"Smart" and "Stupid" Questions - Feel Free To Ask

[binntho]

It's because wipneus is a prophet haha just kidding.  It takes CT area a few days to process and release their data, but they release the raw data immediately.  Wipneus figured out their formula and calculates it for us the same day, with a small margin of error.  When CT releases the data, wipneus adjusts his numbers, if necessary.

I'm still not clear on how to read the dates in Wipneus' posts, for instance this one from yesterday (Thursday):

day  CT-date       NH               SH                Global
Wed 2016.4493   +7.8  8.576390 +104.3 10.728776  +112.1 19.305166
Thu 2016.4521  -57.1  8.519276  +52.5 10.781309    -4.6 19.300585
Fri 2016.4548 -108.3  8.410998  +66.3 10.847582   -42.0 19.258580
Sat 2016.4575  -40.5  8.370483  +95.5 10.943110   +55.0 19.313593

Which of the four days is "today": Thursday the 16th of June?

... if any of us ever run into wipneus in person, we should immediately hand over some beer.

Totally agree!

[Wipneus]

I'm still not clear on how to read the dates in Wipneus' posts, for instance this one from yesterday (Thursday):

day  CT-date       NH               SH                Global
Wed 2016.4493   +7.8  8.576390 +104.3 10.728776  +112.1 19.305166
Thu 2016.4521  -57.1  8.519276  +52.5 10.781309    -4.6 19.300585
Fri 2016.4548 -108.3  8.410998  +66.3 10.847582   -42.0 19.258580
Sat 2016.4575  -40.5  8.370483  +95.5 10.943110   +55.0 19.313593

Which of the four days is "today": Thursday the 16th of June?

Binnto, I have tied myself to the rather clumsy way that CT reports time and when. Because CT's method does not seem to  be unambiguous and different people interpret if in several ways I am giving you two dates.
The first date is the date that CT is expected to report the value. Everybody should agree about that as long as CT reports ( which it does not at the moment).
The second is the date that will be in the CT data file, people that interpret CT's data file can find it back there.

If this is all too confusing (I can imagine), remember the last line is always based on the latest available data. That is the NSIDC data of the previous day, in this case 2016-06-15.
 

[binntho]

Ok, thanks Wipneus! I think I've got it now!

[AmbiValent]

When sunlight warms Arctic waters, does it only warm the (relative) freshwater surface layer or also deeper layers?

[Gray-Wolf]

When sunlight warms Arctic waters, does it only warm the (relative) freshwater surface layer or also deeper layers?

I imagine where ever the sunlight penetrates too will feel the benefit as the incoming interferes with the water molecules? The top surface will 'milk' most of the energy though ( top 20m???)

[Andreas T]

The water warms by absorbing light (i.e. energy) so to answer your question you have to look at a "how much light goes in - how much light goes out " balance (like an accountants balance sheet).
A "layer" of water which lets light through to the lower water levels doesn't absorb it and doesn't warm (but it never is actually so clear that it absorbs none at all)
If a layer of thickness X absorbs 10% the next layer receives 90% of which it absorbs 10% (i.e.9% of the surface input) the next layer receives 81% .....
So absorption gets less and less because less and less comes into the deeper layers.
How large the thickness X is in my example depends on the "turbidity" of the water. Clear water absorbs over large depth , water rich in sediment or algae absorbs over a much smaller depth, assuming we talk about uniform clarity of the water over that depth, absorption is always higher near the surface where there is more light.
Absorbing over large depth means a large volume of water absorbs the incoming sunlight, so temperature will rise more slowly than if a thinner layer of smaller volume absorbs the same amount of energy. But it also looses less energy because its surface is less warm.

How that relates to the Arctic I don't actually know because I don't know how thick this fresher surface layer is and how clear it is. I suspect there will be large differences depending on location. Algae grow under and in the ice which can make melt water fairly murky I think.

[JimboOmega]

Does ice ever significantly "spread out"? I don't mean in terms of floes.

I mean, does thicker ice ever turn into thinner ice that covers a larger area in a significant way?  Or does it merely crack into floes where the overall covered area is the same?

[magnamentis]

no it won't spread like slime LOL, the latter is what happens. ice is a crystalline structure which can be crushed but not "flattened (rolled) like steel in a rolling mill or dough.

perhaps someone can confirm or deny since i'm not a glaciologist and under presser almost anything can change it's consistency what might happen at the bottom of glaciers, not sure though but a assumed you were talking about sea-surface ice, hence my 2 cents.

[seaicesailor]

I think that is right, although ice has some plasticity important for glaciers ( ice that has been submitted to high pressure) it is negligible for thin sea ice mechanics, I always assumed.

If you hear that sea ice can be treated as a viscous-plastic fluid, I think this is modelling for large-scale simulation purposes. Models (as HYCOM) cannot resolve meter or kilometer scale physics with fractures and ridges, so constitutive equations of 2D flow are developed with modeled terms akin to non linear viscosity (as thick chocolate, non newtonian fluid), ice mass conservation with sources terms (freezing), sink terms (melting), thickness divergence/compaction (as if gas expansion/contraction), external forces (wind pulling and ocean dragging, Coriolis) some inertia (not so important since the flow is typically viscosity-dominated as a very low speed flow)... and more.
But all that is for simulation of ice with coarse resolution.
I'd consider ice a fragile crystal. Not plastic. Crystal.
I may be wrong too

[crandles]

Take 2m thick sea ice. Crack off a bit averaging 1m wide. This is going to float on its side and have ~twice the area and ~half the thickness. There has surely got to be some of this but it is pretty small scale stuff and may well be negligible for most purposes.

[seaicesailor]

Take 2m thick sea ice. Crack off a bit averaging 1m wide. This is going to float on its side and have ~twice the area and ~half the thickness. There has surely got to be some of this but it is pretty small scale stuff and may well be negligible for most purposes.

Yes and since a big simulation cannot resolve that fracture it will calculate an stretched ice that is thinning out as a pizza mass

[JimboOmega]

Take 2m thick sea ice. Crack off a bit averaging 1m wide. This is going to float on its side and have ~twice the area and ~half the thickness. There has surely got to be some of this but it is pretty small scale stuff and may well be negligible for most purposes.

Yes and since a big simulation cannot resolve that fracture it will calculate an stretched ice that is thinning out as a pizza mass

It seems like so far, we've seen ice break into large chunks, but that's because we see from satellites which only have so much resolution.  And the ice being only single-digit meters thick, we would never see a situation where such a thing would happen.

But what about frazil ice? Is there a situation where formed "pack" ice degenerates to something more akin to a thin slush or soup (again, in any significant way, not just briefly at the margins or something).

[seaicesailor]

I have no idea, conservation laws, external sources and forces hold but internal forces  probably very difficult to model having lost integrity. Others may know better.

[oren]

Jimbo, I very much doubt it. Ice floes are large things, they might shatter at the edges and those pieces might float on their side (and melt and disappear very quickly) but will not normally turn into a huge heap of shattered ice cubes.

[JR-ice]

Okay, here's my "stupid question."

Why are the folks on the 2016 melting season thread tending to believe that this season is likely to not end up as a record?  At least it seems that a majority, especially of the longer-term posters, are saying that.

When I look at the NISDC daily graph, this season seems to be at the same point as 2012.  So, is it just a matter of whether a big storm comes along that weakens the ice?  If so, what is the probability of such a storm happening in the next three weeks? 

When I looked at Wipneus' graph showing the ratio of melt extent/total extent, it also doesn't seem that impossible - if melting extends later than normal - that this could be a record season?

Also, when I look at the "rubble" condition of the ice, to my totally untrained eye, it doesn't look that great.

So,  what are the things that other people looking at that leads them to believe that this would not be a record?  If we are coming off an El Nino, wouldn't there still be accumulated heat? 

Just wondering, and thanks for any help given.   

A concerned lurker, who hopes the ice lasts forever....

[Tor Bejnar]

JR-ice,
Near the end of June, I was guessing that, even though June was not good for melting (clouds, etc.) I predicted actual melt volume would 'keep up' with other years because of the warm late winter through May.  According to the PIOMAS model, however, June ice melt volume was even less than what Neven predicted.  Therefore, my guess 'proved' wrong - June weather is much more important than I thought. 

We have seen other years with a great deal of melange (rubble) in the CAB that never melted out.  It might be a little bit earlier this year, and a GAC (Great Arctic Cyclone), should another one occur, may have a larger window to 'disappear' a lot of ice.  But GACs are rare - only one summer-time GAC has been reported (I'm pretty sure).

Extreme weather could have a significant affect on Arctic ice these next two months, either positive or negative, but for that, time will tell.

My experience might give you some insight as to why so many don't expect a record year.

[icy voyeur]

Does ice ever significantly "spread out"? I don't mean in terms of floes.

I mean, does thicker ice ever turn into thinner ice that covers a larger area in a significant way?  Or does it merely crack into floes where the overall covered area is the same?

Do you mean, does 1,000,000 sq ft of 3 meter thick ice convert to 2,000,000 sq ft of 1.5 thick ice? Then no, not really.  Ice does not stretch out.  1,000,000 sq ft of 3 meter ice thins, first to something like 300,000 sq ft of 2 meter thick ice and 700,000 sq ft of 2.5 meter ice. Apologies for mixed dimensions and cartoonish simplifications.  But ice volume does not significantly flow into broader area.

[Neven]

My experience might give you some insight as to why so many don't expect a record year.

I'm with Tor on this one. And I'm looking at whether this year can end up in the top 3 (or top 4, as 2011 and 2015 were on a par). Breaking the record is nigh impossible.

[AmbiValent]

Looking at Wipneus' map, the current cyclone seems to have pushed ice towards the surrounding peripheral seas. Could that be accompanied by Ekman pumping of warmer deep water, or is there something missing for that to happen?

[Nick_Naylor]

Just imagine if we hadn't invented computers and launched satellites.

We might still be years from understanding what fossil fuel burning is doing to the climate, especially given the commitment certain folks still have to not understanding.

[JR-ice]

To Tor and Neven,

Thanks very much for taklng the time to read and respond to my message.  It was helpful.
    

-Jessica

[TerryM]

Looking at Wipneus' map, the current cyclone seems to have pushed ice towards the surrounding peripheral seas. Could that be accompanied by Ekman pumping of warmer deep water, or is there something missing for that to happen?

Ekman pumping (the upwelling of deep, warm water due to cyclonic flows) breaks up the cold, fresh water layer protecting the ice from bottom melt. The low wandering about the Arctic for the past week is stirring things in this direction & will result in thinning if not the disintegration of affected ice.
Bottom melt and upwelling is difficult to see or measure, particularly with this year's dearth of buoys, but I do expect to note a drop in thin first year ice once the skies have cleared.
Terry

[Darvince]

Why do lows disperse ice and highs compact ice when the general wind flow of a low is towards the center and of a high is away from the center?

[TerryM]

Why do lows disperse ice and highs compact ice when the general wind flow of a low is towards the center and of a high is away from the center?

The coriolis force causes things in the Northern Hemisphere to turn to the right. Clockwise= compaction, CCW = dispersal.
Ekman pumping is related with the fastest spinning surface water moving away from the center to be replaced with deeper, warmer water.


Terry

[ktonine]

Okay, here's my "stupid question."

Why are the folks on the 2016 melting season thread tending to believe that this season is likely to not end up as a record?  At least it seems that a majority, especially of the longer-term posters, are saying that.

One of the reasons you see this is because people become infatuated with numbers, trends, and numerical comparisons based on previous years.  This will often lead to realistic projections, but it will rarely catch out of the ordinary events.

So, if one looks at extent or area one sees a set of numbers that don't indicate anything special.  OTOH, if one simply looks at a map of concentration like Univ. Bremen's AMSR2, then one sees an arctic that has been almost drawn-and-quartered.  One sees a central pack that has been decimated like no other year.  But though this is a special event - it still doesn't necessarily lead to a record low melt season.

[Andre]

Long time lurker here.

Have been following the forum for quite some time now and decided it was time to ask my first question. I am aware of people's criticisms of HYCOM, however, I still check it regularly.

I have recently noticed that there are two versions with significantly different current maps and forecasts. Could someone explain the difference to me and how they end up with such radically different results?

1)
https://www7320.nrlssc.navy.mil/GLBhycomcice1-12/arctic.html

2)
https://www7320.nrlssc.navy.mil/hycomARC/arctic.html

Seems to be about ARC vs GLB but would appreciate some insight. Thanks.

[Gray-Wolf]

Why are we seeing a positive spike forming on DMI 80N?

I thought Latent Heat of Fusion was supposed to keep temps pegged around melting until the ice was gone???

[jdallen]

Why are we seeing a positive spike forming on DMI 80N?

I thought Latent Heat of Fusion was supposed to keep temps pegged around melting until the ice was gone???

Dump enough moisture and warm air into the arctic via cyclones, and that could overwhelm they typical buffering caused by phase change.

[Gray-Wolf]

Why are we seeing a positive spike forming on DMI 80N?

I thought Latent Heat of Fusion was supposed to keep temps pegged around melting until the ice was gone???

Dump enough moisture and warm air into the arctic via cyclones, and that could overwhelm they typical buffering caused by phase change.

And that would be a first?

[ghoti]

Usually during the beginning of the freezing seasons people chime in "that's from latent heat released when ice forms" whenever there's an uptick in temperatures above the average. I'm wondering why the same people aren't suggesting it is a burst of water freezing up now...

[jdallen]

Usually during the beginning of the freezing seasons people chime in "that's from latent heat released when ice forms" whenever there's an uptick in temperatures above the average. I'm wondering why the same people aren't suggesting it is a burst of water freezing up now...

Physics... Because phase change pulls temperatures back towards freezing, not away from it.

[Gray-Wolf]

So what would be the 'Tell' if open water began to exert an influence greater than the Latent Heat of fusion?

Would it not be a late season uptick in temps (as the ice proportion crashes and open water influences win out) followed by a long tail off ( as we saw in 2012) as the water sheds heat before refreeze?

[jdallen]

So what would be the 'Tell' if open water began to exert an influence greater than the Latent Heat of fusion?

Would it not be a late season uptick in temps (as the ice proportion crashes and open water influences win out) followed by a long tail off ( as we saw in 2012) as the water sheds heat before refreeze?

The only way that comes to mind would be temperatures consistently remaining above -1.8C.  You won't be able to see a "tell" I think, if SSTs are close to that.

The "tell" might be indirect also - for example if you examine net loss out of the atmosphere, and there is no import of heat from lower latitudes, but no freezing occurs, and temperatures remain flat at or near freezing.

[be cause]

Why are we seeing a positive spike forming on DMI 80N?

I thought Latent Heat of Fusion was supposed to keep temps pegged around melting until the ice was gone???

Hi GW .. whatever the cause it is not that unusual eg. 1987 had a strong spike at this time of year ..

[Gray-Wolf]

Hi 'B'!

Yup but we know the pole was real solid back then?  so Jd's imports would explain those? as it does with the earlier in the year spikes?

It is just that we had Jim's secret santa pool early on in the season and the ice is pretty well mangles across the basin? I just got to wondering as to what DMI80N would do if more heat was being shed from around the ice than being held down due to LHF?

[ktonine]

Why are we seeing a positive spike forming on DMI 80N?

I thought Latent Heat of Fusion was supposed to keep temps pegged around melting until the ice was gone???

The Atlantic Sector has a significant amount of open water north of 80 degrees.  There are also very high temperature anomalies in these ocean waters. I suspect it's these ocean SST anomalies that account for the uptick in DMI temps.

[ktonine]

SST maps give a clue where the uptick is coming from.  I've approximated 80N in blue.

[Dundee]

After skimming half a dozen papers, I'm not finding what I am looking for.

Hypothetically, imagine a melt pond with 0C 100%RH air above, and radiative gain/loss in balance.

If the salinity of the pond is less that the ocean in contact with the ice beneath it, then the pond will be warmer than the seawater interface. This should result in heat flow down, freezing the pond and melting the base of the flow.

In real life, nothing is in balance, but late in the season when the internal temperature of the flow approaches melting equilibrium and solar input winds down, the same heat flow should occur. As melt ponds wrap up for the year, this could result in 10-15cm of bottom melt over and above that driven by external heat flows.

So my question is this - we pay a great deal of attention to the area of melt ponds, but I haven't seen anything on the volume of meltwater (and the bottom melt potential it represents late in the season). Has anybody come across the topic?

[etienne]

Hello,

I found an interesting article about the impact of the Pinatubo eruption (1991) on sea level rise.

http://www.nature.com/articles/srep31245

Looks like the Pinatubo eruption had an impact on the earth albedo during at least 10 years.

On the https://ads.nipr.ac.jp/vishop/#/extent, when I select "yearly graph" than "draw linear fitting line from visible region", I get a graph where sea ice extend is above the trend from 1992 until 2004, exepted for 1995.

Don't know if this is of any interest.

Best regards,

Etienne 

[Thawing Thunder]

This is a really useful resource on density and freezing point at different salinities

http://linkingweatherandclimate.com/ocean/waterdensity.php

If I understood it right, then the salinity from the deeper water, once moved to the surface by the storm, avoids freezing not only because of its higher salinity, but also, and even more, by convection: Once the saltwater cools near its freezing point, it also reaches its highest density and sinks down into the ocean where it mixes with warmer water - the opposite effect appears with freshwater, where an upper layer freezes above the densest water (which in that case is 4 degrees "warm"). Is that correct?

But how does the arctic freeze every year despite that convection? Must the water cool near freezing point many meters down into the depth? Or does the surface freeze by shock? O did I get it all wrong?

[Andreas T]

You are spot on about density of sea water increasing as it cools to the freezing point (another place to look is https://nsidc.org/cryosphere/seaice/index.html).
Because ice crystals don't contain salt (it can be trapped in the form of concentrated salt water between ice crystals though) ice has lower density than sea water. Once ice forms it floats.
It is therefore possible to freeze the surface while water below the surface is still above its freezing temperature if the cooling is so strong it extracts heat from the water faster than it can move downwards driven by the (not so strong) density gradient.
For the cooling water to sink, warmer water below has to "get out of the way" and take its place at the surface which takes time and requires some lateral movement across the surface before that water gets away from the surface where heat transfer to the atmosphere occurs.

[Thawing Thunder]

Thank you Andreas. Now I have a basic idea of the whole mechanism. It's fun to begin to understand that strange world up there (and down there, too).

[Iceismylife]

...

But how does the arctic freeze every year despite that convection? Must the water cool near freezing point many meters down into the depth? Or does the surface freeze by shock? O did I get it all wrong?

Rate of cooling exceeds rate of convection.  Add a persistent GAC and convection may win.

[2phil4u]

I have little knoledge about the arctic now, so i know some concepts.
But surely i cant understand it fully, because im a hobby observator.
My question.
Is this storm we saw important for the future ?
We have not hot summer and if ice will shaken and refreezing not this good, although temperatures are low and cloudy weather.
From a thermodynamical standpoint, if not this much energy is going in the N85 region, is some beaking ice maybe good for giving more heat to space ?
I readed in a wikipedia style paper, that if water is refreezing later, it also groth faster, because in total it will lose more energy to space before refreeze and so the bottom freezing is faster.
So are the next few weeks really important if you are not interested if the value is exactly like little below 2007 or something like that.

[Sourabh]

I have a question on dipole. Are there multiple kinds of dipole formation in and around arctic?  For example

    High pressure at the pole and low pressure in the surrounding areas (as I think was in 2007/2012)?
    Current one in which low pressure at the pole and high pressure in the surrounding areas?


Which kind of pressure arrangement would be more severe for ice? If this question has been answered before, please point me to that post/thread.

Thanks,
Sourabh

[Neven]

This is my opinion, not my knowledge:

First of all, it depends on the time period. And it also depends whether it's good/bad for the ice, or good/bad for sea ice extent/area. A classic Dipole anomaly, for instance, end of August, where the high sits on the American side of the Arctic, and the low over the Siberian side, will be bad for sea ice extent/area, due to compaction. But this perhaps helps thicken the ice, which would be good over all for the ice.

In June or July, however, extensive high pressure over the Arctic is really bad for the ice, as it causes widespread melt ponding/preconditioning.

[dnem]

i'm sure this has already been answered but why is there a mask directly over the pole?  Why can't satellites see there or estimate cover there?

[LarsBoelen]

That depends on which satellite data you look at: polar satellites pass over the poles several times a day and are the only ones with a clear view of the poles themselves. Satellites revolving round the equator or geostationary satellites have very shallow vision in the polar regions that may lead to that region being blacked out.
Satellites imaging in visual light of course are dependent on available light, so expect the North Pole to become black after September 21st (plus the blacked out region growing rapidly after that)

[dnem]

specifically Wipneus's maps in the Home brew AMSR2 thread.

[Juan C. García]

It is possible in nullschool to check how the wind was 24 hours or 48 hours ago? How can I do it?