Saturn's hexagon and Earth's jet streams

[eekee]

A long time ago, before I first saw or heard of the hexagon around Saturn's north pole and long before I had access to the Internet, I read about Earth's jet streams in a book. Part of the northern jet stream was depicted on a map, showing a sine-wave like shape, and the text said it was that shape too. This bothered me because the map was an ordinary one with north at the top. I realised the jet stream wouldn't be anything like a sine wave on the actual globe of the Earth. (I had neither software nor mathematical skills to plot the shape, but I'm very good at visualising things.) I realised the northern arcs of the sine shape would be flattened and the southern arcs sharpened until it looked something like a regular polygon, perhaps an octagon or a hexagon. Without mathematical tools and exact data on the jet streams I couldn't be quite sure; I thought the sides of the polygon might bow in or out, but I was fairly sure of the basic shape.

Many years later I saw APOD featuring Saturn's hexagon, (not today's picture,) and to my surprise it was just like what I figured Earth's jet streams must be like! It's even more regular than I dared to imagine, with barely any curve in the sides at all. It took a while for my past musings to fully come to mind, but now I see it again I'm almost sure Earth and Saturn have something in common here, despite the tremendous difference in size. I wonder if it's a resonance arising from Coriolis forces?

That's about all I can post, my brain hasn't been good for much of anything since a severe illness when I was 12 years old, but I wanted to share this. Drawing conclusions based on things I can visualise is about all I'm good for, and typing them up is a bit hard.

Edit: When I say "Saturn's hexagon," I mean the outer border; the thick band around the dark region. It seems to have a constant thickness. (See https://apod.nasa.gov/apod/ap170403.html.) That's the part I'm comparing to Earth's jet streams.

-- Ethan Grammatikidis
Feel free to reproduce this post.

[rstevenson]

There's a PowerPoint presentation at http://www.powershow.com/view1/1daefb-Z ... esentation which shows the Earth's jet stream, idealized, from a polar view and explains how it occurs. It seems to be a lot more dynamic than what we see on Saturn, as it flexes in a rhythmic pattern. Here's a screen grab of one slide...

Rob

[eekee]

Ah, I see it can curve far more than I thought. Oh well. Thanks for finding the slide.

I still wonder if there's some resonance prompting it to form in the first place, but I don't think I can really explore that idea.

[rstevenson]

I'm sure there is resonance within the atmosphere of Saturn, and Jupiter too probably, but modelling it is a problem. Extrapolating from Earth's atmoshere has limited utility though, as our atmoshere is so thin by comparison with that of the giant planets, and is therefore so strongly affected by the temperature of the land, ocean or ice cap beneath it. Understanding the atmospheres of the giants will keep generations of atmospheric scientists busy.

Rob

[Chris Peterson]

Understanding the atmospheres of the giants will keep generations of atmospheric scientists busy.

Your point about the complexity of such atmospheres in comparison with Earth's is well taken. All the same, at the rate our ability to run complex simulations is progressing, I wouldn't be surprised if we largely understand the dynamics of gas giant atmospheres within a decade or two.