The Earth’s Atmosphere Overview of the Earth’s atmosphere Overview of the Earth’s atmosphere Other planetary atmospheres Other planetary atmospheres Vertical

The Earth’s The Earth’s AtmosphereAtmosphere

Overview of the Earth’s atmosphereOverview of the Earth’s atmosphere Other planetary atmospheresOther planetary atmospheres Vertical structure of the Vertical structure of the

atmosphereatmosphere Weather and climateWeather and climate

Overview of the Overview of the Earth’s Earth’s

AtmosphereAtmosphere• The atmosphere, when scaled to the size of an

apple, is no thicker than the skin on an apple.

• The atmosphere is a gas.

• The atmosphere is a fluid.

• There is a surface but no “top” – the atmosphere gradually thins out with increasing altitude

Composition of the Composition of the AtmosphereAtmosphere

permanent gasespermanent gases

variable gasesvariable gases

trace gasestrace gases

aerosolsaerosols

• roles of nitrogen, oxygen and argonroles of nitrogen, oxygen and argon

• role of water vaporrole of water vapor

• carbon dioxide, methane, ozone, CFCs, et al.carbon dioxide, methane, ozone, CFCs, et al.


The “dry atmosphere”: The “dry atmosphere”: 78% N78% N22, 21% O, 21% O22, , 1% Ar1% Ar

• NN22 is primordial – it’s been part of the is primordial – it’s been part of the atmosphere as long as there’s been an atmosphere as long as there’s been an atmosphereatmosphere

• OO22 has been rising from none at all about has been rising from none at all about 2.2 Gya – comes from photosynthesis2.2 Gya – comes from photosynthesis

• ArAr4040/Ar/Ar3636 tells us that the atmosphere has tells us that the atmosphere has been outgassed from volcanoesbeen outgassed from volcanoes


Water Vapor: HWater Vapor: H22O 0-4%O 0-4%• HH220 can exist in all three phases at the surface 0 can exist in all three phases at the surface

of the Earth – solid, liquid and gasof the Earth – solid, liquid and gas• Liquid or solid HLiquid or solid H22O can be suspended by O can be suspended by

atmospheric winds (clouds) or fall to the atmospheric winds (clouds) or fall to the surface (precipitation)surface (precipitation)

• VERY powerful greenhouse gas (both in vapor VERY powerful greenhouse gas (both in vapor form and as clouds)form and as clouds)


The Hydrological CycleThe Hydrological Cycle

Table 1-1, p. 3


Carbon dioxideCarbon dioxide• 390 ppm (by mass) and counting…390 ppm (by mass) and counting…• Natural and anthropogenic sources/sinksNatural and anthropogenic sources/sinks• Strong Strong greenhouse gas (GHG)greenhouse gas (GHG)

COCO22 is neither the strongest atmospheric GHG pound-for- is neither the strongest atmospheric GHG pound-for-pound nor molecule-for-molecule…pound nor molecule-for-molecule…

Why the fuss?Why the fuss?

COCO22 is a product of the reaction that allows modern is a product of the reaction that allows modern civilization to exist: combustion.civilization to exist: combustion.

Fig. 1-4, p. 5


The Global Carbon CycleThe Global Carbon Cycle


MethaneMethane• CHCH44 concentration: 1.8 ppmv concentration: 1.8 ppmv• anthropogenic and natural sources/sinks anthropogenic and natural sources/sinks

tootoo• powerful greenhouse gaspowerful greenhouse gas• oxidizes rapidly, hence low oxidizes rapidly, hence low

concentrationsconcentrations• Large concentrations proposed to explain Large concentrations proposed to explain

greenhouse warming of early Earthgreenhouse warming of early Earth


Ozone, CFCs and NOOzone, CFCs and NOxx Ozone (OOzone (O33) )

• shields the surface from UV raysshields the surface from UV rays• produced by reaction with NOproduced by reaction with NOxx and sunlight near the and sunlight near the

surfacesurface CFC’s (Chlorofluorocarbons) CFC’s (Chlorofluorocarbons)

• destroy stratospheric ozonedestroy stratospheric ozone• chlorine is a catalyst: it destroys one Ochlorine is a catalyst: it destroys one O33 molecule molecule

and then is free to find another and then is free to find another • Ozone at high altitudes (stratosphere) is “good”;Ozone at high altitudes (stratosphere) is “good”;ozone at low altitudes (troposphere) is “bad.”ozone at low altitudes (troposphere) is “bad.”


AerosolsAerosols• DustDust• Sea-spraySea-spray• MicrobesMicrobes

Suspended particles in the atmosphere are Suspended particles in the atmosphere are responsible for cloud formation: water responsible for cloud formation: water drops nucleate on themdrops nucleate on them

Cloud Condensation Nuclei (CCN)Cloud Condensation Nuclei (CCN)

The Early AtmosphereThe Early Atmosphere

reduced primitive atmosphere(H, He, CHreduced primitive atmosphere(H, He, CH44, , NHNH33))

outgassing and the second atmosphere (Noutgassing and the second atmosphere (N22, , Ar – still no oxygen!)Ar – still no oxygen!)

The evolution of life and the atmosphere are The evolution of life and the atmosphere are closely linked – life produced the oxygen closely linked – life produced the oxygen (photosynthesis) and cycles the carbon ((photosynthesis) and cycles the carbon (e.g. e.g. limestone)limestone)

Oxidized modern atmosphere (NOxidized modern atmosphere (N22, O, O22, CO, CO22, , etc.etc.))

Other AtmospheresOther AtmospheresYES NO

Earth The Moon

Mars all the other satellites

Venus Mercury

Jupiter asteroids

Saturn

Uranus

Neptune

Pluto

Triton (Neptune’s moon)

Titan (Saturn’s moon)

The Sun

Other AtmospheresOther AtmospheresPlanet Composition Temperature Pressure

Venus CO2 96.5%, N2 3.5%

750 K 90000 mb

Earth N2 78%, O2 21%, Ar 1%

290K 1000 mb

Mars CO2 95%, N2 2.7%, Ar 1.6%

220K 10 mb

Vertical Structure of Vertical Structure of the Earth’s the Earth’s AtmosphereAtmosphere

A Brief Look at Air A Brief Look at Air Pressure and Air DensityPressure and Air Density

air density (ρ pronounced “row”)air density (ρ pronounced “row”) air pressure (p)air pressure (p) sea-level pressure (psea-level pressure (pss))

• Baseballs travel farther in higher-altitude air (Denver)Baseballs travel farther in higher-altitude air (Denver)than they do in lower-altitude air.than they do in lower-altitude air.

Fig. 1-7, p. 8

Fig. 1-8, p. 9

Layers of the AtmosphereLayers of the Atmosphere

vertical temperature (T) profilevertical temperature (T) profile tropospheretroposphere stratospherestratosphere mesospheremesosphere thermospherethermosphere

• Temperatures, winds, Temperatures, winds, humidity and pressures high humidity and pressures high above the ground are above the ground are measured twice-daily by measured twice-daily by radiosonde.radiosonde.

Weather and Weather and ClimateClimate

(Chalkboard)(Chalkboard)

Elements of WeatherElements of Weather

air temperatureair temperature air pressureair pressure humidityhumidity cloudsclouds precipitationprecipitation visibilityvisibility windwind

• Certain weather elements, likeCertain weather elements, likeclouds, visibility and wind, areclouds, visibility and wind, areof particular interest to pilots.of particular interest to pilots.

ClimateClimate

average weatheraverage weather• time-averagetime-average• regional (spatial) averageregional (spatial) average

extremesextremes trendstrends

Weather Weather vs.vs. Climate Climate

Weather is Weather is the dynamical the dynamical way in which the way in which the

atmosphere maintains atmosphere maintains the equilibrium the equilibrium climate.climate.

A Satellite’s View of the A Satellite’s View of the WeatherWeather

geostationary satellitesgeostationary satellites• Atmospheric observation Atmospheric observation

from satellites was an from satellites was an important technological important technological development in development in meteorology. Othermeteorology. Otherimportant developments important developments include computers, internet, include computers, internet, and Doppler radar.and Doppler radar.

Storms of all SizesStorms of all Sizes

midlatitude cyclonic stormsmidlatitude cyclonic storms hurricanes and tropical stormshurricanes and tropical storms thunderstormsthunderstorms tornadoestornadoes

• Storms are very exciting, but they also play an Storms are very exciting, but they also play an important role in moving heat and moisture around important role in moving heat and moisture around throughout the atmosphere.throughout the atmosphere.

A Look at a Weather MapA Look at a Weather Map

wind speed and directionwind speed and direction cyclones and anticyclonescyclones and anticyclones frontsfronts

• Wind direction is defined in the opposite way asWind direction is defined in the opposite way asocean currents: a southerly current means water is ocean currents: a southerly current means water is moving moving towardstowards the south. the south.

Fig. 1-13, p. 17

Scientific NotationScientific Notation


Dimensional AnalysisDimensional Analysis


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The Earth’s Atmosphere Overview of the Earth’s atmosphere Overview of the Earth’s atmosphere Other planetary atmospheres Other planetary atmospheres Vertical