Clouds form when air containing water vapor rises and condenses, creating visible bodies of water vapor. Evaporation and transpiration are vital in this process. Heat causes the air to rise, expand, cool, and condense. The shape and type of cloud depend on how long the vapor particle rises. Heavy cloud formation can occur on hot days. Cloud classifications include stratum, cirrus, and cumulus, and a nimbus produces precipitation.
Regardless of the type of cloud, the basic principles behind how they form are the same. Air containing water vapor rises, the water vapor condenses from the air, and a visible body of water vapor, or cloud, is formed. There are several types of clouds, but the basic classifications are stratum, cirrus, and cumulus clouds.
The first step of cloud formation is the evaporation, transpiration and heating of the air. Evaporation and transpiration, collectively called evapotranspiration, are vital parts of the hydrological cycle. Evaporation occurs when a body of water, such as a lake or ocean, is heated by the sun so that the surface water sublimes or turns into vapor. During transpiration, plants “sweat” water through their leaves and stems as part of a cooling process. This water then turns into steam and mixes with the air. Similarly, ground water can also turn into vapor when exposed to heat and air.
As a result of the heating of soil and water surfaces, the air near them is also heated. Because warm air is less dense than cold air, the heated air begins to rise into the atmosphere. As the vapor particle rises, the atmospheric pressure decreases and the particle begins to expand. This expansion causes the steam to cool, and the cooling causes the water to condense, or clump, in the air. This is because cold air is unable to hold as much water vapor as warm air.
In summary, heat causes the air particle to rise, pressure drop with increasing altitude causes the air to expand, expansion of the air causes it to cool, and cooling causes the air to condense. water from the air in the form of liquid droplets. The temperature at which condensation begins is called the dew point. The dew point occurs when the air is saturated or holds as much water vapor as possible given its temperature and pressure. More water continues to condense as the air rises, until the air particle reaches the same temperature as the surrounding atmosphere, or its equilibrium temperature. If water vapor condenses into enough liquid water to become visible, it is called a cloud.
The shapes and types of clouds largely depend on how long the vapor particle rises after reaching the dew point, or in other words, the distance it rises between the dew point temperature and the equilibrium temperature. A particle of air that continues to rise for a long time after reaching the dew point will create a tall, soft mass, such as a cumulus cloud. This type is puffy and has defined edges. A particle of air that reaches equilibrium at nearly the same time it reaches its dew point will create a flatter, more layered mass, usually a layered cloud. They form on the ground and look like a gray blanket.
On a particularly hot day, the air particle can take a long time to cool down, resulting in heavy cloud formation. Cirrus clouds, otherwise known as “maretails,” are wispy or feathery masses that sit so high in the atmosphere that their droplets crystallize. There may be combinations of cloud classifications, such as cirrostratus or cirrocumulus. A nimbus is a cloud that produces precipitation.
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