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Messages - Rob Dekker

Pages: 1 ... 47 48 [49]
2401
Arctic sea ice / Re: IJIS
« on: May 29, 2016, 08:17:55 AM »
Guys, is IJIS down ?
https://ads.nipr.ac.jp/vishop/vishop-extent.html?N
I have not been able to connect today.

2402
Granted in contrast to your model just knowing that number (of marginal ice volume melted because of albedo) doesn't have predictive power because it doesn't directly give you an extent number, and so the feedback effect is lost, but it's still a cool number to know.

Most of the ice that melts will be First Year Ice, which does not vary that much in thickness (square-root of FDD, as Chris Reynolds explained).

In fact, now that most of the MYI is out of the picture, FYI will be a better estimate for thickness of ice that will melt out than in the past, so in fact makes predictions easier.

2403
For that matter, if we have a good satellite photo, can't we just average the reflectivity of the entire area - clouds and all? If our satellite can measure longwave, so much the better, we can see exactly how much outbound radiation there is (reflected or emitted), and we know how much it receives,

That is a GREAT suggestion, and it could be done by analyzing the MODIS images (available daily).
I have not seen anyone actually trying that, although MODIS does not have much history (they also had a disk-crash in 2010 IIRC, which wiped out much of the prior years of observation).

2404
The absorbed energy in July (ocean only so far) for example has some correlation with the September minimum

Yes. Now you are seeing some of the correlation that I found in the monthly data.
Just be careful : If you correlate absorbed energy (mainly judged by ice "area") then there will be implicit correlation with September ice extent (low area in July means low area in September).
A better metric may be to correlate ice LOSS (after July) against absorbed energy. But there you need to be careful since some of the absorbed energy until July already caused ice losses until July.
So this is not easy.

2405
Arctic sea ice / Re: 2016 sea ice area and extent data
« on: May 28, 2016, 06:54:21 AM »
Thank you much, Wipneus, for your continued updates on area and extent.
One quick question : In your daily maps, there are signs of losses and gains in areas that clearly do not have any more ice. Like in the Baltic, St. Lawrence, [edit] the great lakes and around Sakhalin Island.

Are these artifacts of the methods used, and do they affect the area and extent estimates you report ?

2406
Arctic sea ice / Re: The 2016 melting season
« on: May 28, 2016, 06:03:00 AM »
Slater Probabilistic Ice Extent seems to be running fine now http://cires1.colorado.edu/~aslater/SEAICE/
worth a look

Thanks Mike. Yes, Slater's site is back up an running.
And the results are quite intimidating.

For starter, he projects 7.42 M km^2 by July 15. This is while 2012 at that date was at about 8 M km^2. So he projects that 2016 NOT show any significant 'stall' and will maintain its lead over 2012 (by some 600 k km^2) at least until halfway July.

But it gets worse. Remember that his model is based on ice concentration. Sort of like extrapolating how melting ponds will develop over time. And so far concentration has been average, and is just now reducing over the remaining ice pack now that area is dropping faster than extent (see Wipneus's assessment on this).

So it would be interesting to see how Slaters projections will change over the next week.
Maybe that steep downward trend at July 15 in his model is telling of how bad 2016 may turn out to be....

2407
Arctic sea ice / Re: The 2016 melting season
« on: May 27, 2016, 08:58:59 AM »
Hi everyone,

finally decided to register here, woop, woop!

I don't know if it was already mentioned, but the Slater Probabilistic Ice Extent (SPIE) seems to be up and running for this year:

http://cires1.colorado.edu/~aslater/SEAICE/

Thanks Egal, and welcome to the forum !
And thanks for pointing us to Slater's probabilistic ice extent estimate. It was missed.
It seems that Slater had his estimate for 2016 up for a day, but now its gone again.
Seems he is still working on it...

2408
Arctic sea ice / Re: IJIS
« on: May 27, 2016, 08:47:14 AM »
Oh. Forgot to mention :
The temps that matter for ice melt (2m temps) are still going up according to Slater :
http://cires1.colorado.edu/~aslater/ARCTIC_TAIR/index_80_t2m.html

2409
Arctic sea ice / Re: IJIS
« on: May 27, 2016, 08:40:17 AM »
Sleepy, I hope you are right about that stall similar to 2015, but I'm not convinced.

This is the first time in 2016 that Arctic temps touch the median. And they are still higher than they were in 2012 and 2015 at this date.

And even if that stall happens, 2016 has a lot of ground to make up.

2410
Hi Jimbo,
I've seen you ask these questions about perspective on the various heat sources into the Arctic at several forum sites now.

Here is some idea :
- River runoff : At another forum thread, I estimated that (even with 6 C water) a major river like the McKenzie inserts something like 1 TW of heat into the Arctic.
- Ocean currents : Neven's blog here
http://neven1.typepad.com/blog/2012/06/ocean-heat-flux.html
suggests that a major current like the one flowing through Bering Strait inserts about 10 - 20 TW.
- Albedo feedback on open water :
I have suggested here :
http://neven1.typepad.com/blog/2016/05/beaufort-final-update.html?cid=6a0133f03a1e37970b01b8d1ea5de2970c#comment-6a0133f03a1e37970b01b8d1ea5de2970c
that the open water in the Beaufort (some 200,000 km^2 at this point) absorbs something like 50 - 90 TW of solar power.
- Snow albedo :
Using an estimated 250 W/m^2 of on-the-ground insolation this time of year, and a 0.5 difference in albedo between no-snow and snow cover, a 1 M km^2 of land snow anomaly will absorb about 125 TW extra solar power. Some of that will go into warming the ground, but much of it will go to warming the atmosphere, some of which (probably half) will go north and thus enter the Arctic.
- Atmospheric heat input.
This varies quite a bit, with little heat entering in the early stages of the melting season, but quite a bit at the end (think August). I'd have to dig-up the paper, but I've seen estimates of some 200 W/m^2 heat input in the later parts of the melting season. Over the full 10 M km^2 of the Arctic, that is something like 2000 TW.

Does this provide some perspective... ?

2411
Arctic sea ice / Re: IJIS
« on: May 27, 2016, 07:27:03 AM »
The ice is so bad now and a storm is all that it takes, but right now I think we will see something similar like in 2015, as noted by rob and oren above.

Not so sure about that. That was why I was asking. Why do you think we will see something similar (major stall) like in 2015 ?
And a storm would be nice right now. It would sure reduce insolation into the major open water areas in the Arctic, and reduce the colossal albedo feedback at this time of the year.

2412
Arctic sea ice / Re: The 2016 melting season
« on: May 27, 2016, 05:44:02 AM »
I agree, Rob, but it's the wind that caused those polynyas in the first place, and winds cause water to open faster than melting (at this time of year).

You are right, Neven.
A-team's latest animation also shows that indeed the winds play a significant role in the further opening of the Beaufort open water. The ice is certainly on the move, along the coast, towards the Chukchi, and it is not all caused by melting as I feared.
Just curious why that ice does not seem to increase the Chukchi ice extent. Is it just piling up ?

2413
Arctic sea ice / Re: IJIS
« on: May 27, 2016, 05:33:25 AM »
Thanks Espen,
We appear to be rather close to the extent amount where the next runner-up (2015) started to seriously slow down its decline.
I wonder if 2016 will follow suit.

2414
what you described is the summer solstice in June and not the equinox in March/September. I extra looked up the correct terminology before posting my comment.

I'm sorry. I got confused.
I thought you meant the summer solstice.
Yet, the insolation around the equinox (on the latitudes where there is sea ice) is so small that even wide variation doesn't seem to matter much for your albedo energy calculations.

What to do next depends on where you want to take this.

If you want to just calculate for Arctic albedo, then using sea ice "area" (and land snow cover) will give you a good metric. (No need to get 'extent' involved).

If you want to actually calculate (estimate) (day-to-day, or accumulated) how much more energy the Northern Hemisphere absorbs due to reduced ice cover (and snow cover) than you would need to estimate how much of that TOA insolation makes it to the ground, and what the difference in albedo is between open water and sea ice, and between open ground and land snow cover.
For that, Hudson 2011 may be a good reference.
Tamino uses that too with his model, and he gets to an estimated 0.2 factor (reduction of insolation w.r.t. TOA).
https://tamino.wordpress.com/2012/10/01/sea-ice-insolation/

Let me note that Tamino's goal was to calculate albedo 'forcing' (global), so in that respect your calculations (day-to-day and calculating albedo energy input into the Arctic) are already more refined.

But if your goal is to build a sea-ice extent (at end of season) estimation model, then you would need to consider the influence of these albedo factors (like sea ice "area" and land snow cover) on how they affect sea ice melt. To do that, I came up with some parameters for these factors, set them to "educated guesses" and then refine them based on linear regressions. There, you may also want to include something like "extent - area" since that represents open water right next to the ice, which almost certainly has a rather direct effect on ice melt.

All in all, I like your approach and it has a lot of potential for developing a 'running' sea ice extent estimation model. But let me know how far you want to go.

2415
Arctic sea ice / Re: The 2016 melting season
« on: May 26, 2016, 12:39:31 AM »
Hi Neven,

Yes. It is melting. But only indirectly because of the wind. The prime cause is warm water :

The vast amount of open water in the Beaufort (some 150,000 km^2 according to A-teams latest measurement) has absorbed massive amount of heat since it opened up a few weeks ago.

By my assessment here http://neven1.typepad.com/blog/2016/05/beaufort-final-update.html?cid=6a0133f03a1e37970b01b8d1ea5de2970c#comment-6a0133f03a1e37970b01b8d1ea5de2970c we are talking about 50-90 TW.

That is enough heat to melt out some 10,000 - 16,000 km^2 of FYI per day.
Now that the winds are blowing (stirring the pot) that warm water comes in contact with the ice, and yes, then the ice just melts.

Also note on your animation that the floes that move along the edge of that open water are also disintegrating and melting away, which causes the Beaufort to loose some 15,000 km^2 per day over the past couple of days (according to Wipneus' assessment).

The Beaufort's open water is now so large and growing that the Beaufort may simply melt out at this rate all under its "own power" so to say. The awesome power of albedo feedback.

2416
Arctic sea ice / Re: Sea Ice Extent Dynamics
« on: May 25, 2016, 08:29:19 AM »
FWIW, global warming affects both the ocean/atmospheric and solar heat inputs directly. And again, I as I conjectured, it may affect the timing (changing the date at which snow, land, and melt ponds take their part in the process). The effect of the latter on SIE overall may be one of those non-linearities we've been looking for WRT CO2 forcing.

I've been thinking about these non-linearities a lot. But over the years I've been surprised how 'linear' the decline has been. Both for SIE as well as volume.
It may be related to the albedo-amplification factor (caused by snow and ice extent decline) during the melting season. If that factor is constant (as kind of could be expected), then the decline in sea ice volume will be linear. And if the ice thickness of the ice that melts out (mostly FYI) does not differ that much, then SIE will also decline linearly.

I still expect some non-linearity once ice volume gets really low, as best shown in this graph by Chris Reynolds :



Since there is no physical reason why volume would not continue to decline linearly, there will come a point that SIE will decline rapidly, and non-linearly.
As prof. Wadhams once stated : "In the end, it will just melt away quite suddenly. ".

2417
Arctic sea ice / Re: Sea Ice Extent Dynamics
« on: May 25, 2016, 08:08:02 AM »
Remember "melt starts" at the Spring zero crossing and ends at the Autumn crossing, so no, the charts do not suggest a change in timing of melt.

You are right. That was poorly worded.
What I wanted to say is that the main rate of loss of ice seems to accelerate in spring, while it seems to be unchanged during the rest of the season.
That I find surprising and interesting.

2418
Sure I would love to. At the moment my main objective is to convert my current model with a single latitude to a gridded model, because the insolation varies significantly with latitude around the equinox.

Going gridded is a commendable effort, but remember that insolation does not vary THAT much with latitude around the equinox. Just some 10%, and within the ice margin (70-80deg) only some 5%.
https://tamino.files.wordpress.com/2012/10/insol.jpg

That variation is negligent variation compared to the actual insolation on the ground, as Andreas' links and graphs suggest.

Please let me know when you want to include land snow cover or polynia/melting ponds into your calculations. I'd love to help out.

2419
Arctic sea ice / Re: The 2016 melting season
« on: May 24, 2016, 07:54:35 AM »
I agree, oren.
Great animation, A-team ! Thank you !

Seems to me that the ice floes at the edge are breaking up and melting away quickly in that wide-open water area in the Beaufort that has been warming up so nicely under the bright clear skies.

Shows what happens if you "stir the pot".

2420
Arctic sea ice / Re: Sea Ice Extent Dynamics
« on: May 24, 2016, 07:46:53 AM »
Dundee/Tealight,
These are very interesting finds.
It is less apparent in Dundee's graphs than it is in Tealight's graph, but both seem to suggest that melt started earlier, but then the RATE of melt did not change much over the decades, at least not during the June-Sept main melting season.
Or is that a side-effect of taking the 30-day average ?

2421
Sorry, that 1 M km^2 snow cover anomaly is a 280 TW heat source. Still an awesome amount of heat.

2422
Tealight, that is great work !
Albedo effect on sea ice melt is my favorite topic, and I've done some work on that in the past :
http://neven1.typepad.com/blog/2013/07/problematic-predictions-2.html

What I found there is that, yes, sea ice "area" plays an important role in albedo effect and ice melt, but other factors are also involved :

1) The influence of "land snow cover" is crucial. Not only does "snow cover" serve as a sort of "thermometer" of the Arctic (if it is warmer, there is less snow) but equally important is it's albedo effect, which works as a "feedback". For example : In June, with insolation averaging at 280 W/m^2, just a 1 M km^2 of snow cover anomaly generates a whopping 2,800 TW heat source very close to the ice.

2) The influence of dark ocean right next to the ice is important : For polynia and melting ponds, the sun's energy goes right into the ice, almost certainly directly causing ice melt.
I fingured that Extent - Area is a reasonable variable to consider as this "open water right next to the ice", which has a stronger, more direct influence to sea ice melt than "area" or "land snow cover" itself.

So, I figured that there are different parameters to these variables (snow cover and "extent-area" and "area") which combined produce a formula that is indicative of how these albedo-varying variables affect sea ice melt.

Result is that (using linear regression) these 'albedo' variables combined serve as a pretty good "predictor" of final sea ice extent in September :


What I have not done yet, and which is where you are ahead of me, is to produce a "day-to-day" model of how these variables ultimately affect sea ice melt.

Maybe we can combine forces and produce a prediction model that works on day-to-day basis ?
Caveat : There does not seem to be any day-to-day "land snow" data available.
Only monthly data from Rutgers Snow Lab.

2423
Arctic sea ice / Re: 2016 sea ice area and extent data
« on: May 24, 2016, 06:59:33 AM »
Wipneus,
I'm sure that I speak on behalf of the ASIB/ASIF community if I want to THANK YOU for the marvelous work you are doing.
Due to the F-17 issues, many of the regular sea ice information sources are disfunctional, which leaves your data as a crucial source of information of what is going on during this epic melting season.

Especially the AMSR2 regional graphs that you produce on the arctischepinguin site are essential, as and the 'shadow' CT area and 'shadow' NSIDC area and extent info are just phenomenal.

Just one question : Do you have a graph (or a data file) for the 'shadow' CT area and 'shadow' NSIDC area and extent ?

2424
Arctic sea ice / Re: The 2016 melting season
« on: May 23, 2016, 07:05:12 AM »
JayW,
Regarding CFSv2, here is a report of what they were struggling with since 2012 :
http://www.cpc.ncep.noaa.gov/products/outreach/CDPW40/Seaice_40thCDPW_WWang.pdf
Seems Wang et al did not resolve the issues with their model yet.

2425
Arctic sea ice / Re: The 2016 melting season
« on: May 22, 2016, 08:08:28 AM »
You make a good point seaicesailor.
Seems melt-ponding in 2015 was more intense at this time last year than it is now.
Yet, in 2015, the Beaufort melted out slowly.

I wonder, maybe melting ponds do not have that much as an influence as we thought they do...

2426
Arctic sea ice / Re: The 2016 melting season
« on: May 21, 2016, 07:26:51 AM »
Regarding the heat flow out of rivers, I'd like to propose some physical perspective :

Assuming the flow out of the McKenzie is some 35,000 m^3 / sec at somebody posted above, and assuming the water temperature is 6 deg C, then the amount of heat carried with that flow can quite easily be calculated :

35,000 (m^3/sec) * 1000 kg/m^3 * 6 (deg above freezing) * 4180 (J/kg) = 877 GW.

That's quite a bit of heating power, but compare that to the amount of heat absorbed in late May (about 200 W/m^2) of open (dark) ocean of 60x60 km :

200 W * 10^6 (m^2/km^2) * 60 * 60 = 720 GW.

which is comparable.
Can somebody make an estimate of how large that open water area is in the Beaufort right now ?
It sure looks a lot bigger than 60x60 km...

Now, compare that to the amount of heat flowing into the Arctic via Bering Strait : 10 - 20 TW.
http://neven1.typepad.com/blog/2012/06/ocean-heat-flux.html

That 10 - 20 TW is still a factor 10 - 20 larger than the heat input from the McKenzie river.

2427
Arctic sea ice / Re: Home brew AMSR2 extent & area calculation
« on: July 18, 2013, 11:20:02 AM »
I'm sorry. I meant the high area/extent ratio, and specifically the high area compared to Cryosphere Today.

2428
Arctic sea ice / Re: Home brew AMSR2 extent & area calculation
« on: July 18, 2013, 11:10:48 AM »
Wipneus,
Awesome work you present here ! Thank you !

You may have explained this before, but considering the interesting high extent/area ratio that your calculations show, could you give again a precise definition of how you calculate extent and how you calculate area on your grid ?

2429
I'm voting in the 2.5-2.75 slot.

The method I used is the same as the one I posted here :
http://neven1.typepad.com/blog/2013/07/problematic-predictions-2.html

Method briefly explained again :

I take 3 variables known in June : (snow-cover in June, SIE in June, and SIA in June) that I think best represent how much energy is getting absorbed into the Arctic, and thus should serve as  good predictors for later state of the ice (including predictions about area and extent in September).

I then run linear regression (and essentially principal component analysis) to determine the parameters for these variables that obtain the best correlation over the past years data.

Don't want to go back too far, since before 2000, the state of the Arctic was very different than now (and thus resp, and thus no combination of parameters obtains a correlation better than simple extrapolation of trends.
But with 3 variables, I need at least 10 data points or so, or else I will surely be 'over fitting'.

I found that going back to 2002 works well and seems to be representative to how well the Arctic responds to these 3 variables.

For SIA daily minimum, the formula for energy that gives the best correlation over the past 12 years or so is this one (june_area normalized (to 1.0) :

 june energy = 0.38 * june_snowcover - 1.57 * june_extent + 1.0 * june_area ;


 *************** Linear Regression Analysis *****************
 11 years analysed (2002-2012) :
 Mean energy -6.289610 Mean ice cover 3.466049
 SD energy 0.660019 SD ice cover 0.622146
Correlation (R): 0.990791
 Beta(slope delta-icecover/delta-energy) 0.933936
 Alpha (ice-cover at energy 0) 9.340144
 ice cover = 9.340144 + 0.933936 * energy
 *************** Prediction and confidence intervals *****************
 2002: energy -5.78, area 9.13, extent 11.70, predict 3.94, final 4.03, delta 0.09
 2003: energy -5.59, area 9.05, extent 11.77, predict 4.12, final 4.14, delta 0.02
 2004: energy -5.27, area 9.19, extent 11.52, predict 4.42, final 4.28, delta -0.13
 2005: energy -5.63, area 8.74, extent 11.30, predict 4.08, final 4.09, delta 0.01
 2006: energy -5.85, area 8.34, extent 11.06, predict 3.87, final 4.02, delta 0.14
 2007: energy -6.78, area 8.15, extent 11.50, predict 3.01, final 2.92, delta -0.09
 2008: energy -6.77, area 8.53, extent 11.37, predict 3.02, final 3.00, delta -0.02
 2009: energy -6.38, area 8.92, extent 11.47, predict 3.38, final 3.42, delta 0.05
 2010: energy -6.72, area 8.02, extent 10.83, predict 3.07, final 3.07, delta 0.01
 2011: energy -6.73, area 8.20, extent 10.99, predict 3.05, final 2.90, delta -0.15
 2012: energy -7.69, area 7.71, extent 10.97, predict 2.16, final 2.23, delta 0.07
# -2013: energy -7.33, area 8.57, extent 11.58, predict 2.50, final ????
Standard Deviation for de-trended prediction : 0.084


Note the amazing correlation factor R of 0.99, and resulting Standard Deviation on the prediction of only 84 k km^2.
Now, gotta take that SD with a grain of salt, since I included all known data in the analysis.

So I ran the entire process again, this time excluding individual years and then see how well this method can predict SIA that it did not know about. With that method, I get R=0.987 and resulting SD of about 100 k km^2. Which is still remarkably good and much better than straight line extrapolations of area and extent alone.

Which brings my prediction for 2013 SIA to 2.4 - 2.6.
No slot for that, but my got feeling is that 2013 will go to the high end of this range, so vote into the 2.5-2.75 slot.

Sorry for the long post, but after many experiments, I'm getting some confidence in this method.
We'll see in September if the Arctic agrees :o)

2430
Wipneus, you are awesome.
Thanks !
Tomorrow, I'll try my correlation method on these numbers.
http://neven1.typepad.com/blog/2013/07/problematic-predictions-2.html
and see if there is a pattern there that makes sense in terms of physics of energy input.

2431
Maybe a silly question, but does anyone have a list of the "Cryosphere Today 2013 Arctic SIA daily minimum" over the past 10 or 20 years ?

2432
Arctic sea ice / Re: Bottom melt in Central Arctic ?
« on: June 27, 2013, 09:37:14 AM »
Juan C. García said
Quote
Quote
Maybe your 2013 "North Hole" post will mean something totally different...
http://www7320.nrlssc.navy.mil/hycomARC/navo/arcticict_nowcast_anim30d.gif
The link that wanderer put made me see the possibility of a 2013 bottom melt on Central Arctic, so I recommend seeing this link

Thanks Juan.
The purpose of HyCom is not to determine ice thickness accurately, but instead provide a reasonable estimate of ice encounters for US Naval vessels, so please take this model with a grain of salt.

For example, HyCom mostly overestimates ice thickness (for examle, in 2011 HyCom suggested 3 meter ice in the Beaufort, while the USS Healy was cruising along at 20 kts in that same area through 1 meter ice). Also, HyCom seems to have inherited it's predecessor (PIPS) attitude of asserting a "hole" in the NP area :
http://neven1.typepad.com/blog/2011/07/pips-is-back-more-info.html

It'd be more interested in the PIOMAS assessment of ice thickness in the Central Arctic.

2433
Arctic sea ice / Re: Bottom melt in Central Arctic ?
« on: June 27, 2013, 08:55:27 AM »
jdallen said
Quote
Final note - I *do* think that the buoys are on MYI, and that is part of why we see them reporting low melt rates.  I further think that while they are giving us a read of local conditions, they aren't telling us what the FYI may be doing in the same area.  While MYI may not melt at -1.5C at all, over time, FYI can and will melt extensively.  The threshold for melt rate is very sensitive.  Half a degree can mean the difference between virtually no melt, and 20MM of melt a day.  As such, a relatively brief (24 hours or even less) fluctuation of sea water temperature can be highly localized, and have a very pronounced effect on the ice.

Thank you. Yes, I do think that these buoys have been placed on MYI, and yes, if salty, warm water bubbles up to the surface, it should affect (saltier) FYI more than (fresher) MYI.

So you are right that even if salinity increases under the ice surface that we may not see that reflected in melting on site, if the buoy is an IMB, simply because the energy goes to melting FYI nearby.

That is a good argument, and I wonder if we can find some evidence for that effect in the buoy data.

2434
Arctic sea ice / Re: Bottom melt in Central Arctic ?
« on: June 26, 2013, 11:07:42 AM »
Richard Rathbone "Can you put numbers on the turbulence increase expected and show its large enough to cause the observations you ascribe to it?"

and

"I think you have a sound argument for a local effect causing a local melt, but you need to put some numbers on the amount of mixing that PAC 2013 would generate to turn that into a sound argument for 2012J being representative and 2012E and 2012B being outliers rather than vice versa."

You are right Richard.
Unfortunately, it is very hard to calculate the "amount of mixing" caused by any storm, and especially one that is moving around and changing in intensity as much as the PAC 2013 did.
Not to mention the influence of other storms around.

So I can't give you a good answer, but I do have some humbling observations from at least one of the buoys I reported :

Jim Hunt : "Rob - Having checked a few more CSV files it looks like ITP 61 is actually colocated with 2013B, "

I realized that too, Jim. Both ITP 61 and IMB 2013B share the instrument set of NPEO 2013, which also features NP webcam 1 :
http://psc.apl.washington.edu/northpole/NPEO2013/webcam1.html

Since IMB 2013B does not show any bottom-melt, while co-located ITP 61 shows significant cooling of the upper 100 m ocean, I was scratching my head at this apparent contradition.

Until I analyzed the path that this instrument pack has taken.
ITP 61 shows increased salinity (and cooler temps) in the upper 100 m since about year day 145. Now it turns out (from ITP 61 track record) that these NPEO instruments just about moved from the West side, over the Lomonosov ridge into the deep of Nansen basin.

Now, obviously, Nansen basin supports a different ocean current than the Makarov basin, and thus 2013B's lack of bottom melt is easily explained : the 100 m water under the ice did not cool, instead the buoy moved over a different area, with different salinity.

This does not mean that 2012J's bottom melt is not caused by salinity changes due to the PAC 2013 as I suggest, but it does reduced the evidence for my whole argument to 2 buoys only. So let me analyze the track record of ITP 57 and 58, and see if their salinity changes may also be caused by them moving into Nansen Basin. If so, then I have no more evidence for my hypothesis, and will thus drop it.

Interesting still is that it seems that Nansen Basin contains more salt at the surface than usual this year. I've seen ITP data from Nansen Basin recording 32 and 33 psu, but never the 34+ psu that we see from e.g. ITP 58 :
http://www.whoi.edu/itp/images/itp58dat3.jpg

2435
Arctic sea ice / Re: Bottom melt in Central Arctic ?
« on: June 26, 2013, 10:30:36 AM »
jdallen "Melt rates are pretty low at that temp - looks like -1.5C or so, which is about 3mm/ day or so."

I don't think that you can determine bottom melt <i>rate</i> by looking at the temperature of the water right under the ice alone.

In general, the temperature of water right under the ice will always in balance with the melting point of ice at the salinity level of the water. If it's higher, melt will occur, if it's lower, freeze will occur, but all that only in a thin layer of water right under the ice.

If you want an instant snapshot of the melt rate, then you would need to do a micro-temperature and velocity analysis of the water moving right under the ice. Exactly what Flux Buoys are doing :
http://www.oc.nps.edu/~stanton/fluxbuoy/

Unfortunately, the only Flux buoy deployed in the NP area is AOFB 28 (part of the NPEO 2013 instrument set) but this buoy apparently gave up already on June 4, and no bottom-melt flux calculations have been made with the couple of weeks of data this buoy collected.
Incidentally, we DO see an increase in salinity in the surface (right under the ice) over these few weeks, even with this buoy.

In absence of Flux buoy data, to determine the amount of melting the PAC 2013 caused, I looked at how much 'cooling' occurred in the upper 100 meters after the salinity increased in that layer. My reasoning is that the heat that used to be there must have gone to bottom melt, and ITP data suggest this can easily be 30 cm of bottom melt.

Long story short : You cannot determine bottom melt by looking at water temps under the ice, since they will always be at the temp you expect given the salinity of the water. Similar to how you cannot determine top melting by looking at DMI atmospheric temperatures, which will always be close to 0 C, melting temp of fresh-water snow.

2436
Arctic sea ice / Re: Bottom melt in Central Arctic ?
« on: June 26, 2013, 09:53:03 AM »
Guys, thank you so much for some great feedback.

Couple of responses, in no particular order :

TerryM "If I understand correctly Ekman pumping draws AW up into contact with the ice, then with melt water cooling & mixing down to 100 M we have a convection current constantly gnawing away at the bottom ice forcing more brine against the ice & continuing the rapid bottom melt."

Correct, as long as turbulence persists, Ekman pumping will bring warm/salty water to the surface, causing bottom melt, and the fresh cold water will be driven back down.
But since salty water is still heavier than fresh water, mixing (and thus bottom melt) stops almost right away when the turbulence ends (when the storm overhead passes). After that, it can take a week of two, but since salty water is heavier than fresh water, the salt water will sink and fresh water will rise, and stratification restores.

In the case of GAC 2012, we do not have enough buoy data to assess the true amount of bottom melt that is storm caused, although I have gone on record using ITP data that suggests that not just the upper, but even the lower halocline was disrupted during that storm down to some 500 meter,
http://neven1.typepad.com/blog/2012/08/arctic-summer-storm-open-thread.html?cid=6a0133f03a1e37970b0177440b63e5970d
and that there should have been at least some 100 W/m^2 bottom melt going on due to Ekman pumping during the storm. That may sound like a lot, but it lasted only for a week, and only for the 7-8 day duration of this storm, so it should have caused 20 cm bottom melt or so. That's pretty good for the first week of August, similar to clear skies over fragmented ice, but not overly spectacular.

Also, the PIOMAS team did a model run to see what the direct (bottom melt) effect of the GAC 2012 must have been, and ended up with "only" 150k km^2 lost due to bottom melt due to Ekman pumping, salt and heat distribution under the ice :
http://onlinelibrary.wiley.com/doi/10.1002/grl.50190/abstract
which seems a bit on the low end to me, but is not inconsistent with the ITP data and rough calculations.

Either way, it seems that a storm needs to be very large and very strong and long-lasting to cause enough Ekman pumping to rival heat absorption of clear-sky summer insolation over fragmented ice in August.
For June, there is no argument : clouds dominate energy uptake, and even a persistent cyclone like PAC 2013 does not even theoretically approach bottom melt due to direct sunshine into polynias and top-melt due to sunshine on melted snow and bare ice.

So I take my own argument with a grain of salt.

2437
Arctic sea ice / Re: Bottom melt in Central Arctic ?
« on: June 25, 2013, 09:52:57 AM »
Rob, I'll fix them tonight when I get back. You need BBCode instead of HTML tags (use the buttons in the editor). Welcome to the ASIF.

Excellent thread BTW.  :)

I'm sorry Neven. And thank you for offering to correct HTML to BBCode.
I'll do better in the next post.

Still hope for comments on my hypothesis and analysis from the great people here on the forum.

2438
Arctic sea ice / Re: Bottom melt in Central Arctic ?
« on: June 25, 2013, 09:41:51 AM »
Rats. These HTML tags did not work.

2439
Arctic sea ice / Bottom melt in Central Arctic ?
« on: June 25, 2013, 09:36:03 AM »
So far, measuring by SIE and SIA, it looks like 2013 is following a path of 'recovery' from the devastating 2012 melting season.

However, as several posters on Neven's main pages have pointed out, the ice in the Central Arctic is in dire straights, after continued pounding and dispersion due to persistent lows over the Central Basin.

It remains to be seen if the dispersion of ice and the many polynias currently present in the Central Basin will be persistent and will collect enough heat to basically "burn a hole in the North Pole" area this year, or if the ice there will compact, and still has enough resilience to withstand the remainder of the summer, to prevent an ice-free North Pole come September.

Interesting in the discussion about the resilience or vulnerability of the Arctic Basin is the observation of Ice Mass Balance buoy 2012J, which seems to show significant bottom melt over the past month :




This buoy is currently located at 87.75 N, 24.30 E, which puts it smack in the middle of the "damage zone" inflicted by the persistent lows which dominated late spring and early summer 2013, and that Neven rightfully names, the Persistent Arctic Cyclone (PAC) of 2013.

There has been some questions about the integrity of the data from this buoy (for starters, it's thermometer went haywire earlier this month, and it's bottom sounder is unreliable) but the data from the thermistor string insists significant bottom melt is occurring there, at least 30 cm over the past month, even though atmospheric temperatures are still close to salt-water freezing (-2 C).

Purpose of this post is to investigate if the bottom melt recorded by 2012J is real, and if so, what is causing it.

For that, I consulted the Ice Tethered Profiler buoys from the good people at Woods Hole Institute. These buoys record temperature and salinity below the ice, from the surface down to 700 meter below the ice.

There are three ITP buoys in the NP area (Nansen basin) which may shed light on 2012J's melting profile. ITP 57, 58 and 61.

ITP 57, at 86.9271° N, 88.2188° E, is closest to 2012J, and just like 2012J also smack in the middle of the slush zone that was affected by the PAC 2013.

The buoy status graphs shows that ITP 57 has been rocking-and-rolling over the past month, presumably as a result of PAC 2013 :



But here is the interesting part :
There area where 2012J, ITP 57, 58 and 61 hang out has a rather shallow halocline.
For example, the halocline under ITP57 is only 25 meters below the surface.
And now it seems that with the Ekman pumping and general turbulence created by the PAC 2013, the salinity right under the ice has increased quite dramatically. For ITP57, salinity increased from 31.5 psu a few months ago to close to 34 psu currently. ITP58 shows an increase from 31.5 to 34 and ITP61 shows increased salinity from 28.5 to 33 psu over just the past month.



Now of course, with increased salinity under the ice, we can expect water temperature below the ice to drop, and the heat to go to bottom melt, since the melting point of ice will be lower. But how much bottom melt does this increased salinity cause ? That depends on how fast and how deep the cold fresh melting water will get mixed with the lower salty waters.

In the case of all three ITPs (57,58 and 61) it seems that the upper 100 meter layer of water has cooled something like 0.2 C over the past month. That suggests that some 82 MJ of energy was transferred from the saltier water to the ice, which would represent something like 25cm bottom melt.

Incidentally that is pretty close to what we see has happened with 2012J.

Also, some posters suggested that maybe 2012J is close to a polynia, and thus may absorb solar energy that causes bottom melt as well. However, if solar energy caused the bottom-melt, then we would expect the water to "freshen" right below the ice. Instead, ITP 57, 58 and 61 all show increased salinity at the surface, which suggests the bottom melt is dominated by salinity increase, not insolation into nearby polynia.

So the hypothesis I propose is that currently bottom melt is occurring in the Central Basin, due to salinity increase below the ice, caused by increased turbulence by the PAC 2013, which stirs up the shallow halocline in the region.

In favor of this hypothesis is data from buoys in the area, notably 2012J, ITP 57, 58 and 61.
Notably also : Against this hypothesis is data from IMB buoy 2012E and 2012B in the area, which show not much bottom melt (yet).

I'm curious to read your thoughts.

2440
I wonder what effect all of this heat in the high-latitude land masses will have on the Arctic. I figure this extreme heat will cause river temperatures leading into the Arctic to reach all-time record highs. Will these warm river discharges lead to enhanced ice melting?

Snow free land mass should make a tremendous difference, mostly by direct insolation.

At this point (summer solstice) an average of 250-280 W/m^2 insolation will make it to the ground anywhere in the Arctic / sub-Arctic, even including cloud cover.

The albedo difference between snow covered and base soil is something like 0.5 or 0.6, so we can expect for average weather, with cloud cover included, an additional 125-170 W/m^2 addition warming over areas that are normally snow covered.

June 2012 NH snow anomaly, turned out to be a record 6 million km^2,
http://climate.rutgers.edu/snowcover/chart_anom.php?ui_set=1&ui_region=nhland&ui_month=6

this year the snow cover is only marginally larger than last year's :

http://128.6.226.99/~njwxnet/png/daily_dn/2013175.png
http://128.6.226.99/~njwxnet/png/daily_dn/2012175.png

which suggests that currently the Nothern Hemisphere is currently absorbing a whopping 750-1000 TW additional heat above "average".

So yes, all that snow-free land DOES make a difference. It's absorbing a tremendous amount of heat right now, which warms the atmosphere and since half will be blown South and half North, some very significant part of that will cause ice melt later in the summer.

I ran an analysis comparing NH snow cover in June, and final Sept ice extent, and found remarkable correlation (R>0.9), which suggests that snow cover (decline) over the NH explains a great deal of the summer sea ice reductions we have been confronted with over the past decades.

Moreover, if I re-do the analysis including June "sea ice area" as well as June snow cover, the correlation gets even better and approaches R=0.98, which actually makes it (snow and ice cover in June) a pretty good "predictor" for September sea ice extent.


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