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Jenny E. Ross

Erimaasa,

Did you use the August 9 or August 10 AMSR2 map for calculating your numbers?

Kevin McKinney

Henry, if you truly don't understand why the 'cooling since 2002' meme is deeply wrong, I would be glad to discuss it offline, and that's all I have to say on that topic in this forum.

Jenny E. Ross

Sorry, Erimaassa -- I was so focused on the numbers that I didn't notice the date you put at the beginning!

Kevin McKinney

"...moshpit of gnosticide..."

Delicious phrase about a not-so-delicious reality.

John Christensen

@wayne,

Please note how sea ice area and sea ice extent are defined:

http://arctic-roos.org/observations/satellite-data/sea-ice/ice-area-and-extent-in-arctic

It is possible that SIE numbers are being increasingly overestimated as you mention, but area should not have this problem.

John Christensen

For reasons similar to yours I prefer following the SIA numbers, but scientists tend to prefer extent numbers, I believe due to estimation errors related to melt ponds that impact area numbers more, but not entirely sure.

Neven

Thanks for the off-topic Gish Gallops, Henry, but I'm the janitor of this blog, not the policeman. So have fun at WUWT celebrating the fact that Arctic sea ice records aren't broken every melting season.

I hate blocking people, but I really don't have time for that same-old, same-old.

Espen Olsen

"""It is possible that SIE numbers are being increasingly overestimated as you mention, but area should not have this problem."""

I think so, I have a feeling we have a lot of 15.something % cells all over the Arctic Sea.

wayne

Thanks John,

NSIDC link I gave shows otherwise :


"Area takes the percentages of sea ice within data cells and adds them up to report how much of the Arctic is covered by ice; area typically uses a threshold of 15%"

this explanation may need some refinement.

Doug Lofland

Espen, A-Team did a nice post over on Update 6, but if you look at his favorite microwave channel in Aug 2012 http://www.ijis.iarc.uaf.edu/seaice/data/INDEX/201208/AM2SI20120810IDX_high.png and again this year http://www.ijis.iarc.uaf.edu/seaice/data/INDEX/201308/AM2SI20130811IDX_high.png your 15 something is more than a feeling, I think. This year is so different.

Gerhard Trausner

The Drift !
The full-Text-Version of the Dissertation !
http://ediss.sub.uni-hamburg.de/volltexte/2011/5257/pdf/Dissertation.pdf
--

A fundamental difference from winter storms to summer storms is the deviation of the drift. In winter storms, the ice drift differs by about 5 ° to the right. In summer, it differs by 18 ° to the right.
These are for guidance only. The SST is just only one
Semester and no ST. The SST rather shows us the
Air temperature directly on the water surface.
In August, the sun was casting long shadows.
But because it penetrates under the clouds.
If the reflected short-wave radiation of ice (and water) to the top. Be absorbed by the clouds and scattered than longer waves diffuse. The air and the water take on it. The ice itself can to the rim, which acts rather wedge-shaped, reflect sunlight directly into the water. These are situations that can have very different effects that we only understand when the storm is over and the wind strikes an opposite direction. A not to be underestimated is the effect of salt to raise the water to the small ice floes. Even fresh snow can not prevent a basal melt. and
Deviation of 18 ° to the right makes the ice closer to the coasts., The Laptev Sea and the ESS are very flat. That is, sunken water with a temperature of 4 ° is not very deep down. It mixes quickly back up. But, we'll see what happens.

Gerhard Trausner

...

In recent years we have had not a single "El Nino" year. There were consistently "La Nina".
You can see the SST anomaly at the equator in the eastern-Pacific. This does not mean that the sea has become colder. Only at the surface. It is very difficult to determine the average overall temperature of the sea. The ocean stores a large amount of energy that only comes to the surface again when the salinity of the deeper waters to equalize again in the salinity of the upper water. Then the flow behavior will change. A "ElNino" year can not be predicted. Not yet. A strong and pronounced "El Nino", the large-scale freeze the Bering prevent what a much earlier melting of the Chukchi sea can bring. What does this mean for the thin ice, as you can imagine. At the last "El Nino" was very much thicker the ice. however
even the many years in which we only had "la Nina", the melt of the ice could not prevent.

John Christensen

@wayne,

That is ood. I find this at NSIDC:

http://nsidc.org/cryosphere/seaice/data/terminology.html

"Area
When we use this term, we mean the region covered by sea ice, typically given in square kilometers. For a grid cell, it is the area of the portion of the cell covered by ice. For an entire hemisphere, it is the total area covered by ice, which corresponds to sum of the area of each cell multiplied by the fractional concentration for that cell."

"Extent
Extent defines a region as either "ice-covered" or "not ice-covered." For each data cell, it is a binary term; either the cell has ice (usually a value of "1") or the cell has no ice (usually a value of "0"). A threshold determines this labeling. A typical threshold is 15 percent, meaning that if the data cell has greater than 15 percent ice concentration, the cell is labeled as "ice-covered." The Sea Ice Index products have a threshold of 15 percent. A threshold can also be as high as 30 percent."


Henry1

I thought my account was hacked for a minute. But apparently that is another "Henry".

Allen W. McDonnell

Personally I have always thought the 15% or more standard is a bit odd, I would think 45% is a much more logical place to pick for rounding up or down than 15%!!!

If you went back through all the gridded data for the last 34 years of the satellite record and calculated everything from a 45% standard I bet things would look even worse than they do today. It made some sense early on because a grid area with 15% ice meant a ship passing through had to navigate a little cautiously to avoid risking damage. Today I don't think that is a major concern when so much of the area is down right open water but obviously the major research organizations do not agree with me.

Using the 15% standard the entire Arctic ocean could be a giant slushy with 20% ice per grid point and it would show on the records as 100% ice/extent--area. Then a few days later it could drop 6 % to 14% average and suddenly it would be classified as ice free. This makes no sense to me.

wayne

John, look up:

http://nsidc.org/arcticseaicenews/faq/#area_extent


"What is the difference between sea ice area and extent?"...................


Area takes the percentages of sea ice within data cells and adds them up to report how much of the Arctic is covered by ice; area typically uses a threshold of 15%. So in the same example, with three 25 km x 25 km (16 miles x 16 miles) grid cells of 16% ice, 2% ice, and 90% ice, multiply the grid cell areas that are over the 15% threshold by the percent of sea ice in those grid cells, and add it up. You would have a total area of 662 square km (255.8 square miles).

Blaine

Gerhard:

A fundamental difference from winter storms to summer storms is the deviation of the drift. In winter storms, the ice drift differs by about 5 ° to the right. In summer, it differs by 18 ° to the right.

I presume you mean to say that these are the clockwise deflections of the ice motion from cyclonic. I find this surprising.

The clockwise Coriolis deviation of the drift direction from the forcing wind direction should depend only on the time friction would take to stop the ice, and should be larger for longer times. The ice and entrained water should be deeper in winter, so it should have a larger deviation.

The only good explanation I can think of is that the storms would be larger in winter, which would increase the speed of drift, increase friction, and result in a smaller deviation.

Have you tried comparing the deviation with storms of identical strengths in winter and in summer? Can you see it changing with time, as the ice gets thinner?

Rob Dekker

Blaine,
Coriolis force dictated that the acceleration (in clockwise direction) depends on the speed of the moving ice.

Therefor, it should not be surprising that in summer, when the ice is thinner, the acceleration is large and thus the angle of deflection is also larger.

Rob Dekker

More evidence for decreasing ice thickness as a cause for the increasing difference between ice drift and wind speed in this paper :
http://onlinelibrary.wiley.com/doi/10.1029/2011GL048970/abstract

which explicitly writes :

Between 1992 and 2009, the spatially averaged trend in drift speed within the Arctic Basin is 10.6% ± 0.9%/decade, and ranges between −4% and 16%/decade depending on the location. The mean trend is dominated by the second half of the period. In fact, for the five years after a clear break point in March 2004, the average trend increased to 46% ± 5%/decade. Over the 1992–2009 period, averaged trends of wind speed from four atmospheric reanalyses are only 1% to 2%/decade.

Thus it seems that the drift speed of Arctic sea ice is increasing while wind speed is not increasing significantly. The conclusion reflects that ice thinning is the cause :

... thinning of the ice cover is a more likely cause of the increase in ice drift speed.

which also explains the increased angle of deflection during summer, compared to winter.

John Christensen

@wayne,

Yes, just read the text you inserted, and you should understand.

Area is looking at concentration.
Extent will consider a cell filled, if it passes 15%.
Both area and extent calculations disregard any grid cell with less than 15% ice concentration.

Fairfax Climate Watch

notice that the Navy CICE models hindcasts have been properly adjusted, at least for ice movement ...at least to the extent possible

Blaine

Rob:
Yes, but the momentum is also proportional to the speed, so the angular rate of rotation has the velocity term cancel out. This of course makes sense because the Coriolis force isn't a force at all but the Earth turning and making the velocity appear to turn in its reference frame, and the Earth's rotation speed does not depend on the velocity of the object.

The only terms which actually enter into the calculation of the angle are the ratio of drag to the applied force and the latitude.

John Christensen

@Allen,

For the reasons you stated most institutions calculate both extent and area.

It also gives you meaningful information to compare development in both numbers for any given portion of the Arctic Ocean or seas.

Charles Craver

@Neven,

off-topic Gish Gallops

i like to think of a big bag full of a gish-gallop of bafflegab.

a "gish-gafflebag" if you will.

Gerhard Trausner

Blaine

The 5 ° in winter and 18 degrees in summer
Values ​​at the same strong storms.
This information I have from the dissertation
by Arne Kriegsmann

Gerhard Trausner

Blaine


The link to the dissertation
http://ediss.sub.uni-hamburg.de/volltexte/2011/5257/pdf/Dissertation.pdf

Gerhard Trausner

Blaine

I also agree with you. The Coriolis force is not a force, only an apparent effect.
The deviation from winter to summer can also be caused by the lower ice concentration in summer. Characterized the ice has less resistance to the outside.

Rob Dekker

Blain said

The only terms which actually enter into the calculation of the angle are the ratio of drag to the applied force and the latitude.

I've been trying to reproduce that statement with some simple physics diagrams, but were unable to do so.

In fact, after a few tries, I'm quite puzzled (and thus curious) as to how that angle can be determined from simple physics of ice motion and Coriolis forces due to wind sheer.

Do you have a reference to where you obtained your assertion, or if you based in on physics alone, can you give the calculations you used ?

I like this kind of puzzles.

Robert S

Regarding SIE and SIA, I find the ice concentration graphics in this product : http://ocean.dmi.dk/arctic/icedrift_anim/index.uk.php to be most useful, as a way of visually understanding the development of ice breakdown,impacts of storms, etc. The current lower concentration band through the middle of the ice is interesting, and appeared to be exacerbated by the storm.

Rob Dekker

Gerhard, thanks for the full dissertation to the angle of divergence observations.

I found this in the paper :

Thorndike und Colony (1982) fanden anhand vom Bojenmessungen, bezogen auf den geostrophischen Wind, einen geostrophischen Windfaktor zwischen 0,7 % im Winter und 1,1 % im Sommer und eine im Vergleich zum geostrophischen Wind um 5◦ im Winter und 18◦ im Sommer nach rechts gedrehte Eisdrift.
Sie erkl¨aren die jahreszeitlichen Schwankungen mit verschiedener atmosph¨arischer Stabilit¨at und mit verschiedenen internen Kr¨aften zwischen den Eisschollen.

which suggests that further clarification of the angle of divergence (and the difference between summer and winter) due to wind sheer can be found in Thorndike and Colony (1982).

Artful Dodger

Rob Dekker wrote August 13, 2013 at 07:40

Do you have a reference to where you obtained your assertion, or if you based in on physics alone, can you give the calculations you used ?

Hi Rob,

This classic paper on the topic of Ekman transport introduced the physics nearly 50 years ago:

Hunkins, K. (1966, August). Ekman drift currents in the Arctic Ocean. In Deep Sea Research and Oceanographic Abstracts (Vol. 13, No. 4, pp. 607-620). Elsevier.

Abstract:

Current observations from a drifting ice floe in the central Arctic Ocean give clear evidence of a clockwise spiral structure in the upper layers. The data for steady conditions show a boundary layer just beneath the ice and an Ekman spiral layer below it. The depth of frictional influence is 18 m for winds of 4 m/sec. This is apparently the first detailed confirmation of the Ekman spiral in deep waters.

Hope this helps, and your local resources allow you access to the full paper. If not, there's a reasonably complete description of the math at Wikipedia.

Cheers,
Lodger

Kevin McKinney

Apparently the topic of ice drift is not as simple as one might think:

http://scholar.google.com/scholar?q=ice+drift+law&btnG=&hl=en&as_sdt=80005&sciodt=0%2C11&cites=11421538101964309241&scipsc=

Blaine

Rob: I was doing the calculation myself.

Assume a constant driving acceleration A0 in an x direction along the surface of the earth, a drag acceleration -V/Tau, and Acoriolis = -2 Omega x V, and motion fixed to zero vertically.

Wait for steady state velocity.

Then 0 = Atot = A0 - 2 Omega x V - V / Tau

Take the y component along the surface of the earth, perpendicular to x and set it to zero.

0 = -Vy/Tau - 2 Omega Vx sin Latitude

Vy/Vx = -2 Omega Tau sin Latitude

Clockwise Coriolis Deflection = Arctan (2 Omega Tau sin Latitude)

This assumes that the effect of the ice stress is negligible, which Grehard says is not true in his thesis. The convergence-strain resisting stress of the ice would of course be greatest in winter when the ice is thickest, and Gerhard appears to be saying that this is the reason why the actual deflection differs in the opposite way from what would be predicted by free Coriolis drift. Or at least, I think that's what he means by characterized the ice has less resistance to the outside.

Rob Dekker

Thanks Blaine !
I have only a few minutes today, and assuming your first equation is a 'vector' equation, with x being the outer product, and your second one a scalar equation, I can't find anything wrong with your calculations.

Your calcs seem to suggest that the heavier the object (mass of ice floe) the larger its angle of deflection, given a certain wind shear (force).

That's interesting, and does indeed question why Thorndike and Colony (1982) found that in reality the angle seems to be smaller in winter than in summer.

I hope to have a bit more time tomorrow, to double check your equations, but it seems that you are on to some apparent paradox here.

Good work !

Glenn Tamblyn

So, given what has happened this season, the suggestion from HYCOM of what is happening in the Eastern Arctic, is it going to happen?

will we see a virtually Ice Free Eastern Arctic this year? An Ice Free North Pole.

Or is this some sort of coitus interruptus in potentio.

Aaargghh.....

P-maker

The third Persistent Arctic Cyclone (PAC-C Aug13) died off a couple of days ago. It lasted six days – peaked below 980 hPa - and fulfilled the general criteria suggested earlier ahead of “PAC-B Jul13” (see http://neven1.typepad.com/blog/2013/07/the-naming-of-arctic-cyclones.html ) .

A few questions were raised during this event, e.g. whether this was a real “storm”?.

In Denmark we use the term “snowstorm” when at least 10 cm of snow falls within 6 hours and wind speeds exceed 10 m/s. Similar criteria are used in lowland parts of Sweden and Germany.

New evidence from a recent GRL paper ( http://onlinelibrary.wiley.com/doi/10.1002/grl.50517/pdf ) point to the fact, that even moderate winds (8-12 m/s) have a significant impact on the heat transfer from ocean to ice. Measurements taken north of Svalbard last year on a 0.8 m thick ice floe documented that - during windy conditions (similar to conditions this year during PAC-B & -C) - the heat flux from the ocean increased to near 70 W/m2.

Others have asked about the energy source for this storm. Advection of moist air from much lower latitudes (as alluded to here: http://neven1.typepad.com/blog/2013/07/second-storm.html?cid=6a0133f03a1e37970b01901e9abeaa970b#comment-6a0133f03a1e37970b01901e9abeaa970b ) may be one of the sources, leading to condensation and snow fall over the ice pack. A rough back-of-the-envelope calculation gave a record low (since 1948) SST gradient from the Caribbean to the Barents Sea of roughly 17 K (30-13 deg C) during the storm. The distance is roughly 11,000 km, which means that the average gradient is around 0.0015 K/km. This number happens to be in the same ballpark as the Equator to Pole temperature gradient applied by W. Langford (see the second diagram in slide 25 in his presentation: http://www.fields.utoronto.ca/programs/scientific/10-11/biomathstat/Langford_W.pdf ). It is a disturbing fact that such a low temperature gradient may have led to direct advection of moist air all the way from the Caribbean to the Barents Sea at the same time as the low was churning in the Arctic. If NH single cell configuration and persistent Arctic cyclones is one and the same thing, we may indeed be closer to the tipping point, than we thought.

The lasting impact from this particular cyclone remains to be seen, as the clouds disappear later in the melting season. Recent photos from some of the buoys show up to 15 cm of fresh snow on the remaining ice floes, which may affect both albedo and insulation of the sea ice.

Do I have to mention, that a new deep Arctic cyclone has appeared in the far end of the current weather forecasts…

John Christensen

@P-maker,

Thanks, these are very interesting findings.

Referring to this article, The Summer Cyclone Maximum over the Central Arctic Ocean, Mark C. Serreze and Andrew P. Barrett, 2008, Journal of Climate, which was referenced in the 'On persistent cyclones' thread, I guess you are not saying that Arctic summer cyclones are a new phenomena, but rather that the apparent formation of a NH single cell would further fuel the Arctic cyclones and therefore further enforce these, as the channeling of tropical moisture is enhanced?

If that is the case, it would seem this is a negative feedback, as it appears the cyclones are reducing ice melting (which we will be able to evaluate by the end of the melting season).

P-maker

John

Please have a look at the Barrow Web Cam: http://seaice.alaska.edu/gi/observatories/barrow_webcam and
the Healy Web Cam: http://icefloe.net/Aloftcon_Photos/index.php?album=2013 and
the North Pool Web Cam: http://psc.apl.washington.edu/northpole/NPEO2013/18.jpg and
the Canadian Met Service analysis: http://weather.gc.ca/data/analysis/935_100.gif and
the DMI NE Greenland satellite imagery: http://ocean.dmi.dk/arctic/images/MODIS/NEW/201308141358.jpg and
the ECMWF 240h forecast: http://www.wetterzentrale.de/topkarten/fsecmeur.html

and tell me once more that all of this is the result of a negative feedback.

You’d better put the kettle on for that cup of coffee you promised me a while ago.

My bike is pumped and ready to roll!

Cheers P

John Christensen

@P-maker,

See:
James A. Screen, Ian Simmonds and Kevin Keay, 2011, Journal of Geophysical Research

From the introduction:

The perennial (September) Arctic sea ice cover exhibits large interannual variability, with changes of over a million square kilometers from one year to the next. Here we explore the role of changes in Arctic cyclone activity, and related factors, in driving these pronounced year‐to‐year changes in perennial sea ice cover. Strong relationships are revealed between the September sea ice changes and the number of cyclones in the preceding late spring and early summer. In particular, fewer cyclones over the central Arctic Ocean during the months of May, June, and July appear to favor a low sea ice area at the end of the melt season. Years with large losses of sea ice are characterized by abnormal cyclone distributions and tracks: they lack the normal maximum in cyclone activity over the central Arctic Ocean, and cyclones that track from Eurasia into the central Arctic are largely absent.

- taken from 'On persistent cyclones'.

Late season cyclones will certainly have a different impact on the ice and I do not know what it will look like by the end of the melting season, but it does appear the cyclones have reduced melting this far. Barrow had perhaps some ice in 2008, but has since been ice-free by this time.

That said, I live in Nærum and you are very welcome to come over. Espen is 5km from here, so could join - irrespective of the ice development in the next weeks.

John Christensen

@P-maker,

The Healy is passing the Aleutian Islands right now, so had you expected to see any ice there in August??
And I checked the NP webcam this morning - looks cold up there.

But that is not the point; in data from PIOMAS and CT, it appears that the cold brought by the cyclones has more than outweighted the increase in melting caused by the force of the storms, but again we really need to see what everything looks like by mid/end-Sept to analyze the impact.

Right now the ice is certainly very thin, with huge red areas(on CT), dotted with yellow and green holes in the pack, except in the highest concentration areas right north of CAA and Greenland.

Espen Olsen

John,

She is docked in Barrow at the moment?

http://www.sailwx.info/shiptrack/shipposition.phtml?call=NEPP

John Christensen

Espen,

You are right, I had just checked on marinetraffic.com and had not noticed their last position was from 7/30, thanks.

Will you join for Arctic coffee?

John Christensen

I really don't like ice coffee BTW, so it would be nice and hot - like the Arctic..

Espen Olsen

What coffee?

John Christensen

Sorry; I was going on earlier on the entry for the second cyclone (PAC-2) back in July that the cyclone could cause the melt to slow down, as we saw with PAC-1, and that by the end of August if the cyclones turned out to have a net negative impact on ice, I would offer coffee..

Kris

A fourth one:


Fourth storm on it's way!

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