# ch04 - Jon Ahlquist 9/29/2006 Chapter 4 Atmospheric...

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Jon Ahlquist 9/29/2006 MET1010 Intro to the Atmosphere 1 Chapter 4 Atmospheric Moisture ± Phase changes of water ± Hydrologic cycle ± Evaporation and saturation ± ± Boiling ± ± Why is Florida more humid than California? ± Humidity and human comfort ± Measuring humidity ± Humidity and musical instruments Phase Changes (pp. 86-88) ± Evaporation: liquid to vapor ± Condensation: vapor to liquid ± Sublimation: ice to vapor without liquid ² Example: freeze drying ± Deposition: vapor to ice without liquid ² Example: Frost forming on ground and windshields ± Transpiration: plants give up water as vapor to atmosphere through small openings on the underside of leaves Circulation of Water in Atmosphere: Hydrologic Cycle (p. 88) ± In the Earth’s hydrologic cycle, water exists in all 3 phases, solid, liquid, and gas (phase). ± 85% of evaporation occurs over oceans ± If all vapor in atmosphere were to condense and fall out, there would be 1 inch (2.5 cm) of rain or the equivalent in snow (about 10”) over the whole Earth. ± Why is it impossible for all the vapor to condense out of the atmosphere? ± Given the 1 inch of rain statement above, how is it possible to have several inches of rain in a day? Evaporation, Condensation, and Saturation (fig. 4.3, p. 87) Evaporation: More liquid becomes vapor than vapor becomes liquid. Condensation: opposite is true. Saturation (or equilibrium): Balance between rates of Expressing amount of vapor in atmosphere (pp. 89-90) ± I will not ask you about absolute humidity, specific humidity, and mixing ratio defined on p. 89. ± If you want to be a meteorology major, learn specific humidity and mixing ratio. Absolute humidity is just water vapor density. Vapor pressure (pp. 90-91) ± Vapor pressure = that part of air pressure which is due to water vapor. ± Vapor pressure is < 4% of total pressure, and that is found only in the most extremely humid tropical air. ± Saturation vapor pressure = vapor pressure that would exist at equilibrium with flat surface of water. Depends on temperature only. Saturation vapor pressure is normally greater than or equal to vapor pressure. ± You can forget about the rest of the air when talking about water vapor. Air does not “hold” water vapor.

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Jon Ahlquist 9/29/2006 MET1010 Intro to the Atmosphere 2 Saturation vapor pressure (pp. 90-91) ± Triple point (temperature and pressure at which all three phases of water coexist at equilibrium): 0°C, 6 mb ± Table of saturation vapor pressure vs temperature For details, see p. fig. 4.10, p. 91 ± For each 10°C (roughly 20°F) increase, saturation vapor pressure roughly doubles ± To do all sorts of weather calculations, see: http://www.srh.noaa.gov/elp/wxcalc/wxcalc.shtml
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## This note was uploaded on 07/21/2011 for the course MET 1010 taught by Professor Staff during the Fall '08 term at FSU.

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ch04 - Jon Ahlquist 9/29/2006 Chapter 4 Atmospheric...

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