Walk Softly - Clouds

by Geoffrey Carpentier

Well, even though the days are marginally longer now, the sky still seems dark and foreboding. In the summer, clouds seem to vary in shape, size and colour, but in winter they often seem to be just dark, grey and gloomy. Let’s explore these clouds a bit and see if we can understand them a little better.

Clouds are made up of water droplets or ice crystals which are so light they defy gravity. So, how did they form in the first place and how did they reach such lofty heights? The water and ice which makes up these clouds, moves upward as water vapour, the gaseous state of water, through evaporation. As these droplets rise in the atmosphere, the warm, moist air in them begins to cool. As the temperature and air pressure continues to drop, the water vapour it carries condenses into tiny liquid droplets or ice crystals, depending on the temperature of the surrounding air. These droplets coalesce, around microscopic particles in the air, such as dust or pollen, and when enough of these droplets cluster together, clouds are formed.

That’s nice and simple, but the origins which create the circumstances, where the clouds can form, are variable and are dependent on temperature, landforms and other naturally occurring phenomena. As the sun shines and warms the ground, the surrounding air also naturally gets warmer, and rises. As it does so, the temperature and pressure decrease, and ‘typical’ clouds are formed.

Clouds which arise from this simple process include cumulous, cumulonimbus and stratocumulus clouds. These are the fluffy clouds of summer. Another phenomenon which can create clouds has to do with the action of winds on mountain slopes or elevated ground. As the warmer air is pushed up rapidly, over the sloping ground, it rises and produces beautiful lenticular clouds. These often appear as ‘fuzzy’ horizontally elongated clouds, of indeterminate shape, often just above the sloping ground. Third and fourth forms of cloud generation arise when air is forced up as winds converge at the centre of a low-pressure system or two large air masses collide at the earth’s surface, again causing the air to rise rapidly above them.

Do all clouds produce rain?

At a warm front, warm air slides over a cold air mass and is pushed upward, forming various types of clouds. Similarly, at a cold front, the colder, denser air pushes the warm air upward with the same outcome. Only some types of clouds, such as nimbostratus and cumulonimbus, produce rain and thunder. Most clouds are defined based on shape, colour, where they form (e.g. mammatus clouds form under other clouds) and altitude. High clouds form 5-13 km above the earth and appear as wispy (cirrus), hazy (cirrostratus) or puffball-like (cirrocumulus) shapes. Middle altitude clouds can be found at 2-7 km and appear as fluffy (altocumulus) or gossamer-like (altostratus) clouds. Finally low altitude clouds form at 2 km and look dark and ominous (nimbostratus and stratus) or like a thick banket (stratocumulus). Note: these heights vary a bit, because one moves north to south, as their height is linked to the troposphere, but you get the idea.

Let’s close out this discussion with a look at the impact of these clouds on weather. Due to their density, colour, and height above the earth, some clouds cool the earth, and others have a warming effect. Cirrus clouds (those high wispy ones) let most light reach the earth but can trap rising heat, generating a net warming effect. Cumulus clouds (those big, blocky, massive clouds) can block sun from reaching the earth’s surface, leading to a cooling effect. Stratus clouds (dark gray, blanketing clouds) also block light from reaching the earth, even more so than the cumulus clouds, leading to a net cooling effect. It is expected, by the majority, for various reasons, more evaporation will occur as climate warms and therefore more clouds will form, enhancing even further the warming trend of the earth, as more heat is trapped beneath them.

This is just a brief overview of the complexity of clouds, how they form and how they affect weather and ultimately climate. Hope you liked it!

Geoff Carpentier is a published author, expedition guide and environmental consultant. Visit Geoff on-line on LinkedIn, Facebook and Instagram.