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Process where the sun's energy transforms enormous quantities of liquid water into water vapor.
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Evaporation
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Process where the winds transport the moist air to other regions, where the water vapor changes back into liquid, forming clouds.
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Condensation
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Rain snow or hail falling to the earth.
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Precipitation
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Total number of molecules escaping from the liqyid would be balanced by the number returning
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Saturated air
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Tiny particles upon whose surfaces condensation of water vapor begins in the atmosphere.
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Condensation nuclei
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A general term that refers to the air's water vapor content.
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Humidity
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The pressure exerted by the water vapor molecules in a given volume of air.
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Actual vapor pressure
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The maximum amount of water vapor necessary to keep moist air in equilibrium with a surface of pure water or ice. Represents the maximum amount of water vapor that the air can hold at any given temperature and pressure.
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Saturation vapor pressure
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The ratio of the amount of water vapor in the air compared to the amount required for saturation. The ratio of the air's actual vapor pressure to its saturation vapor pressure.
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Relative humidity
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Air with a relative humidity greater than 100 percent.
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Supersaturated air
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The temperature to which air must be cooled (at constant pressure and constant water vapor content) for saturation to occur.
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Dew-point temperature (dew point)
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The difference in degrees between the air temperature and the wet-bulb temperature.
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Wet-bulb temperature
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An index that combines air temperature and relative humidity to determine an apparent temperature- how hot it actually feels.
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Heat index(HI)
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What the air temperature "feels like" for various combinations of air temperature and relative humidity.
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Apparent temperature
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An instrument used to measure the water vapor content of the air. It consists of two thermometers. After whirling the instrument, the dew point and relative humidity can be obtained with the aid of tables.
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Psychrometer
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