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Unformatted text preview: 6 Atmospheric Moisture 16/02/2009 21:54:00 Most atmospheric moisture occurs as water vapor, not as liquid water. One distinctive attribute of water is that it occurs in 3 physical states: Solid snow, hail, sleet ice Liquid rain, water droplets *Gas water vapor Impact of Atmospheric Moisture on the Landscape Precipitation produces dramatic short-run changes in the landscape; the long- term effect of atmospheric moisture is more fundamental. Water vapor stores energy that can galvanize the atmosphere into action. Nature of Water: Commonplace but Unique Water occupies more than 70% of Earths surface area. Pure water has no color, taste, or smell. It solidifies at 0C (32F) and boils at sea level at 100C (212F). Very high heat capacity Good solvent Moves upward into narrow openings The Water Molecule: o Two hydrogen atoms and one oxygen atom held by covalent bonds the oxygen and hydrogen atoms share electrons o Because of its geometry, a water molecule has electrical polarity the oxygen side has a slightly negative charge, the hydrogen side has a slightly positive charger. This weak electrical polarity gives water molecules interesting properties Tend to orient themselves toward each other so that the negatively charged oxygen side of one molecule is next to the positively charged hydrogen side of another forms hydrogen bond So water molecules tend to stick to each other - cohesion Properties of Water: o The liquidity of water greatly enhances its versatility as an active agent in the atmosphere, lithosphere, and biosphere. o When freshwater gets colder, it only contracts until it reaches 4C , then expands at it cools from 4C to its freezing point of 0C. This is why ice is less dense than water! From 4C to freezing, water molecules form hexagonal structures held together by hydrogen bonds. When frozen, water is made entirely of these hexagonal structures Phase Changes of Water Evaporation liquid to vapor Condensation vapor to liquid Sublimation vapor directly to ice, or vice versa Latent heat in each phase change, there is an exchange of latent heat o Even as heat is added, the temp. of water doesnt increase while it is undergoing a phase change. o Latent heat of melting energy required to melt ice For ice to melt, energy must be added to agitate water molecules enough to break some of the hydrogen bonds energy added doesnt increase temp. of the ice but instead increases the internal structural energy of water molecules so that they can break free to become liquid o Latent heat of fusion energy released as water freezes When water freezes, the liquid molecules must give up some of their internal structural energy in order to revert to a less agitated condition in which ice can form....
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- Spring '08