It might be useful to start by defining just exactly what clouds are! Oh, we all look up and see those fluffy white shapes, or those big, dark, heavy-looking masses, blanking out the sun, hiding the stars and moon. But how rarely do we think what they actually are? A basic explanation is that they are massed particles of water or ice crystals, hanging there in the lower atmosphere, or the sky, really. Depending on where you are on the Earth, what you are doing, and what your part of the world needs, you may perceive clouds as a threat or a hopeful blessing. After several years of drought in Australia, for example, the inhabitants of that continent would bless the appearance of huge clouds swelling and growing in the empty skies. But how do they form?
Clouds form when water on the Earth’s surface evaporates; it becomes vapor. Think of seas, lakes, rivers, the ground itself, the breath you breathe out, and there you have the start of your clouds. This water vapor rises up, cooling and condensing. It actually condenses around tiny, invisible particles of salt, dust and sand, so moisture droplets form. If the atmosphere in which they form is below freezing point (of water) the tiny droplets turn into ice. Very high clouds, known as ‘cirrus’ are white and stringy. As clouds get lower in the atmosphere, they take on different shapes and colours, from grey to black, such as ‘nimbostratus,’ your rain and snow clouds, or even become those lovely white flluffy ‘cumulus.’ Beware the dark, thick ‘cumulonimbus,’ for they can deliver a thunderous punch – a big storm. They come right down to touch the ground, and tower upwards to around 75,000 feet. Whatever type of cloud you encounter, all are formed in exactly the same manner, and so it goes, in an eternal cycle.
So clouds are formed by water evaporating, a little bit of dust or sand, and their power comes from height, temperature, winds and so forth. They help to keep the Earth cool in the daytime, by reflecting the rays of the sun back into the atmosphere. They do a useful job at night, too, by helping to keep in the heat that rises from the Earth when the sun has gone. This aids the maintenance of a warmer temperature. Consider how it can be freezing cold at nights in the desert, simply because there are no clouds to keep in the day’s heat, and this will illustrate exactly what an important little item those clouds are. And of course, after they drop their cargo of water of ice, sleet, snow or gentle warm rain, water to the Earth, the whole process begins again.
