Interesting bits from the NSIDC monthly analysis:
Arctic sea ice enters the spring melt season
Arctic sea ice reached its annual maximum extent on March 18, after reaching an initial peak early in the month and declining briefly. Ice extent for the month as a whole was higher than in recent years, but still below average.
As the melt season begins, researchers look at a variety of factors that may contribute to summer ice melt. While the maximum extent occurred slightly later than average, the new ice growth is very thin and likely to melt quickly. Ice age data indicate that despite the higher extent compared to recent years, the winter sea ice continues to be dominated by younger and thinner sea ice.
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Ice cover remained extensive in the Bering Sea, where it has been above average all winter. Ice extent was also higher than average in Baffin Bay, between Greenland and Canada, and the Sea of Okhotsk, north of Russia. These conditions stemmed from a combination of wind patterns and low temperatures. Air temperatures were 6 to 8 degrees Celsius (11 to 14 degrees Fahrenheit) below average over the Bering Sea, Baffin Bay, and parts of the Sea of Okhotsk, at the 925 millibar level (about 3,000 feet above sea level). View a map of Arctic regions.
In the Kara Sea, where ice extent had been below average during January and February, ice extent rebounded to near-average levels in March. Winds that had been pushing the ice cover back shifted, allowing areas of open water in the Kara Sea to freeze over and the ice to spread out. Ice extent in the Barents Sea remained well below normal. In both the Barents and Kara seas, temperatures remained above normal by 4 to 6 degrees Celsius (7 to 11 degrees Fahrenheit).
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Over the past thirty years of satellite data, the day of the maximum has varied by over six weeks, occurring as early as mid-February and as late as the end of March. However, even with so much variability, there is a small trend towards later maximum ice extents. This year’s maximum ice extent continued that trend, occurring 12 days later than average.
It is not clear why the maximum ice extent would happen later, given that in general, ice extent is decreasing. 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. Researchers do not expect the late maximum ice extent to strongly influence summer melt. The ice that grew late this winter is quite thin, and will melt rapidly as the sun rises higher in the sky and the air and water get warmer.
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In the Bering Sea, off Alaska, ice extent reached a record high for the month of March. Persistent winds pushed the sea ice southward and froze more seawater into ice.
As winds from the north pushed Arctic ice southward through the Bering Strait, the ice locked together and formed a structurally continuous band known as an ice arch, which acts a bit like a keystone arch in a building. The ice arch temporarily held back the ice behind it, but as the winds continued, the arch failed along its southern edge, and ice cascaded south through the strait into the Bering Sea. Sea ice also piled up on the northern coast of St. Lawrence Island, streaming southward on either side of it.
Ice age data shows thin ice cover
Ice age data this year show that the ice cover remains much thinner than it was in the past, with a high proportion of first-year ice, which is thin and vulnerable to summer melt. After the record low minimum of 2007 the Arctic lost a significant amount of older, thicker ice, both from melting and from movement of ice out of the Arctic the following winter. In the last few years, the melt and export of old ice was less extreme than in 2007 and 2008, and multiyear ice started to regrow, with second and third-year ice increasing over the last three years.
After the near-record melt last summer, second-year ice declined again, but some of the ice that had survived the previous few summers made it through another year, increasing the proportion of third- and fourth-year ice. However the oldest, thickest ice, more than four years old, continued to decline. Ice older than four years used to make up about a quarter of the winter sea ice cover, but now constitutes only 2%. First-year ice (0 to 1 years old) this year makes up 75% of the total ice cover, the third highest at this time of year in the satellite record. In 2008 the proportion of first-year ice was 79%, and in 2009 it was 76%.
Rapid Arctic warming and mid-latitude weather
The Arctic has warmed about twice as fast as the rest of the Northern Hemisphere in recent decades. Summer Arctic sea ice has declined by 40%, and snow is melting earlier in spring on the surrounding land. This dramatic change in the climate system is expected to affect weather patterns well beyond the confines of the Arctic—but researchers are working to understand exactly how those changes are affecting other regions.
New research by Jennifer Francis of Rutgers University and Steve Vavrus of the University of Wisconsin suggests that warming in the Arctic is causing weather patterns in mid-latitudes to become more persistent. This persistence can lead to conditions like heat waves, cold spells, drought, flooding, and heavy snows. The researchers found that as temperatures in the Arctic warm and become closer to temperatures in lower latitudes, the waves of the jet stream tend to spread out, and west-to-east winds slow down in the upper level of the atmosphere (where storm tracks form). Both of these effects tend to slow the progression of weather patterns, which means that a weather pattern, whether hot or cold, is more likely to stick around.
>"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.
Posted by: crandles | April 05, 2012 at 12:43
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)
Posted by: crandles | April 05, 2012 at 14:49
@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?
Posted by: John Christensen | April 05, 2012 at 16:13
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?
Posted by: John Christensen | April 05, 2012 at 16:36
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.
Posted by: crandles | April 05, 2012 at 16:49
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.
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:
For people who want to compare the MYI graph with the one from last September, it's in this post.
Posted by: Neven | April 05, 2012 at 23:34
crandles wrote:
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?
Posted by: Simon | April 06, 2012 at 13:34
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:
Posted by: Neven | April 06, 2012 at 14:27
Thanks. I remembered the question and discussion, but not the answer!
Posted by: Simon | April 07, 2012 at 17:48