UNIT 5: Atmosphere

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UNIT 5 Atmosphere WeatherChapter 18 Water in
the Atmosphere

• C/S 18.1 Humidity and Condensation
• C/S 18.2 Clouds
• C/S 18.3 Precipitation

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C/S 18.1 Humidity and Condensation

• Water vapor is everywhere and it is always on the
  
• move.
• Characteristics of Water
• It is unique because it exists in all three
  states of matter, depending on its temperature.
• Solid at 0oC or below, Liquid between 0oC-100oC,
  and a gas (water vapor) at 100oC or above.
• Condensation-the change from water vapor to
  liquid water. Ex. dew, fog and clouds.
• Condensation releases heat and evaporation
  absorbs heat.

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C/S 18.1 Humidity and Condensation (cont)

• Humidity
• Specific Humidity-the actual amount of water
  vapor in the air at a given time and place.
• Air is saturated when the rate of condensation
  equals the rate of evaporation.
• Relative Humidity-How near the air is to its
  maximum capacity for holding water vapor. See
  example on page 392.
• Humidity is measured using a psychrometer.

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C/S 18.1 Humidity and Condensation (cont)

• Condensation
• Dew Point-The temperature at which saturation
  occurs and condensation begins.
• Two conditions are needed for water vapor to
  condense 1) there must be materials for the
  water vapor to condense on and 2) air must cool
  to or below its dew point.
• If temperatures are 0oC or less dew turns to
  frost.
• Fog forms when a cold surface cools the warmer
  moist air above it.

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C/S 18.2 Clouds

• Clouds form when air cools to its dew pt.
• Types of Clouds
• Four main types-low, middle, high and clouds of
  vertical development.
• If air movement is horizontal then the clouds
  form in layers called stratiform. If the air
  movement is mainly vertical, clouds grow upward
  in great puffs called cumuliform.
• Stratus and Strato-describe clouds that form in
  layers and are low.
• Cumulus and Cumulo-describe clouds that grow
  upward. They are puffy with flat bases.
• Cirrus and Cirro-describe high, feathery ice
  clouds.
• Alto-describes clouds located between 2000 and
  7000 meters.
• Nimbus and Nimbo-refer to dark rain clouds.

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C/S 18.2 Clouds (cont)

• Cloud Formation
• Condensation Level-atmospheric level at which
  condensation occurs.
• Adiabatic lapse rate-the rate at which air cools
  as it rises.
• Cumulus clouds-Form when moist air rises and
  cools to its dew point.
• Stratiform clouds-Form when the air is stable and
  the cloud can't move up or down.
• Clouds

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C/S 18.3 Precipitation

• Precipitation-is any form of water that falls
  from a cloud to
• the earth's surface.
• How Precipitation Forms
• Condensation droplets collide and combine to form
  bigger droplets.
• Ice crystals form in clouds that are below
  freezing.
• Sleet-Frozen raindrop
• Freezing rain-is rain that freezes when it hits
  the f ground.
• Hail-Is a frozen raindrop that grows by colliding
  with other drops.
• Measuring Precipitation
• The National Weather Service uses a rain gauge to
  measure rain in hundredths of an inch.
• The measurement represents what the depth of
  water would be if it did not soak into the
  ground, flow away or evaporate.

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C/S 18.3 Precipitation (cont)

• Where does is occur?
• The main cause of precipitation is the rising and
  cooling of moist air.
• Near the equator and across mountain ranges are
  great areas to find precipitation.
• There is little or no precipitation where air
  sinks and warms.
• Also air that sinks on the downwind side of
  mountain is very dry. See pg. 404.
• Weather Modification
• Implementing methods of changing the weather.
• Rain Seeding-Droplets of frozen carbon dioxide or
  silver dioxide are dropped into a supercooled
  cloud.
• Hail forming.