The daily ice extent minimums are behind us, and now the story is how fast will be this year’s recovery of ice compared to other years.
First the daily situation at the end of September:
September 30 day 273 results from MASIE. 2015 has overcome 2/3 of 2014 ice extent lead.
Since the annual minimum on day 262, 2015 recovery rate was 60k m2 per day compared to 41k per day in 2014.
2015 ice extent now trails 2014 by 6.1%, which is about 337k km2 difference.
Extent in BCE region is building ice now at 81% of last year. Largest recent increases were in Laptev 43k, Kara 33k, Beaufort 15k, CAA 23k, and most importantly, the Central Arctic is now 220k above its minimum 29 days ago.
The graph shows that a gap opened when 2015 ice dropped at the time of an Arctic cyclone late August. The differential of almost 1M km2 has now been cut to 337k km2. and closing. 2015 ice extent was lower than 5M km2 for only 28 days.
The 30 days of September 2015 are in the books, so we now have the melt season conclusion beyond the daily minimums.
For most of the season, 2015 Arctic sea ice extent was tracking 2014. In fact the July average extent was slightly higher than 2014. Then weather intervened in the last week of August. A large and strong cyclone centered over Chukchi Sea began breaking up ice in the BCE Region and affecting CAA (Canadian Archipelago) and the Central Arctic. In addition, most of the summer the Arctic Oscillation (AO) was in negative phase, meaning fewer clouds, more direct insolation and ice melting. More discussion of these two factors is at the end of this post.
The effects of this storm are seen in the rapid increase in water extent ( 482k km2 in one week) so that August 31 2015 had less ice than did 2014 at minimum September 19. Water extent continued to grow, and then stabilized once the storm abated and the AO went from negative to neutral. Now the ice is growing beyond the daily minimum.
Comparing MASIE and NOAA Ice Extents.
The table shows July 2015 was above 2014 but late August weather caused a drop in monthly averages. The August average shows ice extent dropped ~2.7M km2 from July, compared to a 2014 loss of ~2.0M. That difference persisted until the minimum was reached. NOAA typically reports a lower extent than MASIE, a difference that averaged ~300k km2. Then in one week MASIE dropped while NOAA plateaued, and until recently NOAA September extents were quite close to MASIE, some days showing a higher number.
With the September daily ice starting out lower than 2014 the monthly average ended up smaller. The SIPN median forecasts for September (dated July and August) were 4.8M km2 and NOAA came in a 4.6M.
In any case, I am not alarmed over open water in the Arctic. Steadily increasing and above average September ice extents signify the coming of the next ice age, a genuine threat to human life and prosperity. Fortunately, that is not the indication this year.
Current and Recent Weather in the Arctic
In addition to the storm, the negative AO has been conducive to accelerating ice melting by increased insolation.
September 30 Arctic Oscillation Forecast from AER:
Currently, the AO is neutral but is predicted in the short term to trend positive and peak at moderate to strong positive values this weekend (Figure 2). The positive AO trend is reflective of the below normal geopotential heights dominating the Arctic basin while positive geopotential heights dominate the mid-latitudes, especially the North Atlantic sector. The AO value for this past July and August was the second lowest observed since 1950.
“The positive trend in the AO and the setting sun may have brought an early end to the Arctic sea ice melt season but not before sea ice extent achieved its fourth lowest value since observations began. It is likely that the extremely low AO values observed in July and August are reflective of atmospheric conditions (sunny and warm) that were conducive to rapid sea ice melt.”
The Alaska Dispatch News reported August 27 on the storm effects at Barrow, Alaska:
“The service has issued a coastal flood warning for Barrow until Friday morning, along with a high surf advisory for the western part of the North Slope and a gale warning for much of the Beaufort and Chukchi Seas. Seas up to 14 feet were forecast for Thursday in the Chukchi. . .Thursday’s high waves and flooding are products of a large storm that’s being felt as far as Southcentral Alaska, where high winds are forecast, Metzger said. “It’s a pretty big low-pressure system that’s over the Arctic Ocean,” he said. ”
This storm is reminiscent of the 2012 event that resulted in the lowest ice, greatest water extent this century. The high winds, waves and swells have several effects: Gales push ice floes, opening water between them and pushing them toward warmer waters; Ice pieces are churned and fractured increasing the melt rate; Wave action can flood ice packs or can cause compacting, further reducing extent.