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Messages - slow wing

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1
Arctic sea ice / Re: The 2019 melting season
« on: August 15, 2019, 06:49:42 AM »
May I ask where I can get that ice concentration map?

I get today's map from here:
https://seaice.uni-bremen.de/data/amsr2/today/Arctic_AMSR2_nic.png

A bit later it gets posted to the archive, which also has the previous maps from this month:
https://seaice.uni-bremen.de/data/amsr2/asi_daygrid_swath/n6250/2019/aug/Arctic/


 (Edit the month and year to get the analogous archived maps from prior to this month.)

2
Arctic sea ice / Re: The 2019 melting season
« on: August 14, 2019, 01:49:26 AM »
Ascat with NSIDC ice age overlaid at 20% transparent, mar21-aug12.
Thanks for your great animations, Uniquorn. Really interesting to see this one and it shows that some of the outlying ice has a multi-year component.

3
Arctic sea ice / Re: Error in "2019 melting season" thread - HTML 500
« on: August 13, 2019, 08:09:29 AM »
It didn't work for me but then I hit "Reload" and it worked.

4
Arctic sea ice / Re: September predictions challenge 2019
« on: August 10, 2019, 05:37:50 AM »
JAXA:     3.50 to 4.00,  medium (minimum day extent)
NSIDC:   4.00 to 4.50,  medium (September average extent)

5
"Between 4.00 and 4.50 million km^2"

This is just half a million km^2 more than my estimate for the daily minimum.

6
"Between 3.50 and 4.00 million km^2"

Sneaked in just before closing and raised my estimate by half a bin...  :P

I didn't see any 'surprises' that would take out much extra ice.

True, there's currently that high pressure system in the ESS that's also acting in a dipole configuration to blow hot air from Russia into the Laptev sector, where the ice already has holes.

But it still takes a lot of energy to melt ice. By mid-August, sun and hot air can only do so much. It's the heat in the water that can still make a real difference. So, yes, wind can help by stirring things up and exposing the ice to more of that heat. Uniquorn also showed a great map of warmer currents expanding in the Beaufort Sea and also near and under the ice edge just north of Svalbard. So I expect more melting there.

But more overall melting to come than in other years? I don't see that there is particularly more vulnerable ice. Average melt would leave around 3.8 million km^2 at minimum, according to the helpful posts in the "2019 sea ice area and extent data".

So that's around the bin center for my chosen bin: "Between 3.50 and 4.00 million km^2"



7
Arctic sea ice / Re: "Stupid" Questions :o
« on: August 10, 2019, 12:23:40 AM »
Uniquorn, the formulae for orthographic projection are here:
https://en.wikipedia.org/wiki/Orthographic_projection_in_cartography

They are taken from a book for which the .pdf file is available online: https://ia802909.us.archive.org/34/items/Snyder1987MapProjectionsAWorkingManual/Snyder%201994%20Map_Projections_a_Working_Manual.pdf

They are actually simple though, and simplify still further when centred on the North Pole.
phi_0 = 90 degrees
lambda_0 = -45 degrees (example with 'Greenland down')

x = R cos(phi)sin(lambda+45)
y = -R cos(phi)cos(lambda+45)

R ~ size scale of your map. You will presumably have to calibrate it using known coordinates, e.g. Svalbard.

8
Arctic sea ice / Re: The 2019 melting season
« on: August 08, 2019, 05:46:29 AM »
7 August is another date where Neven has a year-to-year comparison of the U. Bremen AMSR2 sea ice concentration maps.

See figure below. The latest 2019 map is bottom right. It can be compared by eye to some of the previous worst years for sea ice minimum extent. Other recent years are available for comparison on the web page.

2019 looks worse to me on this date than any of the previous years other than 2012 and 2007. (2016 caught up later in the month - see the web page.) Even so, it's still to be determined how much of this year's lowered-concentration regions -- particularly in the Laptev sector, and north of the CAA -- will melt out by the minimum.

9
Arctic sea ice / Re: The 2019 melting season
« on: August 04, 2019, 09:11:51 AM »
The heat can mostly move through conduction
You mean convection I assume?
Nope. Conduction.  No convection through the halocline unless wave action stirs things up.

Very little heat moves up through conduction - the thermal conductivity of seawater is just too poor.


I just did a quantitative calculation of that here on the Stupid Questions thread. The amount of heat reaching the ice will seldom be enough to melt more than of order 1 millimeter of ice in a year.

10
Arctic sea ice / Re: "Stupid" Questions :o
« on: August 04, 2019, 05:56:11 AM »
Q. Can it? My response to this statement on the 2019 Melting Thread.

There is more than enough heat in the deep water to melt the ice and keep the arctic ice free year round. 

However, the heat can not move upwards through the halocline. 

The halocline is 50 meters thick (at least) and is very difficult to breach.  If it ever happens, look out!   The arctic will be a completely different place.


I've often wondered if/why the thermal conductivity of seawater is insufficient for significant melting of the ice just by thermal conduction, when the halocline is stable.

So let's see...


Consider the year-round loss of ice thickness due to thermal conduction from a 1-degree-C-warmer layer at a 50 meter depth.


ASSUMPTIONS & PROPERTIES:




CALCULATIONS:

Upwards heat flux = (temperature gradient) x (thermal conductivity) = 2e-2 K/m x 0.6W/mK = 1.2e-2 W/m^2

Thermal energy added to ice in 1 year = (Upwards heat flux) x (time in 1 year) = 1.2e-2 W/m^2  x 3.1e7 s = 3.7e5 J/m^2; multiply by 1e-4 m^2/cm^2 = 37 J/cm^2

Depth of ice melted = thermal energy added / (heat of melting x density)
= 37 J/cm^2 / (334 J/g x 0.9 g/cm^3) = 0.12 cm depth



CONCLUSIONS

So the thickness of ice melted over a year in the above scenario is only of order a millimeter.

Indeed, the thermal conductivity of seawater is insufficient to provide significant melting from deep layers of warmer, saltier water below the ice.

11
For now I'm sticking with last month's estimate: "Between 3.25 and 3.75 million km^2".

I'll keep watching and may exercise my discretion to change it before the poll closes.


July has been at least average and arguably a bit worse than that for the ice. No major storms or events but usually some wind and sometimes a fair bit of sun.

The reference area I always use to compare to is the 80N circle, which encloses an area of about 3.9 million km^2. So I'm guessing the ice extent will end up a little lower than that.


If 'no surprises' then it would probably end up at around 3.8 million but any surprises are likely to push it lower.


Considering the areas where there is currently ice south of 80N:

->  the Pacific side has already almost melted out - more so for this date than happened in any other year besides 2007;

-> The usual 'Beaufort tail' in front of the west CAA will presumably melt away to a large degree as the ice there is already broken up and there appears to be plenty of heat in the water in that region;

-> Yes, the CAA will retain some ice, but it will only be a couple of hundred thousand km^2. To balance that, the Greenland Sea is looking to end barer than in some years, including the record year 2012.


As for the ice detachment from the CAA, the degree to which that has happened is unprecedented in the years of the satellite record. I still expect the pack to drift back to the land before the extent minimum, but it might not. Also, that ice sanctuary has probably seen more heat than any previous year in the record, so some extent will be nibbled away there.


In addition to the possibility of a strong storm anywhere over the ice pack, I look to the Atlantic side for potential 'surprises' even if there is no such storm. The ice there has held on so far, but what about the claimed 'Atlantification' of the water there within the past couple of years? (More salinity and heat.) The Navy thickness map estimate shown below (for 2019-08-09) has relatively thin ice north of Svalbard and the Fram Strait. As we have seen on the Atlantic ice front in some previous years, some of that ice above the shelf of shallower water might disappear fast due to any heat in the water.

The Laptev sector may also get eaten away to well inside 80N.


So here is my guessed boundary, to be compared by eye with the 3.9 million km^2 enclosed by the 80N line. Again, it looks like "Between 3.25 and 3.75 million km^2".


So guessing a second place finish for low extent, behind only 2012. Guessing a record low volume, beating even 2012.

12
Arctic sea ice / Re: The 2019 melting season
« on: August 02, 2019, 02:00:13 PM »
Here's Neven's year-to-year comparison maps for Arctic sea ice on 1 August.


2019 definitely appears to be one of the worst years on this date. How bad will this melt season end up compared to previous worst years? Too early to tell?

13
Arctic sea ice / Re: The 2019 melting season
« on: July 31, 2019, 03:41:39 AM »
Given the accuracy of past Slater projections to minimum, a record should not happen this year, but I don't think a Slater projection for 2012 is available.

Slater's prediction for 2012 can be seen at http://cires1.colorado.edu/~aslater/SEAICE/Slater_AGU_2013_poster.pdf.


His model did successfully predict a record low extent minimum 2012, but not as low as reality. The predicted 2012 minimum was just a bit under 4 million km2 - which is also what the Slater model predicts for this year.

Given its similar predictions for the extent minima in the record year 2012 and in 2019, the Slater model can't be said to rule out a new record low extent this year.

14
Arctic sea ice / Re: Slater's thread
« on: July 28, 2019, 08:21:59 AM »
OK, I'm somewhere in the middle here.

I do agree with petm that the model does make a prediction for each day.

On the other hand, consider the prediction for 1 September (showing as about the current lowest) vs. the 15 September (which is where we are up to now). The 1 Sept prediction was made with the data for 2 weeks ago.

If the Slater model instead used today's data for the 1 September prediction then it would have more skill than the point shown on the plot because it would be a 36-day prediction rather than a 50-day prediction.

Would a 36-day prediction for 1 September likely be higher, or lower, than the value shown? We might suspect higher, given that later predictions have tended to be higher (and also that the mimimum in prior years has usually (always?) been later than that). That is oren's point.

They don't do predictions for days 1-49 into the future (see .pdf referenced by petm), only for 50 days. So the model hasn't really been optimized for finding the extent minimum - that's not its purpose.

15
Arctic sea ice / Re: The 2019 melting season
« on: July 28, 2019, 03:36:33 AM »
Slater's model seems to have settled on an early minimum near the end of August of approx. 4 million sq. km.
No. No. No. Those values for the end of August are historical, predicted exactly 50 days earlier in every case.

If you go to that website every day you will see that the curve remains the same. Every day it just gets a new 50-day prediction value added on at the end.

The Slater model's latest estimate of the actual minimum extent is not shown on that plot. Nor is its date. Presumably it's some time in September and is not much less than the 4.25 million square km value shown for 15 September - i.e. 50 days from now.

16
Arctic sea ice / Re: The 2019 melting season
« on: July 25, 2019, 07:29:23 AM »
it seems that the heat at / near the surface will determine the melt, not the heat 1,000 feet up.

It's a fair question. The short answer is that the air near the surface holds hardly any heat energy because it's a gas and so it contains hardly any mass per unit volume.



In more detail, these 3 points are relevant:

1) If we are just looking at the air temperature then we are ignoring water vapor, which can be important. (The dew point shows how much water vapor is in the air.) But now considering just dry air...

2) The temperature at 2 meters is not representative of the amount of heat in the air column as it is somewhat tied to the ~0 degrees temperature just below it.

3) The (dry) air in the meters just above the ice is carrying very little energy and so can melt only a negligible depth of ice. To get significant melt, a significant fraction of the heat in the air column has to be transported somehow into melting the ice (water vapor, infrared radiation, convection...)




To illustrate point 3, consider how much warm air would be required to melt, e.g., a 1 cm thickness of ice.

 (We assume some quasi-static conditions where the air column above the ice causes the melt directly below it - with the caveat that this is not normally a very good assumption.)


To melt, e.g.,  a 1 cm depth of ice requires (334 J/g specific heat of melt) x 0.9 g/cm^3 = 300 J/cm^2.

So 300 J would need to be supplied by the air column above each square cm of ice.

But the specific heat of air is only 1 J/g.(degree C) and the mass of air in the entire column all the way up into space is only about 1000 g/cm^2 (i.e one atmosphere) What average loss of air temperature, dT_air, would be needed to supply the 300 J/cm^2 to melt a 1 cm thickness of ice?

Require:

dT_air[Celsius] x 1.0 J/g.[degree C] x 1000 g/cm^2 = 300 J/cm^2

=> dT_air = 0.3 degrees C.


So THE ENTIRE COLUMN OF AIR UP INTO SPACE would need to lose 0.3 degrees C to melt a 1 cm depth of ice. Obviously, the air just directly above the ice can't melt much ice at all.

17
Arctic sea ice / Re: The 2019 melting season
« on: July 25, 2019, 06:44:45 AM »
What you miss in the basic picture of the process - is basics about how absorption works. You assume that all 180...300 W/m2 goes into melting the ice. In reality it does not: like already mentioned above, some of that energy is lost via evaporation (mostly from liquid water at the surface, but even dry ice actually evaporates slowly).

Further, whenever there is any noticeable open water - most of those 180...300 W/m2 gets absorbed at significant depth of downwards water column, since you know, water is a transparent thing. Noticeable amounts of light are present even at ~200 meters depth if my memory serves, - that's basically how deep significant fraction of absorption happens.

Same effect also happens to a lesser degree through the ice itself whenever there is no snow cover on it, increasingly so when the ice getting thinner: much sunlight simply goes through it and into water column below it, since ice is often significantly transparent, itself.

With water density being the highest at +4 Celcius iirc, a layer of colder melt water often remains near remaining ice, with warmer water sinking down as it's a bit heavier (though this much depends on water column mixing factors present at the location), which is another "sink" for some absorbed heat.

...

Sadly, this kind of calculations takes more than a single small napkin.

Yes, I assumed the bolded part as an approximation: that the heat absorbed by the ice goes predominantly into melting the ice.

 I've further speculated that -- before even reaching the ice -- a significant fraction of the solar insolation incident at the top of the atmosphere (at an elevation angle of only about 20 degrees above the horizon, remember) may have already been lost through absorption or scattering in the atmosphere before it gets to reach the ice, and that applies even in what appears to be 'clear sky' conditions.


But back to considering only that part of the insolation that has already been absorbed by the ice...

Someone else already suggested an alternative mechanism -- namely, heating of the ice up to zero degrees C -- that may use some fraction of the energy. I already posted the back-of-the-envelope calculation for the size of that, and shown that it should indeed be much smaller than melting.

Now you've suggested several further mechanisms where heat that's already been absorbed by the ice might be lost or absorbed elsewhere, rather than melting the ice. (Likewise, I've assumed all of those to be fractionally much smaller than melting.)

I do invite you to bring out your napkin as calculations on envelopes and napkins are used all the time in science with complicated processes, in trying to assess what is relevant or important and what is not.

So which one of your stated mechanisms do you think is the most important in competing with direct melting to use up the solar energy absorbed by the ice? I suggest you pick one and then do a back-of-the-napkin calculation to estimate the fraction of absorbed solar energy that is lost to your chosen process instead of melting the ice.

I'm skeptical that any of them are important but it will be interesting to see which of the other processes you suggest, if any, are comparable in energy scale to the energy that goes into melting the ice.

18
Arctic sea ice / Re: The 2019 melting season
« on: July 24, 2019, 11:47:12 PM »
If I'm not mistaken, your calculation assumes the ice is already at a temperature of 0°C.

Yes it does. It's a back-of-the-envelope calculation with implicit approximations and assumptions.


The assumption is a reasonable approximation because:

1) The specific heat of ice is only 2.1 J/g-(degree Celsius), whereas the melting heat is 334 J/g. So even if the ice starts at, say, -10 degrees C, then that is only a 6% effect.

2) By the start of August, I presume that the ice will anyway be close to zero degrees C.

19
Arctic sea ice / Re: The 2019 melting season
« on: July 24, 2019, 11:05:59 PM »
i'd say we can safely settle on very approximate range of ~180...300 W/m2 absorbed at the surface under clear skies (high pressure systems) for late July / early August

So about 5-9 cm of ice per day might be melting under the clear skies of the big high pressure system soon to arrive in the CAB.


Reason: it takes about 35 W/m^2 to melt each centimeter of ice per day:

Energy flux to melt 1 cm thickness of ice per day [in units of W/m^2] = 1 cm x (10^4 cm^2/m^2) x (334 J/g latent heat of melt) x (0.9 g/cm^3 density) / ( 3600x24 seconds/day)
= 35 W/m^2


(Uses the definition W = J/s)




DISCUSSION POINT

Doesn't that seem a bit high?

Let's say, roughly speaking, that the Arctic sea ice is observed to lose on average about 2 cm per day (that's 200 cm over a 100 day melt season). Then, from the above calculation, that's 70 W/m^2 delivered to the ice on average from all sources combined: sun, air and water.

Is that compatible with the insolation plot shown - where 'clear skies' are presumed to add 180-300 W/m^2 - and that is for more than a month past the Summer solstice?


If we believe '180-300 W/m^2' then it seems like only a small fraction of 'clear skies' over the ice would use up the energy budget to produce the amount of melt we observe.


So I'm skeptical that all the insolation shown in the plot actually does get to heat up the ice, even under 'clear skies'.


Asking the experts then: is that insolation plot for the top of the atmosphere and, further, is a considerable fraction of that energy lost even under what we consider to be 'clear skies'?

That's my suspicion.

20
Arctic sea ice / Re: The 2019 melting season
« on: July 24, 2019, 10:34:43 PM »
Another gain on Slater today, appears to be that their model predicts the first August minimum rather than a September minimum.
No, that's not how the plot works. Each day, an independent estimate of extent is produced and added to the plot. The older estimates are still displayed in the plot but their current estimates for those August dates are not shown. Presumably, their current estimates for those August dates will be higher than the old extent estimates that are displayed and also higher than the current predictions for 11 or 12 September.

21
Arctic sea ice / Re: The 2019 melting season
« on: July 24, 2019, 08:14:25 AM »
Thanks uniquorn and aslan for your replies on the salinity trends.

The amount of model data sounds huge.

The actual physical data though - the salinity data recorded from tethered buoys, drifting buoys and ships - is presumably quite manageable.

Wouldn't looking at the actual physical data give us some idea of salinity changes prior to the modelling from June 2017? (It's a genuine question - I don't know how sparse or rich the physical data is, and I don't know how easy or difficult it would be to notice salinity trends from looking at the physical data.)

I posted a suggestion for one way to present the salinity physical data, on the "Arctic Ocean salinity, temperature and waves" thread.

22
Arctic sea ice / Re: Arctic Ocean salinity, temperature and waves
« on: July 24, 2019, 04:37:04 AM »
Inspired by your salinity movies, uniquorn, the illustration below is a suggestion for displaying the actual physical data they are based upon.

It would give a 'traffic light' of salinity at e.g. 0m, 30m, and 100m at the location of each recording device on that date - whether from a tethered buoy, drifting buoy or a ship.


My main immediate motivation in suggesting this is that it would allow a movie that extends back before the June 2017 start of the mercator display movie that uniquorn posted here on the 2019 melting season thread. That would give us a longer term view of how the salinity has changed.

I realize that it would probably be a lot of work to make this, but I think to could be a useful visualization tool. The picture is just an illustrative cartoon - I'm hoping someone will be kind enough and interested enough to produce such a display, or similar, using the actual data. (It's beyond my own personal skills at the moment, unfortunately.)

23
Arctic sea ice / Re: The 2019 melting season
« on: July 23, 2019, 11:34:34 PM »
Yay! The Slater prediction has updated.  :)


The latest prediction is 4.11 million square kilometers for 11 September 2019 - which should be around the date for the extent minimum.


Bearing in mind that the map is indicative only, and is posted as a courtesy, it is seen that neither the Alaskan side nor the Russian side are predicted by the model to advance much inside 80N.

24
Arctic sea ice / Re: The 2019 melting season
« on: July 23, 2019, 11:25:15 PM »
... the albedo of the underlying surface is in large part a function of the angle of incidence of the solar radiation. This is true not just for water but also for sea ice.


Source: Hudson, 2011 https://doi.org/10.1029/2011JD015804

At 90°N latitude at this time of year the solar zenith angle is about 70° so that all the time is spent in the high-albedo part of the curve. South of 30°N, once the sun rises, almost all daylight hours have a solar zenith angle less than 70° and for much of the day less it's than 40°; at tropical latitudes it can obviously reach 0° at high noon. The end result is a great deal of time is spent in the low-albedo part of the curve.

I have no idea how to quantify this difference. My point is that it's not as simple as calculating the theoretical 24-hour solar insolation based on latitude alone and calling it a day.

Excellent plot, thanks edmountain.

Any melt ponds will presumably act like the 'clear sky over ocean' line and so, at the current solar zenith angle of ~70 degrees, the plot suggests they will still absorb about 85% of the incident solar radiation - which the plot shows to be about twice as much energy absorbtion as even dark ice.

This might be 85% x 460 W/m^2 ~ 390 W/m^2, if binntho's plot is applicable. Is it? Can anyone confirm that the insolation plot is for ground level and not for the top of the atmosphere?

25
Arctic sea ice / Re: The 2019 melting season
« on: July 23, 2019, 11:12:43 PM »
I think, for reference purposes regarding this season, it doesn't hurt to be aware of what the mercator model shows at 34m depth over the last 2 years (The current mercator model began ~ jun2017)
Thanks uniquorn, that is fascinating. I've played it several times already and will play it again.

Just a brief question so as not to get too far off-topic with this melting season:
Is there any prospect of extending the model back in time to before June 2017?

(I've always been very interested in the longer term trend in salinity.)

26
Arctic sea ice / Re: The 2019 melting season
« on: July 18, 2019, 05:25:55 AM »
My condolences Neven.


Last week (July 10-16), 3-day lagging median.

Click to animate.

Much appreciating the fine graphics displays made by the scientific community and very nicely presented on this forum. They give some of the best insights into what is going on in the Arctic.

Adding in July 17 reinforces that the Pacific-side sea ice is already collapsing to well inside the 75N latitude line.

27
Arctic sea ice / Re: The 2019 melting season
« on: July 13, 2019, 09:55:09 AM »
In discussing the rate of melting, it's good to always bear in mind that it is not accurately measured by the day-by-day extent drop.

A big low pressure system is the dominant feature in the Arctic Basin at the moment, as shown below. The counter-clockwise winds cause dispersion -- 'spreading out' -- which in turn tends to increase the extent even though no new ice is being formed.

That may be one reason for the lower extent drops over the past couple of days -- the ice melting is being partly counteracted by the spreading of the ice. However, dispersion is generally bad for the health of the ice because it creates gaps in the ice that the sun can heat up and, also, the movement of the ice through the water exposes it more to whatever heat is in the water.

So at the moment the melting will tend to be worse than is represented by the daily measured extent drops.

28
Arctic sea ice / Re: September predictions challenge 2019
« on: July 11, 2019, 12:05:20 PM »
Missed the cutoff time again, sorry.

June

JAXA: 3.75 to 4.25, medium
NSIDC: 4.00 to 4.50, medium

July

JAXA: 3.25 to 3.75, medium
NSIDC: 3.50 to 4.00, medium

29
Missed the time cut-off but would have gone "Between 3.50 and 4.00 million km^2". Like last month, that's 1 bin higher thanmy daily minimum prediction.

30
Missed the cut but would have gone "Between 3.25 and 3.75 million km^2".

That's dropping down 2 bins from my prediction last month, after a month's brutal weather for the ice.

That agrees with my eyeballing of the Navy ice thickness prediction. Like last month, I drew a boundary line partitioning the ice pack at, for this month 0.7-0.8 metres thickness (last month was 1.3 m thickness) - depending on how close the line is to the edge of the ice pack.

Like last month, on comparing by eye with the area inside 80 degrees latitude -- which is 3.9 million km^2 -- the enclosed area is a little less: about 3.5 million km^2 of ice, including a couple of 100,000 km^2 in the CAA.

So that confirms the bin I'm predicting as "Between 3.25 and 3.75 million km^2".

31
Arctic sea ice / Re: 2019 sea ice area and extent data
« on: July 09, 2019, 06:26:29 AM »
… DMI shows it right on the line.  Still just a hair above most years it seems.

Note the 'average' line is for 1958-2002 when the Arctic was a different beast.  (Don't ask me how it was 'warmer' then.)  Looking through the archive, you'll see recent years have an occasional bump above the above-0ºC green line segment, but averaging between the zero and the green line.  For 2019's trace to be right on the green line is actually rather spectacular!

[Remember, DMI 80N is a North-Pole-centric calculation of temperature and should not be confused with "average" temperature for a territory in the usual sense of the term.]

That's something I've wondered previously, as well. Why would the North Pole and nearby have been slightly warmer  in those earlier years, when the ice was thicker?

This is just speculation, but it may be that thick ice with few leads better supported melt ponds than today's ice does. Remember, ice ponds also drain away if the ice is porous. So those earlier years may have had a bigger surface fraction as durable melt ponds. These could then heat up in the sun, raising the temperature of the air just above them.

As I say, that's just speculation. It could well be another reason. Does anyone know?

32
Arctic sea ice / Re: Latest PIOMAS update (July 2019)
« on: July 09, 2019, 05:39:00 AM »
Slow Wing, you write SIA but mean SIE.
Thank you. Corrected.

33
Arctic sea ice / Re: Latest PIOMAS update (July 2019)
« on: July 09, 2019, 03:35:12 AM »
Thanks Neven, great update, as usual!


Just want to check that I am understanding you correctly with your "top 3", which you have talked of several times.
I'm convinced that 2019 is assured of a top 3 spot when it hits the minimum in September

If you're talking about JAXA SIE September daily minimum then, with the way the data from previous years has fallen, this year is more likely to end up in 4th place than 3rd place.

That's because the bin width for 3rd (50,000 km^2)  is so much narrower than for 4th (190,000 km^2).

For it to be third, it would have to be greater than 4.02 but less than or equal to 4.07 million km^2 (hence the 50,000 km^2).


Might you instead mean "top 2" - that is, either first or second? That would apply for any 2019 lowest extent less than or equal to 4.02 million km^2.

Source: table posted by Juan Garcia in his poll thread.

34
Arctic sea ice / Re: The 2019 melting season
« on: June 30, 2019, 09:24:21 AM »
... there is a 30kg/m2 river of moisture flowing in through the Bering Strait all week...

Does anyone have an idea how much of that moisture is arriving at the ice edge as vapour? How much latent heat is being transferred to the ice?

Nearly all of it is vapour, in my understanding.

The 2 plots below are from Nullschool, for current conditions. The green circle is an illustrative point just north of the Bering Strait and just before the wind reaches the current edge of the ice pack.

Shown are 2 of the options provided by Nullschool (click on "earth" to toggle into/out of the menu):
1) TPW = Total Precipitable Water
2) TCW = Total Cloud Water

I presume the cloud water is the part of the water that is condensed rather than vapour. Can anyone confirm or else correct me?

Their values at the illustrative point are:
1) TPW = 20.4 kg/m^2
2) TCW = 0.1 kg/m^2

So it's essentially all vapour - the amount that is condensed is a fraction of one percent.

As someone already said above, 1 kg of water vapour can melt about 7 kg of ice. (Reason: water's heat of vaporization/condensation = 2257 J/g, which is nearly 7 times its heat of melting = 334 J/g.) So the air column can potentially melt ~ 7 x 20 = 140 kg/m^2 of ice. Assuming an ice density of 900 kg/m^3, that's a thickness of 140/900 m ~ 15 cm of ice.

The amount of ice melted also depends on the wind velocity - i.e. the rate at which the wind brings air and, hence, water vapour over the ice. You can integrate the perpendicular component of wind flux along the ice pack edge to calculate the potential ice volume lost per day, say in units of km^3/day. I'll leave that as an exercise for the reader. :)

35
Arctic sea ice / Re: The 2019 melting season
« on: June 30, 2019, 12:49:16 AM »
Amazing~
all gone!
click to animate~

No, that ice hasn't gone. In the summer, the SMOS maps aren't showing thickness, so the scale is misleading. It's best to crop that scale out of the images, gifs.

36
Arctic sea ice / Re: The 2019 melting season
« on: June 28, 2019, 02:25:18 PM »
Some of the people knocking the Slater map may not understand it?

I'm a big fan of it - it's a great approach to predicting future extent. I appreciate what Dr Slater did and also appreciate those who have continued to maintain it since his untimely passing.

I look at it every day when it updates; it gives an indication of where the ice is vulnerable in the coming weeks.

It can also be compared with thickness plots, such as this US Navy prediction for 4 July. (Unfortunately, they use different orientation conventions, so you have to mentally rotate one or the other by 45 degrees.)

Of course we always bear in mind that these are all imperfect models, and we are even aware of some of the shortcomings:

So there is a survival probability for each ice concentration, but we know, that 70% ice concentration is sure to melt out in the Barents, but not so sure to melt out in the CAB.

... Nonetheless, this is a very nice tool.

However, I agree with El Cid that they're valuable all the same in visualizing what is going on with the Arctic ice.

37
Arctic sea ice / Re: The 2019 melting season
« on: June 27, 2019, 08:56:12 AM »
The discoloration of ice in early summer in the Chukchi is an annual thing, I've posted about it previously and nobody seems to have an explanation. Sometimes the discoloration is striated, i.e. there are bands of different colors following the edge of the ice...

Growth of algae, mostly on the undersurface of the ice, may well be the cause of dirty ice you have been seeing each year in early summer in the Chukchi Sea.

The photo -- and others in the article -- are from June 2009 in the Chukchi.

"This was not dirt, but massive blooms of sea ice algae, such as the aptly named ice diatom Nitzschia frigida."

The algae grow when the ice is just thin enough for the sunlight to penetrate.

The author, Dr. Bruce Marcot, speculates that warming of the Arctic may lead to more of this algae growth, potentially enhancing the melting of the ice.

38
Arctic sea ice / Re: The 2019 melting season
« on: June 26, 2019, 06:22:37 AM »
2019 is certainly still in the running for a top 2 finish (+/- 1), with the two main reasons besides the relentless weather:
Low area inside the Inner Basin (courtesy of Wipneus).
Extreme export into the Atlantic throughout the season, which has taken a lot of the MYI - shown in lighter shades on Ascat - out of the basin (courtesy of A-Team in the Test Space thread). The FYI has now reached the North Pole.
[link to post]

Thanks A-Team, and to Oren for posting it in this thread.

That is impressive differentiation between MYI and FYI in the ASCAT gif!

A-Team has posted in the Test space thread that ASCAT uses microwaves: "a real aperture active radar operating at 5.3 GHz (5.7 cm wavelength)".

That Test space post also refers to the other microwave data we are looking at regularly here: "SMOS, a passive radar operating at 1.3 GHz (21 cm wavelength)".

A-Team has also been reading the SMOS literature and reports:

"SMOS is not a melt pond tool. If it were, they would be shouting hooray. Elsewhere, over land, it measure moisture in soil. It does not measure moisture per se in ice/snow/re-frozen melt. At 21 cm wavelength, it is greatly affected by an assortment of surface properties, most but not all salinity-related."

  So, referring that back to the ASCAT gif, given that SMOS and ASCAT are both microwave measurements -- albeit with significant differences -- may I ask this: does the good ASCAT differentiation between (lighter) MYI and (darker) FYI come from picking up the characteristic differences in ice thickness, or does it instead come from the characteristic differences in ice salinity, or even something else?

Asked briefly: is that gif showing ice thickness or, instead, ice salinity?

39
Arctic sea ice / Re: Arctic Image of the Day
« on: June 18, 2019, 11:20:44 PM »
Found on Reddit, not sure if the Arctic. Edit: of course not Arctic, there are trees!

But it's freaking awesome...

It might be Lake Baikal. Similar amazing photos here, here, and here.

40
Arctic sea ice / Re: The 2019 melting season
« on: June 18, 2019, 11:15:11 PM »
SMOS is showing a record low dry ice area for 16 June.

Where does the BEIGE pixel chart update?
The links are both there.

All the SMOS maps are here. The page updates daily by adding the new daily maps at the bottom - so you have to scroll to the bottom. The specific map I post is [date]_hvnorth_rfi_l1c.png

Steven's graph is here. It, also, updates daily and the updating appears to be automated as it seems to update as soon as the SMOS map appears.

The daily updates may be at ~07:00 UTC, but I might be wrong on that.

41
Arctic sea ice / Re: The 2019 melting season
« on: June 17, 2019, 12:39:06 PM »
Meanwhile, the Slater 50-day prediction is dropping like a rock, now showing 5.75 million square kilometers for 5 August 2019.

P.S. does anyone know the meaning of the LIGHT blue line in the Slater graph? I have already asked previously in the 'stupid questions' thread and nobody answered there.

Each day a prediction is made 50 days in advance based on the most recent ice conditions, and a statistical assessment of how much ice is likely to melt given those conditions.  These predictions are plotted as the light blue line.  The fact that it is dropping like a rock is not a prediction near the end is not a prediction that ice will go along following the blue line and then drop like a rock.  It is a reflection of the fact that conditions several days ago were better.  Updating the prediction based on changes in the last few days has caused the prediction to drop like a rock.

If the methodology was updated to give a prediction of change over time, my guess is that it would be a reasonably smooth line joining today's ice extent with the predicted ice extent in 50 days time - at the end of the thin blue line.

Thanks Michael. However, you are describing what I understand to be plotted as the DARK blue line, which is labelled "50 Day Lead-Time Forecast". I have the same understanding as you on the meaning of that line.

My question concerned the other blue line on that plot, the LIGHT blue line labelled "Anom. Forecast", which may well be short for "Anomaly Forecast". I have no idea how this line was derived.

42
Arctic sea ice / Re: The 2019 melting season
« on: June 17, 2019, 09:14:26 AM »
Meanwhile, the Slater 50-day prediction is dropping like a rock, now showing 5.75 million square kilometers for 5 August 2019.

If the Barents and Laptev sectors will already be getting destroyed by then, as the plot suggests, then a new record low minimum extent would be quite on the cards.


That's not even to mention the prospects for a record low sea ice volume, which is more likely - and, for me, more concerning - than an extent record.


P.S. does anyone know the meaning of the LIGHT blue line in the Slater graph? I have already asked previously in the 'stupid questions' thread and nobody answered there.

43
Arctic sea ice / Re: The 2019 melting season
« on: June 17, 2019, 09:05:11 AM »
SMOS is showing a record low dry ice area for 16 June.

44
Arctic sea ice / Re: The 2019 melting season
« on: June 16, 2019, 09:19:33 AM »
25cm loss in thickness in 1 day in some areas.

That's not what these maps are showing. Don't use them for thickness during summer. They say something about how wet the ice is, roughly. That's it.

Why does any credible organization put out a map with a legend for ice thickness that reveals something else?


Is this basically a misleading garbage map?

No, it's valuable measurements made in a frequency range - microwaves - that is unique and providing an orthogonal view of the ice to all the other satellite measurements.

That scale is correct for the Winter months. University of Bremen have been kind enough to continue sharing the map even over the summer months where their calibration is not valid but where the map is perhaps the best single resource we have for quantifying the amount of melt ponding and wet sea ice.

45
Arctic sea ice / Re: The 2019 melting season
« on: June 16, 2019, 09:13:52 AM »
According to the SMOS maps -- which show satellite microwave measurements, displayed on a map of the Arctic by University of Bremen -- 15 June 2019, just released, may have had the smallest area of 'dry' Arctic sea ice on record for the date, going back to 2010 and just pipping the exceptional melt year, 2012.

That's according to the 'beige pixel count' graph by Steven.

EDIT: as Neven has just pointed out in such a timely and informative manner..  :D

46
Arctic sea ice / Re: The 2019 melting season
« on: June 15, 2019, 01:59:52 PM »
SMOS (satellite microwave measurements) beige pixel count on the University of Bremen maps has just dropped to second lowest in the years from with data, beginning from 2010, on the latest date for which the Bremen SMOS map is now available: 14 June 2019.

That ranking is according to the very useful graph that Steven puts out.


The beige pixel count provides a measurement of the area of Arctic sea ice that has NOT yet been wetted by (mainly) melt ponds, and that is therefore still reflecting most of any direct sunlight rather than absorbing it as heat.

So a lower beige pixel count corresponds to more of what Neven calls 'melting momentum'.


For 14 June, this year, 2019, is still well above the anomalous year 2012 and is just below the 3rd lowest year, which is 2016.

A large part of the reason for the drop into second place is the notable appearance of non-beige pixels on the Canadian+Greenland side of the Arctic sea ice on 14 June 2019, indicating the onset of significant surface melting there.

47
Arctic sea ice / Re: The 2019 melting season
« on: June 15, 2019, 01:10:08 AM »
Similar to as posted above by b_lumenkraft. Terra satellite true colour image of Englefield Fjord. The red dot is the location of Qaanaaq, aka Thule.

48
Arctic sea ice / Re: The 2019 melting season
« on: June 13, 2019, 10:35:53 AM »
Click on the .gif to see an SMOS (satellite microwave measurements) map comparison for the 12 June on 2010 through this year, which is all the years in the database.

I find it easiest just to eyeball and compare the sizes of the beige area for each year, which tends to represent ice without a noticeable layer of surface water.

The size of this year's beige area is seen to be still 'within the pack' - with 2012, the year that still holds the record for lowest extent at the end of the melt season - standing out as having much less beige area than all the other years on this date, 12 June.

How much was that a coincidence for 2012; how much was it causal?  :P

49
Arctic sea ice / Re: The 2019 melting season
« on: June 12, 2019, 11:51:48 PM »
The entire Asian sector is actively collapsing. This is a catastrophe.

No it's not. (Thanks Pagophilus for pointing this out.) The SMOS microwave maps must be interpreted with caution during the melt season.

I always post this when I post them...

These images are sensitive to melt ponds.
IGNORE THE COLOR LEGEND'S NUMERICAL SCALE & LABEL (the color order progression should be valid though) - DURING THE MELT SEASON THESE ARE NOT LEGITIMATE THICKNESS MEASUREMENTS. Instead, my understanding is that any color other than beige indicates ice that is:
a) thin, ~<50 cm; &/or
b) has concentration well below 100%; &/or
c) has surface liquid water.
In particular, colours other than beige in the ice pack interior are likely to indicate the presence of surface water.


According to the SMOS maps, this year is only in the middle of the pack for the years beginning with 2010, or at least it was on 10 June.


Steven, looking forward to any updates of your very informative plot.


Meanwhile, a direct comparison of SMOS maps for this date can be made by looking at the archive here: https://seaice.uni-bremen.de/data/smos/png/.

50
Arctic sea ice / Re: September predictions challenge 2019
« on: June 12, 2019, 05:23:46 AM »
June

JAXA: 3.75 to 4.25, medium
NSIDC: 4.00 to 4.50, medium

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