Mon, 5 Dec 2022

Cloudy Thoughts

— SjG @ 4:23 pm

In another life, I would have been a nephologist (or more general meteorologist). I have always found clouds, fogs, and mists fascinating.

Cirrus clouds

When I go walking, I tend to look at the sky and wonder exactly what’s going on up there. Are the boundaries of the clouds I’m seeing some threshold of a gradient of temperature, pressure, or moisture content? Why are the patterns the way they are?

One can often see distinct wave action in the atmosphere, but sometimes there will be high-frequency patterns that collide in unexpected ways. There may be different conditions at different altitudes, but in some cases the patterns seem to be at the same altitude.

At least three patterns; two at the same apparent height

There are also interesting effects when one layer of clouds (or a contrail) casts distinct shadows on another layer of clouds.

Contrail shadow

Some cloud patterns look a lot like convection in reverse.

Upside-down sunset convection

And then there are mysterious places where the conditions just change. For example, the contrail in the picture below. Does it end at some kind of invisible thermocline?

Encyclopedia Brown and the case of the Vanishing Contrail

There are a lot of resources for cloud classification and identification online, but I haven’t found as much about the whys of the structure. Some types of cloud structures make intuitive sense. Cumulus clouds sort of look like what you’d imagine a rising bubble of wetter air would. The ripple patterns you sometimes see in altocumulus clouds look like wave action. The elongated wispy patterns of cirrus clouds make some sense if you imagine the wind stretching out a mass of cloud. But why would there be the filaments? The guides I’ve found online just take it for granted. Similarly, the globular altocumulus structure is regarded as a matter of definition.

What’s going on in there?

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