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Messages - slow wing

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101
Arctic sea ice / Re: The 2017 melting season
« on: June 26, 2017, 05:38:55 AM »
University of Bremen's AMSR2 Arctic sea ice concentration map has updated, now on 25 June, which is one of the dates of Neven's year-to-year comparison graphic: https://sites.google.com/site/arcticseaicegraphs/concentration-maps/sic0625.

At bottom right, 2017 has more blue showing around the edge of the Arctic Basin than in previous years. This is in agreement with Wipneus' extent calculation for the restricted central regions of the Arctic Basin that has 2017 as the year with the lowest extent.

Some melt ponds are showing in the interior by now, catching up with the other years. Note again that the palette has changed: 2017 doesn't show the white flecks at just below 100% concentration that the other years do.

Still early days in the melt season.

102
Arctic sea ice / Re: The 2017 melting season
« on: June 24, 2017, 10:19:11 PM »
  The persistent storm in the CAB is currently at around 985 hPa.

  As shown below, the models (& have added the ensembles) are backing off on how much it will strengthen over the next couple of days. They now predict it to bottom out at around, or a bit below, the 2013 record for June of 980 hPa.

103
Arctic sea ice / Re: The 2017 melting season
« on: June 24, 2017, 02:59:12 AM »
The weather models on tropicaltidbits.com are now all predicting the storm pressure to bottom out in about 3 days' time.

 They all predict it to beat the previous record in the satellite era for low sea level pressure in the Arctic Basin in June, of 980 hPa in 2013, and by a fair margin.

As shown below, the predictions range from 966 hPa up to 974 hPa.

104
Arctic sea ice / Re: Arctic Image of the Day
« on: June 24, 2017, 02:26:49 AM »

105
Arctic sea ice / Re: Stupid Questions :o
« on: June 23, 2017, 03:07:13 AM »
Kate, was it ASI graphs?

It's actually linked at the top of this page, immediately below the graphic, but the link isn't underlined so it isn't obvious.

106
Arctic sea ice / Re: The 2017 melting season
« on: June 23, 2017, 12:42:35 AM »
Neven, Re your #2218, yes ECMWF has backed off on the strength of the predicted 'weather bomb' storm and also pushed it later.

  The same is true of 3 other models on tropicaltidbits.com that previously predicted it. (The exception is CMC, which still shows it at the same time and strength.)

  NAVGEM is now at 976 hPa on their 12z run - close to their 978 hPa prediction from 12 hours earlier - so they were the only model not predicting 970 hPa or lower.

The updated predictions are attached. They can be compared with the predictions from 12 hours ago shown in my post #2198.


  So it looks more likely that there won't be a 960s weather bomb after all in the next few days.


  The persistent storm does look like it will re-strengthen though over that timeframe, perhaps down to the mid- or high- 970s. That would still be a strong storm and as far as I know a record low pressure for June in the satellite era (beating 980 hPa, in 2013).

  The ice appears to be mobile this year so this persistent storm will likely, by its end, have displaced ice by up to hundreds of kilometers over much of the Arctic Basin.

  As Romett1 notes above at #2202, HYCOM predicts this as well. The main effect will likely be a lot of ice pushed over towards the Barents Sea and Fram Strait, along with gaps opening up in the interior of the pack.

107
Arctic sea ice / Re: The 2017 melting season
« on: June 22, 2017, 12:35:46 PM »
On viewing the model predictions at tropicaltidbits.com, the models all agree on a strong pressure minimum on or around 00z Monday, June 26 2017.

NAVGEM shows the 'weakest' storm prediction: already relatively strong at 978 hPa.
CMC has the strongest storm, bottoming out at 961 hPa.

The current predictions of the various models for pressure minima are summarised in the attached table.

108
Arctic sea ice / Re: The 2017 melting season
« on: June 21, 2017, 02:45:45 AM »
  19 June is one of the dates displayed in Neven's excellent year-to-year comparison of U. Bremen's AMSR2 sea ice concentration maps: https://sites.google.com/site/arcticseaicegraphs/concentration-maps/sic0619.

  I mainly look at the ice pack in the Arctic Basin as that is what mainly determines what sea ice is left at the end of the melt season.

  This year's Arctic Basin at 19 June shows the melt at the pack edge is advanced this year inside the Bering Strait and relatively advanced in the Beaufort Sea and on the Russian side.

   However, the pack itself looks generally darker than in previous years.

   What should be pointed out as at least a partial explanation is that THE COLOUR PALETTE CHANGED THIS YEAR.

There is no longer a light concentration band near 100% that can produce light flecks all over the ice pack.

Shown below is the 19 June map comparison as well as the colour palettes for 2016 and 2017 with the change circled.



109
Arctic sea ice / Re: The 2017 melting season
« on: June 20, 2017, 05:48:03 AM »
Neven, thanks for Reply #2121 and its links, informing that in 2013 the Arctic Basin also had a strong and persistent low pressure system in June.

That's mildly comforting given that 2013 was a recovery year from the carnage of 2012.

There are differences from this year though that may make comparisons unsafe.

Firstly, the 2013 system was earlier in the melt season, beginning towards the end of May.

The CAB ice pack has already opened up more than was the case in 2013 and is starting to melt out more, particularly on the Russian side.


  In both years, the melt will be retarded by increased cloud cover.


  I'm wondering if this year there may be a stronger competing effect from ice movement induced by the storm winds generated.

  The ice is thin and may be more likely to move around than was the case in 2013.

  Also, the winds North of Greenland will be from West to East, so pushing the ice in the direction of the Atlantic and the Fram Strait 'ice sink'. This year's thick ice is already biased over towards that side and so we may lose thicker ice.

  Also, that displaced ice will likely produce leads and other gaps in its wake. Right at the Summer solstice now, those areas of open water will then heat up and seed melt in the adjacent ice.


  Quantitatively? If those winds persist for 1-2 weeks then the thicker ice will likely move a couple of hundred kilometres towards the Atlantic. (To set the scale, the Fram Strait is 450 km wide, so perhaps half of that.)

  If the ice front is of order 1000 km long then the total displacement towards the Atlantic might be of order 200 km x 1000 km ~ 200,000 km^2.

   Given that the Fram Strait and Atlantic are 'death zones' in recent years, that 200,000 km^2 might be considered extra ice lost.

   Correspondingly, the leads opened up in the pack behind might also have a total area of 200,000 km^2. That would be significant in seeding melt in the adjacent ice.


  This is all speculative and back-of-the-envelope, but it will be interesting to see how much the thicker ice is pushed East to the Atlantic and also to see if any visible leads are opened up.

  Then there will be Ekman pumping as well, which might melt some more ice.

  Having said that, the cloud cover afforded from the 24 hour a day sunlight is a big loss of melting potential to compensate for.


  So, in summary, this storm might be steering us towards a weaker melt season, like in 2013, but there are compensating effects so it might not.















110
Arctic sea ice / Re: The 2017 melting season
« on: June 20, 2017, 01:38:31 AM »
ECMWF 12z op:  967 hpa bomb cyclone at +144h

GFS 12z op run: 967 hpa bomb cyclone at +126h

The fact that both models put the cyclone down to sub 970 hpa is really ominous. ...

You've only looked at those two models though. I checked with two other models on Tropicaltidbits.com and they don't show the same level of 'weather bomb'.


Viewing CMC instead, the 12z 19 June run only drops to 977 hPa (is at 150h).

At 126h - when GFS has its 'bomb' - CMC has gone in the other direction with that system, to 992 hPa.


Viewing NAVGEM 12z 19 June run, the lowest that drops to is 976 hPa, at 136h.


The models sometimes generate very low pressure predictions out beyond 5 days that don't come to pass. So in my view this one is still too uncertain to be concerned about just yet.

111
Arctic sea ice / Re: The 2017 melting season
« on: June 18, 2017, 09:46:37 PM »
The current and forecast weather provides more evidence that the Arctic has become more windy over the past couple of years (could pick December 2015 storm as starting point), even during the melt season.

  Currently a large cyclone of 985 hPa sits in the Arctic basin, fairly central and towards the Atlantic side. That is already unusual for June and perhaps almost unprecedented in the satellite record. (Does anyone remember similar or lower in June?)

  All of ECMWF, GFS, CMC, NAVGEM and JMA expect it to stay there and even intensify down into the high or mid 970s in around six days from now.

  I presume that such persistent and strong low pressure over the Arctic Basin is new territory over the satellite record for June.

  It is unclear to me that this helps to preserve the ice for this melt season, as some above appear to be suggesting. To the contrary, it generates a lot of wind to carry heat and moisture in from the land and to fracture and push the ice around.

  I view it as concerning both for this melt season and also as a sign of changes in the Arctic climate occurring within timescales of only a few years.

   Shown below is the furthest forecast displayed by Nullschool, about 5 days from now. It uses GFS forecasting and the predicted MSLP at the cyclone's core, currently at 985 hPa, has dropped by then to 980 hPa.

112
Arctic sea ice / Re: The 2017 melting season
« on: June 16, 2017, 02:29:49 AM »
Wipneus posted a fascinating and potentially alarming gif on his Home Brew thread.

The state of the ice north of Greenland catches the eye. Wipneus cranks up the contrast for those gifs in order to pick out features, so how bad and/or unusual is the situation there?

Looking on Worldview, I was surprised to see the amount of year-to-year variation in that area.

Hoping this 7.7 Mb gif loads so you can see what I mean.

The year is displayed in the top right hand corner.

I score it:
2014 worst
2013 second worst
2012 ~ 2017
2015 and 2016 the ice looks in good shape.


In any event, 2017 doesn't stand out as anomalous. Apparently there are 'good years' and 'bad years' for the sea ice at this particular date and area.


What do more experienced ice watchers than me have to say on the gif?

113
Arctic sea ice / Re: Accuracy of poll predictions
« on: June 16, 2017, 01:42:49 AM »
X would be an estimate of the bias only and probably not a very good one as it's only 4 years of data and Mother Nature has had a big say.

  The actual bias could be defined as the difference between what the forum votes and what some idealised observer with essentially perfect knowledge of the physics would vote.

  The trouble is, the weather fluctuates away from the climate mean so the idealised observer also won't predict the exact answer each year. (It's a chaotic system so the fluctuation is not predictable even with essentially perfect knowledge of the physics.)

  2013 was a rebound year. Was that mostly physics or fluctuation? Given the resumption of the downward trend culminating in the record low maximum volume this year, I suspect the latter. So even the idealised observer would have voted high[EDIT]low - perhaps in all 6 polls for 2013.

  For the other 3 years, its a more difficult question whether the fluctuation was upwards or downwards.

  In my view we can't even rule out that the idealised observer would have voted high[EDIT]low on the other 3 years as well - and maybe in 23 out of the 24 polls. In that case, there would be no evidence whatsoever for bias in the forum.

  It's a shame we don't have polls from 2012 as well. I suspect 2012 was a downwards fluctuation and so the idealised observer would have voted high in 2012, maybe in all 6 polls.

  Maybe the forum would have voted high as well in most or all of the 6 hypothetical polls for 2012. That would have given a very different look to the graphs in the opening post. Does anyone remember if the forum was generally thinking higher or lower than the final numbers for 2012?
 
  In summary, it's easy to over-interpret the graphs in the opening post and difficult to establish bias from only 4 years data in a complicated and chaotic system.

114
Arctic sea ice / Re: The 2017 melting season
« on: June 13, 2017, 01:51:51 PM »
More widespread melt ponds might be expected to appear once much of the Arctic Basin has surface air temperatures rising above freezing.

Nullschool shows this happening around 5 days out - admittedly at the limit of any sort of predictive power for GFS forecasting.

The forecast for 0600 UTC on 18 June shows a fair amount of wind over the Arctic Basin and with nearly all of it above freezing.

115
Arctic sea ice / Re: The 2017 melting season
« on: June 13, 2017, 06:37:12 AM »
Tigertown, the Worldview image doesn't confirm a hole there, looking around (165W, 77N) - maybe a bit of grey showing surface melting.

Nullschool confirms that was a hotspot yesterday, at above +1 degree Celsius, near the centre of a high pressure system.

So the hole in that U. Bremen reconstruction of AMSR2 might well be modified for their 13 June map. It's still above freezing around there so the melt pond hole might possibly even get bigger and/or track the centre of the high pressure system heading northwards.

116
Arctic sea ice / Re: Latest PIOMAS update (June)
« on: June 12, 2017, 11:44:19 PM »
  Incredible graph, thanks Wipneus!

  When comparing the ">1.46m" curve with the "Area 10 September" curve, it is striking how the latter curve is above the former for every single year before 2007, below for 2007 and every single year afterwards.

  It's perhaps the most convincing illustration I have seen showing 2007 as a tipping point year.

  Is it because 2007 wiped out a lot of older ice, resulting in younger ice age distributions in the years after?

  Or was a tipping point reached in area? The ice could move around more within the Arctic basin. Longer fetches became available for waves to develop and crash into the edges of the pack? More moisture arising from open water? More wind due to the open water?

   Or some combination of the above?


   In any case, there appears to be a genuine discontinuity between the years up to 2006 and those from 2007 onwards. At the very least, there is a strong trend for the "10 September area" curve progressively dropping to below the ">1.46m" curve. Thicker ice is now melting out by September than used to be the case in the earlier years. I don't think it can be palmed off as a statistical variation.

117
Arctic sea ice / Re: How soon could we go ice free?
« on: May 29, 2017, 01:06:40 AM »
... the 1'000'000km2 line some will claim ice-free which IMO, can only repeat over and over, is more to get the headline than it would have anything to do with ICE-FREE.

since we're still far away from even that number the topic is a bit neglect but as soon as we get down to the million this will become a hot topic because i'm sure i'm not the only one who is not happy with that 1 million mark. no clue where it even comes from, the wine cask will be empty when the last drop has gone but earliest once one cannot fill a wine glass anymore and 1 MIO km2 is a real lot of ice especially should it consist of ice that is perhaps a bit thicker than just a few cm.

those who like to stick to that 1MIO number so that the event will happen earlier, should at least come up with corresponding thickness = volume numbers.

further it's never good to try to fool the public to get an effect. once people start to claim ice-free arctic while satellite images who everyone can see still show significant ice cover <1'000'000km2 but still, people will say: you see, it's a fake, they try to fool us.

hence the satellites will better show no significant ice-cover once the news will be fed with the "ice-free" term.
One million square kilometres is an established operational definition of ice-free.

In my view it is a good definition.

 In practice there has to be some sort of non-zero threshold chosen. Otherwise the Arctic cannot be ice-free until, for example, the Greenland ice sheet has almost completely melted out to the extent where there are no more icebergs calving off it into the Arctic Ocean.

  The chosen value of one million square kilometres is sensible in my view as it is a round number that is small compared to the area of the Arctic basin (~7-8 million kilometres?). The satellite photos will look very blue when we reach that level.

 The almost-blue status of the Arctic Ocean means that reaching that threshold will act much like 'ice-free' in terms of changes in the weather relative to today, so the definition also makes sense in terms of consequences.


  The beef I have with politicization of the science is somewhat to the contrary: I'm actually not too thrilled at the recent change (was it around a year ago?) in the IPCC that the Arctic reaching the one million threshold in one year now doesn't count - the Arctic now needs to cross the threshold five years in a row before it has officially reached the status of 'ice-free in Summer'. To me, that artificially delays the announcement and it smells of political interference.

118
Arctic sea ice / Re: What the Buoys are telling
« on: May 16, 2017, 12:17:10 PM »
Making use of the same code as last year, but for 2017A.
I have placed the origin in what I believe is the thermistor at the ice surface, but I may be wrong. Anyway, that discontinuity is pretty clear.
I am afraid we'll have fun for less than one month with this one...

Great plot!

So maybe it began with nearly 20 cm of snow but had lost several cm of that by the end?


(Safe) Prediction: that remaining snow isn't going to see out the month!



EDIT: but wait..

Thermal conductivity of ice = 0.005; of water = 0.0014.

So ice has about 3.5 times the thermal conductivity of water.

Conversely, the same depth of water will show about 3.5 times the vertical displacement between the thermistors as ice. There must be some densely packed snow - almost ice but with some trapped air - that shows similar. And maybe that's what we are seeing from 2017A in March? How do we know if it melts? It just gets a little more compact in turning into water, with a similar displacement between thermistors. Perhaps that's what has already happened here - an alternative explanation?

Now I'm uncertain what is going on in that plot, but my apologies for the stream-of-consciousness post!

119
Arctic sea ice / Re: The 2017 melting season
« on: May 15, 2017, 03:10:36 AM »
My eyes keep getting drawn to this area on the west coast of Banks Island. The ice keeps pulling away, there's now a lead of about 50 miles width, I am watching for signs of refreezing. Should I expect much refreezing at this time of year? Images from Worldview, May 1-14. Click to view.
Not at the moment. Look up eight posts, where the Nullschool figure shows a green swathe around that area, indicating the encroachment of temperatures above zero degrees Celsius.

EDIT: FishOutofWater beat me to it, showing it even more clearly.

PS. that gif is spectacular, thanks Vigilius. The Beaufort Sea ice is already breaking up and looking to melt outwards from its Amundsen Gulf corner, and it's only mid-May.

120
Arctic sea ice / Re: The 2017 melting season
« on: May 14, 2017, 01:50:52 PM »
In about two days' time, the first Arctic Basin storm of the 2017 melt season will also provide the first test by wind for the allegedly thin ice in the Laptev Sea. It's forecast to bottom out at about 984 hPa. Nullschool...

121
Arctic sea ice / Re: 2017 sea ice area and extent data
« on: May 13, 2017, 12:45:05 AM »
Thanks Wipneus! I really like your plots restricted to the Arctic Basin regions.

Note the big offset scale - the fractional declines shown in those plots by 11 May are only a couple of percent at most.

2016 has the biggest declines by 11 May. (The purple line on Wipneus' plots.) The reason can be seen from the concentration maps for 13 May (but 11 May for 2017):

https://sites.google.com/site/arcticseaicegraphs/concentration-maps/sic0513

In all the other years, all of the Arctic Basin sea ice is nearly intact through 13 May. In 2016 though, it is seen that the Beaufort Sea had already opened up by a significant amount by 13 May, as shown by the red arrow:



122
Arctic sea ice / Re: The 2017 melting season
« on: May 12, 2017, 01:21:05 PM »
Agree, RikW.

F.Tnioli, you can check out Wipneus' graphs for both extent and area contributions from all the Arctic seas/regions at:

https://sites.google.com/site/arctischepinguin/home/amsr2/grf/amsr2-extent-regional.png
https://sites.google.com/site/arctischepinguin/home/amsr2/grf/amsr2-area-regional.png


It can be seen that these are currently high for Barents Sea, Greenland Sea, Baffin/Newfoundland Bay.

  They are notably low for the Bering Sea.

   The graphs also show that the extent and volume minima are determined largely by only one of the graphs, namely, the Central Arctic Basin, as all the other seas/regions will have melted out, or nearly so, by the end of the melt season.

  Conversely, the Central Arctic Basin remains at essentially full extent and area until, typically, later this month, May.

  Those two observations essentially explain why the current values for extent and area may have little or no correlation with their values at the end of the melt season, as deviations from the usual values are driven mainly by:
 a) for end of season, the Central Arctic Basin; but
 b) up until mid-May, by all the peripheral seas, excluding the Central Arctic Basin.
 

  Before mid-May then, the Arctic sea ice volume is a much better indicator than the area or extent of where the ice will be at the end of the melt season.

123
Arctic sea ice / Re: The 2017 melting season
« on: May 10, 2017, 01:39:16 PM »
Paddy,

D is several orders of magnitude lower. You can pretty much discount it.
C is the biggie directly.
A & B are large follow-on effects depending on weather.
Agree on D.

C is still tiny though. Specific heat of water is 4.2 J/(g.K); heat of fusion is 334 J/g (assumed salt-free). So 4 mm of rain at 2 degrees C will only melt 0.1 mm of ice before cooling to freezing point.
(And the resulting 5 mm puddle of water might still then freeze anyway.)

124
Arctic sea ice / Re: The 2017 melting season
« on: May 10, 2017, 05:19:10 AM »
... Each wave of heat over the next week in the forecast sends  a band of rain right into the heart of the basin - and at the end of tuesday 12Z run there's suggestions of a third


At this time of year is the essential threat of rain more that:

A) it ruins the insulating effect of any snow cover on the ice pack?

&/or

B) it acts like melt ponds in raising the absorption of solar radiation?


(I'm guessing still A, because it is probably going to freeze quickly?)

125
Arctic sea ice / Re: The 2017 melting season
« on: May 02, 2017, 11:16:37 PM »
All the tropicaltidbids.com ensembles are showing high pressure over the Arctic basin as far as the forecasts can see - 18 days - especially on the American side.


 It would be interesting if the weather experts here could please comment on whether the forecast is robust, for how far out, and what are the fundamental causes?


'Melt pond May'?

126
Arctic sea ice / Re: Latest PIOMAS update (May)
« on: May 02, 2017, 11:38:00 AM »
Thanks Wipneus! So was 25 April the date of maximum sea ice volume by that method?

127
Arctic sea ice / Re: The Fast Transition
« on: April 28, 2017, 12:16:52 AM »
Jim, that's interesting and scary. Can you give a reference and/or more information on that?

128
Arctic sea ice / Re: The 2017 melting season
« on: April 20, 2017, 01:37:56 AM »
Attached is a month-by-month gif of the ice coverage maps from the Arctic and Antarctic Research Institute, St. Petersburg, Russia,
http://www.aari.ru/odata/_d0015.php?lang=1.

The maps are interesting because they track the old ice that has survived at least one melt season - shown in reddish-brown.

One example map was chosen for each month from 2016-10 to 2017-04, with a date around 18th of each month.

Apologies for my poor gif-making skills.

 The gif seems to show a continuing loss of the old ice on the Russian and Atlantic sides that extends in time all the way through to the January 2017 frame. This happened despite new ice completely surrounding the old ice region.

  It is seen that the old ice has been pushed away from the Russian side and also nibbled away at on the Atlantic side - the infamous 'Atlantic kill zone'.

   The pattern by now seems to be a continuation of that movement away from the Russian side. That is now driving a bifurcation, with some of the compressed ice turning left and heading towards the Atlantic side kill zone and the rest turning right towards the Beaufort Sea.

   The latter seems to be the 'Beaufort gyre' setting up due to the recent high pressure systems in the Beaufort. If that continues then this year will again have a wall of old ice between the Beaufort Sea and Central Arctic Basin (CAB), albeit thinner ice than last year.

129
Arctic sea ice / Re: The 2017 melting season
« on: April 15, 2017, 12:58:06 AM »
Great animation Andreas. Any idea of the total distance moved? Is this something like 1000 km?
sorry, that 100km marker is only partly shown. On average the northern edge of the area is just south of 85degN. That makes it a little over 500km long. Width is about 300km
Yes, very nice plot Andreas. Thanks for posting it.

Concerning the length of the designated region and its Northern edge, the North Pole is where the two lines of constant longitude intersect.  I used 2 rulers to find the point of intersection (i.e. the position of the North Pole, not shown in the images) and to extimate that the Northern edge of the designated area intersects the 0 degrees longitude line at ~86degN.

The length of the line segment inside the area and down to the 80degN curve is therefore 6 degrees of latitude, which is around 670 km.

So that means the ice starting at the Northern end of the line segment travelled about 670 km
out through the Fram Strait in the 2 months beginning on 12 February. That's an average flow speed of around 20 km per day.


Approximating your area by a rectangle with the Southern side at 80degN then the width of the rectangle is about 60% of its length.

So the ice area enclosed is ~ 0.6 x (670 km)^2 ~ 270,000 km^2

That area can be considered lost by export in ~61 days, or ~4400 km^2/day.

If assuming the ice thickness averages 2.3m = 0.0023 km then 4400 x 0.0023 = 10 km^3/day
is lost by Fram export; a total of ~600 km^3 over the 2 months.


If we approximate the maximum sea ice volume this year at ~20,000 km^3 (from PIOMAS) then the fraction lost is:
~600/20,000 ~ 3%.



So Andreas' animation shows about 3% of this year's maximum Arctic sea ice volume has been lost by export through the Fram Strait over the past 2 months.

130
Arctic sea ice / Re: Stupid Questions :o
« on: April 06, 2017, 07:55:03 AM »
No, the break even day is not the equinox.

The vernal equinox has passed but I very much doubt that break even has been reached for a clear sky over the North Pole.

Break even - presumably defined as when the surface temperature holds steady - requires the outgoing energy to balance the incoming energy.

The plot below from NASA, though intended for a slightly different purpose and displaying numerical values that wouldn't be appropriate at the North Pole, shows the contributions.

Outgoing from surface:
longwave thermal radiation from surface (will dominate at the moment at North Pole)
sunlight reflected from surface (EDIT: this isn't part of the thermal energy balance)
thermals
evapotranspiration


Incoming from atmosphere:
downgoing longwave thermal radiation from atmosphere (will dominate at the moment at North Pole)
incident sunlight absorbed


The values and relative sizes of these terms will depend on surface temperature, atmospheric temperature profile, surface emissivity/reflectance (which depends on wavelength and is very different for ice than for liquid water), atmospheric moisture content and the elevation of the sun above the horizon.

So there's no fixed date for break even.

In general, break even at the North Pole or in the Arctic, with a clear sky, can only occur when the sun is well above the horizon - so that will be well past the vernal equinox.

131
Arctic sea ice / Re: Latest PIOMAS update (April)
« on: April 05, 2017, 11:24:04 PM »
Thanks for the update Wipneus, much appreciated.

Those year-to-year differences maps for 31 March are telling: the ice appears in worse shape this year than in any of the previous years shown, apart from that blob of thick ice poised over Fram Strait.

132
Arctic sea ice / Re: The 2017 melting season
« on: April 05, 2017, 10:21:52 AM »
Looks like it's setting up for a Siberian high.
Yes, I'm thinking that should offer some temporary respite for the ice, following all the strong low pressure systems of past weeks.

  The forecast winds around the Arctic basin over the next several days are relatively weak and, with the sun still low on the horizon, clear skies from the high should allow long wave thermal radiation to escape to space without the ice being exposed to too much down going short wave radiation.

133
Arctic sea ice / Re: The 2017 melting season
« on: April 02, 2017, 12:58:31 PM »
Arctic Sea Ice Currently Taking a Hit From All Sides
Yes, the Arctic sea ice seems to be taking a hit from all 4 sides of the Arctic Basin at the beginning of the melt season.

Summarising recent posts above:
1) Russian side - big cracks and areas of low concentration as the ice is blown out to sea
2) Atlantic side - ice blown out into the Barents sea, where bottom melt might be expected
3) Ice transport through the Nares Strait seems to be setting up
4) Ice is being blown out through the Bering Strait and the ice already South of there is breaking up and being blown further South.


U. Bremen Ice Concentration Map Year-on-Year Comparison for 1 April
April 1st is one of the chosen days for Neven's useful year-to-year comparison of the U. Bremen Arctic sea ice concentration maps.

As attached below, this comparison shows the ice this year on the Russian side - i.e. the ESS and Laptev Sea (red arrow) to be, on the face of it, in the worst state for this date of any of the illustrated years.


CPOM/ESA Spring Ice Thickness Maps for 2011-14 and 2017
The CPOM/ESA measurements of ice thickness are wrapping up for the end of this freeze season. As they are actual measurements - albeit with corrections - rather than more model-based assessments, I tend to consider that they probably give the most accurate picture of the ice thickness distribution over the Arctic Basin. Also attached then is a gif showing their latest 28-day map compared against the years for which they publish well-calibrated Spring maps, namely 2011-14.

  From these maps, the 2013 Arctic sea is seen to have been in terrible condition after the carnage of the record 2012 melt season. On the face of it, 2013 had less thick ice around this date than even this year, in contrast to the other years shown having considerably more ice than this year.

   And yet 2013 turned out to be a recovery year for the sea ice, which suggests that this year also has that potential in the case that this year's upcoming melt season turns out to be mild. On the other hand, is this year's ice already being blown around more than was the case in 2013?

   The bottom line from this comparison is that a mild melt season this year could still lead to a recovery in the Arctic sea ice but, on the other hand, a historic low minimum extent in 2017 is looking quite likely. It's early days yet.

134
Arctic sea ice / Re: The 2017 melting season
« on: March 31, 2017, 02:48:07 AM »
WorldView shows the big tears in the ESS and Laptev Sea and the exposed water gaps next to them.

Compare with last year on the same date: the outer boundary of the fast ice was still visible as a crack but the ocean side still had solid ice right next to the crack (albeit with some smaller fractures visible).

EDIT:
2015 was similar to last year.

A bit more action was seen in the Laptev in 2014 although less dramatic than this year and, again, there was no big water gap in the ESS.

135
Arctic sea ice / Re: Home brew AMSR2 extent & area calculation
« on: March 29, 2017, 04:18:12 PM »
Wipneus and SeaIceSailor,

  Thanks for your comments on the potential causes of the concentration loss observed in the Laptev Sea.

  Yes, a snow/rain connection looks reasonable: toggling to the "3-hour precipitation" option on Nullschool and stepping through the 3-hourly displays does indeed show precipitation of order 1 mm (which could be ~1 cm if it fell as snow) drifting over the region around that time.

136
Arctic sea ice / Re: Home brew AMSR2 extent & area calculation
« on: March 29, 2017, 02:32:59 PM »
The crack in the ESS is getting real wide. The Laptev fast ice is torched.

Wow! So what is happening here?

 EDIT: U. Bremen's AMSR2 concentration map for 2017-03-28 is also showing the loss - with around 75% concentration in the fast-ice region of the Laptev Sea that has gone dark in Wipneus' graphic.

Is it melt ponds or is there actually no ice over around 25% of that region?

Options:
A. We're only just past the equinox, there presumably won't be enough sunlight to cause melt ponds, fair?
B. But it's plausible that winds could have melted some snow cover?
C. Alternatively, the ice could have been in such a poor state that the winds tipped it over the boundary to where much of it is no longer classified as ice cover?
D. Or it might be tearing in the wind and now full of micro-cracks?

Anyone more knowledgeable have a take on which of the options is most likely?

The screenshot is from Nullschool at 12:00 UTC on 2017-03-27.
The illustrative chosen point in the Laptev Sea with the green circle is showing 25 kph winds at -2.6 degrees C.

137
Arctic sea ice / Re: The 2017 melting season
« on: March 27, 2017, 10:05:16 PM »
SeaIceSailor,

  My guess at the reason why there are no visible cracks in the Beaufort Sea at the moment is because it has been under fairly constant compression over at least the past month. So the lack of cracks probably doesn't speak much to the quality, or otherwise, of the ice there.

138
Arctic sea ice / Re: Roundhouse punches from the ApocalyptoKraken
« on: March 27, 2017, 08:41:29 AM »
Thanks Hyperion, I agree that it's interesting to look at the potential contribution of atmospheric water to Arctic sea ice melt so I will take you up on your 'peer review' offer...

...
Quickstab at what this setup might mean numerically. Peer review and alternative approaches most welcome:
 ;)

1,680,000,000,000,000J
18.748 kg/sqm
200km x 50kmph (ballpark flow estimate) x 24hr = 240 000 sqkm = 240 000 000 000 sqm
240 000 000 000 sqm x 19 kg x 4200J = 19,152,000,000,000,000 Joules per day
=19.52 petajoules per day
...
That's the specific heat capacity of water - the amount of energy required to raise the temperature of 1 kg liquid water by 1 degree Kelvin \ Celsius. Better to use the heat of evaporation as the "Total precipitable water" is almost all vapour (use "Total cloud water" option to see the small part that isn't) and can melt ice by condensing. This contribution to heating the ice is much larger than the heats from temperature changes.

Water properties here.
It's actually even easier to use the ratio of heats of vaporisation to fusion.
Latent heat of melting - 334 kJ/kg
Latent heat of evaporation - 2257 kJ/kg
Ratio ~ 2257 / 334 ~ 6.76. So each kg of water vapour can, by condensing, cause the melt of nearly 7 kgs of ice.

Expressed in scientific notation, you estimated 2.4e11 m^2 of moist air entering the Arctic per day, carrying 18 kg/m^2 of water vapour, so on multiplying you say about 4e12 kg/day of water vapour entering the Arctic.

From above, this could melt 2.4e11 x 18 x 6.8 kg/day ~ 3e13 kg/day of ice.

To see if this would be a relevant amount, we should ask how many kg of ice are in the Arctic?

From PIOMAS, we see that the volume of Arctic sea ice at the end of the freeze season is around 20 000 km^3 ~ 2e13 m^3. Ice weighs around 900 kg/m^3, so this is ~ 2e16 kg of ice.

On comparing the two, it would take several hundred days to melt all the ice at the assumed rate of ingress of water vapour and assuming a large fraction of it condenses to melt ice.

  As an initial impression, I would also say that the rate of ingress you assume is anyway much larger than would be typical, perhaps by an order of magnitude or more.


So this back-of-the-envelope calculation suggests that the ingress of atmospheric water vapour into the Arctic can't account for a large fraction of the yearly ice loss. However, it wouldn't be surprising if it contributed at the percent level or maybe up to a few percent of the ice loss.

Given the observed rise in atmospheric moisture beginning around the start of 2016, this could still mean a significant rise in sea ice loss by this mechanism.

Presumably this has been studied at a more rigorous level. Does anyone know of such a study and their findings?
EDIT: already answered and it has been studied. Thanks, Jai Mitchell.

139
Arctic sea ice / Re: The 2017 melting season
« on: March 26, 2017, 03:09:27 AM »
Terrific, Hyperion!

Yes, start a thread please.

The greatest of respect to the many dedicated scientists, technicians etc. who are already providing the experimental information we rely on to understand the state of the Arctic.

Having said that, it's a disgrace that we don't have more coverage; a disgrace that we need inadequately calibrated models for the currents, water temperatures and salinities, etc - as well as information on the ice and snow state and thickness.

   Smart probes for the Arctic are difficult to fund even while smart bombs are streaming off the assembly lines.

   More broadly than your particular solution, it makes a lot of sense to have a thread on the future experimental program for monitoring the Arctic.

   Better in"Policy and solutions" or in "Science"?

   I had a look previously and couldn't find an existing thread. (Did I just miss it?)

   So there were a series of posts in the "What the Buoys are telling" thread kicking off with this one from me and then with those more knowledgeable and experienced posting valuable content.

Maybe all that can be moved to a new dedicated thread for e.g. "Existing and proposed experimental apparatus and programs for the Arctic" and add your stuff and other proposed solutions?

140
Arctic sea ice / Re: The 2017 melting season
« on: March 24, 2017, 12:50:07 AM »
"...the Arctic turns into a single gyre"?

 There hasn't even been a gyre lately. Instead the ice in the Arctic Basin has been blown from the Russian side and compressed against the Canadian side, with some leaking out towards the Atlantic...




  The good news is that the compression has helped to heal the Beaufort Sea back to around a 2 metre thickness.

   And if the pattern ends soon then there is still well over a month left of weather cold enough to somewhat heal the tears on the Russian side.

   But what if the tear-and-compression continues well into April or May? Will large stretches of water remain open on the Russian side, efficiently absorbing the peak insolation around the Summer solstice?

  A broader question is why so much compression? Is there enough thin and weak ice this year in the Arctic Basin that any wind pressure from the Russian side will always result in movement and compression? And is this movement replacing the Beaufort gyre of seasons past, with the ice now compressing rather than transferring the force for rotation?

   If so, does this mean that maximum Arctic sea ice volume for the year has descended this season to a transition value, or even a tipping point, where the ice will continue to tear-and-compress from the Russian side heading into the Summer melt season, with the Russian side therefore opening up anomalously early?

   Or, instead, will the movement damp down within a few weeks and those consequences won't come to pass this year?

   Either way, the plot twists and turns of the melt season are going to provide us with riveting viewing.

141
Arctic sea ice / Re: Arctic Image of the Day
« on: March 20, 2017, 10:16:59 PM »
It's Icepacman!  :o

142
Arctic sea ice / Re: The 2017 melting season
« on: March 14, 2017, 08:42:52 PM »
Thanks Romett1. Yes, the HYCOM prediction is scary, with a lot of thicker ice either exiting through the Fram Strait or else heading in that direction.

  A lot of the thickening in the Beaufort Sea appears to be from compression, with the ice blown towards the Alaskan and Canadian Arctic coastlines.

  It's going to be critical how much new ice grows over the next month on the Siberian side to replace the ice that has migrated West. Are we going to have much of the thin ice on the Atlantic side of the Laptev Sea melted out and exposed to peak insolation by around the Summer solstice?

143
Arctic sea ice / Re: Stupid Questions :o
« on: March 14, 2017, 04:41:55 AM »
OK, that's a different statement. Note however that last year, 2016, didn't top out early and last year also had anomalously high 80N+ temperatures at this time of year.

At the beginning of March this year was about 2K km^3 below 2016 - which topped out as the record min-max (~tied with 2011) - so, yes, it wouldn't be too surprising if we ended up around 2K km^3 below that.

144
Arctic sea ice / Re: Stupid Questions :o
« on: March 14, 2017, 03:14:43 AM »
This is as much ice as we are going to get.

Based on what? It's only mid-March. According to PIOMAS, ice volume typically grows into mid-April - so another month or so.


145
Arctic sea ice / Re: Latest PIOMAS update (March)
« on: March 05, 2017, 01:10:42 AM »
Terrific information, thanks Andreas! Your reply, #1387 above, beautifully addressed my question on how much insolation the Arctic actually receives.

What a great forum this is!

146
Arctic sea ice / Re: Latest PIOMAS update (March)
« on: March 04, 2017, 10:46:35 PM »
I'm still uncertain on how much insolation the Arctic actually gets.

Is the plot showing insolation on a horizontal surface? Or on a tracking surface always perpendicular to the sun? (I presume the former.)


More importantly, does it include a model or measurement of the effects of the atmosphere, including the variable moisture content and cloud cover? If it's insolation at the top of the atmosphere then that's much larger than what reaches the ground. That is particularly true in the Arctic, given the typically low solar elevations from the horizon.

  The Arctic was cloudier than usual last summer, so the insolation reaching the ground would also have been less than usual. Will this summer be similar?


So the question of how much insolation reaches the Arctic is not simple and is not fully addressed by a single graph.

147
Arctic sea ice / Re: Poll: 2017 PIOMAS Maximum Monthly Figure
« on: March 04, 2017, 10:27:46 AM »
Voted 20.5-21.0 x 10^3 km^3.


At day 59 we were at 18.6 in those units.

Archimid posted on the PIOMAS update thread that, in past years, the average gain to maximum from there has been 2.1. Taking the average gives 18.6 + 2.1 = 20.7 - hence the choice of bin.


It could be argued that the Arctic Basin hasn't been as cold as usual this year, with FDDs way down. That trend may well continue over the next month or two.

On the other hand, I see lots of potential for adding volume in the 'ice factory' on the Russian side of the Arctic Basin. Offshore winds there have been, and still are, exposing new sea surface there which is rapidly freezing over and thickening.

So I think taking the average gain from day 59 to maximum ice volume is reasonable.







148
Developers Corner / Re: Mapping GeoCoded Data Sets
« on: February 26, 2017, 11:58:06 PM »
Hi CognitiveBias

   Yep, that should also be fine. I might have been getting ahead of myself thinking about a problem that doesn't matter - your option of using Sept 1 everywhere is simpler and it would be great to get a first look at the distributions!

149
Arctic sea ice / Re: The 2016/2017 freezing season
« on: February 26, 2017, 11:27:49 PM »
2/2 (needed a second post due to 4 attachment limit)

Continuing with inspecting the Canadian Ice Service (CIS) charts of the 2009 melt season in the West Arctic, which corresponds roughly to the Beaufort Sea as well as some of CAB between the Beaufort and the North Pole. Recall from the posts above that the sea ice in the West Arctic currently (late February) looks worst in the CIS archives and that 2009 looks the second worst.

  It turns out that the first year ice mostly melted out anyway by the end of the 2009 melt season in the West Arctic, but much of the multi-year ice survived.


  So that gives us some idea of what might happen again in the West Arctic this year, in the scenario of similar weather to 2009 over the next several months. Unsurprisingly, the Beaufort Sea will melt right out. But the multi-year ice North of that could survive.


  In the alternative scenario that the stormier weather of 2016-7 persists into the 2017 melt season, then much of the multi-year ice currently in the West Arctic may also be lost, due to transport by the wind into either the CAA 'garlic press' or into a Beaufort Sea 'kill zone' that has already melted out.

Attached: Canadian Ice Service chart for West Arctic on 2009-09-28.

150
Arctic sea ice / Re: The 2016/2017 freezing season
« on: February 26, 2017, 11:17:54 AM »
[EDIT: I redid this post as I was dissatisfied with my original characterisation of the 2009 charts]

1/2
Had further look at the archived Canadian Ice Service(CIS) sea ice charts for the Beaufort Sea. Previously, I had only looked back to 2010 whereas the archive goes back to 2004.

It turns out that the 2009 Beaufort ice also looked fairly weak at this time of year - the weakest in the archive outside of this year.  (The years earlier than 2009, however, had considerably more thick ice than this year.)

  As one historical surrogate then for the potential Beaufort sea ice development this melt season, the 2009 progress of the Beaufort ice can be examined for through the end of the freeze season and then for the melt season. On inspection, it turns out the 2009 Beaufort ice continued to thicken until at least mid-March and most survived well into July.

The relevant charts from the CIS archive follow, for dates in this order:
2017-02-20 (repost) - the ice condition this year; note all the light green = 1st year ice <120cm thick
2009-02-16 - note that 2009 also had a lot of light green around mid-February
2009-03-16 - one month later, the light green has ~all gone dark = >120 cm
2009-07-13 - the Beaufort hadn't melted out much by mid-July 2009

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