View Full Version : Question re: Jupiter's Great Red Spot

2006-Mar-28, 09:21 PM
If Jupiter's Great Red Spot is some kind of inevitable process for a gas giant of Jupiter's size and location, then shouldn't we expect to see a pair of these storms, one in the northern and one in the southern hemisphere?

2006-Mar-28, 09:58 PM
It's not necessarily inevitable; it's about half as big now as it was a hundred years ago and there apparently was a long period during the 18th century where it either faded or completely disappeared.

2006-Mar-28, 11:30 PM
Actually there are TWO red spots on Jupiter right now, The one we all know and love. . . . And Red Spot Junior in the Band further to South.

Junior is still large enough to encompase earth itself, where as the big daddy has about 4.5 earth diamaters.

2006-Mar-29, 01:55 PM
So why no red spots in the northern hemisphere? The only difference between north and south would be due to Jupiter's inclination (basically seasonal differences) but given that the GRS has survived for several full Jupiter years, I don't see how a seasonal difference could explain it.

Do you understand the point of my question though? What is different about Jupiter's southern hemisphere? Why the asymmetry?

2006-Mar-29, 03:04 PM
That seems to me kind of liking asking why didn't a hurricane hit Rio de Janeiro at the same time Katrina hit New Orleans. Atmospheres are chaotic processes - you shouldn't expect tidy symmetry.

2006-Mar-29, 03:59 PM
That seems to me kind of liking asking why didn't a hurricane hit Rio de Janeiro

But Earth is asymmetrical because of its landmasses. So you're right, it doesn't make any sense to ask why a hurricane didn't hit Rio. But imagine if Earth was entirely covered by oceans, wouldn't you expect the same number of hurricanes in the northern and southern hemisphere if you looked at a long enough time-period?

at the same time Katrina hit New Orleans.

Not at the same time! That would be unreasonable for me to ask. But if the Earth was perfectly symmetrical, and if you got hurricanes in the northern hemisphere in August, then wouldn't you expect to see hurricanes in the southern hemisphere in February?

I realize that weather is chaotic - but even chaos bows to statistics. It's raining outside my house right now. Wouldn't you agree that the individual paths of raindrops are chaotic? Of course they are, but nonetheless, I expect that if I pick one square inch of my yard at random, and count the number of raindrops that hit it, that number I get will be representative of the number of raindrops that hit any given square inch.

If I find that on average, 100k raindrops hit each of the patches of my yard that I sampled, then I have used statistics to learn something about a chaotic system.

If I then find a patch of my yard that received 0 raindrops, doesn't it make sense to ask why? Maybe there is a tree overhead, I don't know. I just know that there is some specific cause for this statistical discrepancy. It's insufficient to say, "well rain is chaotic." There is some specific reason. The reason hurricanes don't hit Rio is that the South Atlantic isn't quite big enough (I guess).

But Jupiter is symmetrical as far as I can tell. Jupiter's northern hemisphere is exactly the same as its souther hemisphere. Whatever physical laws affect the north also affect the south. It's just a bunch of gas. If heat from the sun creates a giant storm in one hemisphere during one time of the year, then why doesn't it create a giant storm in the other hemisphere during another time of the year?

There is some reason for this. If Jupiter's orbit was highly elliptical, and if the southern hemisphere was facing the sun at Jupiter's closest approach to the sun, then that would easily explain this, wouldn't it

2006-Mar-29, 04:57 PM
We don't know if the GRS is an inevitable event. We've only observed the planet for an infinitesimal fraction of its history, and there is much about its interior and atmosphere that we don't understand. For what it's worth, I've read that the zonal wind shear at the GRS's location is the strongest on the planet, which is another way of saying that the wind patterns in each hemisphere are *not* symmetrical.

I'm attaching a graphic from an old Scientific American special issue, that shows the winds as measured by the Voyagers (the winds have apparently not changed much since then). As you can see, the zonal wind patterns are almost, but not quite symmetrical; for instance, the E-W winds at the GRS latitude are of nearly equal strength, while the equivalent latitude in the NH is has a much stronger eastward jet with only a weak westward one.


Ingersoll, Andrew P. "Jupiter and Saturn". In Bruce Murray, "The Planets",
San Francisco: W.H. Freeman and Company, 1983, pp. 60-70.

John Kierein
2006-Apr-02, 04:10 PM
Maybe the red spot is due to a comet hitting Jupiter like Shoemaker-Levy and the one that rained red organic stuff in India.http://observer.guardian.co.uk/world/story/0,,1723913,00.html

2006-Apr-02, 04:30 PM
But Jupiter is symmetrical as far as I can tell.That's certainly a big assumption. I guess what you're driving at is that there may be structure farther down, that we can't see.

A lot of people have speculated on that--one of the theories was that the giant red spot was a Taylor column (http://www.deas.harvard.edu/brenner/taylor/physic_today/taylor.htm)