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Unformatted text preview: Chapter 5 Atmospheric Water and Weather Water on Earth • Water, water, everywhere… • Water is most common substance on face of the Earth • Occupies 71% of the area of our planet • Weighs 8.337 lb./gal • Constitutes almost 70% of our bodies (by weight) • Moisture of the world found in 7 types of storage: – Oceans – occupy 71% of Earth’s surface but contain 97.2% of all water – Glaciers – contain 2% of all moisture, but ¾ of world’s fresh water – Underground water – 0.5% of world total – Surface waters (rivers, lakes, inland seas) – less than 0.2% of all water – Soil moisture – 0.1% of total – Atmospheric moisture – tiny fraction (0.0001%) – Biological water (stored in plant and animal tissue) -- negligible Ocean and Freshwater Distribution Water • Temperate location of Earth in solar system allows water to exist in three physical states – liquid, gas, solid • Water is a compound – 2 atoms of hydrogen, 1 atom of oxygen Æ strong bond • Hydrogen side = positive charge • Oxygen side = negative charge • Water molecules bond ( hydrogen bonding ) – positive side of one molecule attracted to negative side of another • Hydrogen bonding responsible for surface tension and capillary action Heat Properties • Change from one physical state to another requires addition or loss of heat energy • Amount of heat must be sufficient to affect hydrogen bonds between molecules • Relationship between water and heat energy is important driving force in weather • Heat exchange involved in phase changes of water provides over 30% of energy that powers the general circulation of the atmosphere Water’s Phase Changes • Liquid (water) to gas (water vapor) = evaporation, vaporization (boiling water) • Gas to liquid = condensation • Liquid to solid (ice) = freezing • Solid to liquid = melting • Gas to solid (and vice versa) = sublimation Three States of Water Solid Phase (Ice) • As water cools, it contracts in volume until it reaches a certain temperature (39 o F) • Below that temperature, water begins to expand as hydrogen bonds form among slower-moving molecules Æ hexagonal structure • Expansion in volume results in decrease in density – ice 0.91 times the density of water so it floats • Iceberg: 1/11 (9%) on surface, 10/11 (91%) hidden beneath ocean’s surface • Expansion in volume responsible for broken pipes, roadway cracks in winter Liquid Phase (Water) • Non-compressible fluid – assumes shape of container • Heat energy increases motion of water molecules in ice, breaks some of hydrogen bonds, melting occurs • 80 calories of heat required for 1 gram of ice to melt to 1 gram of water • Latent heat: stored within water and liberated when water freezes Æ latent heat of melting and freezing Gas Phase (Water Vapor) • Invisible, compressible gas • 540 calories are required to convert 1 gram of boiling water to vapor Æ latent heat of vaporization • Evaporation requires more energy than if water were boiling:...
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This note was uploaded on 04/20/2008 for the course GEOS 200 taught by Professor Hanchette during the Spring '08 term at University of Louisville.
- Spring '08