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FAA Aircraft Dispatcher (ADX)MeteorologyMedium

A parcel of air at a given temperature contains exactly half the amount of water vapor it could hold at saturation for that temperature. What is the relative humidity of this air parcel?

  1. A100%
  2. B25%
  3. C75%
  4. D50%
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Correct answer: D. 50%

Relative humidity is the ratio of the actual amount of water vapor present in the air to the maximum amount the air could hold at that temperature, expressed as a percentage. Half of the saturation amount equals 50% relative humidity.

Why the other options are wrong

  • A. 100% relative humidity indicates full saturation, not half.
  • B. 25% would require only a quarter of the saturation water vapor amount.
  • C. 75% would require three-quarters of the saturation capacity present.

Relative Humidity

The ratio, expressed as a percentage, of the actual water vapor content of the air to the maximum amount the air could hold at that temperature.

  • 100% relative humidity means the air is saturated
  • Relative humidity changes with temperature even if moisture content stays constant
  • Warming air lowers relative humidity; cooling raises it toward saturation

Memory trick: RH is a percentage of a 'full glass' of water vapor capacity.

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