Mid March 2015 Status

So far the sea ice extent maximum was set on 22 February 2015, however as of 13 March extent is only 0.14M km^2 below, so it is too early to claim a maximum. That noted there are good grounds to suspect that the 22 February maximum may hold. PIOMAS data is covered at the end of the post.




This post uses data to the 13 February 2015 for NSIDC Extent, Wipneus's calculation of extent (hereafter known as Extent) and PIOMAS gridded data for February.

There are 36 years from 1979 to 2014, considering the date of maximum for NSIDC Extent:

• 28 years (78%) had maxima on or before 13 March.
• 8 years (22%) had maxima after 13 March, of which 4 happened in the week following 13 March.
• 7 years (19%) had maxima in February, 1987 and 1996 had joint earliest maximum on 21 February.
• The latest maximum was in 2014, on 31 March.

So from the most simple considerations it seems likely that we have already passed the maximum. However what counts for an individual year are ice and weather conditions.

As previously I have amalgamated sea ice extent data for the Cryosphere Today regions into larger sectors.

• Pacific sector: Okhostk & Bering Seas.
• Alaskan Sector: Beaufort & Chukchi Seas
• Siberian Sector: East Siberian & Laptev Seas
• Atlantic Sector: Kara, Barents, & Greenland Seas
• Central Sector: Central Arctic & Canadian Arctic Archipelago
• Canadian Sector: Baffin Bay, Gulf of St Lawrence, Hudson Bay

The Alaskan, Siberian, and Central Sectors are not factors in determining this years minimum, all three have maximum extent and will not decline until later in the year. So we are left with Pacific, Atlantic, & Canadian. The data for these three sectors are plotted below.

The Pacific Sector has flatlined and has been low all year, the February extent is the lowest since 1979. 

I do not expect this pattern to change during the remainder of March, the PNA remains neutral in the ensemble forecasts (which are well grouped).

The Atlantic Sector has declined from a maximum 2.36M km^2 on 15 February 2015, the decline has been 17%. Most of the decline in the Atlantic sector is due to the Barents Sea, Barents has declined 33% from its maximum on 2 February 2015. It is not unusual for large declines of this nature to occur in late winter and such declines can be followed by increases of a similar magnitude, but any such increase will probably be fighting reductions in the Pacific and Canadian Sectors over the coming weeks.

As can be appreciated from the above plot in terms of the post 2000 period the summer decline starts from around mid April. Considering the 1981 to 2010 average seasonal cycle (NCEP/NCAR anomaly baseline period), it can be seen that the Atlantic plays relatively little role in determining the overall maximum of extent.

It is the peaks in the Pacific and Canadian Sectors that play the dominant role in setting the maximum around March.

From the plot of Sector Extent it can be appreciated that Canadian Extent is still rising. This is totally due to Baffin Bay, Hudson Bay is flatlined at maximum extent, and the Gulf of St Lawrence has risen to a plateau in March, showing little change throughout March. However Baffin Bay is likely near peak extent.

The highest annual maximum extents in Baffin Bay are around 1.8M km^2.

From the behaviour of Post 2000 extents in Baffin Bay I consider it very unlikely that extent can reach 1.8M km^2 over the rest of this month, it seems too late in the season for that to be a realistic prospect. 

In terms of the two datasets the Wipneus dataset and NSIDC Extent differ slightly. This was the reason I gave up processing myself and it is due to a problem with masks. However there is a new version of gridded sea ice data now available which might help to rectify the discrepancies, more about that in due course. That noted, in this instance the agreement is reasonable. The following table shows the date of maximum, maximum extent, extent on 13 February, and drop from maximum to 13 February, for this year (2015). All extents in million km^2.

	Date of Max	Max Extent	Extent on 13  Feb	Drop
Wipneus	22-Feb	14.36	14.22	0.14
NSIDC	22-Feb	14.54	14.40	0.14

0.14M km^2 is an achievable increase considering that the Pacific Sector has shown a slight recent upturn, the Atlantic has levelled, and the Canadian Sector continues to increase. So I am not quite willing to call the maximum at 14.54M km^2 on 22 February 2015, not yet anyway. If the 2015 maximum has been set on 22 February it will be the lowest on record, however weather has played a large role in this, as discussed previously with regards the Pacific Sector.

Now for the PIOMAS February data. 

PIOMAS shows a substantial thickening of ice in Beaufort.

HYCOM and the Drift Age Model both show that this is part of a large export of thicker multi-year ice (MYI) into Beaufort, Chukchi and the East Siberian Sea (ESS). The following week is for early February (Week 5 of 2015).

This intrusion of MYI can be expected to play a strong role in the coming melt season.

Volume is higher than previous years in the Central Arctic region, note that in the above plot the scale for the Central Arctic is four times higher than for the other regions. This localised source of the 2015 volume increase shows up in the difference between February 2015 and February 2013 (immediately after the 2012 record).

Looking at the breakdown of volume attributable to five bands of grid box effective thickness, this year is more similar to 2008 than any of the intervening years. However due to the areal restriction of the thicker ice to the Central Arctic volumes attributable to ice below 2.9m thick remain similar to previous years.

The peak of extent and area will happen shortly, if it has not already happened. However because of continued thickening within the Arctic, where thickness is greatest, the peak of volume will not happen until April.

The volume gain from 2013 and 2014 will largely carry over into 2015's summer season.

The above graph is different from my previous post because this time I have used the twelve months after the 2012 record minimum as a baseline. As happened in 2014 following a peak of the increased volume in late 2014 the volume increase is falling off. Whilst this is in part due to export of ice through the Fram Strait, it is also a result of first year ice thickening thermodynamically (and increasing volume as a result) faster than the thicker ice that survived the previous summer. March and April will show a further reduction in the volume difference because of more vigorous late season thickening in 2012.  

The volume increase from 2013/2014 will largely carry over into 2015, I consider it likely that even if it reduces through spring it will re-emerge in late summer and it virtually removes the possibility of a sea ice free state in Beaufort, Chukchi & the East Siberian Sea by September 2015.