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Unformatted text preview: ts) crystals Humidity Humidity: Humidity: The amount of water vapor present in the air present Several methods in which water-vapor Several content can be expressed: content 1) mixing ratio 1) 2) relative humidity 2) 3) dew point temperature 3) Saturation Saturation Saturation: Saturation: The maximum quantity of water vapor that the air can hold at any given temperature and pressure given During saturation, the number of water During vapor molecules returning to the surface will equal to the number of water molecules leaving the surface Mixing ratio Mixing Mixing Mixing ratio: The mass of water vapor in a unit of air compared to the remaining mass of dry air mass Mixing ratio is not affected by changes in Mixing temperature and pressure temperature Mixing ratio is not easy to measure by Mixing direct sampling Relative humidity Relative Relative Relative humidity is the ratio of the air’s actual water-vapor content to its potential water vapor capacity at a given temperature temperature If relative humidity is 100%, the air is If saturated saturated Relative humidity (cont.) Relative Relative Relative humidity can be changed one of two ways: 1) Add or remove water vapor from the air from 2) change the temperature of the air the Dew-point temperature Dew-point Dew Dew point temperature (also called the dew point): The temperature in which air has to be cooled to reach saturation has When air is cooled below its dew point, When some of the water vapor condenses to form clouds form Since Since dew point is the temperature at which saturation occurs, high dew point temperatures indicate moist air, whereas low dew point temperatures indicate dry air air Measuring humidity Measuring Humidity Humidity can be measured using a hygrometer hygrometer A hygrometer consists of two parts: 1) hygrometer dry bulb, which gives the present air temperature 2) wet bulb, which aids in determining the humidity determining NOTE: If the wet-bulb and the dry bulb NOTE: temperatures are the same, the humidity is 100% is When When air in the atmosphere is cooled below, some of the water vapor condenses to form clouds condenses When moist air rises, it cools and forms When clouds clouds Cloud formation Cloud Clouds: Clouds: visible aggregates of minute droplets of...
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- Fall '10