Chapter 7 Physical Geography Water Atmospheric Moisture GEOGRAPHY 1710 DAVID R SALLEE Water on Earth Atmospheric Moisture When atmosphere contains enough moisture water vapor may condense to form z z z z z z z Haze Fog Cloud Rain Sleet Hail Snow Land and Water z z z z Water vapor is a colorless odorless tasteless invisible gas that mixes freely with the other gases in the atmosphere Evaporation the conversion of moisture from liquid to gas Involves molecular escape molecules of water escape from the liquid surface into the surrounding air Evaporation can take place at any temperature but higher temperatures cause molecules to move faster and collide more forcefully Depends on three factors Temperature of water and air Amount of water vapor already in the air Whether the air is still or moving Hydrologic Cycle 1 Evapotranspiration 1 Transpiration the process whereby plants give up moisture through their leaves 2 Evapotranspiration total amount of water vapor entering the air from land sources plants soil and other inanimate objects 3 Potential Evapotranspiration the amount of evapotranspiration that would occur if the ground at the location in question was saturated all the time Humidity z Relative Three States of Water Relative Humidity Humidity Saturation Dew point z Expressions of Relative Humidity Vapor pressure Specific humidity z Instruments Water Vapor in the Atmosphere Humidity Patterns 2 Humidity Instruments Atmospheric Stability z Adiabatic Processes z Stable and Unstable Atmospheric Conditions Figure 7 13 Adiabatic Processes Adiabatic Processes z Dry adiabatic rate 10 C C 1000 m 5 5 F F 1000 ft z Moist adiabatic rate 6 C C 1000 m 3 3 F F 1000 ft Stable and Unstable Atmospheric Conditions Clouds and Fog z Cloud Formation Processes z Cloud Types and Identification z Fog 3 Clouds and Fog Clouds collections of minute droplets of water or tiny crystals of ice visible expressions of condensation Classified by two factors form and altitude at any given time 50 of Earth is covered by clouds not all clouds precipitate but all precipitation comes from clouds Cloud Formation Processes Clouds and Fog precipitation only comes from clouds that have nimb in their name receive both insolation from above and terrestrial radiation from below then either absorb reflect scatter or reradiate this energy Moisture Droplets z Moisture droplet z CloudCloud condensation nuclei Cloud Identification Cumulonimbus Development 4 Fog Advection Fog z Advection fog z Evaporation fog z Upslope fog z Valley fog z Radiation fog Valley Fog Radiation Fog Figure 7 25 5
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