That is a 100 day animation and all of the ice is rotating clockwise.
Whoa, back up a ways. The
last eight years of Arctic sea ice motion were posted up-forum as a simulcast. There was also a 541 consecutive day mp4. Not all the ice is rotating CW this month, look at the ESAS. During the last storm, the ice surged strongly across the central Arctic in anti-TransPolar Drift direction. No ice has managed to cross the line between the New Siberian Islands and North Pole since May 2017.
ice is thinner, so more mobile
That seems intuitively sensible but to actually compare different years requires a quantitative measure of mobility. And what might that be?
The ice pack today rarely moves as a rigid unit, ie by translations or rotations. Did it ever? You can browse the OSI SAF archive of two-day displacements but it only goes back to 2016; NSIDC has a much longer series but in non-graphical format.
Here you would want to generate a straight translation and a shearless rotation in Panoply to be sure how these vector fields look in flat-earth projection view. However flipping through hundreds of OSI SAfs doesn't even kick out any plausible candidates.
At the scale of satellite animation data, the 4000 km wide Arctic Ocean is represented by only 440 Ascat pixels, which has the effect of completely
smoothing over opening leads, ridges, over-rafted ice, narrow ribbons of land-fast ice and pockets of open water, anything below the size of 9x9 km pixels.
On any given day, at this resolution, the ice pack appears to move and stretch smoothly in response to different local and regional forces acting on it. Features are deformed yet remain recognizable for many months. This is sometimes called viscoelastic deformation even though no balancing restorative force exists as it would for an idealized elastic rubber band, metal spring or rebounding pizza dough.
However that's not to say the ice is not acting back on itself to damp regionally conflicting motions/ Given a stationary cyclonic feature, the pack would like to rotate but is always playing catch-up to moving weather systems, not to mention land boundary conditions acting like the cup of a Couette viscometer. The properties of compressible and incompressible media are very different. While ice area is not strictly conserved, it's quite close on short time scales.
The CAA stringer is speeding up as it extends further to the west. That is, the deformation has been more extreme the farther along the stringer, the outer floes are moving faster causing the stringer to stretch out. Ice already in the Chukchi has to move aside to accommodate the intrusion.
The immense MYI-fringed feature off the Laptev-SZ has also been deforming rapidly westward the last few days. And ice of all origins approaching the Fram speeds up and so extensionally deforms. Meanwhile shapes and distances in the pole region itself are quite stable and features move in unison.
Can time-dependent triangulation of ice deformation, up-forum, lead to an actual mobility metric? Sure, if the intrinsic propensity of ice to deform can be disentangled from possibly systemic variation in wind speed strength and frictional coupling that acts on the ice.
The nice graphic below from @zlabe shows the multi-year seasonal variation of Bering Sea ice, putting this month well into unprecedented anomaly territory. Very warm air foreseen seven days out.
Technical note: Little Diomede in the Bering Strait is at latitude 65.75ºN, Longyearben in Svalbard is diametrically opposite at 78.22ºN so the difference is 24.25 + 11.78º = 36.03 so at 111.67 km per degree latitude on the ellipsoidal earth, the width of the Arctic here is 4023 km. In the archived Ascat view, that measures 440 pixels so each pixel is about 9.1 km on a side. Polar stereographic projection is not quite equal area..