Arctic Sea Ice

Hole

I just saw that Anthony Watts couldn't restrain himself and has posted one more instalment in his series of predictions for the Arctic that have supposedly failed to come about. I know there's no use in telling him that the IPCC projects the Arctic to become ice-free somehwere between 2080 and 2100, or that for instance Wieslaw Maslowski revised his projection for an ice-free Arctic to 2016 ± 3 years after receiving constructive criticism from his peers, because Watts will simply always prefer smear over truth. But this latest thing he just posted is interesting.

As a reaction to the overblown story of the North Pool - when a couple of weeks ago NPEO's North Pole Webcam showed a large melt pond right in front of the webcam - Watts has a couple of quotes from 2000 by Al Gore etc. about large expanses of water at or near the North Pole. His timing couldn't be better, because in the past week a very large expanse of water has been opening up, not too far from the North Pole. We saw some of that in 2010 (see North Hole blog post), but this event looks like it's going to be even bigger and widespread.

It has finally started to show up on several sea ice concentration maps:

Many commenters here and on the Forum have been keeping an eye on this ever since that persistent cyclone in May and June started churning up the ice pack in an anti-clockwise fashion. Due to this melting season's almost constant cloudiness and the back and forth shifting of ice floes, it was difficult to see what exactly was going on down there. But now that the zones of low-concentration sea ice in the interior of the ice pack are getting one last beating of warm winds (and who knows what is happening below the ice) things can't remain under cover.

The hole near the North Pole is most outspoken, but how about the North Pole itself? Are we going to see another North Hole? Here are a couple of images showing the current situation, when the many clouds allow a view of what goes on below.

Peeking through the clouds

When low-pressure areas take over the Arctic, they do two things: make the ice pack diverge and increase cloudiness. The diverging of the pack is hidden by the clouds, but we can sometimes see the holes in the ice pack through holes in the cloud cover on the LANCE-MODIS satellite images. We saw some early examples of that this year, ever since lows started to invade the central Arctic (for instance here and here), but it was and remained difficult to get an idea of the extent of holes in the ice pack. Until commenter Dr Tskoul came up with this tip:
MODIS Composites by Environment Canada.

Every Wednesday EC releases a 7 day MODIS satellite composite image, compiled to create a mosaic image of the Arctic Basin. They make a True-Colour Composite image as well as a False-Colour Composite image. I find the latter particularly interesting because it shows the holes best, as it highlights colour differences between sea ice and cloud. As a result, sea ice and snow appear light blue and clouds appear white (and purple over water).

This is the latest composite image (found in this directory):

North Hole 2

I've made a blink comparison animation of today's combined MODIS satellite image (day 250) and that of the first combined image from the first North Hole post (day 247):

By concentrating on some of the larger floes you can easily discern the southward transport. If we then look at what is north of the North Hole (which almost sounds like a Hitchcock movie), we can see that the maximum of open area showing sea water instead of ice is expected to occur tomorrow or the day after. Here it is:

If the ice continues to be transported southwards of course, but I expect it will for at least another day or two.

North Hole

This is a blog post in progress. I'm calling on all you commenters to think along, advise and correct wherever necessary.

I vaguely remembered a short discussion about discrepancies between various area and extent datasets in the comment section of SIE update 21 (perhaps somewhere else too). One of the possible causes mentioned was what I have just started referring to as the North Hole, also called the 'pole hole' by NSIDC:

Note that unlike ice extent, the Arctic values for ice area do not include the area near the pole not imaged by the sensor, called the pole hole. This area is (...) 0.31 million square kilometers for SSM/I (from July 1987 to present).

IJIS also makes mention of this on their extent page:

The black dot seen at the North Pole is an area lacking data where AMSR-E cannot observe the Earth’s surface due to the limit of its observational coverage (i.e., orbit inclination of 98deg. and swath width of 1600km). Please note that this area is also counted as sea-ice cover in our estimation of sea-ice extent. We may change the policy (i.e., filling the gap with full coverage of sea ice) in the near future due to the recent drastic reduction of Arctic sea ice. We will announce this if it is implemented.

The black dot is also visible on the sea ice concentration map from Cryosphere Today at the top of the post. In previous years the ice there was practically 100% throughout the summer melt, but this year is different. Large swathes of low concentration ice have recently started to appear under the North Hole, like I noticed when commenting on the latest Race to Fram Strait animation. This could be important, because it means that for instance NSIDC area and IJIS extent are actually lower than reported (I haven't found any info yet on how other agencies, such as DMI, Arctic Roos or Uni Bremen handle the North Hole). But how much lower? That's what the 'in progress' is all about (check out the update below). Let me explain what I did so far.

One of the lessons from Patrick Lockerby's MODIS Rapidfire for Citizen Scientists-series I remembered, is that the North Pole can easily be found on the MODIS Arctic Mosaic because it's in the middle of the four quadrants on row 3 and 4, column 3 and 4.

So I decided to download these 4 quadrants from day 247 (September 4th) and combine them in one large image. So far, so good. But how to determine how big the North Hole is in that image? If I really wanted to get to the bottom of this, it was inevitable I did some calculating. Oh my, not my speciality. Bear with me, please.

As we've seen, the North Hole covers 310,000 square km according to NSIDC. If I've understood correctly each pixel in the MODIS images I downloaded is 1 square km. In other words, the total area of the North Hole circle is 310,000 pixels. The formula for the area enclosed by a circle is A = π r², so 310,000 = π r² (r being the radius of the circle). Moving π to the other side makes 310,000/π = 100,000 = r² (that's not entirely correct, but I'm not a scientist, so I can round off any way I like). The square root of 100,000 is 316, so the radius is 316. Multiplied by 2 I now have the diameter of my circle, which enables me to set the Fixed Size of my Elliptical Marquee Tool in Photoshop to a width and height of 632 pixels.

Here's what the result looks like: