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Unformatted text preview: Chapter 5 Forms of Condensation and Precipitation Cloud Formation Clouds can be defined as visible aggregate of minute droplets of water, or tiny crystals of ice, or a mixture of both Clouds are of continual interest to meteorologists because they provide a visible indication of what is going on in the atmosphere Condensation aloft o Clouds are a form of condensation produced when water vapor condenses in the atmosphere. o The most important cloud forming process is adiabatic cooling Any time a parcel of air ascends, it passes through regions of successively low pressure. As a result, rising air expands and cools adiabatically. At a height called the lifting condensation level, the ascending parcel has cooled to its dew point temperature, and further ascent (cooling) causes condensation. o Condensation occurs when water vapor changes to a liquid For any form of condensation to occur, the air must be saturated. Saturation occurs most often when air is cooled to its dew point. There generally must be a surface on which the water vapor can condense. When dew forms, objects at or near the ground, like blades of grass, serve this purpose. o When condensation occurs aloft, tiny particles known as cloud condensation nuclei serve as surfaces on which water vapor condenses. Growth of Cloud droplets o Particles that are the most effective sites for condensation are called hygroscopic nuclei (water-seeking). o The cloud droplets that form on salt are generally much larger than those that grow on hydrophobic nuclei (water-repelling)....
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- Spring '08