During the melting season I'm writing (bi-)weekly updates on the current situation with regards to Arctic sea ice (ASI). Central to these updates are the daily Cryosphere Today sea ice area (SIA) and IJIS sea ice extent (SIE) numbers, which I compare to data from the 2005-2012 period (NSIDC has a good explanation of sea ice extent and area in their FAQ). I also look at other things like regional sea ice area, compactness, temperature and weather forecasts, anything of particular interest.
June 1st 2014
So far the 2014 melting season has been a bit of a mixed bag. Obviously. There are some similarities with last year's melting season, with air temperatures remaining below average and extent/area decrease not very spectacular either. At the same time we haven't seen a repeat (yet) of the persistent cyclone that kept large parts of the Arctic cold and cloudy around this time last year.
As for me, I'm still completely focused on melt ponds, as May is an extremely important hurdle to take for any melting season that wants to do something memorable. If melt ponds are somehow prevented from forming, like happened last year, the show is as good as over before it has even started. If they do form across the Arctic during May, a celestial computer voice says: You may continue. The melting season can then take a shot at the title, depending on subsequent weather conditions.
I'd like to know how this works exactly. Which regions are most important? What is more important for that initial formation of melt ponds, air temperature or insolation? When exactly does the hurdle end, at the end of May, or do the first two weeks of June count as well?
Nobody knows the (full) answers to these questions. And so we watch.
Sea ice area (SIA)
Sea ice extent (SIE)
The 2014 trend line on the IJIS sea ice extent graph also went down slightly more slowly than the rest, but is still in 4th position:
The monthly average is third lowest after 2006 and 2011.
Here's the link to my IJIS SIE spreadsheet.
Cryosphere Today area per IJIS extent (CAPIE)
It's time we start looking at what the CAPIE graph is doing, as percentages start to drop around this time of year. I repeat last year's explanation of what CAPIE stands for:
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.
CAPIE not only tells us something about the compactness of the ice pack. It can also give us clues about the amount of melt ponds across the pack. Melt ponds can fool the satellite sensors into thinking there is open water where there is none, which gets recorded for SIA and not for SIE, causing SIA to drop faster than SIE, and thus CAPIE to go lower as well.
Right now CAPIE is somewhat higher than the average for the 2005-2014 period, which makes sense as a) SIA is tracking relatively high right now, and b) there probably isn't much melt ponding going on because of low temps (see further below):
Here's the link to my updated CAPIE spreadsheet.
Regional SIE and SIA
Regional graph of the week, taken from the Regional Graphs page on the ASIG:
I briefly mentioned two weeks ago that the ice pack was opening up already in the East Siberian Sea, which was early compared to previous years. By now things had started to open up in other years as well (see here on the Concentration maps page for June 1st), but 2014 is still comfortably in the lead in this region.
The map below, custom-made by Wipneus for this update, shows the changes over the past two weeks. The map is made using University of Hamburg AMSR2 data. Red = ice two weeks ago, open water now; blue the other way around:
One of the reasons for slow SIE/SIA decrease is that a couple of regions on the periphery of the Arctic are slow to melt out for the time being, regions like Hudson Bay, Baffin Bay and the Greenland Sea (see towards the bottom of the the Regional Graphs page).
Sea Level Pressure (SLP)
And now it's time for the two-week animation of Danish Meteorological Institute SLP images that shows us what has happened in the past fortnight:
A short-lived cyclone was replaced by a high-pressure system coming in from the Atlantic, staying put for a few days on the Siberian side of the Arctic, which is the 'wrong' side of the Arctic when it comes to compaction and transport, but does make for clearer skies (although there was quite a bit of fog when I checked LANCE-MODIS satellite images). Towards the end of the animation, however, this high moves over to the American side of the Arctic.
And so it's with piqued curiosity that we look at the weather forecast for the coming 6 days according to the ECMWF model (click for a larger version):
It seems the high is forecasted to stay more or less in position, and even intensify. In fact, high pressure seems to take over the Arctic from all corners, Greenland, the Kara Sea, the East Siberian Sea. I can't say I have seen this often in the past 5 years.
I'm not sure what it'll do for ice transport (for that you need pressure gradients, ie winds, and there won't be much of a low pressure system in coming days), but this basically is an atmospheric set-up that is very conducive to melting, and very conducive to widespread formation of melt ponds. Though not as bad as last year, a relatively cold and cloudy May is now behind us, but maybe the first half of June can still give a boost to melt pond formation (and SIE/SIA decrease) that will keep 2014 in the running for a top 3 position at the end of the melting season.
But for that high(er) temperatures are needed as well.
Temps are relatively low in the Arctic, as can be seen on the NOAA/ESRL 1-day anomaly map:
Also reflected on the DMI 80N temp graph:
However, according to the GFS weather model this is about to change. I've made a short animation, using images from the most excellent and visually stunning ClimateReanalyzer website (produced by the Climate Change Institute at the University of Maine), that shows the forecast for the coming 10 days:
As far as sea surface temperatures are concerned, things have cooled compared to two weeks ago, with not much of a positive anomaly going on in the Atlantic sector, and cool waters on the Pacific side. Last year saw rapid heating in the Barentsz Sea at this time of year:
If it weren't for the recent changes in atmospheric patterns and the current forecast, chances would have already been very slim that this melting season would do something à la 2012, or even 2007/2011. Because the start can potentially break the rest of the melting season. And this year's start has been pretty similar to last year's, though not as cold, cloudy, or cycloney (hey, I just invented a word).
Still, clear skies and higher temps coming to the Arctic right at the very end of the start, do not mean that 2014 will now cruise to record breaking territories either. The Arctic don't work that way. There are a lot of pieces in this puzzle, even though I'm a bit fixated on melt ponds right now. For instance, PIOMAS will update in a couple of days, and should be interesting.
As usual we keep keeping an eye on things, here and on the Forum. Put your sunglasses on.