Stoat

I'm no Met man, but know something about volcanoes. The most important effect is the evaporation of the clouds all around the plume. I'm not sue this can be explained solely by the fact that the rising plume is quite, quite hot, cooling as it rises.

The next most important thing is that the plume has stopped rising at the top and instead is spreading out. I assume this is for the same reasons as when a cumulus cloud forms an anvil top upon rising to the tropopause.

The most beautiful is the reformation of water clouds on the top of the plume. I oine this is because the plume top there is sufficiently cold that condensation is able to recover there.

All told, a most wonderous picture of a phenomenon I am most happy to be viewing from my armchair, not close up and personal.

Posted by: David B. Benson | November 14, 2009 6:32 PM

I saw an explanation of this when it was on Astronomy Picture of the Day. Rising air cools, and when it cools below it's dewpoint it condenses, that's what's happening with the cloud at the top of the ash column. The clear area is because of the descending air that was displaced by the rising ash column. Sinking area heats up, and when a cloud heats up above it's dewpoint it evaporates.

Posted by: GoatRider | November 14, 2009 11:44 PM

I passed this on to the editor of the MetSoc of NZ newsletter back in June (I liked Bob's response: Gareth , your blood is worth bottling. That's an awesome shot, full of physics, and it will bring a twinkle to many a meteorologist's eye. I hope I have space.). This then appeared in the June issue (117)...

Following the publication of this photograph, the atmospheric and volcanic features it captured generated debate among meteorologists, geoscientists. and volcanologists who viewed it. Post-publication, scientists have proposed -- and disagreed about -- three possible explanations for the hole in the cloud deck above the volcano.

One explanation is that the hole in the clouds has nothing to do with the eruption at all. In places where islands are surrounded by oceans with cool surface temperatures, it is common for a sheet of clouds to form and drift with the low level winds. When the cloud layer encounters and island, the moist air closer to the surface is forced upward. Because the air above the marine layer is dry, the clouds evaporate, leaving a hole in the cloud deck. These openings, or wakes, in the clouds can extend far downwind of the island, sometimes wrapping into swirling vortices called von Karmen vortices.

The other two possibilities that scientists have offered appeared in the original caption [here]. One is that the shockwave from the eruption shoved up the overlying atmosphere and disturbed the cloud deck, either making a hole or widening an existing opening. The final possibility is that as the plume rises, air flows down around the sides like water flowing off the back of a surfacing dolphin. As air sinks, it tends to warm; clouds in the air evaporate.

Got a way with words has Bob. (McDavitt)

Posted by: Gareth | November 15, 2009 1:46 AM

Boingboing had it in July at this link and I had it as wallpaper for a while - see comments below the pic for some of the "expert" disagreement:

**Editor’s note: Following the publication of this photograph, the atmospheric and volcanic features it captured generated debate among meteorologists, geoscientists, and volcanologists who viewed it. Post-publication, scientists have proposed—and disagreed about—three possible explanations for the hole in the cloud deck above the volcano.

One explanation is that the hole in the clouds has nothing to do with the eruption at all. In places where islands are surrounded by oceans with cool surface temperatures, it is common for a sheet of clouds to form and drift with the low-level winds. When the cloud layer encounters an island, the moist air closer to the surface is forced upward. Because the air above the marine layer is dry, the clouds evaporate, leaving a hole in the cloud deck. These openings, or wakes, in the clouds can extend far downwind of the island, sometimes wrapping into swirling eddies called von Karman vortices.

The other two possibilities that scientists have offered appeared in the original caption. One is that the shockwave from the eruption shoved up the overlying atmosphere and disturbed the cloud deck, either making a hole or widening an existing opening. The final possibility is that as the plume rises, air flows down around the sides like water flowing off the back of a surfacing dolphin. As air sinks, it tends to warm; clouds in the air evaporate.

From:
http://earthobservatory.nasa.gov/IOTD/view.php?id=38985

Posted by: Luke Warmer | November 15, 2009 12:44 PM

Aside for William, if you're using Firefox (and the addon Greasemonkey) you can clean up sites like Wired by going to the root then invoking the addon Platypus. As you move the cursor, chunks of the web page are hilighted. You'll see all that scripted nonsense that clutters their pages everywhere.

Get the annoying chunk hilighted, then
-- without moving the cursor
-- right-click
-- use the keyboard (s twice gets you to 'Smart Remove' to block that hilighted chunk anywhere on that website).
Once you save and exit, you've got a little script; when you go to any page on or above that root, the nonsense may blink on briefly but then disappears.

Combine that with AdBlock to block images that are slow nuisances to load, and you get something relatively readable.

It's tedious. But I look forward to being able to do it with my eyeglasses some day.

We have one state in the US that bans highway billboards -- Vermont. Using a well crafted Firefox browser to block crap is like driving in Vermont -- you don't know what you could be missing, until you see the world with all the crap removed.

[Hmm. I think I'll just avoid wired instead, unless I need to -W]

Posted by: Hank Roberts | November 15, 2009 2:08 PM

That volcano is from space? Wow. Not only do aliens abduct people, they discard their unwanted volcano on OUR PLANET!!! THOSE BASTARDS!!!

Posted by: llewelly | November 15, 2009 6:43 PM