Soren Harward on 17 Jul 2017 18:01:19 -0700

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Re: [PLUG] Waaaaay Off Topic: Thunderstorm Movement

On Mon, Jul 17, 2017 at 4:28 PM Casey Bralla <> wrote:
So here's a question I've often wondered about, and was hoping someone in this
learned group could help me understand.

When a thunderstorm moves across the landscape, is it like a wave moving on
the ocean, or a inner tuber floating on a river?  In other words, is it the
same moving air mass dumping rain as it moves, or is a storm an atmospheric
wave phenomenon that moves into new air all the time?

Disclaimer: I'm not a meteorologist, but I have done a fair amount of CFD modeling, in which I've talked to people who do weather modeling.

The two images you have are both correct.  The "wave moving on the ocean" component is called "propagation": new air comes into the storm, and old air moves out of the storm.  The "inner tube floating on a river" component is called "advection": the storm is an air mass, being blown along by the surrounding winds.  When you look at it from far away, it seems like a "storm" has discrete boundaries.  But in reality, the boundary between air that is "storm" and "not storm" is a lot fuzzier, especially when you start looking at the microscopic level.

Perhaps a more understandable image is that of a river: just like water flows from high elevation to low, air flows from high pressure to low.  If anything changes the momentum (mass, direction or speed) of the flow, it causes a vortex.  A storm is just like a vortex or eddy traveling in a river: there's some water being pushed into the vortex, and some being spun out of it, and the vortex itself is moving along with the main current.

Soren Harward

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