Friday, 16 June 2017

A report on Arctic sea ice from Neven

Melting momentum: May 2017



Here's a quick blog post, which is mostly a copy of a comment I just wrote on the 2017 melting season thread on the Arctic Sea Ice Forum. For those who want to know more about what melting momentum means, read these blog posts from 2015 and 2016.
I've been in contact with Dr David Schröder from the University of Reading and he has confirmed (or rather his model) that this year (again) there is less melt pond formation than in years with low minimums. Below is a comparison of 2012, 2013, 2016 and this year:
Melt pond distribution May 2017-small
Caveat: This is a model result, and so the distribution of melt ponds doesn't necessarily reflect reality.
As you can see, according to the model, there are even fewer melt ponds than last year. In fact, it looks very similar to 2013. Dr. Schröder wrote to me in an e-mail:
We predict the September Arctic sea ice extent 2017 to be slightly larger than last year: 5.0 +/- 0.5 mill. km2. In spite of the lowest Arctic ice volume in April, the May melt pond fraction in May is the second lowest of the last 10 years in our simulation with the sea ice model CICE. Anomaly figures with respect to 2006 to 2015 are shown for May 2017, 2016, 2012 (highest pond fraction) and 2013 (lowest pond fraction). Stronger melting and pond formation only occurred north of Canada and some parts of the Beaufort Sea. Otherwise the pond fraction is very similar to May 2013. Below average air temperatures (with respect to 2008 to 2015) and increased snow depth seem to have had a stronger impact in reducing pond formation than the thinner ice in increasing pond formation.
What's nice about this, is that it confirms our suspicions back in February when we discussed what could be the reason there was such a divergence between PIOMAS and CryoSat (as mentioned in the March PIOMAS update). The number one suspect was snow cover, mostly due to the relentless series of storms coming in from the Atlantic. Persisting snow on the ice is the best explanation for the fact that we haven't seen much melt ponding (ice turning blue on satellite images) so far, despite ideal weather conditions during the past two weeks.
PIOMAS vs CryoSat December region 8
As I wrote on the ASIF back in February:
This is pretty big, IMO, as it tells us something about snow depth on the sea ice which may have consequences for the state in which the ice pack enters the melting season.
Maybe we're in the process of getting the answer to that question. The last time there was such a divergence between PIOMAS and CryoSat was during the 2012/2013 winter. Remember, 2013 was cold and cyclonic, causing an unexpected rebound after 2012's spectacle. I don't think this year will be the same, if only for the fact that volume is at a record low because of a record mild winter, but 2017 could be 2016's rebound.
As always, everything depends on weather conditions, but also on sea surface temperatures, as I suspect this was a very important factor last year, causing the September minimum to end up as low as it did, despite a lack of melting momentum.
Back to the sabbatical now (this was too important not to mention).


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