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crandles

>"One possibility is that the lower winter ice extents might make it easier for ice to continue growing later in the season. With lower winter extents, a late cold snap or northerly wind could spread ice southward over ocean that would normally be ice-covered at that point."

I don't see any problem with the first sentence. However, with both of 'a late cold snap or northerly wind could spread ice', why doesn't this apply equally to previous years as to recent years?

If there is a trend to warmer weather, does the cold snap explanation actually apply less to recent years than earlier years?

Does the length of ice perimeter matter? Let's start by assuming as likely to get wind from south as from north. Wind from north seems likely to have more spreading effect than a wind from south has compacting effect due to resistance from other ice. So a longer perimeter might cause this to have more effect. If the perimeter wanders to the same extent then the perimeter gets shorter as the ice retreats (seems true at Bering (but not this year though) and Svalbard to NZ but not at Okhotsk)? It is possible that the perimeter wanders more and is typically longer now than previously.

I doubt these explanations have much effect in the direction needed.

My explanation of lower sun angle at more northerly ice edge locations probably also needs some criticism. I fail to see similar criticism of this. However, I wonder if we could attempt to quantify this effect by estimating average distance the ice edge has moved northward and thereby the time before the sun reaches a similar angle. If this only explains a small fraction of the time trend, then we would know we need to look for additional explanations of the trend.

crandles

Recovery rates seem to be declining, though I should also point out 2007 had bigger impact on more recent ice than on oldest ice.

Lines are 2 year averages where possible starting where recovery from 2007 should start ie
2008 - 2010 for 1+ years
2009 - 2011 for 2+ years
2010 - 2012 for 3+ years
2011 - 2012 for 4+ years (only 1 year available)

John Christensen

@crandles; The development towards a steadily younger Arctic icepack seems to be more accelerated than the trend in loss of SIA, and also the reduction in wintertime SIA maximum is declining less than the summer SIA minimum.
It would be very interesting to see how different factors would correlate that also in theory would support why MYI is seemingly being lost faster than summer SIA min and winter SIA max.
One significant factor could be the impact of one or more oscillations that may transport older ice to lower latitudes, causing the inevitable melting of the ice.
Another explanation could be that ocean temperatures are rising more than air temperatures, so that MYI is steadily melting from below, but the area will freeze over again in winter months, as air temperatures are low enough to enable that.
Is this rambling making any sense?

John Christensen

For the late development of winter ice, it also seems that we could blame weather at least for the past three years: In 2009/10 and 2010/11, we had very strong early winter NAO-, which normally has a negative impact on SIA in the Greenland Sea, Barents, and southern part of the Baffin Bay.
Since these events caused lack of sea ice in that area, this helps explaining the extreme high pressure over northwest Siberia this winter, which significantly changed the wind patterns and compressed the sea ice between mid-Jan and early-Feb, after which the SIA increased again unhindered.
And finally, could it be a factor that increased (but still cold) wind during winter time could be a positive factor as it creates temporary gaps in the ice, allowing more ice to be built compared to a solid ice pack, where new ice is built more slowly?

crandles

A Entrance to Safe area.
B Safe Area.
C Fram straight exited.
D At risk of Fram straight exit.
E Beauford exit area that now usually melts rather than completing Beauford gyre in tact.

Look at how small the multiyear entrance zone is compared to the exit zones from the safe or stay put area.

In addition, it seems to have been shown that ice movement is accelerating as the ice gets thinner and therefore weaker.

I should have noted this as a valid reason why winds from north may have more effect on extent in recent years rather than in past.

There could of course also be other reasons for the MYI to be being lost at a faster rate than area.

Neven

Crandles, thanks a lot for stepping in, putting this out, and kicking off the conversation. I've adjusted the title and put in a link and image.

In addition, it seems to have been shown that ice movement is accelerating as the ice gets thinner and therefore weaker.

I should have noted this as a valid reason why winds from north may have more effect on extent in recent years rather than in past.

On the April open thread Arcticio also remarked on this, writing:

The reason for this late maximum seems to be a less packed ice edge. Wind moves the floes easily South and due to low temperatures leads are filled with fresh and thin ice the satellites count as 100% ice coverage. On top this effect is supported by fractured ice at high latitudes shifting the edge even more South.

For people who want to compare the MYI graph with the one from last September, it's in this post.

Simon

crandles wrote:

Look at how small the multiyear entrance zone is compared to the exit zones from the safe or stay put area.

Look, too, at first-year ice extending almost to the pole. Is it fair to say that the Russian arctic is now a seasonal-ice climate? And does this pose a difficulty for the 'grey circle' of no-coverage from various satellites?

Neven

Hi Simon, I wrote about that 'grey circle' (also known as 'pole hole', or 'north hole' as I like to call it) towards the end of the 2010 melting season, when relatively large patches of open water showed up at the pole: North Hole and part 2.

This is how Cryosphere Today handles the hole:

In our area timeseries, we fill in the hole with an average value. The value is obtained by taking the average concentration value over all longitudes for the degree latitude circle surrounding the hole. The size of the hole changes with each sensor/platform, but if the hole is 87 deg. N to the pole, for example, we average all available concentrations in the circle 86 deg. N to 87 deg. N and fill in all points in the hole with that value.

Simon

Thanks. I remembered the question and discussion, but not the answer!

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