Credit: NOAA. Clouds are made of water droplets or ice crystals that are so small and light they are able to stay in the air. But how does the water and ice that makes up clouds get into the sky? And why do different types of clouds form? The water or ice that make up clouds travels into the sky within air as water vapor, the gas form of water. Water vapor gets into air mainly by evaporation — some of the liquid water from the ocean, lakes, and rivers turns into water vapor and travels in the air.
When air rises in the atmosphere it gets cooler and is under less pressure. The vapor becomes small water droplets or ice crystals and a cloud is formed. These particles, such as dust and pollen, are called condensation nuclei. Eventually, enough water vapor condenses upon pieces of dust, pollen or other condensation nuclei to form a cloud. Those particles provide surfaces on which water vapor can change into liquid droplets or ice crystals. Dust and other particles floating in the air provide surfaces for water vapor to turn into water drops or ice crystals.
The tiny drops of water condense on the particles to form cloud droplets. Clouds are made up of a bunch of cloud droplets bundled together with raindrops.
We usually think of clouds as being up in the sky, but when conditions are right, a cloud can form at ground level, too. Although the basic idea of cloud formation is easy to understand, there is much more to learn. In fact, clouds are considered one of the most challenging aspects of climate science.
NASA has a fleet of spacecraft that orbit Earth, called satellites. Many of them study clouds, weather, climate and more. Make a cloud in a bottle with this DIY project! Stratus or layered clouds do have the appearance of fog.
Cumulus clouds, the upper parts of which resemble cauliflower, are a type of convective cloud. These clouds form in rapidly rising air and are composed of many small water droplets. The small drops scatter light effectively and make the cloud appear bright. Likewise, if you smash up glass and separate the small pieces from the large, the grouping of small pieces will appear brighter. As a result, the cloud's boundaries appear sharp.
In contrast is the cirrus uncinus, a type of ice cloud that resembles a comma. These clouds appear diffuse near their bases, where the number of ice crystals decreases as they fall and evaporate into the dry air below. The cloudy air mixes with the clear air, giving the diffuse appearance.
Thus, how sharp a cloud boundary appears is a function of how much the cloud air mixes with the clear air environment. If the surrounding air has a low humidity, the water droplets or ice crystals that make up the cloud quickly evaporate as the cloudy air mixes with its surroundings; this results in the cloud maintaining a sharp boundary.
Have you ever painted a line on a wall? Up close the edges of the line may look wavy and interrupted. Step away, and the line looks sharp and crisp.
The next time you have an opportunity to fly, observe the clouds as you pass through them. You will notice that the edges of a cloud are often diffuse.
Just try to stay out of the cumulonimbus cloud, whose distinctive boundaries could give your airplane a sharp bounce. Some spots are slightly hotter than others; it is at these locations that the water is turned to vapor.
When a bubble gets large enough, the water's surface tension can no longer hold it, and so it rises. Fluids having different densities behave quite independently. The bubble stays a bubble all the way to the top where it breaks free as steam. A spot on the earth's surface gets hotter than the surrounding area.
An example would be the black, flat tarred roof of a large building or a vacant parking lot.
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