Atmospheric Moisture

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Atmospheric Moisture
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Water in the Atmosphere

• Water Vapor
• invisible gas
• absolute humidity
• actual amount of water vapor
• similarly called vapor pressure
• saturation point
• amount air can hold
• similarly called saturated vapor pressure
• increases with increasing temperature

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Water Vapor, cont.

• relative humidity
• proportion of water vapor in the air
• RH ( VP / SVP) 100
• cant exceed 100
• sling psychrometer
• instrument use to determine humidity

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Changes in Humidity

• evaporation of surface water
• absolute increases relative increases (up to
  100)

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Changes in Humidity, cont.

• air warms
• absolute stays same relative decreases

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Changes in Humidity, cont.

• air cools
• relative increases (up to 100)
• absolute stays same until 100, then decreases

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Dew Point

• temperature at which RH reaches 100
• if air continues to cool, then excess water vapor
  condenses into water droplets

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Heat Index

• Temperature air feels like in warm to hot weather
• Feels warmer with increase in humidity
• Your body is less able to cool itself by
  perspiration

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Forms of Condensed Water Vapor

• clouds
• fog
• technically very low-lying clouds)
• radiation fog- inversions
• advection fog- warm, moist air blows over cold
  surface
• dew frost
• in contact with land
• inversions advections

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Cloud Types

• Classified by height and form
• High Clouds
• Cirrus- composed entirely of ice crystals
• Cirrocumulus
• Cirrostratus

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Cloud Types, cont.

• Middle Clouds
• Altocumulus
• Altostratus

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Cloud Types, cont.

• Low Clouds
• Stratus
• possible drizzle
• Nimbostratus
• precipitation
• Stratocumulus
• Cumulus (smaller)

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Cloud Types, cont.

• Clouds with Vertical Development
• Cumulus
• Cumulus congestus
• precipitation
• Cumulonimbus
• precipitation

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ReadingsText pp. 478-483 495-499Homework