4.5 Humidity and Cloud Formation

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4.5 Humidity and Cloud Formation
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Humidity

• Actual amount of water vapor per kg or L of air.
• Relative humidity is defined as the humidity in
  relation to the temperature of the air.
• Relative humidity is measured using a
  psychrometer.

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Relative Humidity info

• When the temp rises-
• There is more water in gas form in the air
• Humidity goes up
• When the temp cools-
• There is more water in liquid form in the air
• Humidity goes down

• 2 factors that change relative humidity
• the amount of moisture in the air
• temperature

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Humidity cont.

• When there is more water in liquid form in the
  atmosphere than gas form, the air becomes
  saturated.
• The relative humidity at saturation in 100
• The temperature at which air is saturated is
  called the dew point.

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Dew Point

• When the dew point is reached, condensation will
  occur.
• Condensation is the formation of water droplets.
• Dew forms when the temp is over 32F
• Frost forms when the temp is below 32F

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Clouds

• Form when water molecules cool below the dew
  point and condense to form water.
• Water condenses onto condensation nuclei.
• Dust particles that cling to the water droplets.

• Water can also freeze to condensation nuclei.

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Types of clouds
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Cirrus

• Thin and wispy
• High clouds
• Found at top of troposphere
• Signal approaching change in weather

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Cirrocumulus

• Patchy or clumpy

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Cirrostratus

• Thin veil across sky

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Cumulus

• Thick and puffy
• Cotton balls
• Found below 2,500 meters
• Composed of water droplets
• Good weather

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Altocumulus

• Found at about 6,000m
• Clumpy
• Formed in lines or bands

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Cumulonimbus

• Thunderstorm clouds
• Tall- reach about 9,000-18,000 m

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Stratus

• Layered and spread out across sky
• Lower part of the troposphere

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Altostratus

• Forms in layers
• Found at 2,500 to 6,000 m

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Stratocumulus

• Lumpy layers
• Can bring light precipitation

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Nimbostratus

• Low clouds
• Bring rain or snow
• When they are at ground level, known as fog