Clouds are so pretty here.
A cloud is a visible mass of water droplets or frozen ice crystals suspended in the atmosphere above the surface of the Earth or other planetary body. Clouds in the Earth's atmosphere are studied in the nephology or cloud physics branch of meteorology. This article concentrates mainly on clouds that form in the troposphere, the lowest layer of the Earth's atmosphere where most of the world's weather is generated.
Cold air holds less water vapor than warm air, so clouds are formed when the air is lifted and cooled to the point at which it begins to shed vapor it can no longer retain. This is the saturation temperature which is also known as the dewpoint temperature. The altitude of the saturation level determines the altitude of the cloud base. The vapor begins to condense onto airborne hygroscopic particles like dust and salt from sea spray and becomes visible as cloud. Very small water droplets form at lower altitudes below the freezing level and ice crystals or sometimes supercooled water droplets at higher altitudes. This process of cooling and condensation continues until the air achieves temperature equilibrium with the surrounding atmosphere and stops rising. The altitude of equilibrium tends to determine the altitude of the cloud tops, although if the vertical air currents have become very strong, momentum can push the tops to even higher altitudes.
The droplets or crystals that make up a cloud are typically about 0.01 mm (0.00039 in) in diameter. If these continue to grow in size, a process facilitated by strong upward lift and abundant condensation particles, they will eventually become too large and heavy to be supported by the upward air currents and fall to the ground as precipitation. If sufficient condensation nuclei are not present at and above the saturation level, the rising air becomes supersaturated and the formation of cloud is inhibited. The most common agents of upward motion causing condensation are spontaneous convective lift caused by daytime solar heating of unstable air at surface level, lift along a weather front or around a cyclonic low pressure area (anticyclonic in the southern hemisphere) that forces a stable or unstable airmass ro rise over top of a cooler airmass, and orographic lift of the air over mountains.
Colder air at surface level absorbs less moisture than warm air and thus tends to be more stable. If this type of airmass moves over water, it may become more unstable and subject to spontaneous convective lift; otherwise it requires the external forces of frontal, orographic, or cyclonic lift to trigger cloud formation. At the other extreme, if an airmass that is already warm and unstable is subjected to the additional forces of a strong external lifting agent like a fast moving cold front, the results can be explosive with very powerful air currents resulting in the formation of severe thunderstorms and tornado's.
This post is for Kyle Silfee. He loves the Colorado clouds.
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Broken Bells: The High Road
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