Clouds are great fun to watch.
Sitting under a tree, high on a hill, you gaze up to the sky for a few moments and you daydream. The rest of your life falls away as you watch the clouds slowly, imperceptibly roll across the heavens . Then you sigh again, take a sip of lemonade, and pick up your book to read for a while.
When you look up again, barely ten minutes later, the sky is totally different. Some clouds are gone and new ones have taken their place. A whole new cloud deck is rolling in. How did the sky manage that sleight-of-hand? You look again and watch, and yes, just as before, the clouds are barely moving. Almost motionless. How did they do that so fast?
But when you play the sky’s endless movie at fast-forward, a whole different story emerges!
The cumulus clouds which had seemed to be simply floating by like cotton balls are seen to be forming and dissolving at the same time, continually flowing through forms, coming and going in random disorder, appearing and disappearing throughout their short lives.
And you can see how the clouds pull themselves up by their own bootstraps: once an area of cloud starts condensing, the condensing moisture releases heat, which warms the air. The air rises. That pulls in more moist air to replace it. That air condenses, warms, rises, pulls in more moisture…the cloud feeds on its own growth in a positive feedback loop, like a microphone held too close to a speaker.
Clouds is Water
There is a classification system for clouds, but it’s only moderately helpful in deciphering cloud mysteries. There are too many types of clouds. There are clouds that fit in more than one category, or fit in between categories. Some defy categorization.
But what all clouds have in common is water. Think of what your cool lemonade glass did once the waiter laid it on your table. The outside of the glass condenses water just like cold air condenses water out of warm, moist air. Then it’s just a matter of how many infinite ways warm moist air can be introduced to colder air, and in what shapes and fashions and situations.
To Make a Cloud
Of all the planets, only Earth (that we know of) has abundant water in all three of its possible phases: solid ice, liquid water, and gas vapor. Mars is too cold, Venus is too hot, but on our world, temperatures are just right. And the sun’s heat makes sure water is changing from one phase to another all the time.
Vapor in the air condenses into droplets that float and we call it a cloud. Droplets bump together and collect to form bigger droplets that sink to earth. We call it anything from a gentle filmy mist to a thundering downpour. Droplets freeze and fall as snow, sleet or hail.
Or vapor directly freezes to frost or rime ice on everything it touches. Or it falls as liquid rain and freezes instantly when it lands, pulling down mighty oaks by sheer weight.
Finally, water which has collected in lakes, oceans, soil, and living things (like us), evaporates back into gas, and we have sweltering humidity, dew and fog, and clouds. Moisture has come full circle, and is reunited with the deep blue sky.
Some of the most dramatic and fascinating displays of weather in the sky are the result of water changing from one phase to another. Nature seems to delight in creating different ways for things to mix and interact. Even a single type of event, like a snowflake or a cloud, is never repeated in exactly the same way twice.
Boundaries, borders and edges
The most interesting things in the sky occur at the boundaries between other things. The point of contact between two continent-sized air masses is where weather occurs. The boundary between earth and sky is the scene for fog, frost and dew, when we get to literally live in the clouds for a while. The boundaries between cold air, warm air, wet air, dry air, dirty, clean, moving or still, high or low, neutral or electrically charged air — all these boundaries produce their own special spectacles.
The border between day and night produces spectacular displays only possible with the low, red light from the sun on the horizon. The low light of dawn and twilight also punches up the contrast of clouds, outlines and defines their shapes more sharply than during the day. Sometimes two, three, four or even more cloud decks are all doing different things at the same time.
But the best way to learn about clouds is to live with them. Watch them. Go back up on the hill and spend some time watching. It’s really great fun!