Lecture 6Outline of Last Lecture I. Earth’s OrbitII. Earth’s AxisIII. The SeasonsIV. Angle of SunV. Seasonal TemperatureVI. Controls of TemperatureVII. Daily High TemperaturesVIII. Nocturnal CoolingIX.The Role of CloudsOutline of Current Lecture X. Water Vapor in the AtmosphereXI. HumidityXII. EvaporationXIII. CondensationXIV. SaturationXV. ConclusionXVI. Increasing TemperatureXVII. Decreasing TemperatureXVIII. Atmospheric HumidityXIX. Vapor PressureXX. Saturation Vapor PressureATMS 100 1st EditionXXI. Relative HumidityXXII. Changing Relative HumidityXXIII. Dew Point TemperatureCurrent LectureXXIV. Water Vapor in the Atmospherea. water vapor is the most important atmospheric gas to weather changesi. rain, snow, and clouds are all forms of water in the atmos-phereii. concentration variable between 0-4% of airiii. greenhouse gasXXV. Humiditya. measure of water vapor in the atmospherei. doesn’t only mean relative humidityb. there are many ways to measure atmospheric moistureXXVI. Evaporationa. liquid water molecules break bonds with other water molecules and become gasi. water absorbs latent heatii. cools surroundingsXXVII. CondensationThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.a. water vapor molecules form bonds with other water molecules and become liquidi. releases latent heatii. warms surroundingsXXVIII. Evaporation and Condensationa. water molecules continuously transition between liquid and gaseous states at the surface of liquid waterb. if more molecules evaporate than condense, water vapor con-centration in air increasesc. if more molecules condense than evaporate, water vapor con-centration in air decreasesXXIX. Saturationa. saturation: water vapor concentration in the air at which evapo-ration and condensation are equalb. air is never so “full of water” that there is no room for any morec. air is not a spongeXXX. Conclusiona. wind increases evaporationXXXI. Increasing Temperaturea. assume saturationb. if the temperature increases, the evaporation rate increasesi. liquid molecules move faster at higher temperatures and become more likely to escape from liquid and become gasc. evaporation > condensationi. water vapor concentration increasesd. condensation rate also increases because there is more water in the aire. warmer air becomes saturated at higher water vapor con-centration than does colder airXXXII. Decrease Temperaturea. Assume saturationb. if we decrease the temperature, the condensation rate in-creasesi. water vapor molecules move slower, more likely to “stick” to the water surface and become liquidXXXIII. Atmospheric Humiditya. How to measure water vapor in the atmosphere:i. vapor pressureii. relative humidityiii. dew point temperatureXXXIV. Vapor Pressure (VP)a. every gas in a mixture of gases contributes to total pressureb. water vapor is a small fraction (<4%) of air, so the pressure ex-erted by the water vapor is a small fraction of total pressurei. called vapor pressure (unit: pressure, mb)c. more water vapor air the air yields a greater vapor pressureXXXV. Saturation Vapor Pressure (SVP)a. saturation vapor pressure is the vapor pressure required to satu-rate the airi. warm air contains more water vapor at saturation than coldairii. it takes more water vapor to saturate at higher tempera-turesiii. SVP increases with temperatureb. SVP does not measure the actual amount of water vapor in the airi. it tells us how much water vapor the air needs to saturate the airXXXVI. Relative Humiditya. ratio of water vapor in air required for saturationb. rh does not indicate actual amount of water vapor in airi. higher rh does not necessarily mean there is more moisture in the airii. higher rh means air is closer to saturationc. called relative humidity because it is relative to temperatured. at saturation, rh=100%XXXVII. Changing the Relative Humiditya. increase:i. add moisture to air (increase VP)ii. cool air (decrease SVP)b. Decrease:i. remove moisture from the air (decrease VP)ii. warm the air (increase SVP)XXXVIII. Dew point Temperaturea. we can saturate the air in two ways:i. add water to the air (while keeping temperature constant)ii. cool the air (while keeping moisture constant)b. if we cool the air while keeping moisture constant, the tempera-ture at which that occurs is called dew pointc. most common in the early morningd. at higher dew point always means there is more moisture in the aire. always less than or equal to temperaturef. increase dewpoint, increase VPXXXIX. Dew and Frosta. surface emits IR radiation (always)i. cools rapidly, especially on clear calm nightsii. air above surface cools via conductionb. if surface cools below dew point of air, get condensation on the surfacei. like on a cold glass in summerc. frost forms if surface cools below freezingd. dew and frost more likely on clear, calm nightsi. nocturnal cooling maximizedXL. Humidity and Densitya. moist air is less dense than dry airb. moist air doesn't not contain more molecules than dry air at the same