MoleculesEverything is made of moleculesA larger volume of air will contain more molecules and will thus weigh moreHow much does air weigh?Imagine square columns of air 1 inch on each side, extending from the surface all the way to the top of the atmosphere. Thy weight of the column depends on how many air molecules are in that column.Atmospheric PressureAt the surface there are the most molecules above youGreatest weightGreatest pressureAs you go up through the atmosphere, there are less and less molecules above you, so weight of column above that level decreasesPressure=Weight/AreaPressure=Force/AreaPressure always decreases with heightPressure change with altitude: 1mb per 10 m (only near surfaceGo up 850 m (2800 ft, about half a mile) and average pressure is same as the eyes of Hurricane Katrina at landfallWeighs less because less of the atmosphere is above youMeasuring PressureUse barometerUnits:Milibars (mb)Pounds per square inch (lb/in^2)Inches of mercury (inHg)Mean sea-level pressure1013.25 mb29.92 in Hg14.7 lb/in^2Meteorologists must correct pressure to sea level to remove this variability in order to get a clear picture of the weatherPressure difference due to weather: varies, but typically 30 mb or so across the USPressure difference due to elevation: Constant; About 300 mb between sea level and highest mountainsDensityGravity pulls most air molecules closest to surfaceDensity=Mass/volumeUnits are kg/m^3Density always decreases with height (like pressure)Surface Weather MapLower pressure generally means a stronger stormMore molecules above highsFewer molecules above lowsOn weather maps, pressures typically around 1000 mbAtmospheric TemperatureWe use temperature to divide the atmosphere into vertical layersLapse rate: the rate at which temperature decreases with heightInversion: layer in which the temperature increases with heightTroposphereLowest layer (8-12 km deep) of the atmosphereContains all the earth’s weatherTemperature usually (but not always) decreases with heightSun heats ground, ground heats airAtmospheric Soundings (Rawinsondes) cover only the troposphere/ and lower stratosphereTropopauseTropopause arks the top of the troposphereAprox 8-12 km highActs as a lid on weatherInversion very stableLevel of jet streamDifficult to breathe because the air is so thinStratosphereTemperature increases with height (inversion layer)Ozone layerOzone absorbs UV radiation, warming the stratosphereIf you looked up from the stratosphere, you would see black space not blue skyStratopause marks the top of the stratosphereMesophereName means “middle atmosphere”Temp decreases with heightLack of ozoneAir very thinLess than 0.1% of surface pressureMesopause marks the top of the mesosphereColdest temps in the atmosphereThermosphereTemp increases with heightOxygen absorbs gamma rays and cosmic raysAir is very thinAir molecules can travel 1 km before colliding with another moleculeYou will freeze regardless of temperatureHigh energy particles from space strike air molecules, creating aurora borealis (Northern Lights)SoundingsData is collected because conditions in the upper atmosphere determine surface weatherCan also determine where clouds are located in the atmosphereRawinsondesCan rise up to 20 miles into the atmosphereMay gbecome 20-25 ft in diameter95 stations in the UD900 stations worldwideData collected only twice a day: at 00z and 12zDewpoint Depression: difference in degrees Celsius between the air temperature and the dewpoint temperatureDPD=temp-dewptIf DPD is 2 deg C or less, a cloud is presentTemperature Inversion: increase in temperature with increasing altitudeLocating tropopauseTemperature starts to increase with increasing heightShould be at around 300 mb or higher in the atmosphere (smaller pressure)Vertical Structure Pressure 09/06/2012Molecules-Everything is made of molecules-A larger volume of air will contain more molecules and will thus weigh more-How much does air weigh?oImagine square columns of air 1 inch on each side, extending from the surface all the way to the top of the atmosphere. Thy weight of the column depends on how many air molecules are in that column.Atmospheric Pressure-At the surface there are the most molecules above youoGreatest weightoGreatest pressure-As you go up through the atmosphere, there are less and less molecules above you, so weight of column above that level decreases-Pressure=Weight/Area-Pressure=Force/Area-Pressure always decreases with heightoPressure change with altitude: 1mb per 10 m (only near surfaceoGo up 850 m (2800 ft, about half a mile) and average pressure is same as the eyes of Hurricane Katrina at landfallWeighs less because less of the atmosphere is above you-Measuring PressureoUse barometeroUnits:Milibars (mb)Pounds per square inch (lb/in^2)Inches of mercury (inHg)oMean sea-level pressure1013.25 mb29.92 in Hg14.7 lb/in^2-Meteorologists must correct pressure to sea level to remove this variabilityin order to get a clear picture of the weather-Pressure difference due to weather: varies, but typically 30 mb or so across the US-Pressure difference due to elevation: Constant; About 300 mb between sea level and highest mountainsDensity-Gravity pulls most air molecules closest to surface-Density=Mass/volume-Units are kg/m^3-Density always decreases with height (like pressure)Surface Weather Map-Lower pressure generally means a stronger storm-More molecules above highs-Fewer molecules above lows-On weather maps, pressures typically around 1000 mbAtmospheric Temperature-We use temperature to divide the atmosphere into vertical layers-Lapse rate: the rate at which temperature decreases with height-Inversion: layer in which the temperature increases with heightTroposphere-Lowest layer (8-12 km deep) of the atmosphere-Contains all the earth’s weather-Temperature usually (but not always) decreases with heightoSun heats ground, ground heats air-Atmospheric Soundings (Rawinsondes) cover only the troposphere/ and lower stratosphereTropopause-Tropopause arks the top of the troposphere-Aprox 8-12 km high-Acts as a lid on weatheroInversion very stable-Level of jet stream-Difficult to breathe because the air is so thinStratosphere-Temperature increases with height (inversion layer)-Ozone layeroOzone absorbs UV radiation, warming the stratosphere-If you looked up from the stratosphere, you would see