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Author Topic: GAC how long will it last?  (Read 4207 times)

Iceismylife

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GAC how long will it last?
« on: August 20, 2016, 06:46:00 PM »
It is my understanding that what drives a GAC is the available heat in the water vs. the cold in the ice.  This explanation is less than scientific and my apologies for that.

So if the limit is not the availability of heat in the water, then is it the presence of ice on the surface?

Will the cyclone persist until the ice is gone?  Or will it run out of heat in the water first?  What is limiting?

Juan C. García

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Re: GAC how long will it last?
« Reply #1 on: August 20, 2016, 07:06:58 PM »
Seems that one week from now (or less), the low pressures will be much less than the ones that we are going to have in two or three days...

Climate Reanalyzer (Try parameter: Mean Sea Level Pressure)
Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

Volume is harder to measure than extent, but 3-dimensional space is real, 2D's hide ~50% thickness gone.
-> IPCC/NSIDC trends [based on extent] underestimate the real speed of ASI lost.

jdallen

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Re: GAC how long will it last?
« Reply #2 on: August 20, 2016, 08:20:44 PM »
It is my understanding that what drives a GAC is the available heat in the water vs. the cold in the ice.  This explanation is less than scientific and my apologies for that.

So if the limit is not the availability of heat in the water, then is it the presence of ice on the surface?

Will the cyclone persist until the ice is gone?  Or will it run out of heat in the water first?  What is limiting?
The GAC is a different kind of heat engine, as it's a cold core cyclone.  It's not dependent on the ice, as that's not what's driving the "cold end" of the engine.   That's supplied by heat exiting through the top of the atmosphere.

The "Hot" side is the ocean, but I expect (and from what I've seen following various weather tools like climate reanalyzer) that heat is mostly coming in from peripheral seas, rather than from the areas under the cyclone proper.  The 8C+ anomalies in the Barents figure highly here, and if you follow the storm tracks, you can see how that heat is getting fed into the Arctic proper.  The storms run up the eastern seaboard of N. America, through the GIUK gap, and hook  into the Barents.  From there the flow has tended to pick up more energy crossing north from Europe, passing over the Kara and then swinging over Severnaya Zemlya into the Laptev after which it gets picked up in the orbit of existing high latitude lows.

At least, that seems to fit what I've seen.
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Jim Hunt

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Re: GAC how long will it last?
« Reply #3 on: August 21, 2016, 01:13:59 AM »
The 8C+ anomalies in the Barents figure highly here, and if you follow the storm tracks, you can see how that heat is getting fed into the Arctic proper.  The storms run up the eastern seaboard of N. America, through the GIUK gap, and hook  into the Barents.

Check out this GFS animation though.

http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=6&mode=0&heure=18&jour=20&mois=8&annee=2016&archive=1&carte=1

The current cyclone near the CAA seems to head out towards the Barents before swinging back in towards the Laptev newly invigorated.
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abbottisgone

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Re: GAC how long will it last?
« Reply #4 on: August 21, 2016, 05:19:46 AM »
I'm not sure if these answers help, but the question raised- and the further questions it raised- was/were excellent!

http://earthscience.stackexchange.com/questions/241/what-are-the-key-differences-between-warm-and-cold-core-cyclones

 ;)
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Re: GAC how long will it last?
« Reply #5 on: August 21, 2016, 06:26:36 AM »
Animation of ECMWF's latest run for the NH, mslp, 850mb wind & temps and 500mb geopot. What happens in the end (28-30) has been visible in the last few runs.

Iceismylife

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Re: GAC how long will it last?
« Reply #6 on: January 10, 2017, 05:59:17 PM »
I asked the wrong question not how long will it last.  But can we get one in the middle of winter?

Neven

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Re: GAC how long will it last?
« Reply #7 on: January 10, 2017, 07:43:23 PM »
I asked the wrong question not how long will it last.  But can we get one in the middle of winter?

Sure, the biggest storms happen during winter time. Remember, the GAC-2012 was the third largest storm on record (depending on which parameters you use), and I believe the only summer storm in the top 10. Maybe that's changed now because of that huge cyclone we saw past summer.

As for the current forecast: It's 10 days out.
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bbr2314

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Re: GAC how long will it last?
« Reply #8 on: January 10, 2017, 11:19:07 PM »
I asked the wrong question not how long will it last.  But can we get one in the middle of winter?

Sure, the biggest storms happen during winter time. Remember, the GAC-2012 was the third largest storm on record (depending on which parameters you use), and I believe the only summer storm in the top 10. Maybe that's changed now because of that huge cyclone we saw past summer.

As for the current forecast: It's 10 days out.
only 7 days now