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Messages - uniquorn

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Arctic sea ice / Re: The 2020 melting season
« on: August 14, 2020, 08:18:29 PM »
amsr2-uhh random comparison of 2012/2020 cyclones

Arctic sea ice / Re: Home brew AMSR2 extent & area calculation
« on: August 14, 2020, 05:13:19 PM »
Thanks. That's more like what I was aiming for, though I'd still be reluctant to lose the gradient in low concentration.
5day pixel count beginning to show a trend.
Another clumsy example of highlighting very low conc. aug6-13

Arctic sea ice / Re: Tides
« on: August 14, 2020, 05:02:03 PM »
October 2, 2015
The Arctic Ocean traditionally has been described as an ocean with low variability and weak turbulence levels. Many years of observations from ice camps and ice-based instruments have shown that the sea ice cover effectively isolates the water column from direct wind forcing and damps existing motions, resulting in relatively small upper-ocean variability and an internal wave field that is much weaker than at lower latitudes. Under the ice, direct and indirect estimates across the Arctic basins suggest that turbulent mixing does not play a significant role in the general distribution of oceanic properties and the evolution of Arctic water masses. However, during ice-free periods, the wind generates inertial motions and internal waves, and contributes to deepening of the mixed layer both on the shelves and over the deep basins—as at lower latitudes. Through their associated vertical mixing, these motions can alter the distribution of properties in the water column. With an increasing fraction of the Arctic Ocean becoming ice-free in summer and in fall, there is a crucial need for a better understanding of the impact of direct wind forcing on the Arctic Ocean.

Arctic sea ice / Re: Tides
« on: August 14, 2020, 03:51:59 PM »
Some interesting short videos on the thread, near FJL on the way to Polarstern

Arctic sea ice / Re: The 2020 melting season
« on: August 13, 2020, 10:55:26 PM »
Hudson Bay hasn't quite melted out yet.

Arctic sea ice / Re: Tides
« on: August 13, 2020, 10:13:47 PM »
Another couple of references

Baroclinic Tides: Theoretical Modeling and Observational Evidence
Vasiliy Vlasenko, Nataliya Stashchuk, Kolumban Hutter
This book was first published in 2005. When an oceanic tidal wave that is primarily active on the water surface passes an ocean shelf or a region with a seamount, it is split into a less energetic surface wave and other internal modes with different wavelengths and propagation speeds. This cascading process, from the barotropic tides to the baroclinic components, leads to the transformation of tidal energy into turbulence and heat, an important process for the dynamics of the lower ocean. Baroclinic Tides demonstrates the analytical and numerical methods used to study the generation and evolution of baroclinic tides and, by comparison with experiments and observational data, shows how to distinguish and interpret internal waves.

An approximate estimate of the energy in the first mode M2 baroclinic tide has been made from satellite observations. Results based on TOPEX/POSEIDON (T/P) precision altimetry indicate that the internal tide patterns are similar to those expected from mid-ocean topographic features in the global oceans. Both the orthotide and harmonic analyses indicate that the total energy in global M2 baroclinic tide is approximately 50 PJ. For a variety of reasons, M2 is the only component that can be obtained reliably from altimetric measurements. Even then, the energy value may be an underestimate and the energy flux, the dissipation rate, cannot be deduced from altimetry. Since it is the tidal currents flowing over mid-ocean topographic features that are responsible for generating internal tides, a model calibrated by M2 observations is a plausible alternative. Currents from a high resolution (
) barotropic tidal model have therefore been used to obtain an estimate of both the energy and the dissipation rate in M2, S2 and K1 baroclinic tides. A simple model of baroclinic tide generation has been used, and the unknown constant in this model has been selected to yield a total energy of 50 PJ in the first mode M2 baroclinic tide. Based on this calibration, the total energy is 8 PJ in S2 first mode baroclinic tide and 15 PJ in K1. The total in all first mode baroclinic tides is 90 PJ, about 16% of the total energy (580 PJ) in barotropic tides. The model results also suggest that about 360 GW of tidal energy are dissipated in M2 baroclinic tides alone, and 520 GW are dissipated in all first mode baroclinic tides. The latter value is approximately 15% of the power input into barotropic ocean tides (3490 GW) by the lunisolar tidal forces. We have preferred to be conservative and hence these are likely to be underestimates, especially since the altimetric tracks do not often intersect mid-ocean topographic features at optimum angles. While these values are very much within the range of earlier estimates in literature, they should be regarded as still uncertain to perhaps a factor of two (the dissipation rate could be anywhere from 400 GW to 800 GW, the most likely value being about 600 GW). The small signal to noise ratio involved in altimetric measurements of the surface manifestation of internal tides, and potential contamination by mesoscale signals are serious problems. In situ measurements at least a few locations underneath altimetric tracks are essential for confirmation and/or refinement of these preliminary estimates. Hopefully, these very first estimates of the energy and dissipation rate in global baroclinic tides, though rather crude, will serve as a catalyst for a better estimation in the future, since internal tides are likely to be a prominent source of mixing in the deep oceans and important to thermocline maintenance.

Quick bathy overlay using worldview, aug11
85.2N 157.4E  1100m drops to 3800m
(then back up to 2400m at 172.2E under the furthest east low conc area. Not sure if that is relevant)

Arctic sea ice / Re: Home brew AMSR2 extent & area calculation
« on: August 13, 2020, 02:48:38 PM »
Here is a rather gaudy attempt to highlight the very lowest concentration pixels shown in the charts above. While less aesthetically pleasing than the default it does show remaining ice in the hudson bay, which is just about visible on the default.
Hopefully the next version will retain this information for those curious enough to extract it. It would perhaps help prevent over expectation of ice going 'poof'
Forgot to change the land colour. NucMed LUT Split_BlackBlue_RedW with 0 changed to black. Should be able to find or create something more attractive

Developers Corner / Re: Test space
« on: August 13, 2020, 02:26:00 PM »
This is still a raw version without filtering. The arc artifacts (end of swaths) will be removed in a next version.
They show up more here as I'm attempting to show very low concentration. Here is a comparison with the default LUT, which I like a lot aesthetically, showing how much lowest concentration is not really visible. Perhaps there is an issue with how reliable detection is at that low level.
The same information, I think, different representation.

Developers Corner / Re: Test space
« on: August 13, 2020, 02:00:29 PM »
this lut loses the ability to track floes but is good for change in concentration imo

Arctic sea ice / Re: What the Buoys are telling
« on: August 13, 2020, 12:13:44 AM »
whoi ftp server is back up again. Many thanks to Rick Krishfield for that :)
Here is itp114, day213-225, after the last high drift speed event. 7-40m temps varying ~0.2C. Larger variations at 70m.

Developers Corner / Re: Test space
« on: August 12, 2020, 11:02:08 PM »
haven't found a good cb lut yet
red is low conc - way too gaudy

Arctic sea ice / Re: The 2020 melting season
« on: August 12, 2020, 10:27:17 PM »
NSIDC ice age was updated to august recently. Here is 2012vs2020 for the melting season.
Beaufort decapitated in 2012. Maybe that is yet to come this year.
2000-2020 here

Arctic sea ice / Re: What the Buoys are telling
« on: August 12, 2020, 09:41:51 PM »
Tbuoy drift and locations, some final.

Arctic sea ice / Re: What the Buoys are telling
« on: August 12, 2020, 09:13:16 PM »
t74, melted out, jul15-aug10
t75, melted out, jul15-aug7
t76, looks like big melt pond, jul15-21
t79, jul15-31

Arctic sea ice / Re: What the Buoys are telling
« on: August 12, 2020, 08:46:09 PM »
mosaic buoy t66, melt pond and melted out, jul15-aug12
t67, looks like low freeboard, jul15-aug6
t69 still going strong, possible ridging very early on, jul15-aug12
t70, big melt pond, possibly still melting, jul15-aug7

Arctic sea ice / Re: What the Buoys are telling
« on: August 12, 2020, 07:37:21 PM »
mosaic buoy m29 melting out, jul15-31
t62 melting out, jul15-aug1
t63 with a traumatic story to tell, jul15-aug9
t64 sudden end, jul15-aug11

Arctic sea ice / Re: What the Buoys are telling
« on: August 12, 2020, 03:15:47 PM »
sidekick has fallen over. sk2 shows sky conditions, sk1 is probably facing down in a melt pond. Well we do like to talk about the weather.

Arctic sea ice / Re: The 2020 melting season
« on: August 12, 2020, 03:05:11 PM »
drift update, may29-aug12

Arctic sea ice / Re: Tides
« on: August 12, 2020, 02:59:00 PM »
The turbulence appears north of the shelf. Depth rises from ~4000m to ~800m. We could do with a few more rammb's of that area to attempt to verify a daily event. Maybe in their own thread. There are currents here too, so tide will only be a contributary factor.

There aslo eddies west of the plateau and the molloy hole, of course.

Arctic sea ice / Re: Tides
« on: August 12, 2020, 01:33:46 PM »
Regarding the Yermak plateau
Thank you JayW. A very interesting paper about a plateau north of Svalbard

In my humble opinion, ~7E to ~13E is significant. Then there is the shelf break all along the Nansen basin

Arctic sea ice / Re: The 2020 melting season
« on: August 12, 2020, 01:33:48 AM »

Developers Corner / Re: Dev library
« on: August 11, 2020, 11:49:39 PM »
for ref
Oren suggested a while back it would be helpful to have an operational description of how Venn diagrams from image pairs are made. Fortunately all manner of boolean logic operations are baked right into Gimp’s color picker.Steps are simple; the trick is keeping color picker at the right setting operating on the right active layer:

open five dates before Aug 10th as a short stack in Gimp, 10th on top
set mode on each to ‘darken only’ to deprecate cloud cover artifacts
capture the view with with ‘new from visible’
delete the other dates and add Aug 01 from below.
set the color picker to desired concentration range on the embedded palette
crop stack to a non-excessive region of interest that works for both
select open water blue in the Bering 10th, change active layer to 1st, change color picker to ’subtract’, make new layer, name to avoid confusion, fill.
select open water blue on the 1st, change active layer to 10th, change color picker to ’subtract’, make new layer, name and fill with 2nd color.
set the color picker to ‘intersect’ to find open water common to both, make new layer, name and fill with 2nd color.

Arctic sea ice / Re: The 2020 melting season
« on: August 11, 2020, 11:33:21 PM »
rare deterioration above NE Greenland.
high contrast view of north of greenland today.
No graticule but the swaths head roughly towards the pole. Click for full resolution and default view

Arctic sea ice / Re: MOSAiC news
« on: August 11, 2020, 10:22:36 PM »
good image of melt ponds, ridging, low freeboard, fractures on fomo today

Arctic sea ice / Re: Arctic Ocean salinity, temperature and waves
« on: August 11, 2020, 09:50:12 PM »
mercator 0m temperature(SST) with amsr2-uhh overlay, jun1-aug10
used 'lighten only' in gimp for a test. Labels are much better
Best viewed at half speed.

Developers Corner / Re: Dev library
« on: August 11, 2020, 08:21:18 PM »
for reference
The Hycom thickness forecast updates every day and so needs a regular reprocessing, as it's not easy to automate. To empower more people per a suggestion of Oren, our moderator extraordinaire, the steps for doing this in Gimp are provided below. Degree of difficulty 2 in 5, ten minutes with practice.

Steps to extract the 7day forecast, enlarge(433.2%) and rotate (45º cw) it to match scale and Greenland-down orientation of AMSR2 uhh, clean up distracting datestamp and excessive palette:

download, open, change to RGB, unoptimize gif (to remove transparencies)
delete early days leaving top 7 frames (mark earliest frame, hold command-x down below it)
duplicate stack, make reusable palette in new window, deleting >3.0 m (not used) to 45x352
duplicate stack file, crop out month and day, adjust width to match palette (45)
crop stack to 631x631 data circle
rotate 45º cw about center
change from indexed to RGB
crop to region of current interest
enlarge 433.2% to match AMSR2uhh (or new AWI as that size finalizes)
enlarge canvas on palette and date to match new width.
tile thickness, palette and date, adjust view, make new layer from visible
move to imageJ and de-tile to make avi/mp4 or gif

Developers Corner / Re: Test space
« on: August 11, 2020, 08:15:32 PM »
will try them out

Lookup tables (LUTs) unambiguous for color blind and non-color blind humans.

The colors were taken from the carefully described work on How to make figures and presentations that are friendly to color blind people by Masataka Okabe and Kei Ito.

LUT files generated using the LUT Panel (source) ImageJ plugin developed by Patrick Pirrotte and Jerome Mutterer.

Developers Corner / Re: Test space
« on: August 11, 2020, 05:46:54 PM »
dev amsr2, blue-green to highlight lower concentration areas. Edited lut101 for a more neutral land colour
Probably much more sensitive to light cloud (or other things)

Arctic sea ice / Re: Home brew AMSR2 extent & area calculation
« on: August 11, 2020, 01:51:22 PM »
Thanks, pixel count over the last 5days
Something harmonic at 33, 50 and 66?

Developers Corner / Re: Test space
« on: August 11, 2020, 01:21:03 PM »
playing with LUT's

Arctic sea ice / Re: The 2020 melting season
« on: August 11, 2020, 12:39:16 AM »
With most of the chukchi under cloud, here are images from worldview and polarview

Walking the walk / Re: Zero-Carbon Farming and Living via the Acorn Path
« on: August 10, 2020, 11:16:24 PM »
Yesterday I uncovered all the beds that were 'locked down' for the autumn because of a storm forecast. Nothing happened and they stayed bone dry with a few weeds trying to survive. Luckily, due to laziness they remained open to the elements and got a thorough but unexpected drenching this evening.
Will cover them up tomorrow.

Greenland and Arctic Circle / Re: The Nares Strait thread
« on: August 10, 2020, 09:19:51 PM »
mind the gap
still, 11 hours isn't very long

Arctic sea ice / Re: The 2020 melting season
« on: August 10, 2020, 09:05:14 PM »
cloudy  north of greenland, so another polarview S1

Arctic sea ice / Re: Tides
« on: August 10, 2020, 08:09:14 PM »
mosaic buoys in the fram strait. Are people really suggesting that continuous rotational movement doesn't affect melt? Please read upthread for further examples.

Arctic sea ice / Re: Tides
« on: August 10, 2020, 07:52:17 PM »
surely there is a paper on this somewhere

Some insignificant lateral movement 280km from the nearest coast  ;)
more details here

Developers Corner / Re: Test space
« on: August 10, 2020, 04:43:10 PM »
Getting there johnm33. ImageJ will make it easier to add dates. Fiji automatically installs many useful plugins.

Good online tutorial
Basically, drag all your files onto imagej
Image>stacks>images to stack
file>save as>gif

then the world is your oyster

Arctic sea ice / Re: MOSAiC news
« on: August 10, 2020, 04:23:00 PM »
drift update, mosaic Pbuoys, jul1-aug10.

Arctic sea ice / Re: The 2020 melting season
« on: August 10, 2020, 02:00:17 PM »
-3- The whole icepack does not rotate CW with the TPD but rather participation is demarcated by immense  curvilinear leads, newly visualized in a dockside posting by L Kaleschke and enhanced on the Mosaic forum by directional convolution. These fracture lines, coincidentally or causally, approximately delimit the puzzling openings to the pole above Morris Jesup. A lot of MYI ice between Greenland and the pole was fractured by lead formation.
The first animation of Kaleschke SIC-LEADS overlaid onto gmrt bathymetry in February when the ice was much thicker shows the location of those fracture lines. Accepted that drift will be different now that Lincoln Sea is not land fast.
The underlying ocean currents will still be there but the recent prevailing winds are preventing southerly drift so the ice north of Greenland is melting in situ and beginning to show the turbulent ocean beneath. The continuous rotation during July and the abrupt halt could also have contributed to the lower concentration in that area.
The second animation shows the rotation and some of the underlying turbulence. Rammb might do a better job over a shorter timescale

Arctic sea ice / Re: The 2020 melting season
« on: August 10, 2020, 12:12:15 PM »
The movement of ice into the CAA from the CAB. Garlic press seeing a little action over the last few days between Borden & Ellef Ringnes Islands.
amsr2-uhh, caa, aug1-9

Arctic sea ice / Re: The 2020 melting season
« on: August 10, 2020, 12:16:14 AM »
polarview S1, north chukchi, aug9.
further north looks no better till 80N

Arctic sea ice / Re: Arctic Ocean salinity, temperature and waves
« on: August 09, 2020, 11:20:20 PM »
Thanks. A good reason for the quick melt. Also coming from the north by the looks of it. Maybe from Nansen Sound, though I thought the current there was supposed to be south.

Bookmarking A-Teams post for ref

Arctic sea ice / Re: The 2020 melting season
« on: August 09, 2020, 10:48:16 PM »
Would normally post this on the megacrack thread but after A-Teams post it seems appropriate here. Worldview aqua modis of CAA/nthGreenland today
click for full resolution
Still some signs of rotation north of Lincoln Sea

Arctic sea ice / Re: Arctic Ocean salinity, temperature and waves
« on: August 09, 2020, 09:18:01 PM »
20200807 eddy centre starts at around 82.5N 9E, moves a little north and to ~13E
81.3N is close to the ice edge.
Worldview shows it at around 82.57N 5.26E on aug7
That's a trip along 2/3 of the plateau northern edge 

Arctic sea ice / Re: Tides
« on: August 09, 2020, 08:50:01 PM »
Fictitious force
From Wikipedia, the free encyclopedia
A fictitious force (also called a pseudo force,[1] d'Alembert force,[2][3] or inertial force[4][5]) is a force that appears to act on a mass whose motion is described using a non-inertial frame of reference, such as an accelerating or rotating reference frame. An example is seen in a passenger vehicle that is accelerating in the forward direction - passengers perceive that they are acted upon by a force in the rearward direction pushing them back into their seats. An example in a rotating reference frame is the force that appears to push objects outwards towards the rim of a centrifuge. These apparent forces are examples of fictitious forces.

The fictitious force F is due to an object's inertia when the reference frame does not move inertially, and thus begins to accelerate relative to the free object. The fictitious force thus does not arise from any physical interaction between two objects, such as electromagnetism or contact forces, but rather from the acceleration a of the non-inertial reference frame itself, which from the viewpoint of the frame now appears to be an acceleration of the object instead, requiring a "force" to make this happen. As stated by Iro:[6][7]

    Such an additional force due to nonuniform relative motion of two reference frames is called a pseudo-force.
    — H. Iro in A Modern Approach to Classical Mechanics p. 180

Assuming Newton's second law in the form F = ma, fictitious forces are always proportional to the mass m.

The fictitious force on an object arises as an imaginary influence, when the frame of reference used to describe the object's motion is accelerating compared to a non-accelerating frame. The fictitious force "explains," using Newton's mechanics, why an object does not follow Newton's laws and "floats freely" as if weightless. As a frame can accelerate in any arbitrary way, so can fictitious forces be as arbitrary (but only in direct response to the acceleration of the frame). However, four fictitious forces are defined for frames accelerated in commonly occurring ways: one caused by any relative acceleration of the origin in a straight line (rectilinear acceleration);[8] two involving rotation: centrifugal force and Coriolis force; and a fourth, called the Euler force, caused by a variable rate of rotation, should that occur.

Gravitational force would also be a fictitious force based upon a field model in which particles distort spacetime due to their mass, such as general relativity.
Fictitious forces and work

Fictitious forces can be considered to do work, provided that they move an object on a trajectory that changes its energy from potential to kinetic. For example, consider a person in a rotating chair holding a weight in their outstretched hand. If they pull their hand inward toward their body, from the perspective of the rotating reference frame, they have done work against the centrifugal force. When the weight is let go, it spontaneously flies outward relative to the rotating reference frame, because the centrifugal force does work on the object, converting its potential energy into kinetic. From an inertial viewpoint, of course, the object flies away from them because it is suddenly allowed to move in a straight line. This illustrates that the work done, like the total potential and kinetic energy of an object, can be different in a non-inertial frame than an inertial one.

Gravity as a fictitious force
Main article: General relativity
The notion of "fictitious force" comes up in Einstein's general theory of relativity.[17][18] All fictitious forces are proportional to the mass of the object upon which they act, which is also true for gravity.[19] This led Albert Einstein to wonder whether gravity was a fictitious force as well. He noted that a freefalling observer in a closed box would not be able to detect the force of gravity; hence, freefalling reference frames are equivalent to an inertial reference frame (the equivalence principle). Following up on this insight, Einstein was able to formulate a theory with gravity as a fictitious force and attributing the apparent acceleration of gravity to the curvature of spacetime. This idea underlies Einstein's theory of general relativity. See Eötvös experiment.

Arctic sea ice / Re: Home brew AMSR2 extent & area calculation
« on: August 09, 2020, 03:05:41 PM »
difference is good, aug7diff8. Have to sort out a scale.
comparison of '3 day darken' in gimp to minimise clouds, equivalent to a worst case scenario for concentration. (crop/scaling not quite right) click

Arctic sea ice / Re: Home brew AMSR2 extent & area calculation
« on: August 09, 2020, 11:22:22 AM »
aug6-8 with LUT overlay. (forgot date labels)
The missing islands are possibly a resolution issue. There are also some missing around Svalbard.
There is probably going to be a graticule, can that be optional so as not to obscure ice data?

Arctic sea ice / Re: The 2020 melting season
« on: August 09, 2020, 12:28:53 AM »
Since Friv is not providing band367 images at the moment here is a closer look at an area north of chukchi/beaufort today
deep red from band 367 indicating bare ice/water (click for comparison)

Arctic sea ice / Re: Home brew AMSR2 extent & area calculation
« on: August 08, 2020, 11:48:12 PM »
Hopefully I'm being helpful here. Herald island is also missing. These islands make a difference when searching for shoals/anchored ice

Arctic sea ice / Re: The 2020 melting season
« on: August 08, 2020, 11:35:39 PM »
Is this the same chart uniquorn?

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