Posts
PAC
2013 Redux? Warm Storm Returns to Haunt Central Arctic
(Image source: DMI)
19
July, 2013
Earlier
this week, a moderate-strength Arctic Cyclone formed near Svalbard.
Since that time it has persisted even as it drifted into the Laptev
sea as a 1000 mb low today. Now, according to forecasts, the storm
threatens to remain in the region for at least the next ten days,
deepening to as strong as 980 mb and chewing into a region of sea ice
that has been consistently weakened by storms since late May.
If
you’ve followed this blog and feel you’ve heard this story
before, it’s because you have. PAC#1 formed in late May and churned
through the central sea ice all throughout June, creating anomalous
thinning of a region near the North Pole and on toward the Laptev
sea. By early July, the storm had finally petered out, but not after
leaving behind a wreckage of thinned and broken sea ice.
Now,
it appears a second storm (PAC 2013 #2) is set to churn through the
same regions so drastically impacted by PAC 2013 #1, this time
lasting for at least two weeks.
So
here we go again:
PAC
2013 #2 Over Beaufort Sea as 980 mb low on July 24th.
The
above image shows a strong 980 mb PAC 2013 #2 over the Beaufort Sea
on July 24th. Current model runs show the storm moving back and forth
over the Central Arctic, Beaufort and East Siberian Seas until at
least July 29th.
Warm
Storm Takes Hold
As
sea ice is much thinner and as atmospheric and ocean temperatures are
much warmer, it is likely that a new Persistent Arctic Cyclone will
have even more obvious and far-reaching effects than the one we
witnessed in June. Average surface atmospheric temperatures
throughout the Arctic are above the temperature at which ocean water
freezes and almost all regions show temperatures above 0 degrees
Celsius. So precipitation in these storm events is more and more
likely to fall as rain.
You
can view how much the Arctic has warmed in the composite weather map
below:
Note
the large pulse of 78-86 degree (Fahrenheit) weather (24-30 degree
Celsius) pushing all the way to the Kara Sea near Archangel and
points eastward. Meanwhile, 40-50 degree (Fahrenheit) temperatures
have become common in areas near Svalbard, the extreme north coast of
Greenland, and even during the daytime over some sections of the
Beaufort (not visible in the current shot above). We can also see a
number of wildfires raging in the heatwave stricken region of Arctic
Russia (fire sites on the map are indicated by vertical black lines
with squiggles on top).
With
all this heat in place, wet, rainy precipitation is much more likely
to fall over areas of the Central Arctic underneath the new storm. As
water carries more heat energy than air, a warmer than freezing
rainfall over the ice sheet is a powerful melt enhancer. In addition,
associated winds are likely to further shatter and disassociate ice
beneath it. Eckman pumping forces will also be more likely to access
warmer waters beneath the colder, fresher layer that tends to protect
the ice. This is due to the fact that a constant sunlight has now
streamed through the ice for two and half months running. This long
duration sunlight is likely to create a warmer water layer in a range
of 40-70 feet beneath the surface. A passing storm of moderate to
strong intensity will likely be able to access this warmer layer and
transport it to the surface where it can do work melting ice.
I
took a look at
a worst case warm storm scenario back in June that may provide a
helpful, if extreme, example of these forces at work.
A
somewhat stark example of what a warm storm can do to thin, fragile
sea ice is also now plainly visible via APL’s North Pole Camera #2.
Even since yesterday we can see that melting has rapidly advanced
around the camera as it now rests in a deepening and expanding melt
lake stretching far about in all directions:
Camera
2 now in icy water.
From
this shot, only a small band of remaining snow cover now surrounds
the buoy in the foreground. It also appears that the camera itself is
now sitting in the water. It is worth noting that this melt lake
currently rests on ice that is probably between 1 and 2 meters in
thickness. But the waters now covering the ice are darker, absorbing
more direct and indirect sunlight even as the above-freezing melt
lake slowly bores down into the ice. If the Eckman pumping forces
engaged by this storm are also bringing warmer waters up from the
depths, the ice near this camera is suffering melt from both above
and below.
Though
the current picture shows somewhat sunny weather, conditions near the
camera have been mostly stormy for the past three days. It is likely
that storm conditions will soon return as this region is mostly
engulfed in cloud.
Sea
Ice Measures Near Record Lows
Major
sea ice monitors now show ice area, extent and volume all falling
rapidly. Sea ice extent, according to NSIDC is at about 7.8 million
square kilometers — or 4th lowest on record. Cryosphere Today also
shows sea ice area tied for 4th lowest on record with about 5.5
million square kilometers of sea ice area remaining. Area losses in
this measure have been particularly cliff-like with nearly 400,000
square kilometers lost in just two days. By mid June, PIOMAS showed
sea ice volume running at about 3rd lowest on record with rapid
losses ongoing since late May.
Despite
a slow early May melt, rates of loss have been near record levels
throughout June and July of 2013. Given this break-neck melt pace and
a state of continued fragility throughout the ice pack, risk remains
high that one or more measures will see new record lows come
September. Sea ice is now also very highly dispersed making it even
more vulnerable to melt and disruption. The most recent Crysophere
Today shot shows broad regions where sea ice concentration is now 60%
or less.
With
such broad areas of ice so vulnerable and exposed, any further
thinning, melt and dispersal caused by the re-emergence of a warm
storm is likely have strong impacts with the potential to
dramatically affect final melt totals.
Links:
No comments:
Post a Comment
Note: only a member of this blog may post a comment.