Heh.

In the unlikely event anyone took Shawn's rant seriously, Jupiter's
cloud systems are divided into zones based on the time it takes for
them to rotate around the planet. Roughly speaking, the equatorial
zone is called System I; the temperate zones are called System II;
and the polar zones are called System III. The GRS just happens to
be on the northern edge of System II in the southern hemisphere.

Systems I and II (the ones interesting to amateurs) have periods that
differ by 5 minutes. That may not seem like much, but it results in
shear speeds at the boundary of hundreds of kilometers per second.
Anyway, it means that you can't maintain a consistent system of
longitude over the entirety of Jupiter--hence the Systems.

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
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