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uniquorn

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Deep diving into buoy data
« on: October 15, 2021, 10:08:22 PM »
Best efforts to get the analysis here correct but most of it will be done 'quickly' in near real time using raw data and it's highly likely that no one else is checking it.

I was going to start with spreadsheet analysis of bottom melt and refreeze but this anomaly on WHOI TOP4 is a bit distracting.
https://www2.whoi.edu/site/itp/data/active-systems/top-04/

TOP4 is co-located with cryoinno SIMB3 551610 and WHOI ITP122
https://www.cryosphereinnovation.com/simb3/551610
https://www2.whoi.edu/site/itp/data/active-systems/itp122/

1. The cryoinno site is great for zooming in on the drift path of these 3 buoys. The first image showing the buoys backtracking over the same area recently.

2. The TOP4 profile contours are only showing temperature.

3. There is some TOP4 salinity data available but it is reporting high numbers from 178-192 which are off the chart. Possibly these are only partially processed. They don't look like noise. The image was made a few days ago

4. Luckily we have ITP122 and though it corroborates the temps we don't see a large change in salinity. So what are these cold blobs?

uniquorn

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Re: Deep diving into buoy data
« Reply #1 on: October 15, 2021, 10:43:38 PM »
1. From the TOP4 and ITP122 temperature profile contours above we can see a large change in temperature at 65m depth, so lets take a look at where that happens on the drift path by clicking on the first image which runs from sep17 to oct15
We can see the 2 cold areas.

2. Next we can take a look at the temperatures from 1m down to 130m in those locations by clicking on the second image (4MB) Some detail is lost by setting the scale to fit the relatively wide range of temperatures.

3. So thanks to Cameron Planck's tutorial here we can develop the code further to look at TOP4 temperatures in finer detail. This small image runs automatically (to count visitors who don't click on anything ;) )

4. On this larger one you can read the scales and titles showing that the temperatures cycle from a very tight limit of -1.6C to -1.4C in 0.2C increments up to -1.6C to +0.6C  (3.7MB)


uniquorn

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Re: Deep diving into buoy data
« Reply #2 on: October 15, 2021, 11:19:45 PM »
Cold blobs at 40m-70m depth. Upwelling? Downwelling? At 80.6N -140 there are no bathymetric features nearby.

A-Team pointed me to an old post of interstitial's
<>
Hycom algorithms
   advdiff.pdf (horizontal advection/diffusion)
   boundary.pdf (boundary conditions)
   diapycnal.pdf (three interior diapycnal mixing algorithms)
   float.pdf (synthetic floats/drifters/moorings)
   hybrid.pdf (hybrid vertical coordinate adjustment)
   ice.pdf (energy loan ice model)
   KPP.pdf (K-Profile Parameterization vertical mixing)
   KT.pdf (three Kraus-Turner mixed layer models)
   mesh.pdf (horizontal mesh)
   momentum.pdf (momentum equation, including pressure gradient force)
   MY.pdf (Mellor-Yamada level 2.5 turbulence closure vertical mixing)
   PWP.pdf (Price-Weller-Pinkel dynamical instability vertical mixing)
   state.pdf (equation of state, including cabbeling and thermobaricity)
   surface.pdf (surface fluxes, including penetrating shortwave radiation)
   vdiff.pdf (solution of vertical diffusion equation)
   Other algorithms used from MICOM (HYCOM’s precursor) include continuity equation barotropic   
   momentum equation advection algorithm and vertical mode splitting
   https://www.hycom.org/attachments/067_overview.pdf
<>


and a wiki
https://en.wikipedia.org/wiki/Cabbeling
Quote
Cabbeling is when two separate water parcels mix to form a third which sinks below both parents. The combined water parcel is denser than the original two water parcels.

The two parent water parcels may have the same density, but they have different properties; for instance, different salinities and temperatures.[1] Seawater almost always gets denser if it gets either slightly colder or slightly saltier.[2] But medium-warm, medium-salty water can be denser than both fresher, colder water and saltier, warmer water; in other words, the equation of state for seawater is monotonic, but non-linear. See diagram.

Cabbeling may also occur in fresh water, since pure water is densest at about 4 °C (39 °F). A mixture of 1 °C water and 6 °C water, for instance, might have a temperature of 4 °C, making it denser than either parent. Ice is also less dense than water, so although ice floats in warm water, meltwater sinks in warm water.

The densification of the new mixed water parcel is a result of a slight contraction upon mixing; a decrease in volume of the combined water parcel.[3] A new water parcel that has the same mass, but is lower in volume, will be denser. Denser water sinks or downwells in the otherwise neutral surface of the water body, where the two initial water parcels originated

and this

Role of cabbeling in water densification in the Greenland Basin

https://os.copernicus.org/preprints/5/S186/2008/osd-5-S186-2008-print.pdf
Quote
Cabbeling may occur in high incidence in high latitude waters. Polar region waters are a place where cold and fresh water melting from sea ice meets warmer, saltier water. Ocean currents are responsible for bringing this warmer, saltier water to higher latitudes, especially on the eastern shores of Northern Hemisphere continents, and on the western shores of Southern Hemisphere continents. The phenomenon of cabbeling has been particularly noted in the Greenland Sea

 Apart from turbulent mixing, important small scale mixing processes include double diffusion, cabbeling and thermobaricity. The driving force of double diffusion is the difference in the molecular diffusivity of heat and salt. Temperature diffuses much faster than salt and thus a water parcel loses heat quickly while salinity remains unchanged, and the density of the water parcel changes without external forcing.

Cabbeling and thermobaricity occur due to the non linear features of seawater. The first is a mixing of water masses with different properties, which produces water denser than source waters, and the second is the densification of a water parcel as a result of compressibility where cold water is more compressible than warm water. In high latitudes, the presence of sea ice cools surface waters nearly to the freezing point and can create a sharp interface in the surface layer between cold less saline water on top and warmer and saline water below. This is a prerequisite for double diffusive convection, and the strong stratification can cause an abrupt overturning through thermobaricity (Akitomo, 1999).

In the Barents Sea, double diffusive mixing plays an important role when the shear-induced turbulent mixing is relatively weak (Sundfjord et al., 2007). At the Arctic Front to the west of Spitsbergen, warm and saline North Atlantic Water and cold and less saline Arctic Water create an ideal hydrographic condition for double diffusion and cabbeling processes (Cottier and Venables, 2007).
My emphasis.

« Last Edit: October 16, 2021, 12:48:25 AM by uniquorn »

uniquorn

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Re: Deep diving into buoy data
« Reply #3 on: October 15, 2021, 11:56:28 PM »
So, a minor distraction from looking at the ice/water interface temperatures made possible by TOP4 temps to 3dp allowing calibration of the co-located SIMB3's.
1. Here staying with 551610 near surface temps 1m to 10m and limiting the scale from -1.515C to -1.45C to maximise the colour differences. 1m temperatures tending to be less cold.

2. The second image aligns those detailed surface temps with the full 200m TOP4 temps and the adjusted 551610 temps sharing the same colour bar.

A recap on the SIMB3 portion of the chart
Quote
Ice surface is at 0m shown as a semi transparent straight line
Snow level in metres is shown above as a thicker white line.
Ice bottom in metres is light blue (aqua)
Water temperature from the SIMB3 is shown, for convenience, on the same scale in degrees C
Digital temperature chain values are shown on the right hand colour bar limited from -2.4C to -0.2C to highlight small differences in ice and water temp.
Air temps are the black line using the right hand scale in degC

The warmer 1m temps appear to coincide with colder surface temps. Would that be slushy/rotten/honeycombed ice near the bottom giving off heat as it phase changes?
Quote
The amount of heat released when the water freezes is also known as the latent heat of fusion and is equal to 80 calories per gram of water or, 334 Joules per gram of water.

Should see some thickening on this thin ice soon

uniquorn

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Re: Deep diving into buoy data
« Reply #4 on: October 16, 2021, 12:21:57 AM »
Still using the same buoys, limiting the temps from -7 to -1.45 the SIMB3 nicely shows the temperature gradient through the ice, which tends to warm and cool as air temperature changes with just a hint of the larger cold blob from TOP4.

I don't think there is that much snow, the top sounder is probably frosted.
« Last Edit: October 16, 2021, 12:56:46 AM by uniquorn »

uniquorn

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Re: Deep diving into buoy data
« Reply #5 on: October 16, 2021, 12:43:06 AM »
Actually we can show approximate snow thickness by focusing on the surface temperatures(-25C to -1.45C).  Since it acts as an insulator, snow surface can be identified by looking for the rapid change in temperature on the coldest days. The chart may need some minor adjustment but it still looks like only a few cm of snow.
« Last Edit: October 16, 2021, 12:55:38 AM by uniquorn »

uniquorn

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Re: Deep diving into buoy data
« Reply #6 on: October 16, 2021, 01:17:22 PM »
Comparing the whoi itp122 salinity profile contours with the home brew version. The extra colours highlight the small differences in salinity. The problem with the home brew colours is they may present a false impression of small changes, a bit like the hycom thickness images. Might need to look at some line graphs sometime.

Calculating the densities in the water column should help to show if the blob is rising, sinking or at equilibrium

edit: re-indexed the temp ani above
« Last Edit: October 16, 2021, 02:14:36 PM by uniquorn »

johnm33

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Re: Deep diving into buoy data
« Reply #7 on: October 16, 2021, 02:12:18 PM »
The surface is incredibly cold, not sure why, but at those temps rapid desalination of seawater saturated ice may lead to some extraordinary brinicles, if so the anomoly should drop.[?]

uniquorn

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Re: Deep diving into buoy data
« Reply #8 on: October 16, 2021, 02:22:32 PM »
the air/snow surface?

johnm33

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Re: Deep diving into buoy data
« Reply #9 on: October 16, 2021, 04:47:49 PM »
Yes and there appear to be cracks which expose the ocean, however temporarily. The airs about -20C humidities high so much sublimation and deep cooling of the ice surface, plus rapid build up of ice 'spines/kes' and widespread brinicle formation, but just trying to make some sense of what's known, low confidence hence [?].

uniquorn

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Re: Deep diving into buoy data
« Reply #10 on: October 16, 2021, 09:10:02 PM »
So you think maybe rapid cooling of an area of low salinity open water causing it to sink through the higher salinity pacific layer. We really need a density map to see if that works. Will take some time.

That blob is pretty big though, ballpark figures
Quote
feature volume maybe  pi*d*d/4 *thickness=30 sq km * 0.010m = 3 cu km?  half and half mix for cabelling?

Meanwhile I took a look at itp121 to see if it has anything similar. Parts of the pacific layer were over 1.2C in October last year.
There is a cool blob candidate in April.

3rd image is static home brew version.
The gif at the bottom is worth a look to see how temps fit with salinity.

johnm33

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Re: Deep diving into buoy data
« Reply #11 on: October 16, 2021, 11:43:06 PM »
"So you think maybe rapid cooling of an area of low salinity open water causing it to sink through the higher salinity pacific layer. We really need a density map to see if that works. Will take some time." Not quite, more like wet ice [seawater saturated ice] rapidly cooling and ejecting salt over a wide area. That brine drops as brinicles at maybe 230K. and with off the scale salinity. A density map should help clarify.
The open water [cracks] seeds the air with spray->salt which cools the ice drastically -> humidity causes more sublimation which cools the ice drastically, the salt is driven out of the freeboad [soaked] ice, which becomes lighter, the brine bleeding through the subsurface ice also rapidly cools that and having passed cools the [?] -1.79C calm water below enhancing the increasing thickening. Then the brinicles drop into the deep carrying the now much denser bottom[of ice] water in their wake, I think.
Unless the brinicles are dissolved they should keep dropping, so the 'blob' should be coldest near it's base, and the ice affected should rapidly gain thickness.

uniquorn

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Re: Deep diving into buoy data
« Reply #12 on: October 17, 2021, 12:49:42 PM »

uniquorn

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Re: Deep diving into buoy data
« Reply #13 on: October 17, 2021, 02:00:05 PM »
1. back to the cold blob which shows up well on the itp122 temperature chart on day280, oct7

2. gif of all the data so far (9.5MB)

Zooming in on the density might show something
« Last Edit: October 17, 2021, 02:28:45 PM by uniquorn »

uniquorn

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Re: Deep diving into buoy data
« Reply #14 on: October 17, 2021, 04:39:56 PM »
no real surprises from zooming in. The gradient flattens out a lot but never reverses. No point in comparing adjacent profiles since the buoy is drifting.

1. example of one of the flatter density gradients

2. all density gradients from day276-290 (oct3-17)

I'm using this formula to calculate density which may be old by now. I'm open to suggestions for other formulas.

<>
http://www.csgnetwork.com/water_density_calculator.html
Quote
The equation used in this calculator can be found in:
Millero, F, C. Chen, A Bradshaw, and K. Schleicher, 1980: A new high pressure equation of state for seawater, Deep Sea Research, Part A, 27, 255-264.
doi:10.1080/15210608209379435
<>

uniquorn

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Re: Deep diving into buoy data
« Reply #15 on: October 17, 2021, 07:41:08 PM »
It's not possible to calculate density for TOP4 without the correct salinity data.
Temperature from 1m to 20m  (6.9MB)

The ice is about 70cm thick so the 1m temps are quite close to the ice bottom. It will be interesting to see what happens as air temperatures stay low.
« Last Edit: October 17, 2021, 07:47:20 PM by uniquorn »

uniquorn

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Re: Deep diving into buoy data
« Reply #16 on: October 17, 2021, 09:02:32 PM »
A quick look at whoi itp129 north of the Laptev sea. 8m-200m temp
Quote
ITP129 was deployed on a 1.0 m thick ice floe in the Transpolar Drift on October 10, 2021 at 81° 32.3 N, 137° 3.3 E in collaboration with the Nansen and Amundsen Basins Observational System (NABOS) project from the Russian Research Vessel Treshnikov. The ITP is operating on a fast sampling schedule of 4 one-way profiles between 7 and 760 m depth each day.

A faint trace of a 25m warm layer

1. whoi drift map
2. whoi profile contours
3. homebrew profile contours
4. hombrew gif, useful for comparing small areas of temp and salinity



oren

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Re: Deep diving into buoy data
« Reply #17 on: October 18, 2021, 03:02:52 AM »
I'm afraid I can't contribute much of anything about the physics here, just want to commend this masterpiece of forum science.

Is it my imagination or is there a warm blob above the cold blob? The TOP4 animations at #6 and #1 seem to show this.

uniquorn

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Re: Deep diving into buoy data
« Reply #18 on: October 18, 2021, 12:41:38 PM »
It looks, to me, like the cold blobs are dropping through the warm layer. Unless the floe retraces I don't suppose we will know.
Data is a little slow coming from top4, simb3 551610 shows the floe drifting away to the north west.

1.homebrew temps to 0ct16
2.whoi profile contours to oct16
3.drift path of 65m temps to oct15
4.551610 latest drift path to oct18

uniquorn

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Re: Deep diving into buoy data
« Reply #19 on: October 18, 2021, 01:10:59 PM »
The open water quick freeze idea may have some validity as there is a large lead nearby. Perhaps there is a paper somewhere on flash freezing and cold blobs.

uniquorn

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Re: Deep diving into buoy data
« Reply #20 on: October 18, 2021, 04:05:48 PM »
I'm not that familiar with brinicles and a quick search didn't throw up any deep water examples

https://en.wikipedia.org/wiki/Brinicle
Quote
A brinicle (brine icicle, also known as ice stalactite) is a downward-growing hollow tube of ice enclosing a plume of descending brine that is formed beneath developing sea ice.

As seawater freezes in the polar ocean, salt brine concentrates are expelled from the sea ice creating a downward flow of dense, extremely cold, and saline water, with a lower freezing point than the surrounding water. When this plume comes into contact with the neighbouring ocean water, its extremely low temperature causes ice to instantly form around the flow. This creates a hollow stalactite, or icicle, referred to as a brinicle.

Formation
The formation of ice from salt water produces marked changes in the composition of the nearby unfrozen water. When water freezes, most impurities are excluded from the water crystals; even ice from seawater is relatively fresh compared to the seawater from which it is formed. As a result of forcing the impurities out (such as salt and other ions) sea ice is very porous and spongelike, quite different from the solid ice produced when fresh water freezes.

As the seawater freezes and salt is forced out of the pure ice crystal lattice, the surrounding water becomes more saline as concentrated brine leaks out. This lowers its freezing temperature and increases its density. Lowering the freezing temperature allows this surrounding, brine-rich water to remain liquid and not freeze immediately. The increase in density causes this layer to sink.[1] Tiny tunnels called brine channels are created all through the ice as this supersaline, supercooled water sinks away from the frozen pure water. The stage is now set for the creation of a brinicle.

As this supercooled saline water reaches unfrozen seawater below the ice, it will cause the creation of additional ice. Water moves from high to low concentrations. Because the brine possesses a lower concentration of water, it therefore attracts the surrounding water.[2] Due to the cold temperature of the brine, the newly attracted water freezes. If the brine channels are relatively evenly distributed, the ice pack grows downward evenly. However, if brine channels are concentrated in one small area, the downward flow of the cold brine (now so salt-rich that it cannot freeze at its normal freezing point) begins to interact with unfrozen seawater as a flow. Just as hot air from a fire rises as a plume, this cold, dense water sinks as a plume. Its outer edges begin accumulating a layer of ice as the surrounding water, cooled by this jet to below its freezing point, ices up. A brinicle has now been formed, resembling an inverted "chimney" of ice enclosing a downward flow of this supercooled, supersaline water.

When the brinicle becomes thick enough, it becomes self-sustaining. As ice accumulates around the down-flowing cold jet, it forms an insulating layer that prevents the cold, saline water from diffusing and warming. As a result, the ice jacket surrounding the jet grows downward with the flow. The inner wall temperature of the stalactite remains on the salinity-determined freezing curve, so as the stalactite grows and the temperature deficit of the brine goes into the growth of ice, the inner wall melts to dilute and cool the adjacent brine back to its freezing point.[3] It is like an icicle turned inside-out; rather than cold air freezing liquid water into layers, down-rushing cold water is freezing the surrounding water, enabling it to descend even deeper. As it does, it creates more ice, and the brinicle grows longer.

A brinicle is limited in size by the depth of the water, the growth of the overlying sea ice fueling its flow, and the surrounding water itself. In 2011, brinicle formation was filmed for the first time.[4] The salinity of the liquid water within the brinicle has been confirmed to vary depending on the temperature of the air. The lower the temperature, the greater the brine concentration. A January 2014 along the coast of the White Sea recorded that at an air temperature of −1 °C the brine salinity was between 30 and 35 psu while the salinity at sea was 28 psu. When the temperature was −12 °C the salinity of the brine increased to between 120 and 156 psu.[5]


Quote
By Nix Sunyata - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=103668726

Brinicle formation; (1) when water freezes, most impurities are repelled from water crystals, sea ice is very porous, cavities between ice contain brine and saline water, (2) the surrounding water becomes more saline as concentrated brine leaks out. (3) Brine-rich water remains liquid, with the increase in density causes this amount of water to sink. Setting for the creation of a "brinicle". (4) Its outer edges begin accumulating a layer of ice as the surrounding water, cooled by this jet to below its freezing point, ices up as a tubular or finger shape and becomes self-sustaining. (5) The down-flowing cold jet continues to grow longer downward, and reach the seafloor. (6) It will continue to accumulate ice as surrounding water freezes. The brine will travel along the seafloor in a down-slope direction.




A bigger version of the gif

johnm33

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Re: Deep diving into buoy data
« Reply #21 on: October 18, 2021, 04:21:10 PM »
I suspect it 'quick freeze' may have been more widespread, another idea of mine about ice rotation as a result of freezing, where the ice loses ground as it expands south [or at least away from it's own geographic center] and thus appears to rotate cw had a demonstration as illustrated by Gero. [there may have been other causes too, but] recently.
Is anyone but you trying to fathom this data?
That's more than I knew about brinicles, thanks.

uniquorn

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Re: Deep diving into buoy data
« Reply #22 on: October 18, 2021, 06:46:15 PM »
There are a couple of problems with the rapid freeze idea. Firstly we are not seeing super cold temperatures just below the ice at itp122's location, in fact, 1m temps are warmer, suggesting that this ice may not ready for brinicle formation at this point in the freezing season. Secondly they are 2 very large bodies of cold water at 60m-100m depth. I have doubts that they could form and sink so quickly. If this was a common occurrence there should be a paper about it somewhere.

Need to look back through the itp buoys to see if there are other examples. This thread is for using buoy data to attempt to verify such speculation

edit: Having said that, there may be a shallower candidate on TOP2
« Last Edit: October 18, 2021, 08:13:42 PM by uniquorn »

uniquorn

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Re: Deep diving into buoy data
« Reply #23 on: October 18, 2021, 09:47:52 PM »
Quote
Is anyone but you trying to fathom this data?

edit: Took me a while to get the humour there
I'm a little surprised that no forum members want to have a go at defining, for example, average bottom melt per week and the day it started. It only requires analysis of 2 columns of numbers in a spreadsheet. Top melt is trickier due to melt ponds and snow. I will get around to it eventually.

2 great candidates for bottom melt analysis are SIMB3 052460 and 443910
https://www.cryosphereinnovation.com/simb3/052460
https://www.cryosphereinnovation.com/simb3/443910

Possible scenarios
052460
fig1. started bottom melt near jun21 and melted out completely on sep3. The buoy survived, floated freely, then drifted into ice that possibly ridged  then drifted into 1.55m ice by sep28. Apart from the spikes there's been little change since then.
fig2. At the moment the bottom 2/3 of that ice still appears to be at water temperature.

443910
fig3. The chart looks simpler because it starts close to the beginning of bottom melt on jun14. (data runs from sep20 2020) Thickness drops to a few cm by sep18 then begins thickening, probably by ridging, to its current thickness of 19cm
 
« Last Edit: October 19, 2021, 11:58:04 AM by uniquorn »

oren

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Re: Deep diving into buoy data
« Reply #24 on: October 19, 2021, 03:34:27 AM »
I'm aware of at least one forum member (myself) that does want to analyze this data, and other data items awaiting, but has no chance of getting to the task due to RL issues. Not that it helps... but I think the interest level is higher than may appear at first glance.

uniquorn

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Re: Deep diving into buoy data
« Reply #25 on: October 19, 2021, 10:28:05 PM »
052460 bottom melt.

fig1. Checking snow depth using temperatures.
From the python chart settings, snow height is 0.5 and the offset is 0.37, snow depth is 13cm, top of the ice is set at 0.
Using the zero base line to determine when all the snow has melted we see that bottom melt starts just after all the snow has gone, I estimate jun20

fig2 shows bottom distance from jun20 to sep4, just before the rapid melt to zero seen in fig1.

jun20     44367   1.08m
sep2      44441   2.1m    74days   1.02m

avg melt = 1.38cm/day
The linear trend line is there for comparison.

Bottom melt slows from jul27 to aug8. It doesn't seem particularly cloudy, maybe better quality ice for a while.


uniquorn

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Re: Deep diving into buoy data
« Reply #26 on: October 20, 2021, 12:14:46 AM »
The Growth and Dynamics of Brinicles  Mahadevan, Kausalya
https://dash.harvard.edu/handle/1/38811488

Quote
1 Introduction
 Sea ice covers up to 12% of the surface area of the ocean during the winter months, which is 7% of the total surface area of the planet (Weeks, 1967). Since the ice has a bright,reflective surface, especially in comparison to the dark ocean around it, so large portions of the polar regions reflect back most of the incoming solar energy and causing the rest of the planet to cool. As sea ice melts, there is less of a reflective surface and more heat is absorbed, which leads to the ice melting faster. Because of this, a slight shift in temperature can lead to a large amount of ice melting and overall warming. While some of this sea ice is permanent and persists all year, much of it freezes every winter. As seawater freezes, the ice formed has a much lower salinity than the water it freezes from. The salt is rejected from freezing ice in the form of cold, dense brine that sinks towards the ocean floor. As large volumes of this brine sink, it contributes to the ocean’s global circulation. Cold, denser water flows along the ocean floor away from the poles, while warmer water flows from the equator towards the poles (National Snow and Ice Data Center, 2017).

 To understand the dynamics of freezing, we must turn to concepts from the materials science of solidification. The binary phase diagram (fig. 1.1) tells us what phases exist in a mixture of a given concentration and temperature. The line separating the liquid and crystalline solid + liquid phases is called the liquidus and is highlighted in fig. 1.1. The point at which the two liquidus lines join is the eutectic point. For a sample at a particular concentration and temperature there exists an equilibrium with a fraction of solid phase and a fraction of liquid phase. As sea ice forms, it exists continuously in near-equilibrium states. At equilibrium, pure ice and brine exist together at a ratio determined by the binary phase diagram (Worster, 2000).

 Ideally, sea ice would freeze and result in a perfect sheet of pure ice over salt-water where all the salt is rejected from the volume occupied by ice into the brine below. In actuality, sea ice initially starts out salty, and over time the salinity decreases (Weeks, 1967). The salinity decreases as brine drains out of brine pockets and mushy regions, into the water below. This brine is much colder and more saline than the ocean water below, as the seawater freezes from the top down due to air temperatures of −10◦C and lower (Perovich et al., 1995). This sinking brine flows into the seawater below in volumes of anywhere from 1.3 to 18 mL/sec depending on the conditions, as observed by Perovich et al. (1995) and Dayton and Martin (1971). Heat can only flow into the brine from the surrounding fresh water, which then freezes into the wall of the brinicle.
 As a large volume of brine flows in, the brinicle continues to freeze and to grow in both length and width. Both the inner and the outer radius of the structure grow with time. As the brinicle freezes and the outer wall grows, heat is transferred across the ice wall to a layer of warmer brine along the inner wall of the brinicle. This warmer brine then dissolves the inner wall, bringing it back to the liquidus. The outer wall grows as heat flows to the cold brine at the center, freezing the fluid at the outer wall. In this way, both the inner and the outer wall of the brinicle grow with time.

 An interesting free-boundary problem arises in characterizing these brinicles. Multiple phenomena, including heat transfer, diffusion of solutes across concentration gradients, and phase changes, intersect in the occurrence of brinicles. The impact of these brinicles, however goes beyond just interesting physics. The process by which salty brine escapes sea ice is a topic of significant research as it impacts the growth of sea ice and the mixing of the Arctic Ocean. The presence of these brinicles could help to throw light on this process in some ways.
 Formation of these brinicles has been connected with the deformation of thin, new sea ice. This highly saline ice has few, small brinicles growing below it, but when it rafts and attaches to another ice sheet, the brine drained rapidly from the growing ice and brinicles grew to a length of 2m (Perovich et al., 1995). Finally, this problem is not already very well investigated, with only handful of publications touching upon brinicles in the last few decades.
my emphasis
« Last Edit: October 20, 2021, 12:50:29 AM by uniquorn »

vox_mundi

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Re: Deep diving into buoy data
« Reply #27 on: October 20, 2021, 12:29:09 AM »
“There are three classes of people: those who see. Those who see when they are shown. Those who do not see.” ― anonymous

Insensible before the wave so soon released by callous fate. Affected most, they understand the least, and understanding, when it comes, invariably arrives too late

oren

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Re: Deep diving into buoy data
« Reply #28 on: October 20, 2021, 07:43:37 AM »
While very interesting (you learn something new every day, especially on this forum), it does not appear brinicles can reach tens of meters and explain the anomaly outlined in the posts above.

johnm33

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Re: Deep diving into buoy data
« Reply #29 on: October 20, 2021, 09:57:33 AM »
Brinicles are merely a means of transfering extreme cold from the ice-air interface through to the bottom of the still waters immediately below the ice. After that the denser highly saline and chilled waters fall of their own accord. They have the structural integrity of burnt card, and are more of a transient dynamic, like lightning, than a 'thing'.
 I am assuming it was driven by a surface phenomenon and that the blob was sinking neither of which is established. There were waves 'swells' passing through the area around the 6th so some rapid surface freezing was likely, also seeding the air with salt and vapour to cause rapid cooling of existing ice and consequent brine exclusion, but it remains a guess.
 There are presently swells moving through further north so we may see a repeat of the phenomenon if we have a buoy thereabouts.

uniquorn

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Re: Deep diving into buoy data
« Reply #30 on: October 20, 2021, 01:10:24 PM »
Perhaps more interesting than the actual brinicle in the video above is the view of the cold, very saline and very dense brine issuing from it. I don't think the brinicles dropping or growing would cause the cold blob, but if there is enough ridging of new ice then we have a possible environment for a larger scale local brine release. Taking partial quotes from the senior thesis above

Quote
<>when it rafts and attaches to another ice sheet, the brine drained rapidly from the growing ice<>

<>This sinking brine flows into the seawater below in volumes of anywhere from 1.3 to 18 mL/sec<>

and this from the wikipedia page
Quote
A January 2014 along the coast of the White Sea recorded that at an air temperature of −1 °C the brine salinity was between 30 and 35 psu while the salinity at sea was 28 psu. When the temperature was −12 °C the salinity of the brine increased to between 120 and 156 psu.[5]
Brine that saline would sink quickly. Does it mix as it sinks forming a large cold blob? Don't know.

https://www.en.pkrug.ru/about/centre/white-sea/
Quote
Salinity of the White Sea is 27.5–28 parts per thousand, that is lower than the mean salinity of the Arctic Ocean.


Seeing that video brought to mind the anchored ice over the shallow shoals in the ESS
https://forum.arctic-sea-ice.net/index.php/topic,2890.0.html

uniquorn

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Re: Deep diving into buoy data
« Reply #31 on: October 20, 2021, 01:15:48 PM »
443910 bottom melt  https://www.cryosphereinnovation.com/simb3/443910
date     dist      day no.
jun13   1.55m   44360
sep20  2.95m   44460

1.4m/100days = 1.4cm/day

similar to 052460 above at 1.38cm/day

edit: I encourage others to look at more buoys, especially those on the Atlantic side to see if they differ. Older SIMB3 data can be found here:

2019-2020
https://www.cryosphereinnovation.com/data#simb3-cards

2017-2018
http://imb-crrel-dartmouth.org/live-data/

2000-2016
http://imb-crrel-dartmouth.org/archived-data/
« Last Edit: October 20, 2021, 09:15:15 PM by uniquorn »

uniquorn

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Re: Deep diving into buoy data
« Reply #32 on: October 20, 2021, 08:27:20 PM »
re the cold blob, there are some papers looking at heat flux and leads. These 2 may be relevant.

WETTLAUFER  ET AL.: THE PHASE EVOLUTION  OF YOUNG  SEA ICE
https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/97GL00877
GEOPHYSICAL  RESEARCH LETTERS,  VOL.  24, NO.10, PAGES 1251-1254, MAY  15, 1997

Quote
Discussion
To  connect  our  results  to  field  conditions  we  note  that the maximum brine flux from a single lead occurs within about 6 hours of its formation [Morison and McPhee, 1997]. After sea ice reaches approximately 20 cm, there is very little  discernible difference in its brine flux from that of the background. As mentioned above, the main, large scale, scientific hypothesis driving the  study of leads is that the very uniform mixed layer structure observed in the Arctic is created entirely from a relatively small area of leads. Therefore these events, whose timescales are short relative to seasonal timescales, and which occur throughout the Arctic,  may be responsible for the creation and maintenance of the large scale hydrography.
 Thus, a major conclusion is that our observed delay in the brine flux (of about 5 hours) is actually very significant on the timescale of the evolution of a single lead and hence has important implications for the link between leads and large scale hydrography. Furthermore, by influencing the  solid fraction in the mushy layer, brine drainage slowed the growth of the layer by up to 15% in this same time period [Wettlaufer et al., 1997]



Lead convection measured with an autonomous underwater vehicle

James  H.  Morison , Miles  G.  McPhee
https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/97JC02264
JOURNAL  OF GEOPHYSICAL  RESEARCH,  VOL.  103, NO.  C2, PAGES 3257-3281, FEBRUARY  15, 1998

Quote
Abstract.
The winter Lead Experiment (LeadEx) was conducted during 1992 in the Beaufort Sea. There the Autonomous Conductivity Temperature Vehicle (ACTV) was operated under and around leads. These are the first measurements of this kind.
Measurements of temperature, salinity, and turbulence parameters were also made at lead edges with sensors fixed to rigid masts. By combining information from the fixed measurements and the ACTV  an inertial dissipation method is used to derive horizontal profiles of salt flux from ACTV  salinity measurements. Comparisons also show that turbulent vertical velocity perturbations can be estimated from the vertical motion of the ACTV.  With these velocity estimates, horizontal profiles of the turbulent fluxes of heat, w' T',  and salt, w'S',  are also computed directly. Data from a wide (1000-m-wide) lead with rapid ice motion indicate stronger turbulence under the lead than downstream, but the character of the flow is that of a convective boundary layer modified by a change in surface buoyancy flux. The convection is characterized by multiple, intermittent plumes that scale in size with the mixed layer depth. At a medium-sized (100-m-wide) lead with slower ice motion the convective circulation set up by the lead is more apparent.
Convective plumes are stronger and more prevalent at the lead edges, particularly the downstream edge. The comparison between the horizontal profiles from the ACTV  and time series from fixed sensors suggests that lead convection is a combination of a near surface convective boundary layer and a deeper quasi-stationary convection pattern.
Quote
The ACTV  data suggest low fluxes initially, as do the other data. This occurs because the initial ice growth is a matrix of frazil ice which retains brine. Peak fluxes occur after 12-24 hours as indicated by the ACTV data, the McPhee [1994] data, and the ice-growth-derived data. This happens after the ice is about 2 cm thick and begins to grow in a columnar structure that allows better brine drainage (J. Wettlaufer, personal communication, 1992). The ACTV  and ice data indicate the same low salt flux by day 100 when the ice growth rate has slowed considerably. By this time, turbulent flux levels were too low to be measured with the fixed mast.

uniquorn

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Re: Deep diving into buoy data
« Reply #33 on: October 20, 2021, 09:25:20 PM »
Brine channels feature in dispatch 22 of the Beaufort Gyre Exploration Project
https://www2.whoi.edu/site/beaufortgyre/expeditions/2021-expedition/2021-dispatches/dispatch-22-observations-projections-and-modelling/

The photo of 4 buoys reminded me that there is a flux buoy co-located with TOP4.
https://www.oc.nps.edu/~stanton/fluxbuoy/deploy/buoy48.html

uniquorn

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Re: Deep diving into buoy data
« Reply #34 on: October 21, 2021, 01:47:19 PM »
Brinicles were called ice stalactites in 1995. Not wanting to turn this into a brinicle thread but there is some interesting discussion on the saline plumes.
Probably OCR conversion since there are some odd words in it.

The formation and morphology of ice stalactites observed under deforming lead ice
Published online by Cambridge University Press:  20 January 2017
Donald K. Perovich, Jacqueline A. Richter-Menge and James H. Morison
https://www.cambridge.org/core/journals/journal-of-glaciology/article/formation-and-morphology-of-ice-stalactites-observed-under-deforming-lead-ice/29021BE4AF13B35ED2F46E59F65DA630

my emphasis
Quote
Discussion

As mentioned earlier, we believe that the subsequent brine drainage of rafted ice provided the source of brine needed to form the stalactite. For this to be true, there must have been a sufficient quantity of brine available in the young lead ice. No direct measurements were made of the volume of brine expelled from the stalactite. while a brine plume draining from the stalactite was observed in the ROY video, we were unable to measure the plume temperature, salinity or flow rate.

It is possible, however, to formulate rough estimates of the heat content of the stalactite and of the volume of rejected brine that served as the necessary heat sink. To first order, the heat content (Q) of the stalactite is simply Q = WLf, where W is the weight of the ice in the stalactite and Lf is the latent heat of fusion of ice (0.33 MJ kg−1). The weight of the retrieved part of the stalactite was 3.1 kg. We can only estimate the weight of the part that was lost. In the video, it appeared to be about 0,75 m long and 0.08 m in diameter. The ice content is not known but from its lack of cohesiveness we shall assume that the lower part was 25% ice and 75% brine. This gives an ice weight for the lower part of approximately 0.9 kg and a total stalactite weight of 4.0 kg. Thus, the heat content of the entire brine stalactite is roughly 1.35 MJ. The volume of rejected brine (V) needed to extract the heat content of the stalactite is

(1)

where β is the fraction of the heat extracted from the brine that goes to freezing the stalactite, ρb is the density of the rejected brine, c is the specific heat of the brine (4.2 kJkg−1 ° C−1), Tb is the temperature of the brine and T0 is the temperature of the underlying sea water (T0 ~ −1.7° C). According to Martin’s laboratory experiments, a minimum of half of the heat extracted by the cold brine contributes to the formation of the walls of the stalactite (β = 0.5). The remaining heat is. lost to ice crystals that grow in the vicinity of the tip of the stalactite but are swept out to the underlying ocean. The density of the brine plume was determined from ice physical-property measurements, which showed that the lead ice had a bulk salinity of 18 ppt and a mean temperature of −10° C. Assuming that the brine was at its salinity-determined freezing point and had a temperature of −10° C, then the brine salinity was 150 ppt (Fujino and others, 1974) and the density was 1120 kgm−3 (Gebhart and Mollendorf, 1977). Substituting these values into Equation (1) gives an estimate of 701 for the volume of brine that flowed through the stalactite. Based on these approximations, then, for a flow period of 15 h (0600-2100 h), the average flow rate was 1.3 mls−1. This is an order of magnitude less than the value of 18 mls−1 estimated by Dayton and Martin (1971) for Antarctic stalactites.
Note: Arctic flow rate estimated at the lower end of the scale

Quote
As expected, the desalination rate in the undeformed ice reached a maximum during the first few hours, when growth rates were large, and then decreased as the rate of growth slowed, In the deformed ice, even using the conservative estimate of brine loss, there was a high desalination rate of 17.6 pptd−1. This value was the average desalination rate for the entire period we observed the stalactite. In all likelihood, the rate was higher when the ice first rafted, then decreased with time. Aside from the initial few hours of growth, when the rates were comparable, desalination was always greater in the deformed ice than in the undeformed. This illustrates that lifting highly saline ice out of the water is an effective desalination mechanism.

Quote
More important to consider are differences in the character of the salt flux. In the undeformed case, the salts are rejected uniformly over a wider area. The deformed case exhibits much more spatial variability, with the brine injected through the stalactite into the ocean as a highly concentrated point source.

To determine the impact of this plume of cold, dense brine on the thermohaline structure of the underlying water, the question of its penetration depth must be addressed. The penetration depth is a function of the density of the brine plume relative to the underlying sea water, as well as the rate and character of the injected brine. In the case we observed, the brine plume exiting the stalactite had a higher density than the underlying sea water: 1120 kg m−3 compared with 1020 kg m−3. The stalactite plume, as seen in the video, appears to become nearly horizontal within 1 m of the stalactite. Since the ambient horizontal flow was an order of magnitude greater than the estimated vertical velocity of the brine in the stalactite, it is likely that the plume would have been carried several hundred meters downstream before it settled to the base of the mixed layer at a depth of 30 m. Rough estimates determined using smoke-stack theory (Csanady, 1965; Slawson and Csanady, 1967) indicate that over this distance the plume would have spread to a few meters across, causing a marked decrease in the salinity perturbation. This suggests that, while the stalactite plumes may be identifiable some distance from the source and could contribute to mixing in the upper layer, it is unlikely that they would penetrate the pycnocline. These comments are speculative but they do suggest that more detailed modeling aimed as assessing the impact of the brine plume on the thermohaline structure of the upper ocean is warranted.


I recommend reading the whole article. There is a lot of interesting detail in amongst the heavy tech. (but no smoking brinicle for the cold blob)
« Last Edit: October 21, 2021, 03:23:28 PM by uniquorn »

uniquorn

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Re: Deep diving into buoy data
« Reply #35 on: October 21, 2021, 03:10:10 PM »


Thinking about it though, 1120kg/m3 is a lot denser than the 1026 at 80m beneath itp122.
From above
Quote
In the case we observed, the brine plume exiting the stalactite had a higher density than the underlying sea water: 1120 kg m−3 compared with 1020 kg m−3

So why wouldn't it penetrate the pacific layer?

Need the volume:

Measurements of salinity and volume of brine excluded from growing sea ice
Masaaki Wakatsuchi, Nobuo Ono, First published: 30 March 1983  https://doi.org/10.1029/JC088iC05p02943
(drat - paywalled)

Quote
Abstract

The volume of brine excluded from growing sea ice and its salinity were measured using a brine sampler. The measurements were made, in both laboratory and field, under various growth conditions of the sea ice. The salinity of the brine becomes higher, and the volume flux decreases as the sea ice growth rate decreases. Consequently, the salt flux of the brine decreases with decreasing growth rate. In the case of sea ice growth at a constant rate, as the sea ice becomes thicker, the salinity of the brine excluded increases while its volume flux decreases. However, the salt flux is nearly independent of the ice thickness increase, at least up to a thickness of 15 cm. For sea ice growth rates between 1.7×10−5 and 1.4×10−4 cm s−1, and for a seawater salinity of 33.0‰, the brine salinity ranged from 42.3‰ to 92.7‰, the volume flux ranged from 6.3×10−6 to 3.4×10−5 cc cm−2 s−1, and the salt flux ranged from 6.4× 0−7 to 1.5×10−6 g cm−2 s−1.

Steep learning curve anyone?
« Last Edit: October 21, 2021, 06:42:27 PM by uniquorn »

kassy

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Re: Deep diving into buoy data
« Reply #36 on: October 21, 2021, 05:11:25 PM »
re the cold blob, there are some papers looking at heat flux and leads. These 2 may be relevant.

WETTLAUFER  ET AL.: THE PHASE EVOLUTION  OF YOUNG  SEA ICE
https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/97GL00877
GEOPHYSICAL  RESEARCH LETTERS,  VOL.  24, NO.10, PAGES 1251-1254, MAY  15, 1997

Quote
Discussion
To  connect  our  results  to  field  conditions  we  note  that the maximum brine flux from a single lead occurs within about 6 hours of its formation [Morison and McPhee, 1997]. After sea ice reaches approximately 20 cm, there is very little  discernible difference in its brine flux from that of the background.
...

That part was a bit weird (to ice amateurs because freezing extrudes but they mention leads) but reading the article it makes sense. Short hint:

Whereas frazil  ice constitutes a significant proportion of the ice cover in the Southern Ocean, and in other seasonal ice zones, the overwhelming majority  of sea ice growth in the Central Arctic Ocean occurs in leads and is columnar.

Thanks for the articles!
Þetta minnismerki er til vitnis um að við vitum hvað er að gerast og hvað þarf að gera. Aðeins þú veist hvort við gerðum eitthvað.

uniquorn

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Re: Deep diving into buoy data
« Reply #37 on: October 21, 2021, 09:12:48 PM »
I'm probably diving too deep for my own good with the cold blob. That paper does say
Quote
Recent  field  observations  in  the  Arctic [Morison et al., 1993] show that the heat loss through these fissures can be up to 300 W m -•,  or fifteen times that  from the surrounding ice.  Hence, although they occupy less than 10% of the surface area, leads can account for roughly half of the total  oceanic heat loss.
Depending upon environmental conditions, sea ice can reach  a  thickness  of  15  cm  in  the  first  24  hours  of growth [Wettlaufer, 1997

Leads would account for a smaller fraction of heat loss these days but the thickening probably still applies.

For now, I'll just make a note of the conditions at the time for future reference and move on.
1. 551610 air temps
2. top4 water temps, 1m-4m
3. Rough measurement of nearby lead and view of drift using aqua modis
https://go.nasa.gov/3DXZtpE
4. S1A on oct4

johnm33

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Re: Deep diving into buoy data
« Reply #38 on: October 21, 2021, 10:52:17 PM »
They may be called leads but IF I'm right in thinking the openings are caused by swells passing through then the Perovich2 image would serve better if imagined on a curved surface, where the freezing undeformed ice 'surfs' both ahead of and behind the apex towards the thicker ice [think of wind too]. IF as I suspect the 'swell' is an overturning/rotating wave then there'd be a downward force in operation within the active layer carrying denser water down from the base of the 'still' layer, directly beneath the ice, to the base of it's 'native' layer. Due to the swell approaching the axis of rotation it may also have it's own orthogonal waves wrapped around it, a little like the field around a live wire, and that may carry sinking water to a point of disruption of the waves motion, concentrating it before shedding it.

uniquorn

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Re: Deep diving into buoy data
« Reply #39 on: October 22, 2021, 02:13:17 PM »
<>overturning<>
Very difficult to verify overturning with drifting buoy providing data every 4hrs. Please take a look at some fixed buoy data. There are 4 fixed buoys for the Beaufort Gyre Exploration Project that may help.
https://www2.whoi.edu/site/beaufortgyre/data/mooring-data/
Data there is currently up to 2018 but they just recovered some more recent data that may be available soon.
https://www2.whoi.edu/site/beaufortgyre/expeditions/2021-expedition/2021-dispatches/dispatch-7-recovey-and-redeployment/

While it has been interesting, concentrating on TOP4 cold blobs has diverted attention away from ice. Looking more closely at co-located 551610 showed up some small errors in the changes I made to Cameron's original code.

When adding the TOP4 data to the 551610 chart I lined it up as a best guess. As the ice cools to the bottom it began cooling slightly below ice bottom line, highlighting my laziness, let's call it enthusiasm to see the results.
Here is the improved code:
Quote
    #define temperature string position (height above ice)
    #192 dtc at 2cm dist = 3.84m, dist between sounders=4.05m, set surface level from temps, add 0.21m to depth
    #218 dtc for top4 and the gap. cheating, at 2cm=4.36m, so try 4.36+4.05=8.41m 
    temp_string_length = 8.41
 

You can see that I'm still cheating, but at least it's a calculated cheat. At the moment I paste the top4 data into the 551610 csv file. Fortunately they both report every 4hrs (almost)

551610, less interpolation on the colours, temp limits -3C to -1.3C.
Added some semi transparent overlay to the snow and ocean layers and took the unadjusted water temp out.

Interesting that the bottom distance anomaly happened as ice cools to ice bottom.

added -25C to -1.3C for reference

« Last Edit: October 22, 2021, 02:38:37 PM by uniquorn »

uniquorn

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Re: Deep diving into buoy data
« Reply #40 on: October 22, 2021, 05:40:07 PM »
SIMB3 resolution may be too course to define the onset of refreeze temperature in this part of the Beaufort. Here are the TOP4 temps for october so far, 1m-3m

uniquorn

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Re: Deep diving into buoy data
« Reply #41 on: October 22, 2021, 07:18:05 PM »
To give an idea of the resolution difference and get a feel for the very small changes in temperature here are the TOP4 1m-3m temps overlaid onto 551610(adjusted). The SIMB3's are a great buoy that tell us a lot about ice temperature at a good price. Without this one we wouldn't know where the ice bottom was. At the moment just ~30cm (0.3dbar) away from the first TOP4 measurement.
« Last Edit: October 23, 2021, 04:30:06 PM by uniquorn »

uniquorn

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Re: Deep diving into buoy data
« Reply #42 on: October 23, 2021, 03:42:14 PM »
Strong possibility that ice below 551610 started thickening yesterday. TOP4 1m water temps were very close to -1.5C

uniquorn

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Re: Deep diving into buoy data
« Reply #43 on: October 23, 2021, 08:50:42 PM »
According to the data on whoi itp128 we have another co-location
Quote
ITP128 was deployed on a 1.36 m thick ice floe in the Transpolar Drift on September 30, 2021 at 77° 26.5 N, 179° 54.3 E in collaboration with the Nansen and Amundsen Basins Observational System (NABOS) project from the Russian Research Vessel Treshnikov. On the same icefloe, a US Army Cold Regions Research and Engineering Laboratory (CRREL) Seasonal Ice Mass Balance Buoy 3 was also installed. The ITP is operating on a fast sampling schedule of 4 one-way profiles between 7 and 760 m depth each day.

That looks like SIMB3 864620   https://www.cryosphereinnovation.com/simb3/864620
The lat/lons are quite close but a little different. Will run an ani sometime to check that. Also the thicknesses are different, itp128 at 1.36m and 864620 at ~0.74m

Anyway, 864620 also looks close to onset of thickening.



Jim Hunt

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Re: Deep diving into buoy data
« Reply #44 on: October 24, 2021, 01:14:31 PM »
The results of my own humble efforts:

https://GreatWhiteCon.info/resources/ice-mass-balance-buoys/winter-2021-22-imb-buoys/#864620

Personally I reckon it'll be a little while yet before significant thickening begins. And what's with the oscillating "snow depth"?
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uniquorn

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Re: Deep diving into buoy data
« Reply #45 on: October 24, 2021, 10:21:37 PM »
Jim, that's a great start from the tutorial. A few quick suggestions that might change your mind.

1. Set the vmin to -20 and vmax to -1.625
Quote
im = ax.imshow(dtc, cmap='jet', vmin=-20, vmax=-1.625,

2. set the whitespace above snow to a low alpha setting to show the air temps. I rem it out completely with #
Quote
ax.fill_between(timestamp, temp_string_top, snow_height, color='white', zorder=2, alpha=0.2)

3. do the same to the snow layer
Quote
ax.fill_between(timestamp, snow_height, 0, color="grey", zorder=1,alpha=0.2)

4. Turn the water layer into a thin line so you can see the water temps
Quote
ax.fill_between(timestamp, ice_thickness, ice_thickness+0.02, color='b', zorder=3)

Now you can use your expert judgement to align the air temperatures with the snow layer using the temp string offset. I think it is around 0.06 to 0.08, a couple of centimetres, but I would love to have a second opinion.

To clarify, onset of thickening isn't significant thickening, it's a first tick down that stays down, but I think it's important for defining when the ice has changed state. I'm not really into forecasting as I'm useless at it, but I'm glad my last post means that at least 2 of us are watching to see when it happens.
Unfortunately we don't have 1m water temps, in this case itp128 starts at 8m.


If you want to try different interpolation add interpolation='blah' to the im= line
Quote
im = ax.imshow(dtc, cmap='jet', vmin=-20, vmax=-1.625, extent=[timestamp[0], timestamp[-1], temp_string_bottom, temp_string_top],interpolation='hanning',

note also that the dtc temps may need to be adjusted.
« Last Edit: October 24, 2021, 10:43:56 PM by uniquorn »

uniquorn

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Re: Deep diving into buoy data
« Reply #46 on: October 24, 2021, 10:33:09 PM »
re the rapid changes in snow depth, there are some suggestions here

Seasonal ice mass-balance buoys: adapting tools to the changing Arctic
https://www.cambridge.org/core/journals/annals-of-glaciology/article/seasonal-ice-massbalance-buoys-adapting-tools-to-the-changing-arctic/B1EB7AEE76BBCEB1A0E5938C05F19D80
 Published online by Cambridge University Press:  14 September 2017
Chris Polashenski, Don Perovich, Jackie Richter-Menge and Bruce Elder

though more about the melt season than freezing. Maybe you have something more recent.

and this one from upthread
I don't think there is that much snow, the top sounder is probably frosted.


uniquorn

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Re: Deep diving into buoy data
« Reply #47 on: October 25, 2021, 01:28:32 PM »
Thinking about calibration of the SIMB3 buoys using whoi TOP and ITP data, here are the 1m, 8m and 9m temps for TOP2-4 with the difference between 1m and 8m inset.
The difference is very small, well below the resolution of the SIMB3 dtc, so I think it reasonable to calibrate to the 8m temps (or 9m if it is more frequent).


uniquorn

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Re: Deep diving into buoy data
« Reply #48 on: October 25, 2021, 01:31:19 PM »
Note the drop in near surface temps on TOP4 above which recently experienced the onset of bottom thickening. If we see a similar drop on TOP2 and 3 after onset we can assume it is due to thickening and not a change caused by local currents.

The snow layer also dropped again, perhaps due to the recent 'warmer' temps (-10C) or stronger winds clearing drifting snow.
« Last Edit: October 25, 2021, 01:38:33 PM by uniquorn »

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Re: Deep diving into buoy data
« Reply #49 on: October 25, 2021, 07:55:34 PM »
Remaining with 551610 and top4
1. Probably jumped the gun in the last post, the cooler water goes down to 25m. I think it unlikely that is due to a change in the ice above. The tight limit from -1.65C to -1.45C highlighting another cold blob, but deeper this time.

2. whoi TOP4 profile contours
3. Wider temp range -1.65C to +0.3C