Here are a few basic facts about clouds that I bet you've forgotten from your grade-school science days.
1. What are clouds exactly? Clouds are visible collections of tiny water droplets (ice crystals, if it's cold enough) that live high in the atmosphere above Earth's surface.
2. What causes clouds to form? Clouds form when a parcel of air rises from the surface up into the atmosphere. As the parcel rises, it passes through lower and lower pressure areas. You may remember that the higher up you go, the lower the pressure gets. So, as the air rises up through these increasingly lower pressure area, it forces the air inside to expand outwards. This expansions uses heat energy and so the mass of air becomes cooler. The farther upwards it travels, the cooler it becomes. When it cools enough to reach it's dew point, the water vapor inside the parcel condenses into droplets of liquid water. The droplets then collect dust, pollen, smoke, dirt, and sea salt particles. And it is these particles that cause clouds to form and become visible.
3. Why do clouds billow and change their shape? Clouds really do change shape and it's not just in the imagination of children. The processes of condensation and evaporation cause clouds to be ever-changing. The process of condensation causes clouds to grow and doesn't stop. This is why clouds can seem to expand into neighboring sky. As currents of warm and moist air continue to rise and feed the condensation process, drier air from the surrounding environment will invade the buoyant column of air, This process is called entrainment (no, not entertainment....) When the drier air gets introduced into the body of the cloud, it causes the cloud's droplets of water to evaporate. This, in turn, makes the cloud smaller.
4. Why do clouds float? Clouds are created high up in the atmosphere and remain suspended there because of the tiny particles they contain. A cloud's water droplets or ice particles are so small, less than a micron, and because they are so tiny, they respond very slowly to gravity. FYI - a micron is less than one-millionth of a meter. The slight movement of air will keep these particles afloat. And because it applies to each particle, it then applies to the cloud as a whole.
5. How do clouds move? Clouds travel with the upper-level winds. They'll move at the same speed and in the same direction as the prevailing wind blows at the cloud's level. High-level clouds will move the fastest and are pushed along by the jet stream.
6. How do clouds get their color? A cloud gets its color by the light it receives from the Sun. Science tells us, "The process works like this: as the Sun's light waves pass through the atmosphere and clouds, they meet the individual water droplets that make up a cloud. Because the water droplets have a similar size as the wavelength of sunlight, the droplets scatter the Sun's light in a type of scattering known as Mie scattering in which all wavelengths of light are scattered. Because all wavelengths are scattered, and together all colors in the spectrum make up white light, we see white clouds. In the case of thicker clouds, such as stratus, sunlight passes through but is blocked. This gives the cloud a grayish appearance."
"When people look at clouds they do not see their real shape, which is no shape at all, or every shape, because they are constantly changing. They see whatever it is that their heart yearns for. "
~ Jose Eduardo Agualusa
May your weekend be filled with clouds in whatever shape your heart yearns for. I invite you back here on Monday. Until then, I wish you