This definitely also a good explanation. It comes from people in the lab looking at the same plasma phenomena but then on a smaller scale.solrey wrote:It's known that an encompassing magnetic field will moderate and balance plasma instabilities resulting in a stable system that can last indefinitely. Focus Fusion uses this concept to control the spin axis of a DPF plasmoid and to keep ion energies much higher than electron energies. The hexagon on Saturn could be a persistent diocotron instability moderated by Saturns strong magnetic field.
Tim
The experiment consists of a stationary cylindrical container in which a circular plate is
rotated by a motor.
So the fluid is trapped in the cylinder and centrifugal force causes the fluid to pile up along the edges forming a depression in the middle resulting in a concave three dimensional structure. I think the polygonal shapes are the result of constructive interference waves generated by the vibrating disc. The side views show a pronounced cup shape like water going down a drain so the structure is three dimensional and not just a pattern on the surface.When the plate is set into rotation the centrifugal force presses the fluid outward, deforming the free surface.
Aside from water, the experiments have been carried out with ethylene glycol with a viscosity of around
15 times larger than water...
We do not see polygons with N > 3 in ethylene glycol. For most polygons with N > 2, the center is dry.
A couple of things about the Saturn hexagon stand out compared to this experiment. For one Saturn's atmosphere is an open system. Another is the fact that the atmosphere within the hexagon is not deeply concaved, yet the structure/shape of the outer walls extends 60 miles deep into the atmosphere and doesn't appear to have the associated vortices at the corners either.In our experiment a shear layer indeed exists due to the no-slip condition on the stationary cylinder wall and could indeed lead to instability of the classical Kelvin-Helmholtz/Rayleigh type. In some cases we actually observe vortices close to the corners of the polygons. This is shown very clearly in Fig. 2(right), where vortices are seen outside each of the four corners. We therefore believe that vortex formation and interaction is very important for the development and stability of the final state.
Earth's plasmasphere at 30.4 nm. This image from the Extreme Ultraviolet Imager was taken at 07:34 UTC on 24 May 2000, at a range of 6.0 Earth radii from the center of Earth and a magnetic latitude of 73 N. The Sun is to the lower right, and Earth's shadow extends through the plasmasphere toward the upper left. The bright ring near the center is an aurora, and includes emissions at wavelengths other than 30.4 nm. (From Sandel, B. R., et al., Space Sci. Rev., 109, 25, 2003.)
bloody hell. as those old people who speak the Queens English are known to say. seen those images before but now seeing them in a new light. cheers solrey.solrey wrote:It's known that an encompassing magnetic field will moderate and balance plasma instabilities resulting in a stable system that can last indefinitely. Focus Fusion uses this concept to control the spin axis of a DPF plasmoid and to keep ion energies much higher than electron energies. The hexagon on Saturn could be a persistent diocotron instability moderated by Saturns strong magnetic field.
Progression of a diocotron instability
I think an external magnetic field could maintain a hexagonal structure similar to the middle frame in the above image. Since we see hexagonal structures in a variety of environments including craters it seems that the physics of fluids is inadequate to explain the cause, especially where craters are concerned. Diocotron instabilities however can easily produce the same hexagonal pattern in a broad range of situations.
cheers,
Tim
Since we already know that Saturn has a very strong electromagnetic environment it just seems logical to consider that environment when describing the polar hexagon. As I see it, EM forces must be involved somehow.The evolution of a strongly magnetized electron system is identical to that of an ideal two-dimensional (2-D) fluid; an electron column is equivalent to a fluid vortex. We have studied the stability of 2-D vortex patterns with electron columns confined in a Malmberg–Penning trap. The following cases are presented: the stability of N vortices arranged in a ring; the stability of N vortices arranged in a ring with a central vortex; the stability of more complicated vortex patterns.
No. More likely we do experience in this case a clear evidence of changed physical parameters (thermal conductivity) of soil after being hit by a discharge.redeye wrote:Tethys and Dione were both found to exhibit "plumes" similar to Enceladus. Could this strange temperature feature on Mimas be evidence of a similar process?
Cheers!
I'm wondering if similar line of thought applies here? They mention "daytime" temperatures. Whereas the THEMIS stuff mentions "nighttime" temperatures. But is the principle the same? Some difference between solid and loosely aggregated materials in how they heat up / cool down?The heat-seeking eye of THEMIS can spot the coarser and rockier portions of a landslide's debris by their residual warmth, shown in redder tints in the image. Late at night, rocky debris on Mars is still radiating heat absorbed during daytime, just as asphalt pavement does on Earth. At the same time of night, however, patches of ground mantled in dust (shown in bluer tints) have long since cooled off.
So the 'speed of rotation' in our solar system seems to be a constant. Might this be due to the frequency of the voltage in our little solar circuit, ya think? o.OThe faster the ring rotated, the less circular the green jet stream became. Small eddies formed along its edges, which slowly became larger and stronger and forced the fluid within the ring into the shape of a polygon. By altering the rate at which the ring spun, the scientists could generate various shapes. “We could create ovals, triangles, squares, almost anything you like,” says Read. The bigger the difference in the rotation between the planet and the jet steam—that is the cylinder and the ring—the fewer sides the polygon had, the team reports in this month's issue of Icarus. Barbosa Aguiar and Read suggest that Saturn’s north polar jet stream spins at a rate relative to the rest of the atmosphere that favors a six-sided figure, hence the hexagon.
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