Arctic Sea Ice

Winter analysis addendum

A couple of things were missing from the 2015/2016 winter analysis posted a few days ago, and so I've decided to present them in this separate blog post. Most of these images come from the website of NSIDC research scientist Andrew Slater.

Another way to express how warm or not-cold the Arctic has been this winter, is through so-called freezing degree days. The NSIDC explains it as follows in the All About Sea Ice segment of their website:

The relationship between thermodynamics and sea ice thickness can be thought of most simply in terms of freezing degree days (FDD), which is essentially a measure of how cold it has been for how long. The cumulative FDD is simply daily degrees below freezing summed over the total number of days the temperature was below freezing.

In other words, the sum of the number of days below 0 °C multiplied by the temperature for each day. Edit April 5th: I came up with a better explanation in the comments below. Here's a graph from the +80N 2m Tair page on Dr. Slater's website that shows this year's FDD compared to those of other years:

What can I say? This year's trend line is not only way outside of the percentile zones, it's falling off the chart. This comparison obviously corresponds well with the temperature charts and anomaly distribution maps I used in the 2015/2016 Winter analysis. But let me repeat that this isn't necessarily telling us anything about the coming melting season. As you can see, the blue line representing FDD preceding the 2011 melting season is rather high, but that melting season still managed to equal 2007, record holder at the time. Conversely, the yellow line is low, but the 2014 melting season turned out to be a second rebound year after the 2012 record breaking melting season.

Even though we don't know what will happen this coming melting season, we do know that those anomalously warm/non-cold temperatures have had a marked effect on the ice pack. As mentioned in the 2015/2016 Winter analysis the increase in sea ice volume so far this year is the lowest on record (PIOMAS will probably be updated in the coming week and I'm expecting March increase to be lower than the average of the past decade).

When it comes to sea ice extent and area, Cryosphere Today reported the lowest Arctic sea ice area maximum on record, as did the NSIDC for their Sea Ice Index (extent), and JAXA sea ice extent had the second lowest maximum on record (just 16K more than last year's record). As we can see on the JAXA SIE and CT SIA graphs this year's trend line is still the lowest of all in the 2007-2016 period:

2015/2016 Winter analysis

I think this winter is going to get studied like crazy,
for quite a while. It’s a very interesting time.
        Jennifer Francis, Washington Post

The extraordinary temperature anomalies in the Arctic since the start of the year haven't gone unnoticed in quite a few media outlets, and I apologize for not having joined the fray of actuality. On the other hand, context trumps actuality, as we need to compare to previous years and get a feel for what this prelude to the melting season may mean. In that sense, I'm early with this year's winter analysis (compared to last year).

Let's start studying like crazy, shall we?

It's a lot of text and images, so if you're feeling a bit tl;dr-ish today,
skip to the conclusion at the bottom of the page.

Surface air temperature

Here are the monthly temperature graphs for November-February in the Arctic Circle, from 2005/2006 to the past winter, based on the NCEP reanalysis dataset:

Last November saw the highest average monthly temperature in the 2005-2015 record, followed by a lower December, relatively speaking. Things then get a little bit crazy after the turn of the year, with the January 2014 record getting broken by almost 3 °C! February isn't far behind either, almost 1.5 °C higher than the already 'warm' February of 2014. This is unprecedented.

To see where temps were least low, I've created average temperature maps using the Daily mean composites page from NOAA's Earth Science Research Laboratory website, comparing the 2015/2016 freezing season to those preceding the years with the lowest minimums on record (click for a larger version):

2014/2015 Winter analysis

If you want to know where you're going, it helps to know where you're coming from. This also goes for Arctic sea ice. Even though the long-term trend is down, it's difficult to tell what will happen in any given melting season. Two things can help us get an idea: initial sea ice state and subsequent weather conditions. This post is about how the sea ice has fared throughout the freezing season and what shape it was in last month when sea ice growth slowly came to a grinding halt and winter started to make way for spring.

For that I'm going to compare the 2014/2015 freezing season with those of the preceding three winters, just like I did last year. That way we can see how the past winter compares to the winters preceding the 2012 record smashing melt and the two rebound years following it. If you want to compare some of the images below with other freezing seasons, you can dig through the 2011/2012 and 2012/2013 winter analyses. And click on the images if you want to have a closer look.

Ice age

We kick off with the AARI ice age maps for the end of April that show the amount of multi-year ice (MYI) in the Arctic (brown colour):

Last year's genetically modified rat has been replaced by a woolly mammoth (I'm sorry, I can't help but seeing animals in these maps), but the amount looks about the same. What is interesting this year is that the MYI looks a lot more fragmented on the Pacific side of the Arctic, with some young ice (pink) and even open water in the Chukchi Sea.

This has everything to do with a cracking event that took place a couple of weeks ago. It wasn't as spectacular as the cracking event of February/March 2013, but it was still quite big, and more interestingly, it took place at the very end of the freezing season. We have to wait and see if there's any consequence for the melting in this region. On the one hand there's a lot of first-year ice (FYI) between the MYI floes which could melt out early. On the other hand heat might be released to the atmosphere, cooling the water below the ice, making it more resistant to melting.

Either way, it's visible on different maps, such as the ASCAT radar images. Here's a comparison for day 109 (April 19th):

2013/2014 Winter Analysis

With another interesting freezing season behind us, it's time to compare to previous winters and get an idea of this melting season's foundation. As we have seen in the last two years, the start of the melting season plays an important role, and so it might very well be that the end of the freezing season plays a role as well (what holds for the Arctic summer often is the opposite during winter). If only for the fact that the end of the freezing season is immediately followed by the start of the melting season. Sorry for being so simplistic.

OK, we'll repeat the format from last year and compare the 2013/2014 freezing season with three other freezing seasons. In this case, I have chosen the last three winters (ie preceding the 2011, 2012 and 2013 melting seasons). No 2007? No 2007. I know it's blasphemy, but we have to move on. Click on the images if you want to see a larger version.

Ice age

It's clear that after last year's 'rebound' the Arctic now contains a lot more multi-year ice than in the last 3 years, as can be clearly seen on these AARI ice age maps for the end of April:

2011's vomiting cow doesn't look all that smaller (the brown colour represents the multi-year ice), but this year's genetically modified mouse is still a tad bigger, with a large bulk of multi-year ice taking up position in the Beaufort and even some of the Chukchi Sea. Whether this will prove to be a protective barrier, as witnessed in 2010 and 2011, remains to be seen.

These ASCAT radar images also show that this year the ice pack contains a lot more whiter ice. Here's a comparison for day 109 (April 19th):

2012/2013 Winter Analysis

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.