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Messages - slow wing

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51
Arctic sea ice / Re: The 2018 melting season
« on: August 28, 2018, 05:24:01 AM »
U. Bremen's false colour ice concentration maps show a week's action in the Arctic basin, ending on the map just released, 2018-08-27...

52
Arctic sea ice / Re: The 2018 melting season
« on: August 27, 2018, 05:38:24 AM »
U. Bremen's false colour ice concentration maps show a week's action in the Arctic basin, ending on the map just released, 2018-08-26...

53
Arctic sea ice / Re: The 2018 melting season
« on: August 26, 2018, 05:24:34 AM »
Today, Aug 25, is one of the dates shown on Neven's year-to-year ice concentration map comparison.

It's easy to forget that, for the most recent two previous years, 2016 and 2017, the ice on this date was in bad shape for close to the North Pole and on the Russian side.

This year, 2018, the ice is compact on the Atlantic side but spread out on the Pacific side. Low atmospheric pressure is expected to begin to dominate within the next day or so, bringing some moderately strong winds. How much of the Pacific-side ice debris will that clean up?

54
Arctic sea ice / Re: The 2018 melting season
« on: August 26, 2018, 05:11:51 AM »
U. Bremen's false colour ice concentration maps show a week's action in the Arctic basin, ending on the map just released, 2018-08-25...

55
Arctic sea ice / Re: The 2018 melting season
« on: August 25, 2018, 06:01:00 AM »
U. Bremen's false colour ice concentration maps show a week's action in the Arctic basin, ending on the map just released, 2018-08-24...

56
Arctic sea ice / Re: The 2018 melting season
« on: August 24, 2018, 05:50:55 AM »
U. Bremen's false colour ice concentration maps show a week's action in the Arctic basin, ending on the map just released, 2018-08-23...

57
Arctic sea ice / Re: The 2018 melting season
« on: August 23, 2018, 01:43:38 PM »
I think this is partially an illusion of clouds.

The other 2 satellites show the same shape against different cloud backgrounds.

58
Arctic sea ice / Re: The 2018 melting season
« on: August 23, 2018, 09:22:15 AM »
After a couple of weeks of relentless Southerly winds from a warm Laptev Sea, the edge of the ice pack here is a smoothly curving line with no structure from individual ice floes.

59
Arctic sea ice / Re: The 2018 melting season
« on: August 23, 2018, 05:22:37 AM »
U. Bremen's false colour ice concentration maps show a week's action in the Arctic basin, ending on the map just released, 2018-08-22...

60
Arctic sea ice / Re: The 2018 melting season
« on: August 22, 2018, 05:24:23 AM »
U. Bremen's false colour ice concentration maps show a week's action in the Arctic basin, ending on the map just released, 2018-08-21...

61
Arctic sea ice / Re: The 2018 melting season
« on: August 21, 2018, 05:57:30 AM »
U. Bremen's false colour ice concentration maps show a week's action in the Arctic basin, ending on the map just released, 2018-08-20...

62
Arctic sea ice / Re: The 2018 melting season
« on: August 18, 2018, 07:37:45 AM »
Quote

The U. Bremen site that I had been using previously has been down for several days. Do we know why and have the reasons been posted here?
Always assume nefarious intent from the usual suspects. Of course I don't have proof they had to move it for disorderly behavior. Politics is not science so I suggest take these insinuating questions elsewhere.
I don't understand that response at all. It was a straight question and it related only to the science, not to politics. I don't know the reasons and asked for them only as a way to help determine how long the site and data is likely to be down for.

At the discretion of anyone who knows, they are of course welcome to instead answer that directly: how long are the site and data likely to be down for? That is what is directly relevant to me and to this thread as I had been posting images sourced from there every day on this thread.

63
Arctic sea ice / Re: The 2018 melting season
« on: August 18, 2018, 01:22:32 AM »
NSIDC ice concentration maps show a week's action in the Arctic basin, ending on the map most recently released, 2018-08-16 - see first figure.

There is a low concentration region showing that, if it happened to melt out completely, would snip off the corner of the main ice pack that extends into the Beaufort Sea. Presumably too late in the season for that though. Rather than the ice melting out, the low concentration region has presumably arisen largely from the ice floes there being separated by winds from the low pressure system currently in the CAA - as shown in the second figure.

The U. Bremen site that I had been using previously has been down for several days. Do we know why and have the reasons been posted here?

64
Arctic sea ice / Re: The 2018 melting season
« on: August 15, 2018, 08:18:53 AM »
U. Bremen's false colour ice concentration maps show a week's action in the Arctic basin, ending on the map just released, 2018-08-14...

65
Arctic sea ice / Re: The 2018 melting season
« on: August 14, 2018, 05:07:46 AM »
U. Bremen's false colour ice concentration maps show a week's action in the Arctic basin, ending on the map just released, 2018-08-13...

66
Arctic sea ice / Re: The 2018 melting season
« on: August 13, 2018, 06:40:38 AM »
After a cloudy July, the Arctic sea ice on the Russian side has suffered under two weeks of high atmospheric pressure and the clear skies that brings.

The ice north of the Laptev Sea, in particular, has also wilted under southerly winds carrying heat from the Siberian land mass.

With that high pressure system expected to finally be displaced by a low pressure system arriving from the Kara Sea, soon the Siberian heat should instead be steered towards the large sea ice lobe that extends southwards into the Eastern Siberian Sea.

That prediction is illustrated below with a earth.nullschool.net 48 hour forecast.

As I understand it, we're transitioning into the late stage of the melt season where exposure to heat and salt in the water becomes more important to melting the sea ice than direct heat from sunlight or winds. Therefore, the predicted arrival of low pressure and relatively strong winds to stir things up, will probably be conducive to a continuation of strong melting in the middle part of August.

67
Arctic sea ice / Re: The 2018 melting season
« on: August 13, 2018, 06:03:25 AM »
U. Bremen's false colour ice concentration maps show a week's action in the Arctic basin, ending on the map just released, 2018-08-12...

68
Arctic sea ice / Re: The 2018 melting season
« on: August 12, 2018, 05:23:33 AM »
U. Bremen's false colour ice concentration maps show a week's action in the Arctic basin, ending on the map just released, 2018-08-11...

69
Arctic sea ice / Re: The 2018 melting season
« on: August 11, 2018, 05:39:23 AM »
U. Bremen's false colour ice concentration maps show a week's action in the Arctic basin, ending on the map just released, 2018-08-10...

70
[4.25,4.75]. Just went up 0.25 from my daily minimum prediction, which I explained in more detail.

71
I voted the [4.00-4.50] million square km bin.

I like the ice movement vector display for today as probably providing a good proxy for where the ice will remain. I'm guessing the ice shown in white will probably remain while that in light blue will probably go.

To set the scale, the area of the circle for 80 degrees latitude is approximately pi*(10,000/9)^2 km^2 ~ 3.9 million square km. (The Earth's curvature has been ignored.)

Just eye-balling, the area of white ice is similar to that area. I think a bit of the light blue ice might remain in the ESS. Hence the bin [4.00,4.50].

If I had to guess the year rank, I think this year will end up in fourth place. Reading off from the opening post, and in units of million square km:
3.18 2012 1st
4.02 2016 2nd
4.07 2007 3rd
[2018 may go here]
4.26 2015
4.27 2011
4.47 2017
...







72
Arctic sea ice / Re: The 2018 melting season
« on: August 10, 2018, 06:58:17 AM »
U. Bremen's false colour ice concentration maps show a week's action in the Arctic basin, ending on the map just released, 2018-08-09...

73
Arctic sea ice / Re: The 2018 melting season
« on: August 09, 2018, 06:41:45 AM »
U. Bremen's false colour ice concentration maps show a week's action in the Arctic basin, ending on the map just released, 2018-08-08...

74
Arctic sea ice / Re: The 2018 melting season
« on: August 08, 2018, 06:42:14 AM »
Nullschool showing continuing heat just above the Laptev Sea - this time 11.0 degrees. As can be seen from the gif I just posted, the ice north of the Laptev is being torched by the sun & warm winds of the large & persistent high pressure system.

75
Arctic sea ice / Re: The 2018 melting season
« on: August 08, 2018, 05:43:38 AM »
U. Bremen's false colour ice concentration maps show a week's action in the Arctic basin, ending on the map just released, 2018-08-07...

76
Arctic sea ice / Re: The 2018 melting season
« on: August 08, 2018, 01:45:31 AM »
Toasty! Nullschool says it's 10.0 degrees Celsius right now in the Laptev Sea and far north of the coastline.

77
Arctic sea ice / Re: The 2018 melting season
« on: August 05, 2018, 05:58:20 AM »
U. Bremen's false colour ice concentration maps show a week's action in the Arctic basin, ending on 2018-08-04...

78
Arctic sea ice / Re: The 2018 melting season
« on: August 03, 2018, 05:31:01 AM »
A week's action in the Arctic sea ice as shown by U. Bremen's false colour ice concentration maps, ending with 2018-08-02...

79
Arctic sea ice / Re: The 2018 melting season
« on: August 03, 2018, 12:25:21 AM »
At tropicaltidbits.com, all of the NAVGEM, GFS and ECMWF forecasts agree that the big high pressure system currently dominating weather over the Arctic Ocean will remain strong for at least the next week.

NASA's Worldview display shows that the high pressure has already cleared away the clouds over much of the Arctic Basic, especially on the Russian side - as shown in the screen capture below.

This persistent high pressure would presumably have wreaked havoc with the Arctic sea ice pack if it had parked up sooner after the summer solstice, exposing the ice to direct sunlight at its strongest. Even in the first half of August, there will still be plenty of solar energy shining down on the exposed ice in the Arctic Basin. How much deterioration of the ice will it cause anyway?

80
Arctic sea ice / Re: The 2018 melting season
« on: August 02, 2018, 06:02:43 AM »
Showing a week's action of the Arctic sea ice, ending with today's false colour ice concentration map from U. Bremen, so 8 consecutive daily maps spanning 7 days and ending at 2018-08-01...

81
Arctic sea ice / Re: The 2018 melting season
« on: August 01, 2018, 08:47:42 AM »
July was cloudy in the Arctic Basin & low pressure systems dominated.

But now a big high pressure system has set up towards the Russian side and looks like it is going to stay for at least the next few days.

So expecting plenty of sun, especially towards the Russian side, as well as warmer winds from the Atlantic sweeping over the 'ice sanctuary' north of Greenland and the Canadian Arctic Archipelago (CAA).

82
Arctic sea ice / Re: The 2018 melting season
« on: August 01, 2018, 06:30:35 AM »
Adding today's false colour ice concentration map from U. Bremen, now 8 consecutive daily maps spanning 7 days and ending at 2018-07-31...

83
Arctic sea ice / Re: The 2018 melting season
« on: July 31, 2018, 05:56:39 AM »
Adding today's false colour ice concentration map from U. Bremen, now 7 consecutive daily maps spanning 6 days and ending at 2018-07-30.

Click to animate...

84
Arctic sea ice / Re: The 2018 melting season
« on: July 30, 2018, 11:43:31 AM »
Adding today's false colour ice concentration map from U. Bremen, now 6 consecutive daily maps spanning 5 days and ending at 2018-07-29.

Click to animate...

85
Arctic sea ice / Re: The 2018 melting season
« on: July 29, 2018, 05:19:35 AM »
Yes, the Beaufort Sea ice front facing the Alaskan north coastline is being pushed northwards. That's unsurprising, given the poor state of the ice there in recent days.

Otherwise a slight bounce-back, particularly in the ESS.

Adding today's false colour ice concentration map from U. Bremen, now 5 consecutive daily maps spanning 4 days and ending at 2018-07-28.

Click to animate...

86
Arctic sea ice / Re: The 2018 melting season
« on: July 28, 2018, 07:40:36 AM »
Worldview visual confirmation is starting to come in for 2018-07-28.

Here is:
1) a screenshot of most of the area showing by now from TERRA satellite - roughly the Pacific side of the Arctic; and
2) a movie of the 10-day interval from 2018-07-18 to 28 for a zoomed-in region well into the ice pack but where the concentration isn't all that high - around 180 degrees longitude & latitude 80 degrees North & maybe ~180 km x 130 km (just a guess to give an idea of the scale). The approximate rectangle of the frame is also sketched roughly in the screenshot of 1 - you can use the ice features for 07-28 to compare the screenshot with the gif.

On watching the movie, it is seen that the ice in the movie region has definitely deteriorated over the 10 days. For example, identifiable larger floes seen close to the (180,80) point in the earlier frames appear to have broken up into non-identifiable smaller floes by the 27th and 28th, presumably with some melting and loss of ice surface area.
EDIT: no! On further inspection it appears that probably the largest floe in the movie started right next to the (180,80) point and ended up closer to the top RHS corner. That would be movement of a few tens of kilometers over 10 days, which is not unreasonable.

There is a lot of cloud cover. Perhaps the cloud obscured some of the changes in some regions, only revealing them in the last 3 days - giving the appearance of a more dramatic collapse.

A large part of the effect, at least in this region in the interior of the pack, appears to just be floes moving around, with gaps between adjacent floes opening or closing. With the floes not bound together, dispersion can create significant gaps without any actual melt.

So the change over the 10 day interval may have come from a combination of the above 3 effects.

Will the sun be shining on this region over the next few days and, if so, will it still be warm enough to put down some serious heat into the exposed liquid water and further melt the ice here?

87
Arctic sea ice / Re: The 2018 melting season
« on: July 28, 2018, 06:03:24 AM »
Yes, the deterioration of the ice pack over the past 3 days has been jaw-dropping!

Click to animate...

88
Arctic sea ice / Re: The 2018 melting season
« on: July 27, 2018, 05:17:48 AM »
Wow! In the Bremen ASI false color maps, the ice seems to have taken a pounding for the second day in a row! Just look at that deterioration in the Beaufort Sea and ESS!

I expected a 'bounce back' today, but no. Still expecting one tomorrow. But once areas go green they are usually in a poor state already.

Gif will need a click to start..

89
Arctic sea ice / Re: The 2018 melting season
« on: July 24, 2018, 06:10:40 AM »
Yes, the ice pack shape expected for around the extent minimum is starting to emerge.

Looking ahead by 50 days, Andrew Slater's algorithm is now up to 11 September, and so should be fairly close to the expected minimum. Its predicted extent for that date is 4.61 million square kilometers.

Personally, I would believe that prediction as well as any other as I like the method used and the execution also looks good.

Note that the predicted extent is still above that given about 2 weeks ago, of 4.56 million square kilometers already by 29 August 2018. Presumably that reflects weather during the past 2 weeks that has not been favorable for melting the ice.

90
Arctic sea ice / Re: SMOS
« on: July 21, 2018, 11:13:18 PM »
Agree, Fish, that there are other processes - that you have given - that can cause a lot of bottom melt even when the top of the ice is dry.

The above discussion relates specifically to heat conduction down through the ice when the top is heated by warm winds.

Parenthetically, there are also a couple of other issues that work against lots of heat transfer by that mechanism: air can carry only very little heat per unit volume - orders of magnitude less than water, and the thermal coupling to the ice will usually be poor. (Water vapour in the air helps though.)

91
Arctic sea ice / Re: SMOS
« on: July 21, 2018, 02:49:20 PM »
This magical bottom-only melt arises because "Ice conducts heat better than water", and so it will conduct the atmospheric energy through to the water under the ice, allowing the ice to melt from the bottom, but not the top.  This is drivel.  Heat cannot of itself pass from one body to a hotter body. i.e. if the ice is conducting heat downwards, then the top of the ice is hotter than the bottom, so the top will melt first.

Commenting in this discussion, this is my understanding of the situation.

Hyperion is technically correct - this situation is possible under some circumstances.

The quote above is correct that the top will be 'hotter' than the bottom, because that is where the heat is coming from.

However, it is incorrect in claiming that means the top will always melt first. The reason is the presence of salt at the bottom, but not at the top, which lowers the melting point at the bottom.

E.g the top will melt at 0 degrees C if there's no salt, but the bottom may melt at -1.8 degrees C at a reasonable salinity for sea water.

So the situation of bottom melt in Arctic sea ice with heat carried from a dry top is theoretically possible.

In practice, on the other hand, I suspect that such a scenario is presumably unlikely to make a big contribution to the overall melt.

The reason is that the thermal conductivity of ice is not all that good: it's around 2.2 W/(mK). So there is going to be a non-negligible temperature gradient in order to carry a non-negligible flow of heat down through the ice.

Consider this scenario, chosen to be a type of threshold case:
1 meter thick ice
0 degrees at the top
-1.8 degrees at the bottom
With both top and bottom at the threshold temperature for melting.

Linearizing for simplicity, the thermal gradient is 1.8 degrees/meter.

This implies a heat flow of ~2.2 W/(m.K) x 1.8 K/m = 4 W/m^2

The heat of melting of ice is 334 kJ/kg (same reference as above).

So rate of melting is ~4 J/(s.m^2) x / (334,000 J/kg x 900 kg/m^3) ~ 1.3e-8 m/s
(presuming a density of 900 J/kg)

A month is ~pi x 10^7s / 12 (using a useful mnemonic for approximate number of seconds in a year)

So that rate of melting would be 1.3e-8 m/s x pi x 10^7 / 12 ~ 3.5e-2 m/month = 3.5 cm/month.

So this threshold situation would be a bottom melt rate of only 3 or 4 cm per month.

If the bottom melt rate is:
a) Above this, then the top will be wet;
b) Below this, then the top can be dry even when the bottom is melting from heat carried downwards.

This is obviously a simplified situation - it is not rigorous - and is for ice that is 1 meter thick.
(If the ice is thinner\thicker then the melt rate can be more\less, in approximately inverse proportion to the thickness.)


But it illustrates the general point that ice dry at the top cannot be carrying much heat down to be melting the bottom.

SUMMARY:

Consider a situation for the Arctic sea ice where the heat to melt ice is coming from above. Then:

1) Bottom melt can only be fast, or even moderately fast, if the top is wet; and

2) The maximum bottom melt rate where a dry top is even possible (where the heat comes from above, & holding to some sort of long term equilibrium) is only of order a few cm/month.

So bottom melt with a dry top but still using heat arriving through the ice and from the top, while physically possible, is likely not the dominant scenario for Arctic sea ice.

92
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: July 20, 2018, 11:06:30 AM »
These polls keep coming up, I thought I just missed voting in one that looked like this.

This is an easy vote as I don't know the answer but the bin 2020-2025 spans 6 years in the near future. That's my choice.

It doesn't look like it is going to be this year, so the 2018-2020 bin only has two potentially realistic years and so can't compete with the 6 years in the second bin. The year 2020 is in both bins so the only year the first bin really has going for it is next year, 2019.

The bins after that are disfavored because the event may well have already happened prior to the years in those bins.


Comment: it looks a little strange to have the bins overlapping by one year. For example, the year  2020 is in both of the first 2 bins. This could have been avoided (and my vote made more difficult) by reducing the second bin to the 5-year interval 2021-25. Similarly, the later bins could be changed to begin in years starting with either a '1' or a '6'.

Also, the units should be km^2, not just km.

93
Arctic sea ice / Re: SMOS
« on: July 19, 2018, 06:07:17 AM »
The maps are here:
https://seaice.uni-bremen.de/data/smos/png/

I've used the ones ending in _hvnorth_rfi_l1c.png, though I don't know why they differ from the _hvnorth_l1c.png ones, nor do I know if there is any reason to prefer one over the other.

By inspection, they look similar but not identical. I'm guessing the "rfi" ones have some extra processing but that's just a guess. Does anyone know?


94
Just missed closing. I would have gone for [3.75,4.25] bin.

95
Arctic sea ice / Re: The 2018 melting season
« on: July 10, 2018, 02:20:58 PM »
Interesting that Andrew Slater's algorithm is now predicting a strong melt season: extent (though if I recall correctly it is their own definition and not exactly equivalent to the other extent definitions we see results from) to drop to 4.56 million square kilometers already by 29 August 2018.

96
Arctic sea ice / Re: The 2018 melting season
« on: July 05, 2018, 07:48:26 AM »
Yes, ESS looks quite impressively dark on Worldview today, also with smoke from Siberian fires...

97
Arctic sea ice / Re: Latest PIOMAS update (July)
« on: July 03, 2018, 11:37:24 PM »
Thanks Wipneus, these are always appreciated!


Calculated from thickness I get 13.8 [1000 km3] for 30th June, fifth lowest place.
Graphs show 6th place? Behind 2010,11,12,16 & 17?


Based on those difference maps, this year is looking closest to 2016.

98
Arctic sea ice / Re: The 2018 melting season
« on: July 02, 2018, 05:26:23 AM »
#1855:
Yearly comparison of HYCOM CICE thickness for July 1st (June 30th on 2017 for the nearest date with data)...

If that year-to-year comparison is accurate then it suggests 2018 is likely to be a huge recovery year.

EDIT: or is it an apples-to-oranges comparison between the years? Has the model changed too much? I recall there have been criticisms of HYCOM modelling in the past. Views?

99
Arctic sea ice / Re: The 2018 melting season
« on: July 01, 2018, 11:48:10 PM »
Concerning the tropicaltidbits.com forecasts in the Arctic Basin, I usually check NAVGEM first -though not for any defensible reason.

Anyway, it's showing the lowest pressure bottoming out at 985 hPa, at 00z Tuesday, 3 July - the [36h] forecast. However, nothing below that for all the way out to [180h].

So that storm is probably a solid prediction but any 'wild' forecasts beyond it don't have the support of NAVGEM at least.

100
Arctic sea ice / Re: The 2018 melting season
« on: June 29, 2018, 03:18:47 AM »
... If the ocean water below is saltwater, then it can be up to -1.8 C, which means that it is then colder than the melting point of freshwater ice. ...

Isn't this a simple sign mistake? Instead, the ocean water can be down to -1.8 C. It can be warmer than that.

At the interface, the ice is always at the same temperature as the sea water just below it as they are in thermal contact. So both are anywhere between 0 and -1.8 C.

In winter the ice is cooled from above until the bulk ice gets colder than the ocean water at the interface and then progressively freezing it - bottom freezing - that's how the ice gets thicker.


In summer the ice is heated from above. Once all the ice is above the temperature of the interface (getting progressively cooler going from the surface to the water interface, though all between 0 and -1.8 C) then bottom melting will start due to the salt ions in the liquid water compromising the ice lattice structure at the interface - bottom melting - making the ice thinner.


This interface melting will start at some temperature between 0 and -1.8 C, depending on how saline the ocean water is at the interface.

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