The melting season is about to shift one gear higher, and so I thought it'd be useful to have a comprehensive look at this past winter (just like we did last year). As we saw in this recent PIOMAS update, it seems that this year's conditions for ice formation were better over on the Siberian side of the Arctic.
The Beaufort Sea had relatively little multi-year ice flowing in which should make the pack weaker there, as evidenced by the large cracking event of February and March. The image on the top right shows a map of the ice pack, where this year's thickness is compared to last year's (red = thicker, blue = thinner).
I want to look further into this by comparing the 2012/2013 winter with those of previous record years, such as 2006/2007, 2010/2011 and 2011/2012. Click on the images if you want a larger version.
We'll start off with ice age, because that shows us the position of the ice that survived the previous melting season. It doesn't necessarily tell us anything about thickness, but it's safe to presume that older ice is thicker than first-year ice.
Below is a comparison of AARI ice age maps for the end of April. They look upside down, because it's from the perspective of the Russians who produced them. I've decided to include 2008 instead of 2007, because the latter wasn't complete and has a different colour scheme (as you can see here):
The shape of the old ice pack looks similar to that of last year, except that there's no barrier of transported multi-year ice in the Beaufort Sea. That means there's no buffer zone on the Pacific side of the Arctic to slow down melt towards the end of the melting season, as happened in 2010 and 2011. This probably has to do with the fact that the barrier got annihilated during last year's record melting season.
Another source of data that can give us a clue on ice age is the archive for ASCAT radar images. For the cracking event blog post mentioned above, I made an animation that shows ice movement since the start of the year for 2010, 2011, 2012 and 2013.
Here's a comparison for day 109 (April 19th):
Except for the missing buffer zone and visible cracks on the 2013 image, the only thing I'm seeing compared to the three other years is that perhaps the upper half of the ice pack looks slightly brighter with hardly any darker areas, which could mean the ice is a tad thicker over there.
Let's look at what the Maslanik ice age distribution maps have to say, as these were recently updated and published in the NSIDC April report:
Although multi-year ice has the smallest shape since 2008, there's more of the white (4+ years old) and yellow (3-4 years old) stuff, as is demonstrated by this accompanying graph that shows the distribution of ice age by percentage:
One is tempted to say that ice-free conditions, ie total sea ice area below 1 million km2, will be a hard nut to crack. But a new record is a distinct possibility.
Sea level pressure and ice drift
The movement of ice floes is largely determined by wind, and wind is largely determined by sea level pressure gradients. So let's first have a look at SLP maps from NOAA's Earth Science Research Laboratory (daily mean composites page). I have divided the freezing season up into 3 parts with a duration of two months each:
This past winter's SLP patterns look markedly different from those of previous seasons, especially from December to March. We see the central Arctic and Greenland being dominated by high pressure, also clearly visible on this image I used for another post. As the winds in a high pressure system follow the pressure gradient (where the colours change from red to orange for instance) in a clockwise manner, it's immediately clear what pulled the ice apart during the recent cracking event.
In a way this could perhaps also account for the slightly brighter white I alluded to with regards to the ASCAT radar images, because the other thing to keep in mind - besides wind direction - when it comes to high pressure areas, is that they make for cloudless skies. And in winter this means a lot of heat gets radiated outwards, causing lower air temperatures below. It might well be that ice had a chance to thicken more due to lower temperatures. But more on that below.
To have a better idea of ice movement/drift during the past winter I have combined these IFREMER/CERSAT sea ice drift maps to show the recent October-March period:
Not much going on for three months, but then the high pressure hits and a huge Beaufort Gyre starts to move the ice around, with a lot of ice pushed towards Siberia, probably one of the reasons the ice is thicker there than last year. There was also increased export of ice through Fram Strait in March.
Air and sea surface temperatures
The daily mean composites page from NOAA's Earth Science Research Laboratory is also great for getting an idea of what winter temperatures have been like in the Arctic. Here, for instance, are the surface air temperatures of the four freezing seasons, divided into two periods:
The red spot that was concentrated over the Kara Sea last year, has moved over to Baffin Bay this year. It looks somewhat similar to 2010 that saw a very rapid melt-out of the Northwest Passage. The Canadian Archipelago region is cold right now, so break-up isn't as far advanced as 2010 yet. But given events on the west coast of Greenland last year, things don't bode that well for this melting season. Despite neutral temperatures in that region last year, things heated up quite a bit once the melting season got underway.
What's also interesting to note is the anomalous cold over Eurasia and Siberia in the 2013 January-March period, which spawned posts in the Looking for winter weirdness series (parts three and four). But to be honest, I had expected more cold over the Arctic Ocean because of the high level pressure mentioned earlier. A three months' average is relatively long for our purposes, so I've decided to divide it up into the first three months of 2013:
The cold is there in February, but gone again in March. I'm not entirely satisfied about this, but it'll have to do. Lots of cold air over the Kara and Barentsz Sea!
And now for the SSTs:
Like I said last year: I'm not really sure how useful this is, because it would seem to me that satellites can't measure SSTs when the sea is covered by ice. Nevertheless, the lower right image (January-March 2013) is almost an exact copy of the lower left image (January-March 2007). And again, similar to 2010, although during that winter SSTs seem to have been higher. A lot less heat in the Kara/Barentsz region than last year, though, despite a large head start back in October.
I don't place a lot of trust in the ACNFS sea ice thickness model from the Naval Research Laboratory, but it's still a very handy tool. And it's always useful to compare apples with apples, even if you prefer oranges.
We've got three apples now:
According to the model there's less of the thickest ice (red) this year when compared to last year, but the ice has grown thicker over in the Kara Sea. That band of multi-year ice pressed againt Greenland is also a lot narrower this year. If ACNFS is right, there's a higher chance of an ice-free North Pole this year. Depending on the weather, of course.
Chris Reynolds from the Dosbat blog used gridded PIOMAS data and visualized the differences with last year as follows:
According to the PIOMAS model there's never been less ice that's thicker than 2 metres since records began, so it'll be interesting to see how this all plays out.
Well, then. This is basically everything that I can come up with to get an idea of how this start of the melting season compares to previous (record) years. If someone has other useful overview stuff, let me know in a comment, and I'll add it to the post.
My feeling right now is that despite a couple of differences, this melting season looks similar to last year's melting season and so it will probably beat the 2007 records. Whether it will also beat last year's records is too early to tell, as weather is still an important factor. We used to see rebounds in the Arctic whenever a record low was hit (also known as 'recovery! recovery!' on fake skeptic blogs), but I'm not sure how bouncy the Arctic is anymore.
I don't think we'll see sea ice area numbers dive below 1 million km2, even though we have now entered the Maslowski-period. He went out on an educated limb about 7-8 years ago by saying that the Arctic could be ice-free by 2016, ± 3 years. It probably won't happen this year (although nothing should be ruled out in the Arctic), but another big melt could pave the way for more crashes to come. Or something unforeseen happens and gives the ice some respite. Either way, we'll be here to see it.
From this moment on the seasonal watching of the ice begins and I will soon start reporting through the regular ASI updates. Most important thing to look out for in this first stage of the melting season is melt ponds.