Red Velvet with Icing

“So Jupiter’s white stripes are huge updrafts of ammonia snow and its dark stripes are weird chemicals we only see when downdrafted ammonia snow evaporates. Fine, but how does that account for my buddy the Great Red Spot? Have another lemon scone.”

“Thanks, Al, don’t mind if I do. Well, those ideas only sort-of account for Spot. The bad news is that they may not have to for much longer.”

“Huh? Why not?”

“Because it seems to be going away.”

“Hey, Sy, don’t mess with me. You know it’s been there for 400 years, why should it go away now?”

“I don’t know anything of the kind. Sure, the early telescope users saw a spot 350 years ago but there’s reason to think that it wasn’t in the same location as your buddy. Then there was a century-long gap when no-one recorded seeing anything special on Jupiter. Without good evidence either way, I think it’s entirely possible we’ve had two different spots. Anyway, the new one has been shrinking for the past 150 years.”

“The big hole must be filling in, then.”

“What hole?”

Juno GRS image, NASA/JPL-Caltech/SwRI/MSSS/Gerald Eichstädt

“The Spot. If the dark-colored stripes are what we see when the bright ammonia ice evaporates, then the Spot’s gotta be a hole.”

“A reasonable conclusion from what we’ve said so far, but the Juno orbiter has given us more information. The Spot actually reaches 500 miles further up than the surrounding cloud tops.”

“But higher-up means colder, right? How come we don’t see the white snow?”

“That higher-is-colder rule does apply within Jupiter’s weather layer, mostly, but the Spot’s different. There seems to be a LOT of heat pouring straight up out of it, enough to warm the overlying atmosphere by several hundred degrees compared to the planetary average. That suppresses the ammonia ice, lifts whatever makes the red color and may even promote chemical reactions to make more.”

“But Sy, even I know heat spreads out. You’ve just described something that acts like a searchlight. How could it work like that?”

“Here’s one hypothesis. You’ve got your sound system here rigged up so the back of the shop is quiet, right? How’d you do that?”

“Oh, I bought a couple of directional speakers. They’re deeper than the regular kind and they’ve got this parabolic shape. I aimed them up here to the front where the traffic is. Work pretty good, don’t they?”

“Yes, indeed, and I’m grateful for that. See, they focus sound energy just like you can focus light. Now, to us the Spot just looks like an oval. But it’s probably the big end of a deep cone, spinning like mad and turning turbulent wind energy into white noise that’s focused out like one of your speakers. Wouldn’t that do the trick?”

“Like a huge trombone. Yeah, I suppose, but what keeps the cone cone-shaped?”

“The same thing that keeps it spinning — it’s trapped between two currents that are zipping along in opposite directions. The Spot’s northern boundary is the fastest westbound windstream on the planet. Its southern boundary is an eastbound windstream. The Spot’s trapped between two bands screaming past each other at the speed of sound.”

“Wow. Sounds violent.”

“Incredibly violent, much more than Earth hurricanes. At a hurricane’s eye-wall the wind speeds generally peak below 200 miles per hour. The Great Red Spot’s outermost winds that we can see are 50 miles per hour faster but those triangular regions just east and west must be far worse. When I think about adding in the updrafts and downdrafts I just shudder.”

“Does that have anything to do with the shrinking you told me about?”

“Almost certainly — we simply don’t have enough data to tell. But the new news is that your buddy’s uncorked a fresh shrinkage mode. Since the mid-1800s it’s been contracting along the east-west line, getting more circular. Now it seems to be flaking, too. Big, continent-size regions break away and mix into the dark belt above it. Meanwhile, the white equatorial zone is getting darker, sort of a yellow-green-orange mix.”

GRS image courtesy of Sharin Ahmad

“Yucky-colored. Does that mean the Spot’s draining into it?”

“Who knows? We certainly don’t. Only time will tell.”

~~ Rich Olcott

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