PIOMAS March 2018

Another month has passed and so here is the updated Arctic sea ice volume graph as calculated by the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) at the Polar Science Center:

During February Arctic sea ice volume increased by 2075 km3, according to the PIOMAS model, which is well below the 2007-2017 average of 2437 km3. Only 2014 and 2016 managed to score lower, at 1930 and 2047 km3 respectively. This means that 2018 has consolidated its second place in the ranking, creeping somewhat closer to 2017. Especially the gap with 2013 has widened spectacularly from 166 to 1261 km3. Closest follower is now 2011 at 817 km3. 

Here's how the differences with previous years have evolved from last month:

Wipneus' version of the PIOMAS graph clearly shows how the 2018 trend line strongly deviates from all the other trend lines during February:

The trend line on the PIOMAS sea ice volume anomaly graph has gone down some more and is now hugging the linear trend line (how romantic!):

As for PIJAMAS average thickness, crudely calculated by dividing PIOMAS numbers with JAXA sea ice extent numbers, the 2018 trend line has crept in second position here as well:

Not quite there yet on the thickness graph from the Polar Science Centre:

Now that we've discussed the monthly numbers, it's time for some interesting stuff, and it has to do with CryoSat-2 observations. Here's a tweet that was tweeted out yesterday by AWI senior scientist Stefan Hendricks:

#CryoSat #SeaIce Feb 2018 thickness and volume update: Extent is at record low, but sea ice volume in Arctic Basin at levels of previous years (6th lowest / 3rd highest). Above average Jan to Feb growth due to ice dynamics? https://t.co/2UQXlZpvUX @esa_cryosat @AWI_Media pic.twitter.com/0GP39Tnxeu

— Stefan Hendricks (@sthendric) March 5, 2018

According to CryoSat February growth was above average, whereas PIOMAS says it was well below average (as stated at the start of this update). So, what's going on here? As the latest NSIDC summary explains, February was very stormy and warm, especially near the end when warm winds swept in via the North Atlantic and caused some unprecedented stuff to happen. In fact, these winds pushed ice back through Fram Strait, as shown on this graph based on PIOMAS data and compiled by Wipneus:

Of course, winds pushing ice back cause compression and ridging, and in theory volume goes up, but that doesn't explain the divergence between PIOMAS and CryoSat. Air temperatures clearly don't either. A more likely culprit, that I've blogged about last year, is snow.

It is known in scientific circles that the sensor on CryoSat-2 has trouble determining the freeboard of sea ice when it is covered by snow. Or to quote from Alfred Wegener Institute scientist Robert Ricker's PHD thesis paper: Recent studies show that the influence of the snow cover is not negligible and can highly affect the CryoSat-2 range measurements. Last year a series of Atlantic storms transported large amounts of heat and moisture into the Arctic, causing PIOMAS and CryoSat to diverge a lot. There has been less of that this year, until February.

My suspicion is that, during last year's melting season, all this snow helped keep the sea ice reflective for a bit longer, slowing down the build-up of melt momentum through melt pond formation, effectively precluding a new record low minimum (there are other factors as well, of course). Whether this event will play a similar role this year, remains to be seen, but it's other side of the warm knife that negatively affected the ice pack this winter.

The second half of the 2015/2016 freezing season was extremely mild, while for the 2016/2017 freezing season it was the other way round. This year seems to be more of an all-rounder, with relatively mild temperatures every winter month, enough to beat last year's record for warmest Oct-Feb, as this tweet by Zack Labe shows (hat-tip to Robertscribbler):

Air temperatures (at 925 hPa) are a record high for the #Arctic freeze season (October - February, >67°N) in this data set

Graphic: https://t.co/kO5ufUWrKq pic.twitter.com/dazYCGqEv8

— Zack Labe (@ZLabe) March 5, 2018

Here are my NCEP reanalysis temperature graphs for February (courtesy of ESRL, Physical Sciences Division). For the Arctic as a whole it was the second highest temperature on record, while individual sectors ranked as follows: Atlantic 2nd, Siberian 4th, Pacific 1st and Canadian 33rd (click for a larger version):

And so, besides all the unknowns, snow seems to be the big wild card again. Whereas the PIOMAS-CryoSat divergence is less pronounced this year, implying there won't be as much snow on the sea ice, it's a different story for the land masses surrounding the Arctic Ocean. Rutgers Global Snow Lab shows the February anomaly is slightly larger than last year, though not as high as in the 2010-2014 period:

At the same time, Northern Hemisphere snow cover seems to be quite extensive, says NOAA's Automated Multisensor Snow/Ice Mapping System:
Moreover, it seems that this snow is quite thick overall, if this snow water equivalent graph from the Canadian Croyspheric Information Network is anything to go by (I'm trying to find out whether the graph is accurate, but haven't received any replies as of yet): 
Depending on weather conditions, it may take longer for all this land snow to melt out, and this in turn may affect weather conditions and temperatures over the ice. ASIB commenter Rob Dekker as well as the late Andrew Slater convincingly theorized there's a correlation between land snow cover and the September minimum.

Snow may very well be what the coming melting season needs to dodge another bullet/cannonball. In the meantime, the forecast is for the Arctic to cool down significantly in the coming week, which also should help a bit, even though it cannot make up for a mild winter and a record low sea ice extent for much of this year so far.

I'll have a post up later this week discussing the sea ice extent maximum which is just around the corner, if it hasn't already turned it. In the meantime, you can follow the latest discussions on the Arctic Sea Ice Forum for the details, and be sure to check out Robertscribbler's latest: 

Delving Further into Uncharted Territory: Arctic Sea Ice Greatly Weakened at Start of Spring 2018.

Comments

[Robert S]

Looks to me like the extent maximum may be in. As you say, Neven, the game now is all about snow cover and melt season dynamics. Going to be interesting.

[Rob Dekker]

Very nice update, Neven, thank you !

Regarding that PIOMAS-CryoSat divergence issue, Your theory makes a lot of sense ; that thick snow cover may fool the Cryosat freeboard measurements into believing there is thicker ice (and thus more volume) than there really. If so, PIOMAS is likely more accurate than Cryosat for years when there is a lot of snow on the ice.

However, just yesterday I read this paper :
http://onlinelibrary.wiley.com/doi/10.1002/2017GL075494/full

They note that is snow load on the ice is so large that the weight of the snow pushes the ice under the water level, then sea water will creep into the snow and form what they call snow-ice. The snow layer does not get thinker after that, since for every kg of snow that falls, an almost equal amount of snow-ice will be formed.

They note that this effect of snow-ice formation occurs with heavy snowfall, and is actually the main reason of ice formation over second-year ice,

If the PIOMAS does not account for that effect (of snow-ice formation under snow), then it may actually be Crysat that is more accurate.

Something to keep in mind.

[Wipneus]

the weight of the snow pushes the ice under the water level

This is actually the normal in the Antarctic (as the paper you linked to mentions), and not so often, perhaps rarely, in the North.

If the PIOMAS does not account for that effect (of snow-ice formation under snow), then it may actually be Crysat that is more accurate.

Assuming that Cryosat under such circumstances has any accuracy left.

I have always suspected that the reason Cryosat never (AFAIK) showed any analysis for the Antarctic was just this fact.

[Neven]

Thanks for that paper, Rob. I didn't know about snow-ice formation, although I have often wondered about what goes on where the snow touches the ice.

[John Christensen]

On snow-ice,

It would appear that DMI's polar portal ( http://polarportal.dk/havis-og-isbjerge/havisens-tykkelse-og-volumen/ ) also does not recognize the snow-ice formation, as February volume growth was low, even with decline towards end of the month.

However, for March with lower temps in the central Arctic basin, DMI's volume measure has gone up again, maybe due to snow-ice turning into a more solid state?

Historically on snow-ice: Even the accounts of the Fram voyage 1893-96 mentions examples of ice being submerged by snow, but also that it was rare and that winters were dominated by high pressure, dry climate, less wind and ice primarily being formed due to pressure ridges and in open lanes.

[Clueless FM]

Eric Holthaus eating some delicious winter max crow today, while pondering whether or not to appear as a guest star on his own ‘Warm Regards’ Green BAU–sponsored climate podcast for the first time in 2018, and, looking back through his archives, for the first time since October 2017. So he’s been on holiday / sick leave for a full five months.

[Neven]

The part about the max crow is funny, because the max is notoriously deceptive and hard to call. You could've left out the rest. Eric Holthaus is a great climate journalist.

[Robert S]

One effect of increased (but still below freezing) Arctic temperatures that I hadn't considered before was the amount of sublimation from snow. A good study of these effects (https://www.igsoc.org/annals/49/a49a050.pdf) shows that there is a significant increase in sublimation rates with increased temperature, as well as with increased wind. These effects will both result in snow mass loss, but also in crystal structure change within the snow, which will interact with the snow ice formation process discussed above. I don't know how much models like PIOMAS take sublimation into account.

[Robert S]

Sorry, the reference should be https://www.igsoc.org/annals/49/a49a050.pdf

[wayne]

Indeed Robert !

How about Gigatonnes??

"Overall, our results show that the 2006–2016 Antarctica average integrated blowing snow sublimation is about 393 ± 196 Gt yr−1, which is considerably larger than previous model-derived estimates. "

"Blowing snow sublimation and transport over Antarctica from 11 years of CALIPSO observations (PDF Download Available). Available from: https://www.researchgate.net/publication/320994814_Blowing_snow_sublimation_and_transport_over_Antarctica_from_11_years_of_CALIPSO_observations [accessed Mar 13 2018]."

Note figure 4 sublimation below -30 C.

"For the same time period, our computed CALIPSO based average blowing snow sublimation is about 50 mm yr−1. This means that on average, over one-third of the snow that falls over Antarctica is lost to sublimation through the blowing snow process. "

In a practical sense the greater the winds the more snow sublimates....

[Robert S]

Makes sense, Wayne. So the variables in the sublimation equation will be temperature, wind speed, and probably snow compaction/cementation (i.e. snow doesn't blow as much because it is cemented). Temperature will have both + and - impacts, since internal sublimation and recrystalization, resulting in more cemented snow layers, will occur faster at higher temperatures up to some temperature. Growing up in Saskatchewan I've certainly seen that effect at work! It'd be interesting to know how this theoretical equation would interact with the expected impacts of global warming in the arctic.

[John Christensen]

Back to Arctic temps:

Interesting to see how the recent SSW event caused a subsequent stabilization of the Arctic vortex with a stable central Arctic high and DMI 80N reaching seasonable levels for the first time in many months:

http://ocean.dmi.dk/arctic/meant80n.uk.php

If my memory serves me right we saw a similar return to stable cold Arctic temps in early 2013 following another significant SSW event.

[wayne]

Correct Robert

As spring progresses top of snow hardens and shines with frozen water vapor from sublimation...

A couple of important events are occurring, I believe a strong La-Nina is in the cards again, Arctic Ocean Atmosphere is finally "drying" out, as we can see with satellite pictures enormous leads spanning great distances.

First Melt, an exotic refraction optical effect occurred on the 14th, repeated on the 20th with quite a showing of persistence, principally meaning the sea ice is very thin :

http://eh2r.blogspot.ca/2018/03/high-arctic-sea-ice-first-melt-2018.html

The earliest date for First Melt in history (2010-2018) could not have come without a much warmer and moist Arctic atmosphere throughout winter, I expand on this clear air moisture topic with an article called:

http://eh2r.blogspot.ca/2018/03/the-case-for-invisible-arctic-clouds.html

[AnotherJourneybyTrain]

Worldview seems to show a fairly shattered Atlantic side and Beaufort Gyre that's already in action.

I say this year is going to be bad!

[John Christensen]

For an early prediction of the coming melt season, I would see 2018 as a continuation of recent relatively low-melt seasons, due to:

1. NH hemisphere continents (Especially Alaska and Siberia) are heating up quickly

2. Significant cold (-25C and lower) area is confined to northern Greenland, CAA, Siberian coastline and the Arctic Ocean:

http://polarportal.dk/en/weather/nbsp/current-weather/

3. We have at least 1000km3 more sea ice within the same area compared to last year due to thicker sea ice cover in the Arctic Ocean:

http://polarportal.dk/en/sea-ice-and-icebergs/sea-ice-thickness-and-volume/

These factors all indicate a high difference between the rising temps on the continents against the cold Arctic Ocean, which tends to increase occurrence of summertime quasi-constant lows over the AO.

[Susan Anderson]

For anyone making predictions based on current events, I'd recommend waiting a couple more weeks for all traces of the recent SSW (Sudden Stratospheric Warming) event to be assimilated into the global system. It has, in my amateur opinion (based on an inadequate sample, which is why scientists are not committing), caused a lot of cold weather in Europe and the US (and possibly elsewhere, I wouldn't have any direct knowledge about that) when it's occured in the past few years. While I know we all know that weather is local and climate about global weather trends over time, it's impossible not to view climate through the lens of local weather. I'm not suggesting we are incapable of objectivity, only that we are human!