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 IJIS sea ice extent (SIE) and Cryosphere Today sea ice area (SIA) numbers, which I compare to data from the 2005-2011 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 that can be of particular interest. Check out the Arctic sea ice graphs webpage for daily updated graphs, maps and live webcam images.
June 2nd 2012
It's that time of the year when trend lines on area and extent graphs huddle up for a short while, before entering the period of rapid melt and going their separate ways. Since the last ASI update the 2012 trend line has started to assert itself, albeit more on the CT SIA graph than the IJIS extent graph. The reason for this could be melt ponds, as much of the Arctic is coming out of the recent cold(ish) spell and insolation is on the rise. Or it could have to do with divergence of the ice pack. Or both. And of course, with IJIS switching from AMSR-2 to WindSat some of the changes (bigger resolution, for instance) might influence the SIE decrease, making it differ from previous years, so let's just keep observing the observations and see how that goes.
Sea Ice Extent (SIE)
I've decided to stick with the way I'm making these monthly graphs, because they show more detail than graphs that show the whole year. On this IJIS SIE graph for May we clearly see the trend lines converging (on the June graph I'll post in the next ASI update you'll see them diverge again). In the last two weeks 2012 has moved to the upper part of the pack of trend lines, for the full thing go to IJIS:
I don't use the last data point because it's unrealistically low before revision, but including June 1st, the current difference between 2012 and the other years is as follows:
- 2005: +140K (-44,778)
- 2006: +343K (-43,432)
- 2007: +116K (-41,991)
- 2008: -30K (-45,171)
- 2009: -42K (-53,952)
- 2010: +362K (-67,661)
- 2011: +320K (-51,008)
Between brackets is the average daily SIE decrease for the month of May. 2012's average daily SIE decrease for May turned out to be -47,818 square kilometers.
Sea Ice Area (SIA)
The Cryosphere Today SIA graph is showing a rapidly declining 2012 trend line, vying for the first spot with a couple of other years:
SIA anomaly is back to the 1 million square km we have grown used to:
The current difference between 2012 and the other years is as follows:
- 2005: -375K (-57,201)
- 2006: -77K (-57,710)
- 2007: -210K (-52,215)
- 2008: -65K (-69,311)
- 2009: -537K (-58,211)
- 2010: +33K (-75,263)
- 2011: -118K (-53,210)
Between brackets is the average daily area decrease for the month of May. 2012's average daily area decrease for May turned out to be -74,932 square kilometers.
Regional SIE and SIA
Regional graph of the week:
Looking at the regional graphs page it quickly becomes clear that 2012 has a few trump cards up its sleeve. Total numbers are just as low (SIA) or not far behind (SIE) other years, despite a respectable remnant of ice in the Bering Sea, Hudson Bay not wanting to start melting out for real, and a slight increase in the Greenland Sea due to a recent big low increasing transport through Fram Strait. If the ice in these regions starts going like it ought to, 2012 will probably take the lead on most SIE and SIA graphs.
For this to happen 2012 of course also needs to stay ahead on the Siberian side of the Arctic (check Laptev, Kara and Barentsz). It's also behind in the Canadian Archipelago which isn't as easy to melt out as the regions mentioned above. It was cold there this winter, so the ice in the channels might be slower to give way. On the other hand, a huge polynya formed early in the Beaufort Sea region, where I also expect the ice to be thicker due to a cold winter. The ice over there doesn't look so great on satellite images.
Cryosphere Today area per IJIS extent (CAPIE)
The biggest factor in the CAPIE percentage going down is melt ponds. These melt ponds get counted as open water for area numbers, but are filtered out in extent calculation. If you then divide area numbers by extent numbers you get a percentage that gives you an idea how much melt ponding there is, compared to other years. Later on in the season, when melt ponds start freezing over again, CAPIE is a crude indicator for divergence of the ice pack. When winds make the ice pack expand the water between floes gets counted for area, but again, not always for extent. So a low percentage means the ice pack is diverging.
It's difficult to tell what is causing CAPIE to be relatively low right now. Again, it could be due to melt ponds, as it's warming up in the Arctic. Polynyas opening up left and right could be causing more open water to be counted for area, but not for extent. Or it could be due to the switch from AMSR-E to WindSat.
Either way, it's not so important. Just like the PICT graph it's a thin line of evidence, nothing more, nothing less. If you want to know how the CAPIE graph came into being, you can read the Area vs Extent blog post from 2010, and its follow-up.
Sea Level Pressure
Unfortunately the Danish Meteorological Institute had some technical problems this week, so SLP (and SAT) maps didn't get updated, which made us miss out on the big low pressure area that came in from Siberia, made the ice in the western Kara Sea retreat eastwards, and increase ice transport through Fram Strait. This is how things look right now:
The model ensemble for the AO Index is forecasting a negative AO for the next week or two, which means more high pressure areas (and thus less clouds). That's interesting, because insolation is now really coming into play as one of the dominant factors for the melting season. The only question is where these high pressure systems will develop, and for that we turn to the ECMWF weather forecast. I wasn't really happy about the animation, so I've turned the forecast for the next 6 days into a panel (click for a larger version):
The next couple of days that high over Greenland is moving over the Beaufort Sea and stays there, intensifying to 1035 hPa. In high summer this means only one thing: big extent/area decreases through melting, compaction and ice transport. But it's not high summer yet. Nevertheless I expect something to come off this, for instance that polynya off Bank Islands quickly becoming bigger, with the fast ice in Amundsen Gulf and McClure Strait (western entrance to the Northwest Passage) disintegrating behind it. Looks like that already started.
It's anomalously warm over Siberia, but not so much over the Arctic:
Nevertheless this year's trend line on the DMI 80N temp graph has kept going up fast, reaching the 0 °C line quite a few days earlier than normal:
Edit: as crandles points out in the first comment, this 80N temp graph could be inaccurate. I hadn't thought of it, but it actually makes sense as the warmth doesn't show up on the NOAA ESRL temperature map and DMI obviously is having üproblems with other graphs.
The red on these images can be jittery from one day to the next, but looking at the 30 day animation at DMI gives a good impression of developments.
I ended the last ASI update with "Sunny June is just 10 days away." Well, Sunny June is here, starting off straight away with a big high pressure area over the Beaufort Sea, meaning lots of sun and a clockwise turning Beaufort Gyre, important ingredients in a record recipe. There's still quite a bit of ice on the fringes that was left after the late freeze-up and subsequent cold spell, but 2012 is right down there battling it out with the fastest decreasing years in the 2005-2012 period. If that ice goes in the next two weeks, and things stay the way they are on the Siberian/Atlantic side of the Arctic, 2012 will be taking the lead without hesitating. Quite a feat, considering the rapid decreases of 2010 and 2011. But maybe that's to be expected, eh?
Whatever will be, will be...