An important part of Earth’s weather, clouds constantly appear high in the skies in an infinite variety of forms and shapes. To be better understood, they’ve been given names and classified under specific types based on how high or low they are formed in the sky and their general shape. Ranging from the mundane, normal clouds we can see on nearly every day when looking up in the skies to the majestic anvil shaped “King of Clouds”, the Cumulonimbus, they have a very dedicated fan base, with many of these “cloud-lovers” spending considerable effort and time to take pictures of – or just simply appreciate special and interesting cloud shapes. Perhaps most importantly, they have been a hot study item for quite a long time, as it is believed they play a key role in climate modeling.
What exactly is a cloud?
In essence, a cloud is a composition of tiny water droplets or, depending on the height of the cloud and the temperature of that height, ice crystals that have settled on dust particles in the atmosphere. They are a part of the natural, endless cycle of water of our planet. In short, a simplified explanation of said cycle goes as follows: The various bodies of water spread throughout the Earth get heated by the sun’s rays, and thus, end up evaporating as vapors to the air. That vapor, raised up high by rising air currents, to where the atmosphere is much colder, eventually condenses into cloud form.
Through the process of precipitation, clouds turn back to liquid form and water is slowly released from them as rain, freezing rain or even snow. After it returns to the Earth’s surface, the process starts again, with the cycle continuing ad infinitum.
How are clouds formed?
There are many ways for clouds to form and grace our skies, most common of which are the following:
- Surface heating: When the Sun causes the ground to heat, which heats the air contacting it causing it to rise. This tends to produce cumulus clouds.
- Topography forcing: The shape and features of an area can cause clouds to be formed. For example, when air is forced to rise over tall mountains it cools as it rises. Layered clouds are often produced this way.
- Frontal: When masses of warm air rise up over masses of cold, dense air over large areas along fronts – boundaries between warm, moist air and cooler, drier air.
- Convergence: When different streams of air converge, they are forced to rise higher. This can cause cumulus clouds.
- Turbulence: Sudden changes in wind speed with height creating turbulent currents in the air.
Why do Clouds float? An interesting analogy
As was previously stated, clouds are made of small water drops and, if cold enough, tiny ice crystals. These are, for the vast majority of clouds, so small that the effects of gravity on them are almost completely negligible. To get your head around this, imagine the following picture: A shaft of sunlight goes through your window. Looking at it, you can usually see tiny small dust particles that appear to float in the air. This is exactly the same as what happens to clouds – their particles continue to float with the surrounding air.
The speed with which any object falls is related to its mass and surface area – which is why feathers fall slower than pebbles of comparable weight. The water and ice particles in clouds are simply too small to really feel the effects of gravity.
Upward air motions: Another contributing factor
As was started earlier, during the water cycle description, the vast majority of clouds are created by getting turned into vapor form by the Sun’s heat. That vapor is raised up by raising air currents, until the temperature changes and water vapor begins to condense into tiny droplets and ice crystals which form clouds.
So, clouds generally form, survive and grow in air that is moving upward. The upward, almost vertical motion of these wind gusts and currents contributes to the floating appearance of clouds as this atmospheric ascent is sufficient to negate the small velocities of cloud particles, for the most part – at least until the warm air keeping them afloat cools, the droplets condense and eventually become heavy enough to overcome the force of the rising air.
Putting things into perspective
By now, you might be thinking something is wrong with the aforementioned explanations. After all, water does have weight. You know it and you have seen it many times over. What you might not yet realize is how miniscule the many liquid droplets comprising a cloud are. They are so small that it would take a billion of them to make a single raindrop – a liquid droplet is about 0.002 millimeters across. A typical cumulus cloud carries about 0.50 grams of water per cubic meter.
To summarize, clouds are Sun warmed water that gets raised up to the sky by rising currents of air in vapor form. These upward, nearly vertical air currents help a great deal with keeping the clouds floating, as their force largely offsets the effects of gravity on the miniscule droplets of water or ice composing a cloud. As for why the effects of gravity have such a negligible effect on these droplets, it is because of their extremely small size: They are practically too small to develop any appreciable fall velocity.
So, clouds do not float in the sense of being buoyant. They are falling through the air, gradually and very, very slowly. It’s just that any updraft is able them carry them upward faster than they are falling down, pretty much. As long as this force balances gravity, clouds remain seemingly afloat. Eventually, the droplets will either coalesce together into bigger drops and finally fall back as rain – or they will break up and turn back into vapor. Until then, they will just keep drifting in the movement of the air.