The Dragon Storm-Giant Thunderstorm on Saturn (With Photo)

I emailed Mr. Del Genio about the Dragon Storm, and here's what he had to say. My comments are in quotes. The false-color image he attached with the email is the picture you see at the URL I provided. I also notified Mr. Del Genio about this thread. As you may be aware of from my earlier posts, he is one of the scientists involved with Cassini.


Dear Saul,

Attached is a false-color picture of the dragon storm and a copy of our just-published paper on Cassini Saturn results in this week's Science, in case you haven't seen them.

"Apparently, from what I've read at the link above, the Dragon Storm is
a long-lived feature."

Yes, as far as we can tell, at depth it may be long-lived. We don't see it all the time in our images, but it flares up now and then in about the same location, so whatever is causing it deep down lasts for a long time. Unlike storms on Earth, which can't maintain themselves for very long times against dissipation by radiation and surface friction, storms on the jovian planets, once formed, can hang around for a while because there's no solid surface and the cold atmosphere radiates very slowly.

"Perhaps Cassini could be focused on trying to
take pics of its vertical structure from the limb?"

Nice idea, but our observations for the entire nominal mission through 2008 had to be planned and sequences designed and sent to JPL a year or two ago, because the mission is too complex and there just aren't enough people working on it at JPL to put in changes on the fly. That grates on me, but those are the fiscal and manpower realities. However, I myself designed at least a few days of observing sequences focused on the 30-45 deg. S latitude band for later this year, so we'll hope it's there during that time. And next year when we're on the night side we'll hopefully get a few cracks at what you suggest.

"This storm looks to be one massive weather system. Judging from its
size, I would surmise that it's almost half the size of the earth, if
not bigger."

That's about right, I'd say. However, if you look at the attached false-color image, it's really only the bright white-yellow oval in the middle that we'd guess is the actual thunderstorm. The rest of the wavy filamentary stuff is probably just the high-level cirrus or cirrostratus blowoff, or anvil cloud, that forms where the convective updraft detrains, or spits out, its condensed water and water vapor into the surrounding environment. Then, givent he strong winds on Saturn, those get stretched out for quite a distance. Nonetheless, I think that the convective core for this storm is easily 1000 km.

"I've often wondered about such storms putting out
super-tornadoes that would be far more devastating than anything we
would encounter on earth."

On Earth, that happens when a storm erupts in a region of strong vertical wind shear, and the horizontal vortex tubes get tilted into the vertical by the updrafts. On Saturn, we don;t yet know whether there's enough wind shear below the visible cloud deck for that to happen, although we have some hints that there is significant shear down there. If you look at Figure 5 of our attached Science paper, you can see the dragon storm apparently giving "birth" to two dark spots at the end of the sequence. We don't know if those are vortices, but they may well be. There are lots of rotating things like that on the jovian planets, much bigger than terrestrial tornadoes, but I can;t rule out similar processes happening. If not, then their generation may have more in common with nor'easters, where a synoptic-scale vortex tube stretches vertically and tightens its radius of curvature (though the instability process may not be the same).

"I would also imagine that hailstones must be
incredibly massive, given how big this storm seems to be. How big
could hailstones get in such a storm?"

I'm not sure whether we get hail in these storms. To get that you need supercooled liquid water being lofted up repeatedly well above the freezing level into the ice-forming region of the storm. We don't know where the bases of the storms are on Saturn, but it's possible they form above the freezing level, in which case they'd be mostly ice and make a lot of snow that turns to rain deeper down, but not much hail. But if the water abundance is large enough on Saturn, then they could form at warmer temperatures and hail would be possible. But I wouldn't necessarily guess the hail would be bigger than on Earth. On Earth you get the biggest hail when the most instability is built up and suddenly you get enough moisture at low levels to kick off the storm, making strong updrafts. That's common in the midwest, which is a farily unique place on Earth meteorologically due to the mountains upstream and the Gulf of Mexico to the south as a moisture source. In contrast, convection is much deeper and more ubiquitous in the tropical west Pacific, but it's weak and makes little hail because instability never has a chance to build up enough to make strong updrafts - there's usually enough humidity near the ocean surface to make a storm from the least bit of instability. Saturn may be more like that than the midwest.

Tony Del Genio