Humidity and temperature

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Humidity and temperature

  1. 1. Meteorology Temperature and humidity
  2. 2. Water Vapor • Source of all condensation and precipitation • Most important gas in the atmosphere for understanding atmospheric processes • Zero to 4% by volume
  3. 3. Water Changes State • Always requires heat • Heat is either absorbed or released • Water must pass through the atmosphere in the form of water vapor • If all the water vapor was in a global layer it would only be 2 mm deep
  4. 4. Solid to Liquid • Melting – Heat is transferred to ice water – Temperature of the water remains a constant 0 degrees C until all ice has melted – Heat breaks apart crystal structure of ice forming liquid water
  5. 5. Liquid to Gas • Evaporation – Changing a liquid into a gas – Requires 2500 joules of energy to convert 1 gram of liquid water to water vapor
  6. 6. Liquid to Gas • “Evaporation as a cooling process” – Energy is needed to evaporate water – Cooling effect after getting out of the pool – Energy needed comes right from your skin • Condensation – Water vapor changes to liquid – Generates clouds and fog
  7. 7. Solid to Gas • Sublimation – Conversion of solid directly to a gas – No liquid state – Dry ice (frozen carbon dioxide) – Generates “smoke” • Deposition – Conversion of vapor directly to a solid – Frost on cold objects, grass, windows
  8. 8. Humidity • Humidity – the amount of water vapor in the air • Saturation – Balance between liquid water and water vapor – Closed jar: half water, half air – Water begins to evaporate  increases pressure in the air – Pressure is caused by more water vapor molecules moving into the air – Pressure in air continues to increase – Forces more water molecules to return to liquid – When a balance occurs, air is said to be saturated
  9. 9. Saturated Air • Depends on temperature • Warm air contains more water vapor than cold air
  10. 10. Relative Humidity • Ratio of air’s actual water vapor content compared to the amount of water vapor the air can hold at the time • How much water vapor can the air hold? – Depends on temperature and pressure • Indicates how near the air is to saturation
  11. 11. Relative Humidity • How can it be changed? – 1 – adding or removing water vapor • Occurs naturally • Oceans and smaller bodies of water – 2 – varies with temperature • Lowering air temperatures causes INCREASE • Raising air temperatures causes DECREASE
  12. 12. Dew Point • The temperature at which one parcel of air would need to be cooled in order to reach saturation • If the air was cooled further it would condense • This would cause dew, fog, clouds
  13. 13. How do you measure humidity? • Hygrometer – used to measure relative humidity • Psychrometer – Two thermometers side by side – One is dry bulb, the other wet bulb – Larger the difference on the reading the lower the relative humidity – If air is saturated the thermometers will have the same reading

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