Chapter 23Chapter 23The AtmosphereThe Atmosphere

Section 1Section 1

Characteristics of AtmosphereCharacteristics of Atmosphere

Notes 23-2Notes 23-2

Atmospheric PressureAtmospheric Pressure

Gravity holds the atmosphere next to the Gravity holds the atmosphere next to the planetplanet– If the gravity were less, there would be no If the gravity were less, there would be no

atmosphereatmosphere– 99% of the total mass of atmosphere is within 99% of the total mass of atmosphere is within

32 km of the surface32 km of the surface– The last 1% spreads upward and becomes very The last 1% spreads upward and becomes very

thin until you reach spacethin until you reach space

Atmospheric PressureAtmospheric Pressure

Ratio of the force of the air to the area of the Ratio of the force of the air to the area of the surface on which it pressessurface on which it presses– Less air at high altitudes means lower Less air at high altitudes means lower

atmospheric pressures at high altitudesatmospheric pressures at high altitudes– When air pressure changes, it causes a When air pressure changes, it causes a

popping sensation in your earpopping sensation in your ear Once the pressure is equal the popping stopsOnce the pressure is equal the popping stops Happens when in an airplane or travel to higher Happens when in an airplane or travel to higher

altitudes in a caraltitudes in a car

BarometersBarometers

Instrument that measures atmospheric Instrument that measures atmospheric pressurepressure– Mercurial Barometer:Mercurial Barometer:

Atmospheric pressure pushes on the liquid mercury Atmospheric pressure pushes on the liquid mercury in a well at the base of the barometerin a well at the base of the barometer

Pressure squeezes the mercury up a tubePressure squeezes the mercury up a tube The tube is marked with readingsThe tube is marked with readings The higher the mercury, the higher the atmospheric The higher the mercury, the higher the atmospheric

pressurepressure

BarometersBarometers

Expressed in how high the mercury risesExpressed in how high the mercury rises Standard atmospheric pressure = 760 mmStandard atmospheric pressure = 760 mm

– Equal to one atmosphereEqual to one atmosphere– Average atmospheric pressure at sea level is Average atmospheric pressure at sea level is

one atmosphereone atmosphere

Millibars (mb) are also usedMillibars (mb) are also used– 1 mb = 0.001 standard atmospheric pressure1 mb = 0.001 standard atmospheric pressure

BarometersBarometers

Aneroid Barometers:Aneroid Barometers:– Aneroid means without liquidAneroid means without liquid– Sealed metal container with a vacuum insideSealed metal container with a vacuum inside

As pressure increases the sides push inAs pressure increases the sides push in As pressure decreases the side pop outAs pressure decreases the side pop out

– The changes is marked by a moving pointer The changes is marked by a moving pointer along a scalealong a scale Scale can be marked in mm, inches or mbScale can be marked in mm, inches or mb

– Also called an altimeterAlso called an altimeter Measures altitude above sea levelMeasures altitude above sea level

Layers of AtmosphereLayers of Atmosphere

As altitude increases, As altitude increases, pressure decreases at pressure decreases at a constant ratea constant rate– Pressure changes don’t Pressure changes don’t

distinguish the different distinguish the different layers of the layers of the atmosphereatmosphere

– Temperature changes Temperature changes do separate the do separate the atmosphere into layersatmosphere into layers

TroposphereTroposphere

Layer closest to the earthLayer closest to the earth Troposphere comes from the Greek word Troposphere comes from the Greek word

that means “change”that means “change” This is where all weather occursThis is where all weather occurs

– Almost all water vapor and carbon dioxide is Almost all water vapor and carbon dioxide is found in this layerfound in this layer

Temperature decreases as altitude Temperature decreases as altitude increasesincreases– Decreases at a rate of 6.5Decreases at a rate of 6.5°C/km°C/km

TroposphereTroposphere

Tropopause:Tropopause:– Zone between the troposphere and the next Zone between the troposphere and the next

layer; upper boundary of tropospherelayer; upper boundary of troposphere– Temperature remains constantTemperature remains constant– Altitude on this boundary changes according to Altitude on this boundary changes according to

latitude and time of yearlatitude and time of year Equator = 17 kmEquator = 17 km Poles = 6-8 kmPoles = 6-8 km

StratosphereStratosphere Second layer of the atmosphereSecond layer of the atmosphere

– Extends from the troposphere to 50 km above Extends from the troposphere to 50 km above the surfacethe surface

Ozone layer is found hereOzone layer is found here At the bottom of the layer the temperature is At the bottom of the layer the temperature is

about -60about -60°C°C– Temperature increases as altitude increases in Temperature increases as altitude increases in

this layerthis layer– Caused by the absorption of solar energy by the Caused by the absorption of solar energy by the

ozone layerozone layer

StratosphereStratosphere

Stratopause:Stratopause:– High temperature zone between the High temperature zone between the

stratosphere and next layer; upper boundary of stratosphere and next layer; upper boundary of stratospherestratosphere

– Highest temperature is around 0Highest temperature is around 0°C - freezing°C - freezing

MesosphereMesosphere

Layer that extends from the stratosphere to Layer that extends from the stratosphere to 80 km above the surface80 km above the surface

Temperature decreases as the altitude Temperature decreases as the altitude increasesincreases– Coldest layer in the atmosphereColdest layer in the atmosphere– Drops to -90Drops to -90°C°C

Mesopause: Mesopause: – Upper boundary of mesosphere Upper boundary of mesosphere – temperature begins to increasetemperature begins to increase

ThermosphereThermosphere

Layer above the mesopauseLayer above the mesopause Temperature increases steadily with altitudeTemperature increases steadily with altitude

– Nitrogen and oxygen atoms absorb solar energyNitrogen and oxygen atoms absorb solar energy

Very thin layerVery thin layer– Thermometer can not accurately measure Thermometer can not accurately measure

temperaturetemperature– Special instruments are needed to determine Special instruments are needed to determine

the temperaturethe temperature Temperatures of more than 2000Temperatures of more than 2000°C have been °C have been

recordedrecorded

ThermosphereThermosphere

To figure out temperatureTo figure out temperature– Scientists find densityScientists find density

Determined by how much drag is on satellitesDetermined by how much drag is on satellites

– Use density to find temperatureUse density to find temperature Ionosphere:Ionosphere:

– Around 80 km to 550 kmAround 80 km to 550 km– Solar rays are absorbed and cause gas Solar rays are absorbed and cause gas

molecules to lose electronsmolecules to lose electrons Creates ionsCreates ions Ion can reflect radio waves back to earthIon can reflect radio waves back to earth Changes altitude depending on time of dayChanges altitude depending on time of day

ThermosphereThermosphere

Exosphere:Exosphere:– Extends for thousands Extends for thousands

of kmof km– Where the earth’s Where the earth’s

atmosphere blends into atmosphere blends into spacespace