"Smart" and "Stupid" Questions About Antarctica - Feel Free To Ask

[Tor Bejnar]

Thanks, Gerontocrat for getting this response.

There is a discrepancy or mis-statement, however:

(2) a “climate” land mask that does not change and is “conservative” - i.e., anywhere that was land or ice shelf at any time during the period of record (e.g., since 1979) is masked as “land”; this prevents any “artificial” increase (or decrease) in sea ice due to changes in ice shelves.

Per the definition, "land" would include the maximum shelf areas "since 1979", and would grow when shelves grow, but would not shrink when shelves calve.

"Conservative" and "prevents ... increase or decrease" would require taking a mask, say 1979, and sticking to it, come hell (land-forming volcanic eruption or high water (shelf calving).

"Artificial": wouldn't that be the area of an icebreaker takes up?  

[gerontocrat]

Thanks, Gerontocrat for getting this response.

There is a discrepancy or mis-statement, however:

(2) a “climate” land mask that does not change and is “conservative” - i.e., anywhere that was land or ice shelf at any time during the period of record (e.g., since 1979) is masked as “land”; this prevents any “artificial” increase (or decrease) in sea ice due to changes in ice shelves.

Per the definition, "land" would include the maximum shelf areas "since 1979", and would grow when shelves grow, but would not shrink when shelves calve.

"Conservative" and "prevents ... increase or decrease" would require taking a mask, say 1979, and sticking to it, come hell (land-forming volcanic eruption or high water (shelf calving).

"Artificial": wouldn't that be the area of an icebreaker takes up?  

"Conservative" and "prevents ... increase or decrease" would require taking a mask, say 1979, and sticking to it, come hell (land-forming volcanic eruption or high water (shelf calving).

And that is exactly what NSIDC (and probably JAXA / VISHOP) have done for all their published sea ice area and extent data (Arctic & Antarctic) since 1979 . i.e. the mask is unchanged for the 44 years of the satellite record.

[oren]

Of course, they could have updated the "climate mask" and reprocessed the past data.

[Tor Bejnar]

My problem is that the definition of "conservative", as given, identifies a growing mask, not a stable one, even as it then said (contrary to the definition) that it prevented a changing mask.

“conservative” - i.e., anywhere that was land or ice shelf at any time during the period of record (e.g., since 1979) is masked as “land”

In 1979, the mask shows the land and ice shelf boundary: no problem.
In 1980, some shelf's will have expanded, other's calved.  The calving will be ignored but the expansions will be added in, per this definition.

If the definition is accurately given, then the follow-up statement

this prevents any “artificial” increase (or decrease) in sea ice due to changes in ice shelves.

is not true.

I suspect the definition of "conservative" [mask] was not communicated correctly.

[wallen]

 Why does the Winter sea ice extent on one side of Antarctica, never extend as far as the rest. That region incidentally aligns with the West to East width of Australia.

[The Walrus]

Why does the Winter sea ice extent on one side of Antarctica, never extend as far as the rest. That region incidentally aligns with the West to East width of Australia.

That is the result of the Antarctic circumpolar current.  The current flows much closer to the continent on the Australian side than elsewhere, disrupting ice formation.

[Tealight]

Why does the Winter sea ice extent on one side of Antarctica, never extend as far as the rest. That region incidentally aligns with the West to East width of Australia.

Did you mean as far north or distance from the shore? The land in this part of Antarctica goes to around 66S. Other parts of Antarctica only go to 75S-70S. This accounts for 500-1100km distance.

The other part is ocean currents and weather systems keep this section warmer the southern Atlantic and Pacific.

[Sebastian Jones]

Feeling especially 'Stupid' today because I can't find what I thought existed- a general 'Stupid questions' thread.
This thread would be fine, but my question is about Greenland.....
Like many I have been following Gerontocrat's terrific updates about Greenland's Snow Mass Balance (SMB)through the seasons.
From what I understand, Greenland has been experiencing far above average melt thus far this summer. However, its SMB is still positive- it's gained snow (and thus ice) so far this year.
My question is about the DMI chart showing daily and cumulative SMB.
Do these charts show that despite all the melting we see, Greenland is steadily gaining snow mass?
This is what I see. I suppose the corollary question would be: When, given the steadily warming climate, will Greenland start losing mass?

[gerontocrat]

The info I post most days is the current year's Surface Mass Balance (SMB)
So every year the surface of Greenland gains mass.

BUT the icesheet and glaciers flow to the ocean, glaciers calve and are melted by ocean water.

So the overall Greenland Ice Sheet  Mass  is in decline, on average by about 270 GT annually. Currently the increase in SMB is just a reduction to that loss. A few more years of AGW may change annual SMB gains to losses.

EDIT
from http://polarportal.dk/en/greenland/surface-conditions/

PLEASE MAKE SURE TO READ THE TEXT BELOW!

The map illustrates how the surface of the Greenland Ice Sheet gains and loses mass on a daily basis. This difference between snowfall and runoff is known as the SURFACE mass balance It is always positive over the course of a year as not all fallen snow runs off the ice sheet again.

The surface mass balance is NOT identical to the TOTAL mass balance (i.e. overall gain or loss of the ice cap), which also includes the mass that is lost when glaciers calve off icebergs, the melting of glacier tongues as they come into contact with warm seawater and frictional and other effects at the bottom of the ice sheet.

[Sebastian Jones]

Thank you very much for your smart answer to my stupid question, which was indeed stupid in that I confused SNOW and SURFACE.

[Carex]

Is there anyone out there who produces annual or other regular updates to an Antarctic land mask?
The real reason to ask this question is to bring the thread back up to the first page.  With the likelihood of more eyes on the Antarctic this year the dynamic mask question is likely to rise again.  If your are one of these people look back to the last post on page 1 "reply #49".  It seems I ask myself this question a couple times every year.

[oren]

I think the correct answer is a static land mask is good enough in practical terms, as the shelf numbers are much smaller than sea ice numbers.
To be fully accurate, NSIDC should have produced two numbers: area covered by ice shelves and calved icebergs, and area covered by sea ice. The static mask should have been actual land only. Even this would change over time as grounding lines move... no way out of this.

[gerontocrat]

Changing the masks? I hope not

I doubt that NSIDC will only consider it as a last resort, as changin g the mask would also requre a decision as to when from, and reprocessing of much of the historial data record, whcih would give me a major headache.

And as Oren says, it is a minor issue especially as the mask is there because of limitations on the technology on their satellite(s).

ps: NSDIDC assure me that there are plans in place for when their ancient satellites fail - but I am not convinced (nor about the Japanese 2012 satellite for JAXA data)

[Carex]

I ask about availability of updates to the land-ice shelf locations not for sea-ice calculations but as a tool to follow the dynamic nature of ocean-glacier-land interface.  As a tool to help visualize the major local changes that are visible on a continental scale.  Things like the 20+Km growth of the Denman glacial tongue since the worldview mask was drawn, the complete collapse of the ice shelf fed by the Glenzer and Conger Glaciers,  the long history of Denman tongue growth and major calvings, the speed up of glaciers after the calving of the Brunt last autumn. I know there are many regional reports but wouldn't it be nice if there was a visual summary update to all these changes.  I know; if wishes were horses than beggars would ride.