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Moisture in the air

Moisture in the air. Heavy Air: (high pressure) cold, because the molecules are closer together. Dry, because nitrogen and oxygen are heavier than water vapor . Think of beautiful blue skies and light breezes. Light Air: (low pressure)

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Moisture in the air

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  1. Moisture in the air

  2. Heavy Air: (high pressure) cold, because the molecules are closer together. Dry, because nitrogen and oxygen are heavier than water vapor. Think of beautiful blue skies and light breezes. Light Air: (low pressure) warm; the molecules have more energy and are farther apart. Humid, because water vapor is a very light molecule. Think of days that are ‘muggy’ and warm. Heavy and Light air

  3. Water vapor and energy • Water vapor enters the atmosphere due to evaporation from surface water and ice. • Energy is required for evaporation, which takes heat away from the surface. • Warm air has more energy, and can therefore cause more evaporation. • Cold air cannot cause as much evaporation, so the water vapor tends to condense or sublimate. • Condensation releases heat back into the air.

  4. Dewpointtemperature • The dewpoint temperature is the temperature at which water vapor will CONDENSE to become drops of water or SUBLIMATE to become ice crystals. • The air must be cooled for this to happen. • The dewpoint depends on the amount of water vapor in the air. It DOES NOT depend on the air temperature. It indicates how humid air is. • A sling psychrometer, compares a ‘wet’ bulb to a ‘dry’ bulb. • A high dewpoint indicates a high concentration of water vapor. Dry air has a low dewpoint. novalynx.com Flickr.com

  5. Relative Humidity • Relative humidity is a percent. • It compares the amount of water vapor in the air, (humidity), to the amount of water vapor the air can hold at the present air temperature. • WARM AIR CAN HOLD MORE WATER VAPOR THAN COLD AIR DOES. • The relative humidity indicates the likelihood of dew or frost or fog forming. • 100% RH at the surface indicates that fog is probably forming. This means that the air is saturated with water vapor. • Clouds are always at 100% RH.

  6. WARM AIR CAN HOLD MORE WATER VAPOR THAN COLD AIR DOES. • Places with low RH%: hot deserts. Cold Antarctica. • Places with high RH%: cold, coastal regions that get lots of snow or rain. Hot coastal places (like New Orleans) and rainforests. ultimatehandyman.co.uk

  7. Using a sling psychrometer • Two thermometers: • The ‘dry bulb’ just measures air temperature. • The ‘wet bulb’ measures the temperature after evaporation from the wet ‘sock’ cools the thermometer. • On a dry day, there will be a lot of evaporation and the wet bulb temperature will get much cooler. • On a humid day, there may be no evaporation, and the wet bulb temperature will be the same as the dry bulb temperature.

  8. Determining dewpoint temperature: page 12 ESRT http://regentsearth.com/Illustrated%20ESRT/Page%2012%20(DP%20&%20RH)/RelHumDewPtMC.html regentsearth.com

  9. Determining relative humidity: page 12 ESRT http://regentsearth.com/Powerpoints/Powerpoint%20Index.htm

  10. What is ‘humid’ air? • Can two air masses with the same relative humidity have different temperatures? Different dew points? • What does dew point really tell us? • When the air temperature and dew point temperature are almost the same, then _________________???? • Review book pages 174-177 • https://castlelearning.com/review/login/login.aspx

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