Clouds look flat on the bottom because of the process of cloud formation. The condensation of rising moist hot air occurs only above a certain height or altitude called lifted condensation level (LCL). This level defines the flat base of the cloud. As more hot air rises from below, the base of the cloud remains the same while the existing clouds are forced upwards. Thus, this process causes clouds to have a flat bottom and a fluffy top.
Why do clouds have flat bottoms?
Have you ever wondered why some clouds are flat on the bottom and puffy on top?
Well, it is an interesting question whose answer lies in the formation process of the clouds. Therefore, let’s try to understand how clouds are formed and why do clouds have a flat bottom base.
On a typical summer day, the most common clouds that are found in the sky are cumulus and stratus clouds. These low-level clouds generally have flat bottoms due to their process of formation. The process of cloud formation begins with the evaporation of ocean and river water due to sunlight. Due to continuous heat from the sun, the saturated air near the ground surface gets warmer and rises upwards (warm air is less dense than cooler air).
We know that the atmospheric temperature and air pressure decreases with increasing altitude. As this moist hot air rises up, it gets cooler with the increase in altitude. After reaching a certain altitude, where the temperature of rising air is equal to the dew point or frost point of the water, water vapors present in the rising air condenses to water droplets and ice crystals. These water droplets are formed on the surface of tiny dust particles. These millions of water droplets and ice crystals come together to form a cloud.
The bottom of the cloud becomes flat at an altitude above which the condensation process occurs. This altitude creates a boundary layer between clouds and hot rising air. This height is also known as the Lifted condensation level (LCL). At LCL, the relative humidity of the air parcel becomes saturated when cooled using dry adiabatic lifting. This LCL is used to estimate the height of the cloud base.
As more hot air keeps rising from the bottom, the base remains the same and flat while the existing cloud gets pushed upwards and forms a puffy top with a flat base.
References
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