July 8th 2013
Here's another rehearsal for when I grow up and make good videos with a title roll and background music and everything. By the way, I make a big mistake as I go along. Can you hear what it is?
This update should actually be called 'Bye bye, Beaufort and Chukchi', but it doesn't sound as good. As announced in the previous ASI update the trend lines on various graphs have started to drop precipitously, with thin ice on the fringes (Hudson, Baffin, Kara) disappearing fast.
Despite a slow start unlike any other in recent years, which I described in this recent blog post, 2013 is still hanging in there, slowly leaving the less aggressive melting seasons behind and moving towards the record years of 2007, 2011 and 2012.
The question now is how things will proceed, as the amount of easy-to-melt ice is starting to run out. Even though this year's ice pack consists of a record amount of first-year ice, the weather still plays an important role. The interesting thing about last year's melting season was that decrease rates slowed down somewhat when the weather turned bad in July, but didn't stall, like they did in previous years under similar circumstances.
I think the same will go for this year as well, also because area/extent numbers are quite bit higher, and thus still a lot of melting potential. But there's no telling what could happen if the weather is very conducive to melting/compacting/transport for a week or two, and it looks like we're having some of that up ahead.
Sea ice area (SIA)
July is a month where trend lines on the Cryosphere Today sea ice area graph get divided in the two camps of winners and losers, with 2010 moving from one to the other. Because of steady, substantial drops since the last week of June the 2013 trend line has slowly started to move from one camp to the other.
Here's the graph based on the latest data:
At one point 2013 was trailing 2012 by an incredible 1.1 million km2, but the difference has been reduced to 781K km2. When it comes to century breaks, there have been just as many this melting season as last year's: 32 (with 2010 in third spot with 31 CBs). If 2013 doesn't falter, it could come a bit closer still until the month is done.
Here's the link to my updated CT SIA spreadsheet.
On July 2nd IJIS reported a drop of 208K km2, which is the largest daily drop for July in the 2005-2013 period. Starting the month with 6 century breaks in 7 days, 2013 has finally left that last spot and could very well be in at least 4th position by the end of the month if some of this momentum is maintained. The 9 million km2 mark has also been passed today:
Here's the link to my updated IJIS SIE spreadsheet.
Cryosphere Today area per IJIS extent (CAPIE)
Because extent has dropped just as fast or even slightly faster than area,
CAPIE has been decreasing much slower than in previous years:
Just a reminder of what CAPIE tells us:
When trying to determine how much sea ice extent (SIE) or sea ice area (SIA) the ice pack covers, scientists divide the Arctic up into grid cells. They then look at what the sea ice concentration is within those grid cells. When the concentration is above the 15% threshold, the whole grid cell is counted as 100% ice-covered for SIE. However, for SIA it's the percentage that is counted, which can be anything between 15% and 100%. For both metrics a sea ice concentration below 15% is counted as zero.
This means that SIA will always be lower than SIE, as for instance holes within the ice pack get counted for area, but not for extent (unless they are really big and cover a whole grid cell, or several grid cells). When we divide Cryosphere Today SIA data by IJIS SIE data, we thus get a percentage that tells us something about how much divergence (in other words: holes) there are within the ice pack when the percentage is low, or how much compaction there is when the percentage is high (ie the difference between SIE and SIA is smaller). See this blog post from 2010 to understand how we got to develop this crude metric and have been using it ever since.
At first I was baffled that CAPIE for this year has been so high so far, because the recent persistent cyclone - or PAC-2013 - caused a lot of divergence within the ice pack, showing holes that haven't been witnessed during the satellite era, at least not that early in the melting season. But the answer was rather simple: because of the generally cold conditions this melting season, there has been less melt pond formation.
Now, melt ponds can fool the satellite sensors into thinking there is open water where there isn't, which gets recorded for SIA and not for SIE, causing SIA to drop faster than SIE, and thus CAPIE to go lower as well. This, by the way, is the main reason why scientists prefer SIE over SIA as a measurement, but most of the amateurs here and elsewhere prefer SIA, because melt ponds eventually get drained or frozen over. That leaves the open holes, a more and more common feature of the Arctic sea ice pack, which are better reflected better in SIA data.
A lot of text, but I want to make sure that people understand what CAPIE is:
a crude, but useful tool to determine how compact or not the ice pack is, compared to previous years.
Here's the link to my updated CAPIE spreadsheet.
Regional SIE and SIA
Regional graph of the week, taken from the Regional Graphs page:
Arctic sea ice virtuoso Wipneus has made me a map (based on data by Uni Hamburg, see blog post here) showing the differences that have taken place since the previous ASI update. Red = ice two weeks ago, open water now; blue the other way around:
Now the MASIE product disagrees with me, but I'm under the subjective impression that there is very, very little ice off the east coast of Greenland. I think the Uni Bremen sea ice concentration comparison page for July 7th on the ASIG (Arctic sea ice graphs page) is showing the same. Except for perhaps 2009, no year in the 2006-2013 period has had as much open water in this particular region.
The reason for this is probably two-fold: warm sea surface temperatures (see further below), and either less transport of ice from the Arctic Basin through Fram Strait, or transport of thinner ice that melts out easier. It's difficult to tell what the exact situation is down on the ground, because clouds have been in the way for quite some time now, maybe fooling sensors into thinking there is ice, where there isn't. Last week one could peek just a bit through the clouds and that's when I noticed how dispersed the relatively small amount of ice floes were (image courtesy of Arcticio):
If the - now very blue - fast ice comes loose, SSTs remain high in the region, and transport is low or consists mostly of thin ice, there could be a lot of open water here in August. We'll see what happens.
Sea Level Pressure (SLP)
It's time for yet another animation of Danish Meteorological Institute SLP images for the last two weeks:
With PAC-2013 gone nothing out of the ordinary has been transpiring in the Arctic in the past two weeks. In fact, this is what I referred to as the 'neither fish nor flesh'-setup of atmospheric patterns in my recent blog post comparing this year's patterns with those of previous years, which is actually the set-up that is least conducive to melting/compaction/transport (MCT). It is also reflected in the AO Index, where a negative AO is a sign of high pressure areas dominating the Arctic (usually the best set-up for MCT) and a positive AO is a sign of lows dominating the Arctic (a slightly worse set-up for MCT, except when a Great Arctic Cyclone comes along):
Although the AO Index has been mostly neutral or slightly positive (cyclones dominating) since May 1st, the rate of ice loss has increased in the past week, mostly because of all that melting potential on the fringes coming to fruition. All bad starts come to an end.
And that brings us to the most interesting of all graphs and maps, the 6-day weather forecast by the ECMWF model (click for a larger version):
This is the big one, this is the ideal set-up for large ice loss, this is the rationale behind this update's subtitle (in case anyone was puzzled). It was in the works for a couple of days already, but the forecast needs to be consistent from day-to-day, and now it shows a huge high-pressure area over the Chukchi and Beaufort Seas. Especially the latter region is what separates 2012 and this year (see, again, the Uni Bremen sea ice concentration map for July 7th).
Because of last year's good start to the melting season with lots of clear skies over the Beaufort Sea, there was a lot of melt ponding there that was a prelude to the big crash in June and July. This year the ice was supposed to be thinner than ever, with hardly any multi-year ice to keep things together. I think most of us expected the retreat to be very fast this year, especially after the big cracking event in February and March, but the Arctic is known for doing counterintuitive stuff, and thus the cracking event may actually have let a lot of heat escape that helped make the ice more sturdy. As it stands, the Beaufort region is still almost completely covered with sea ice.
This might now change in the 7-14 days to come. One week at least of maximum insolation seems feasible, as ECMWF has 10 days of 1025-1030 hPa over the Chukchi, Beaufort and Central Arctic regions. The Chukchi looks especially vulnerable to lots of sunlight.
To quote Frank Zappa: Here comes the ice pick in the forehead!
We've almost reached the midline of the bell on the DMI 80N temp graph, but air temperatures north of 80 degrees northern latitude still haven't gone above average (only 2009 looks similar in the last 13 years):
Compared to two and a half weeks ago sea surface temperatures have gone down considerably in the Bering Strait, but up considerably in the Kara and Barentsz Seas. There's some more orange in the Laptev Bite, and a hint of red on the Beaufort coast:
Still looks pretty benign compared to last year.
2013 has started to catch up, and although the easy ice has almost melted out on the fringes, some perfect weather in the coming 7-14 days is probably going to maintain the pace for a while longer. The Chukchi Sea will melt out, there might very well be a total crash in the Beaufort Sea as well, Nares Strait is about to open up, the ice in the Northwest Passage is about to break and melt in situ (just like last year), the Laptev Hole is getting bigger every day and could eventually connect to that huge region of low concentration slush, that extends from the middle of the ice pack all the way to Franz Josef Land.
It looked for a while as if 2013 was out of the running and wouldn't be able to rival last year's record bonanza. That's only logical after such a bad start to the melting season. But this year's upcoming and first streak of weather that is super conducive to melt, compaction and transport might change all that. The next two to three weeks could be incredibly important in determining where this melting season is going to end up and this might teach us more about the million dollar questions:
How far has the shift in the division of power between weather conditions and ice thickness/volume progressed? Is a slow first half of the melting season enough to cause a (temporary) plateau or even a recovery? Or doesn't the ice give a damn?
Next update is in two weeks.