Bows and flows of angel hairWhen it comes to looking at clouds, I suspect that most people will follow Joni Mitchell in imagining all manner of fanciful resemblances, but clouds are more interesting as an indicator of atmospheric processes. In this regard, the first point to bear in mind is that with occasional local exceptions, clouds form in unstable atmospheric conditions.
And ice cream castles in the air
And feather canyons everywhere
I’ve looked at clouds that way.
I’ve looked at clouds from both sides now
From up and down, and still somehow
It’s cloud illusions I recall
I really don’t know clouds at all.
Joni Mitchell, Both Sides Now.
This may seem like a statement of the screamingly obvious, except that in meteorology, stability has a very specific meaning. It describes the behaviour of discrete air ‘parcels’ as they rise or sink through the surrounding air. A stable parcel will tend to return to its original position once the force that moved it in the first place has been removed, while an unstable parcel will remain where it has been pushed.
I had intended to provide a more detailed explanation of these processes, but when I consulted my copy of Atmosphere, Weather and Climate by Roger Barry and Richard Chorley, a standard university textbook on the subject, I quickly realized that a simple explanation was beyond my powers. I understand the science—I ought to, given that I edited the book—but it is impossible to provide any kind of explanation that doesn’t invoke adiabatic lapse rates, partial vapour pressures, supersaturation and latent heat of condensation, the mere mention of which I suspect will cause most readers’ eyes to glaze over.
Given that the reason for this post is to showcase a series of photographs of clouds as aesthetic compositions, no further explanation will therefore be provided, but I will include the following astounding snippet of information: a mere 4 percent, on average, of all the water vapour in the atmosphere is to be found in clouds.