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Water in the Atmosphere

Water in the Atmosphere. I. Evaporation. Variables that affect evaporation rate Air Temp Inc Air Temp = Inc Evap Water Temp Inc Water Temp = Inc Evap Wind Inc Wind = Inc Evap Surface Area Inc S Area = Inc Evap Water Vapor in Air (Humidity) Inc Water Vapor = Decreased Evap.

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Water in the Atmosphere

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  1. Water in the Atmosphere

  2. I. Evaporation • Variables that affect evaporation rate • Air Temp • Inc Air Temp = Inc Evap • Water Temp • Inc Water Temp = Inc Evap • Wind • Inc Wind = Inc Evap • Surface Area • Inc S Area = Inc Evap • Water Vapor in Air (Humidity) • Inc Water Vapor = Decreased Evap

  3. Energy Changes • Evaporation • Energy is absorbed • Cooling process, water takes in energy from surroundings • Condensation • Energy is given off • Warming process, water releases energy to surroundings

  4. III. Water in Atmosphere • Saturated Air • Air holding as much water vapor as possible (warm air can hold more water) • Dew Point • Temperature the air must be cooled to in order to become saturated • As air temp and dew point temp get closer together, air becomes more saturated and the chance for precipitation increases • Measured using a psychrometer and Reference Tables

  5. III. Water in Atmosphere • Relative Humidity • Comparison between the ACTUAL amount of water vapor and the MAXIMUM amount it could hold at that temp • Saturated air = 100% humidity • Greater the humidity, less evaporation occurs

  6. Rel Humidity Temperature III. Water in Atmosphere • If air temp and dew point are equal, Relative Humidity (RH) = 100% • If amount of water vapor in air stays the same, the RH will decrease as temp increases

  7. Air Pressure Rel Humidity IV. Water Vapor and Air Pressure • Moist air weighs less than dry air • Water molecules replace heavier Nitrogen molecules • Moist air = Low Pressure • Higher Humidity = Lower Pressure

  8. V. Water Leaving Atmosphere • Condensation • Water Vapor to liquid • Sublimation • Change directly from gas to solid (vice versa) ex. CO2

  9. V. Water Leaving Atmosphere • Conditions needed for Condensation • Water in atmosphere • Air MUST be cooled to dew point • Need surfaces for condensation to form • Dust in air gives surface for clouds to form

  10. V. Water Leaving Atmosphere • Conditions caused by condensation • Dew • Temp at ground reaches dew point, above freezing, forms on solid surfaces • Frost • Same as dew but temp below freezing • Fog • Cloud at ground level, when air temp close to ground reaches dew point • Clouds • Water condenses on dust above ground level • Air cools as it rises (less air pressure so it expands)

  11. DEW FOG CLOUDS FROST

  12. VI. Adiabatic Cooling / Warming • Cooling / Heating air w/o removing energy • Cooling • As air pressure decreases, the air expands as it rises • There are fewer molecules in the same volume of space so there is less Kinetic energy, so temp decreases • Heating • As air pressure increases, the air compresses and increases temp

  13. VII. Methods of Cloud Formation • Need rising air to cool air to dew point • Orographic Effect • Clouds form as air rises up mountain, hill, plateau • Lake Effect Snow

  14. Condensation Level GROUND VII. Methods of Cloud Formation • Fair Weather Clouds • Energy is radiated from the ground leading to convection currents Air reaches Dew Point (becomes saturated) RH = 100%, cloud forms TERRESTIAL RADIATION (HEATS AIR) Warm air RISES (less dense) Cools as it rises (adiabatic cooling) INSOLATION

  15. VII. Methods of Cloud Formation • Lifting Air at Frontal Boundaries • Cold Front – leading edge of cold air mass

  16. VII. Methods of Cloud Formation • Warm Front – leading edge of warm air mass

  17. VIII. Precipitation • Cloud droplets must “clump” together until they become heavy enough to begin falling

  18. IX. Atmospheric Problems • Greenhouse Effect (Theory) • Glass from a greenhouse traps the infrared radiation and temps rise • Gases in atmosphere can do the same (CO2, CFCs and methane) • CO2 is increasing from • Burning fossil fuels • Deforestation (cutting down rain forests) • Effects on Earth • Rising Temps • Droughts in food growing regions • Melting of polar ice = rise in ocean levels

  19. IX. Atmospheric Problems • Depletion of Ozone Layer • Caused by CFCs breaking down ozone • Makes increased UV rays hitting Earth • Increased skin cancer • Eye damage • Solutions • Different aerosol propellants • Use less styrofoam • Different types of refrigerants

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