Right, this is all about getting to the right scale as constrained by forum image widths. Previously we've determined that a degree of latitude as marked on S1AB jpg with lines is 2712.26 pixels for what we know is 111.111 km on WGS84 (which we have to use here as all GPS data refers to the earth ellipsoid).
Thus image distances can be measured in pixels (often fractional if points are diagonal) and converted to meters by multiplying by 41.0 for both S1AB jpg and S1AB.8bit.jp2 (at 100% zoom in the polar viewer plugin).
Doing this, it emerges that the Polarstern was 3703 m north of the shear line. The 79 km long open lead created in this area ranged from 730 m in width to a more typical 487 m to 159 m at narrows. A lead of this width cannot be bridged by wooden palettes and a sled, nor is it feasible to kayak across regularly carrying staff, bear guards and fuel for instruments (as Mosaic was doing earlier).
The dramatic regional shear animation of post #412 that compared Dec 12 06:19 to Dec 13 03:43, repeated below, was done in Polarstern-stationary coordinates (lagrangian) which removes background ice pack movement (secular drift).
The rifting took place as the pack as a whole moved almost due westward by 4301 m but with a 410 m north component. Relative to the Polarstern, the shear area moved an additional 4146 m southeastward.
It's worth walking through GPS decimal points which have quite different associated measures for lon than lat.
At 86.6º, a tenth of a latitude degree increment represents 11.111 km, a hundredth 1111 m, a thousandth 111 m, a ten-thousandth 11.1 m and a hundred-thousandth 1.1 m. The first is what we are looking at with sailwx and AWImet; the second what GFS-nullschool can discriminate at maximal scale, the third enough to show a buoy lurch and the last the nominal resolution claimed by typical Mosaic buoys (4th GPS decimal point).
Note the buoys are in motion during whatever time it takes for them to measure their position. Those speeds, given as the color scale on uniq's animations rarely exceed 1 km/hr which is 1000 m per 3600 seconds or 0.27 m/s. So if it took them 5 seconds, that would be 1.4 m which might amount to a correction to their last decimal.
2019 12 13 0343 86.6 119.5 86.5918 119.4764 rough and refined PS locations post shear
2019 12 12 0619 86.6 120.1 86.5982 120.1285 rough and refined PS locations pre shear
So what needs to be done -- and I am
leaving this to Tor B -- is download the data files for 2-3 buoys above the shear and 2-3 below using the map below (or as provided by uniq), delete the irrelevant columns, combine into a single spreadsheet with times of reported synchronized by row. Then add a new column and fill with the subtraction of above/below longitude columns.
The graph should show a big lurch at the hour of rifting.
As a control, go back a week or so to establish the big lurch is way out of the ordinary, not 'normal variation'. Going forward, the winds have hardly been enough to stress the ice, meaning delaunay buoy triangulations across the shear line will have stable edges.
Nonetheless, this morning's pair of S1AB 3 hrs 16 min apart don't show a quiescent situation on the Mosaic ice pack (lower animation). Indeed a small rift seems to be closing at the later time. This does not necessarily affected deployed instruments as only a small flat area near the ship is currently used.
The Kapitan Dranitsyn can be seen crossing the shear line within hours of its formation. It's not clear what would happen to an icebreaker caught in a sudden shear event. The Polarstern, being frozen in for a year, is more at risk.
Shear events with km scale displacements are multi-daily events even at the scale of a single S1AB frame, but one crossing a 118 m object amidship would not be expected unless the ship, like Los Angeles, is sitting on an inactive fault line predisposed to re-awakening.
While the Polarstern has not disclosed the data that would allow analysis (it being below the resolution of S1AB), they have had slabs of ice sliding back and forth in front of the bow, micro-shear events. In addition, the undocumented Dec 6th event saw a larger faulting event come right through Mosaic ice camp.
In summary, the ice has been shifting around a lot already this winter at various scales with only 2 months down and 4-5 months to go. It's tempting to say 'more than usual' but hard to go beyond anecdotal impressions. This has been a very odd winter in terms of no coherent ice pack drift (as visualized above in Ascat whole-Arctic mp4).
