Ticker for July 17, 2008

                
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July 17, 2008      July 17, 2008      July 17, 2008      July 17, 2008



They Say Hats Are In Again

We're taking a break from a long list of "write in" questions today.

We'd like to share a picture of a great pileus cloud taken by OCS's
Nathan Bain:



This photo was taken around sunset, viewpoint is to the east. The
pileus cloud (or "pileus cap") is the lens-shaped "mini-dome" just
above the main updraft of the developing thundershower.

Pilei (yeah, that's the proper plural, and yeah, we've always wanted
to write it) are formed while the updraft pushes a slab of air up
above it as it rises. This process, in itself, isn't unusual; it
happens all the time when something moves through a fluid. When you
rocket through the water at a swimming pool, your head is pushing a
little slab of water along in front of it. The updraft is doing the
same thing.

So, think of this slab as the bug on the windshield of an updraft.
Except by "bug" we mean more of a blanket-like shape, and by
"windshield" we mean something in the very front of the updraft.
And think of the travel as upward, and not along a road.

In fact, scratch that metaphor altogether. We were lost in the Land
of Unintended Similes. By the way, if *you* are ever lost in the
Land of Unintended Similes, don't even bother asking for directions.
Nobody here gives a straightforward answer.

Anyway, back to pilei (what a fun word!). Here's the kicker: actual
cloud formation is not a given. It depends on a few factors, like
the speed of the updraft, the thickness of the slab, and, most of all,
its moisture content.

The thing that makes Nathan's pileus cap kinda unique is that it is
a very prominent, meaty, substantial cap over a fairly innocuous
thundershower. Most pilei (we can't help it; it's fun) are
relatively wimpy and wispy. Nathan's cap is a testament to the
high humidity in the layers just above the developing storm.