Chapter 2Chapter 2

Atmosphere: Origin, Atmosphere: Origin, Composition, and StructureComposition, and Structure

Weather StudiesWeather Studies Introduction to Atmospheric ScienceIntroduction to Atmospheric Science

American Meteorological SocietyAmerican Meteorological Society

Credit: This presentation was prepared for AMS by Michael Leach, Professor of Geography at New Mexico State University - Grants

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Case-in-PointCase-in-Point

Weather and climatic issues in one part of the world can Weather and climatic issues in one part of the world can affect those in another partaffect those in another part

North African dust storms can affect the weather and air North African dust storms can affect the weather and air quality of the southeastern U.S.quality of the southeastern U.S.

Dust can harbor microscopic disease-causing organismsDust can harbor microscopic disease-causing organisms This dust may be harming coral reefs in the CaribbeanThis dust may be harming coral reefs in the Caribbean This dust may increase the frequency of red tidesThis dust may increase the frequency of red tides

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Driving QuestionDriving Question What is the composition and structure of the What is the composition and structure of the

atmosphere?atmosphere?– This chapter covers:This chapter covers:

Evolution of the atmosphereEvolution of the atmosphere How meteorologists monitor the How meteorologists monitor the

atmosphereatmosphere– At the surfaceAt the surface– Upper-airUpper-air

The temperature profile of the atmosphereThe temperature profile of the atmosphere The thermal subdivisions of the atmosphereThe thermal subdivisions of the atmosphere Electromagnetic characteristics of the upper Electromagnetic characteristics of the upper

atmosphereatmosphere

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Atmosphere, Weather, and ClimateAtmosphere, Weather, and Climate AtmosphereAtmosphere

– Gases and suspended particlesGases and suspended particles– ½ of the mass is found in the lower 5500 m (18,000 ft)½ of the mass is found in the lower 5500 m (18,000 ft)– 99% of the mass is below 32 km (20 miles)99% of the mass is below 32 km (20 miles)

WeatherWeather– The state of the atmosphere at a given time and placeThe state of the atmosphere at a given time and place– Variables – temperature, humidity, cloudiness, Variables – temperature, humidity, cloudiness,

precipitation, wind speed, wind directionprecipitation, wind speed, wind direction ClimateClimate

– Weather conditions at a location over a specified time Weather conditions at a location over a specified time period plus weather extremes at that localeperiod plus weather extremes at that locale

– Computed over a 30 year period, beginning with the 1Computed over a 30 year period, beginning with the 1stst year of a decadeyear of a decade

Climatology is the study of climate, climate Climatology is the study of climate, climate controls, variability (change) over space & timecontrols, variability (change) over space & time

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Evolution of the AtmosphereEvolution of the Atmosphere Primeval phasePrimeval phase

– Gases surrounding Earth were primarily helium plus Gases surrounding Earth were primarily helium plus hydrogen compoundshydrogen compounds Methane and ammoniaMethane and ammonia Eventually, these escaped to spaceEventually, these escaped to space

– 4.4 billion years ago, there was enough gravity to retain 4.4 billion years ago, there was enough gravity to retain an atmospherean atmosphere

– Rocks outgassed as they solidified and cooledRocks outgassed as they solidified and cooled Primarily carbon dioxide, nitrogen, and water vaporPrimarily carbon dioxide, nitrogen, and water vapor Trace amounts – methane, ammonia, sulfur dioxideTrace amounts – methane, ammonia, sulfur dioxide

– Water vapor was broken into hydrogen and oxygen by Water vapor was broken into hydrogen and oxygen by UV radiationUV radiation

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Evolution of the AtmosphereEvolution of the Atmosphere Primeval phase, continuedPrimeval phase, continued

– 4.5 – 2.5 billion years ago, sun was much fainter4.5 – 2.5 billion years ago, sun was much fainter Earth was not cooler due to COEarth was not cooler due to CO22 (greenhouse gas) (greenhouse gas)

– COCO2 2 combined with rainwater to form carbonic acidcombined with rainwater to form carbonic acid This reacted with rocks, locked carbon in the rocks, so there This reacted with rocks, locked carbon in the rocks, so there

was less in the atmospherewas less in the atmosphere Living organisms took COLiving organisms took CO2 2 out of the atmosphere via out of the atmosphere via

photosynthesis, locking carbon into carbohydratesphotosynthesis, locking carbon into carbohydrates

– Oxygen became the 2Oxygen became the 2ndnd most abundant gas in the most abundant gas in the atmosphereatmosphere Nitrogen is 1Nitrogen is 1stst. It is an out-gassing product that is relatively inert. It is an out-gassing product that is relatively inert

– COCO22 has been a minor component of the atmosphere for has been a minor component of the atmosphere for

the last 2.5 billion yearsthe last 2.5 billion years Fluctuations play important roles in climate changeFluctuations play important roles in climate change

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Evolution of the AtmosphereEvolution of the Atmosphere Modern phaseModern phase

– Lower atmosphere (to 80 km or 50 miles) Lower atmosphere (to 80 km or 50 miles) circulates and maintains uniform ratios of circulates and maintains uniform ratios of gassesgasses HomosphereHomosphere

– Above this, gases separate based on weightAbove this, gases separate based on weight Results in stratified layersResults in stratified layers HeterosphereHeterosphere

– Nitrogen Nitrogen ≈ 78%, Oxygen ≈ 21% of the ≈ 78%, Oxygen ≈ 21% of the homospherehomosphere Argon < 1%Argon < 1% COCO22 < .04% < .04%

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Note – this deals with dry air. Water vapor varies greatly, and is not included in thetable

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Evolution of the AtmosphereEvolution of the Atmosphere Modern phase, continuedModern phase, continued OO22 in the homosphere in the homosphere O in the heterosphereO in the heterosphere

– 150 km (95 miles) above Earth’s surface150 km (95 miles) above Earth’s surface– UV radiation splits OUV radiation splits O22

Other planets’ atmospheres are much Other planets’ atmospheres are much differentdifferent

May have started the sameMay have started the same Earth’s atmosphere also has Earth’s atmosphere also has aerosolsaerosols

– Liquid and solid particlesLiquid and solid particles– Sources Sources

Wind erosion of soilWind erosion of soil ■ ■ Forest firesForest fires ■ ■ Ocean sprayOcean spray Volcanic eruptionsVolcanic eruptions ■■ Agricultural & industrial activities Agricultural & industrial activities

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Evolution of the AtmosphereEvolution of the Atmosphere Modern phase, continuedModern phase, continued

– Water vaporWater vapor By volume, < 4% of the lowest 1 km of the atmosphereBy volume, < 4% of the lowest 1 km of the atmosphere Necessary for clouds and precipitationNecessary for clouds and precipitation

– COCO22 – even though <.04%: – even though <.04%: Required for essential function to all life – photosynthesisRequired for essential function to all life – photosynthesis

– Both COBoth CO22 and water vapor absorb and emit infrared and water vapor absorb and emit infrared

radiationradiation Keeps the lower atmosphere warmKeeps the lower atmosphere warm Allows for life to existAllows for life to exist

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Air PollutionAir Pollution An air pollutant is an aerosol or gas that An air pollutant is an aerosol or gas that

occurs at a concentration that threatens the occurs at a concentration that threatens the well-being of living organismswell-being of living organisms– Most are human-made, some are naturalMost are human-made, some are natural

Dust storms, volcanoes, pollen, decay of Dust storms, volcanoes, pollen, decay of plants/animalsplants/animals

Primary air pollutantsPrimary air pollutants– Harmful immediately as emittedHarmful immediately as emitted

Secondary air pollutantsSecondary air pollutants– Harmful after combination with Harmful after combination with

one or more substancesone or more substances– Photochemical smogPhotochemical smog

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Air PollutionAir Pollution The Environmental Protection Agency (EPA)The Environmental Protection Agency (EPA)

– Standards for 6 air pollutantsStandards for 6 air pollutants carbon monoxidecarbon monoxide ■■ lead lead ■■ ozone ozone nitrogen oxidesnitrogen oxides ■■ particulates particulates ■■ sulfur dioxide sulfur dioxide

– Primary air quality standardsPrimary air quality standards Maximum exposure levels humans can tolerate without ill effectsMaximum exposure levels humans can tolerate without ill effects

– Secondary air quality standardsSecondary air quality standards Maximum exposure levels allowable to minimize the impact on crops, Maximum exposure levels allowable to minimize the impact on crops,

visibility, personal comfort, and climatevisibility, personal comfort, and climate

– Compliance with standardsCompliance with standards Attainment areas – geographic regions where standards are met or Attainment areas – geographic regions where standards are met or

belowbelow Non-attainment areas – geographic regions where the primary Non-attainment areas – geographic regions where the primary

standard is not metstandard is not met

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Investigating the AtmosphereInvestigating the Atmosphere

Scientists (including meteorologists) use the Scientists (including meteorologists) use the scientific methodscientific method– Identify questions related to the problemIdentify questions related to the problem– Propose an answer to one of the questionsPropose an answer to one of the questions

This is an educated guessThis is an educated guess– State the educated guess in a manner that can be State the educated guess in a manner that can be

testedtested This is the This is the hypothesishypothesis

– Predict the outcome as if the hypothesis were correctPredict the outcome as if the hypothesis were correct– Test the hypothesis to see if the prediction is correctTest the hypothesis to see if the prediction is correct– Reject or revise the hypothesis if the prediction is wrongReject or revise the hypothesis if the prediction is wrong

An hypothesis that stands the test of time is a An hypothesis that stands the test of time is a scientific theoryscientific theory

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Atmospheric modelsAtmospheric models Scientific models are approximations or Scientific models are approximations or

simulations of a real systemsimulations of a real system The Earth-atmosphere system can be The Earth-atmosphere system can be

scientifically modeledscientifically modeled– A conceptual model is an abstract idea that A conceptual model is an abstract idea that

represents some fundamental law or relationshiprepresents some fundamental law or relationship Example – the geostrophic wind modelExample – the geostrophic wind model

– A graphical model compiles and displays data in a A graphical model compiles and displays data in a format that readily conveys meaningformat that readily conveys meaning Example – a weather mapExample – a weather map

– A physical model is a miniaturized version of a A physical model is a miniaturized version of a systemsystem Example – a tornado vortex chamber – next slideExample – a tornado vortex chamber – next slide

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Tornado Vortex ChamberTornado Vortex Chamber

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Atmospheric ModelsAtmospheric Models Meteorologists today use numerical models Meteorologists today use numerical models

rather than physical modelsrather than physical models– Mathematical equations represent relationships Mathematical equations represent relationships

among system variablesamong system variables Example – a global climate model and rising COExample – a global climate model and rising CO22

All other climate variables are held constantAll other climate variables are held constant COCO22 is increased is increased

Results are notedResults are noted

– All have inherent errorsAll have inherent errors Accuracy of component equations may be a problemAccuracy of component equations may be a problem

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Monitoring the AtmosphereMonitoring the Atmosphere

Surface observationsSurface observations– Systematic observations in some areas as far Systematic observations in some areas as far

back as 1644-45 in North Americaback as 1644-45 in North America Old Swedes Fort (Wilmington, DE) had 1Old Swedes Fort (Wilmington, DE) had 1stst systematic systematic

observationsobservations

– Philadelphia began in 1731Philadelphia began in 1731– Charleston, SC – 1738Charleston, SC – 1738– Cambridge, MA – 1753Cambridge, MA – 1753– New Haven, CT – 1781 – uninterrupted to todayNew Haven, CT – 1781 – uninterrupted to today

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Monitoring the AtmosphereMonitoring the Atmosphere

Surface observations, continuedSurface observations, continued– Army monitored weather to compare with troop healthArmy monitored weather to compare with troop health– Mid-1800s – national network of volunteer observersMid-1800s – national network of volunteer observers– 1849 – telegraph companies transmitted weather 1849 – telegraph companies transmitted weather

conditions free of chargeconditions free of charge– 1860s – loss of ships in Great Lakes1860s – loss of ships in Great Lakes

Government took a greater role in forecastingGovernment took a greater role in forecasting

– 1870 – President Ulysses S. Grant established 24 1870 – President Ulysses S. Grant established 24 stations under the auspices of the U.S. Army Signal stations under the auspices of the U.S. Army Signal CorpsCorps

– 1891 – transferred from military to civilian hands1891 – transferred from military to civilian hands New weather bureau under U.S. Department of AgricultureNew weather bureau under U.S. Department of Agriculture

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Monitoring the AtmosphereMonitoring the Atmosphere

Surface observations, continuedSurface observations, continued– Transferred to Commerce Department in 1940Transferred to Commerce Department in 1940– 1965, Weather Bureau reorganized into the 1965, Weather Bureau reorganized into the

National Weather Service (NWS)National Weather Service (NWS) Under Environmental Science Services Under Environmental Science Services

Administration (ESSA), which became National Administration (ESSA), which became National Oceanic and Atmospheric Administration (NOAA)Oceanic and Atmospheric Administration (NOAA)

– 1990s – NWS modernized and expanded1990s – NWS modernized and expanded 122 NWS Forecast Offices (see next slide)122 NWS Forecast Offices (see next slide) Added Automated Surface Observing Systems Added Automated Surface Observing Systems

(ASOS)(ASOS)

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NWS Forecast OfficesNWS Forecast Offices

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Automated Surface Observing Automated Surface Observing System (ASOS)System (ASOS)

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Cooperative Observer NetworkCooperative Observer Network

The NWS also has The NWS also has a Cooperative a Cooperative Observer NetworkObserver Network– Member stations Member stations

record daily record daily precipitation and precipitation and max/min max/min temperatures for temperatures for hydrologic, hydrologic, agricultural, and agricultural, and climatic purposesclimatic purposes

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Upper Air ObservationsUpper Air Observations Kites were used early onKites were used early on

– 1749, Glasgow, Scotland, Alexander Wilson1749, Glasgow, Scotland, Alexander Wilson– 1752, Benjamin Franklin, demonstrated electrical nature of 1752, Benjamin Franklin, demonstrated electrical nature of

lightninglightning BalloonsBalloons

– Manned balloon, 1804, Gay-Lussac & BiotManned balloon, 1804, Gay-Lussac & Biot Air samples taken, measured temperature and humidity up to Air samples taken, measured temperature and humidity up to

7,000 m (23,000 ft)7,000 m (23,000 ft)

– Manned balloon, 1862, Glaisher & CoxwellManned balloon, 1862, Glaisher & Coxwell Weather measurements to 9000 m (29,500 ft)Weather measurements to 9000 m (29,500 ft) Nearly perished from cold and oxygen deprivationNearly perished from cold and oxygen deprivation

Kites carried the first Kites carried the first thermographthermograph aloft in 1894 aloft in 1894 1907-1933 – box kites with 1907-1933 – box kites with meteorographsmeteorographs, up to , up to

3000 m (10,000 ft)3000 m (10,000 ft)

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Upper Air ObservationsUpper Air Observations RadiosondesRadiosondes

– Invented in late 1920sInvented in late 1920s– Transmits altitude readings (soundings) of:Transmits altitude readings (soundings) of:

TemperatureTemperature ■■ Dewpoint Dewpoint ■■ Air pressure Air pressure

– Data is received immediatelyData is received immediately No need to recover equipmentNo need to recover equipment

– RawinsondeRawinsonde A radiosonde that is tracked by direction-finding antennasA radiosonde that is tracked by direction-finding antennas Provides data on wind direction and speedProvides data on wind direction and speed Dropwindsonde is not launched with a balloonDropwindsonde is not launched with a balloon

It is dropped from an aircraft on a parachuteIt is dropped from an aircraft on a parachute

– These devices are launched simultaneously worldwideThese devices are launched simultaneously worldwide Launched at 0000Z and 1200ZLaunched at 0000Z and 1200Z Only 20% of the devices are recoveredOnly 20% of the devices are recovered

2525A radiosondeLaunching aradiosonde

Graphic measurements of air temperature, pressure, & dew point up to about30,000 m (100,000 ft)

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Remote SensingRemote Sensing Measurement of Measurement of

environmental environmental conditions by conditions by processing signals processing signals that are either emitted that are either emitted by an object or by an object or reflected back to a reflected back to a signal sourcesignal source– RadarRadar– SatellitesSatellites

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Temperature Profile of the AtmosphereTemperature Profile of the Atmosphere TroposphereTroposphere

– Lowest layerLowest layer– Where almost all weather occursWhere almost all weather occurs– Temperature decreases with altitudeTemperature decreases with altitude

Generally, but with frequent exceptions (e.g., Generally, but with frequent exceptions (e.g., inversion, isothermal layer)inversion, isothermal layer)

Average temperature drop is 6.5 Average temperature drop is 6.5 °°CC/1000 m (3.5 /1000 m (3.5 °°FF/1000 ft) /1000 ft)

– ~ 6 km (3.7 mi) thick at the poles, ~20 km (12 ~ 6 km (3.7 mi) thick at the poles, ~20 km (12 mi) thick at the equatormi) thick at the equator

– Upper boundary/transition zone to next layer is Upper boundary/transition zone to next layer is called the tropopausecalled the tropopause

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Temperature Profile of the AtmosphereTemperature Profile of the Atmosphere StratosphereStratosphere

– Next higher levelNext higher level– Goes from troposphere up to ~ 50 km (30 mi)Goes from troposphere up to ~ 50 km (30 mi)– In lower stratosphere, temperature is constantIn lower stratosphere, temperature is constant

This is an This is an isothermalisothermal condition condition

– Above 20 km (12 mi), temperature increases with Above 20 km (12 mi), temperature increases with increasing altitudeincreasing altitude Stratosphere is warmed by the energy released by ozone Stratosphere is warmed by the energy released by ozone

absorbing UV radiationabsorbing UV radiation

– Stable conditions are ideal for jet aircraft travel, but can Stable conditions are ideal for jet aircraft travel, but can cause trapping of pollutants (e.g. from volcanic cause trapping of pollutants (e.g. from volcanic eruptions) in lower stratosphereeruptions) in lower stratosphere

– Upper boundary/transition zone to next layer is called Upper boundary/transition zone to next layer is called the stratopausethe stratopause

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Temperature Profile of the AtmosphereTemperature Profile of the Atmosphere MesosphereMesosphere

– Next higher levelNext higher level– Goes from stratopause up to about 80 km (50 mi)Goes from stratopause up to about 80 km (50 mi)– Temperature once again decreases with increasing Temperature once again decreases with increasing

altitude in this layeraltitude in this layer

ThermosphereThermosphere– Next higher levelNext higher level– Temperatures are isothermal (constant temperature Temperatures are isothermal (constant temperature

condition) in the lower thermospherecondition) in the lower thermosphere– Temperatures rise rapidly above thatTemperatures rise rapidly above that

Air temperature particularly sensitive to incoming solar radiationAir temperature particularly sensitive to incoming solar radiation Temperature is more variable than in another regionsTemperature is more variable than in another regions

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Air Air Temperature Temperature and Altitudinal and Altitudinal Relationships Relationships

in the in the AtmosphereAtmosphere

© American Meteorological Society

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The Ionosphere and the AuroraThe Ionosphere and the Aurora The ionosphere is located mostly in the The ionosphere is located mostly in the

thermospherethermosphere– High concentration of ions and electronsHigh concentration of ions and electrons

Electrically-charged atomic-scale particlesElectrically-charged atomic-scale particles Caused by solar energy stripping electrons from Caused by solar energy stripping electrons from

oxygen and nitrogen atoms and moleculesoxygen and nitrogen atoms and molecules– Leaves a positive chargeLeaves a positive charge

– Auroras are found in the ionosphereAuroras are found in the ionosphere Caused by solar windCaused by solar wind

– Sub-atomic, super-hot, electrically charged particlesSub-atomic, super-hot, electrically charged particles Earth’s magnetic field deflects the solar windEarth’s magnetic field deflects the solar wind

– Makes a teardrop-shaped cavity known as the Makes a teardrop-shaped cavity known as the magnetospheremagnetosphere

Auroras are only visible at the higher latitudesAuroras are only visible at the higher latitudes

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Aurora Borealis (Northern Lights)In southern hemisphere,it is called AuroraAustralis

Earth’s magnetic fielddeflects the solar windand forms the teardrop-shaped magnetosphere