 4th lowest on record.
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Antarctica / Re: PIG has calved
« Last post by baking on Today at 03:37:44 AM »
A quick remark: in recent years, historically unusual for the PIG, all calvings have started from the extension of the central rift extending towards the edges and for the moment we do not see any new central rifts (they will arrive, I know)

Central rifts seem like they are important, but they are only a symptom.  They are usually caused when the downstream ice is moving faster than the upstream ice.  The real question is, why is the ice moving so fast.

There are three things that slow down a glacier: 1) Ice shelves in front of the glacier (whether small ones like the Thwaites Eastern Ice Shelf, or larger ones like the Larsen C or Ross ice shelves,) 2) Grounding on the bottom surface, and 3) friction at the shear margins.

The story with the Pine Island Glacier has always been "It has no ice shelf in front to stabilize it, its grounding line is back from the ice front, BUT THANKFULLY it is longer than it is wide and the friction at the shear margins on the sides of the glacier will keep it from a rapid collapse.

UNFORTUNATELY, as the Pine Island Glacier has begun to speed up, the shear margins have started to rift.  It usually starts upstream and spreads downstream.  Rifting in on the Southern Shear Margin was first observed in 1999 and it is just now reaching the calving front.  What it means is that there are now large parts of the Southern Shear Margin that provide only minimal friction to slow down the glacier.

And recently rifting has been observed upstream on the Northern Shear Margin.  If it continues to spread downstream, the same thing will happen on that side.

In short, there is a positive feedback cycle where an increase in the speed of the glacier leads to thinner and weaker ice which will mean even faster speeds in the future.

This does not go on indefinitely.  There will probably a new equilibrium reached at some point, probably when the calving front reaches they upstream point of the current rifts and is much closer to the grounding line.  Of course what this new equilibrium will look like or what it will mean is pure speculation at this point.  Maybe with better data and models someone will be able to make an educated guess, but the path up until that point seems pretty clear to me based on recent history.
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Consequences / Re: Wildfires
« Last post by Rodius on Today at 02:20:24 AM »
I live in Melbourne, the expectation for this year is we will be going through the same thing. It is so horribly dry and it is not going to be broken within the next three or four months.

Melbourne is not hot yet, thankfully. I am enjoying the cooler weather while it lasts, but when it hits in the coming week or two, it will not go away.
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Arctic sea ice / Re: The 2019/2020 freezing season
« Last post by Aleph_Null on Today at 12:59:16 AM »
Full-size version available, with synchronized comparison {2019, 2018, 2017, 2016}, in the Nullschool Animations thread:
https://forum.arctic-sea-ice.net/index.php/topic,2905.msg239938.html#msg239938

pressure, wind & density over sea ice concentration
November 2019 review.

AMSR2 (U. Bremen sea ice concentration) + MSLP (mean sea level pressure) + IWPD@850hPa (instantaneous wind power density: air density ρ, wind velocity v: ½ρv3) [tiny version]
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The rest / Re: SpaceX
« Last post by vox_mundi on Today at 12:57:15 AM »
SpaceX Working On Fix for Starlink Satellites So They Don’t Disrupt Astronomy
https://spacenews.com/spacex-working-on-fix-for-starlink-satellites-so-they-dont-disrupt-astronomy/

... President and COO Gwynne Shotwell said the Starlink brightness problem caught the company by surprise

... Shotwell said the next batch has one satellite “where we put a coating on the bottom.” She noted that this is just an experiment and could not predict if it will work. “We’re do trial and error to figure out the best way to get this done,” said Shotwell.

Shotwell admitted that nobody in the company anticipated the problem when the satellites were first designed.
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Arctic sea ice / Re: Nullschool Animations
« Last post by Aleph_Null on Today at 12:52:14 AM »
pressure, wind & density over sea ice concentration
November 2019 review, with synchronized comparison {2019, 2018, 2017, 2016}.

AMSR2 (U. Bremen sea ice concentration) + MSLP (mean sea level pressure) + IWPD@850hPa (instantaneous wind power density: air density ρ, wind velocity v: ½ρv3) [full-size versions]
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Antarctica / Re: Thwaites Glacier Discussion
« Last post by baking on December 07, 2019, 11:18:32 PM »
. . . looking forward to an actual Sentinel picture of that area in the next days...

Here is today's Sentinel-1 radar image compared with 12 days ago.  Fairly substantial movement, but nothing "surprising" to anyone who has been following along.
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