Clouds

by Read Listen Learn

Clouds

“I wandered lonely as a cloud that floats on high”

William Wordsworth, eighteenth and nineteenth century poet

Huge bits of half-frozen steam floating in the sky. That’s probably the best non-technical description of clouds. At a more minute level, they are made up of tiny particles of frozen water, called aerosols which, together in countless billions, make a cloud. The water gets in the sky through evaporation, the process in which liquid becomes gas, usually because of heat. This could be water rising from the seas and oceans or lakes; or it could be evaporation from places with a lot of plant life, typically a tropical forest. The source of heat is almost always the sun but some evaporation of water is from thermal and volcanic sources.

The size and shape of the clouds, once they are up there, depend on a number of factors like air temperature, wind speed and direction, humidity and what the clouds are floating over at any given moment, e.g. over water, over mountains, over tropical forest, over a big city, etc. Both the shape and the size are very variable but some clouds can contain millions of tons of water. A fact that is hard to believe until you have stood in a heavy tropical downpour.

As we all know, clouds come in an infinite variety but they are classed into finite categories. The different kinds are too many to list here but they are usually made up of two classifications. So, for example, we can start with four basic types: cirrus (whisps); stratus (a layer); nimbus (ready to rain); cumulus (shaped like a hill). If we combine two of these names like ‘stratus’ and ‘nimbus’ to give ‘nimbostratus’ this would be the right name for a ‘layer of rainy cloud’.

And rain is what clouds are really all about. They are a key stage in the water cycle that sends water round and round to keep the planet working. And they are the only stage when the water is, for a time, not water but a kind of steam or lots of little bits of ice, depending on how you like to see it.

Most clouds form in the Earth’s lower atmosphere or ‘troposphere’. In this way, the rain they drop reaches the ground before evaporating into the air once more. Sometimes clouds can be found in the Earth’s upper atmosphere but much more common is cloud that touches the ground which, really, is fog. Fog, if seen as a cloud, is ‘stratus’.

Cloud has two very dramatic friends. These are thunder and lightning. When some clouds get very full of rain, they become electrically charged and quite heavy. When they hit each other, the crash causes both sound and electricity to be let out. The sound is the thunder and the electricity is the lightning. It’s very exciting to watch an electric storm but it can be quite dangerous. One electric storm releases more electricity than a whole city can use in a month. Unfortunately, it is not possible to ‘catch’ and use these explosions of electricity for heating, lighting and power.

There are two basic kinds of lightning: ‘fork’ and ‘sheet’; fork lightning, which shoots towards the ground in an angry streak, is the dangerous one. Recently, in Latin America, three members of the same football team were killed by one streak of lightning. This happened in a mountain city and close to the Equator, which seems to be the recipe for lightning. Tropical warmth meeting cold mountain air produces a lot of electric storms. Colombia, where the three footballers were killed, is the second most lightning-hit country in the world; number one is the Congo in Africa.

Lightning may be what triggered life on our planet. Scientists have suggested that running a strong electric charge through the warm chemicals and minerals on the Earth’s surface could be a way to start biological forms.

Clouds are a part of everyday life for most of us and, for some of us, they are very important. They make flying aeroplanes more difficult and dangerous and they can certainly spoil a day at the beach but, in times past, they were a way for people to find their home island, especially in tropical waters. Every island has a cloud rising over it like a tall column. It can be seen from a distance of one hundred kilometres, sometimes more. An experienced sailor can recognise which island it signals and by sailing from island to island, small boats in, for example, Polynesia can travel thousands of kilometres, often out of sight of land.

In human psychology, clouds represent ‘confusion’ and ‘depression’, as in the expression ‘don’t cloud the issue’. The singer, Amy Winehouse, described her terrible depression as feeling like she had a ‘cloud over her head’. But clouds now have a worse association than depression. Since the atomic bombing of Hiroshima and Nagasaki in August of 1945, the immense mushroom cloud that shot into the air after the bombs exploded has become a symbol of human-made disaster and even the end of the world.

Life on Earth may have started in the clouds and the world may end with a cloud as well.