the atmosphere: composition and structure
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THE ATMOSPHERE:THE ATMOSPHERE:
COMPOSITION ANDCOMPOSITION AND
STRUCTURESTRUCTURE
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The AtmosphereThe Atmosphere
The atmosphere is the envelope of gases thatThe atmosphere is the envelope of gases thatsurround our planetsurround our planet
It is a very thin layer compared to the radius ofIt is a very thin layer compared to the radius ofthe Earththe Earth
We refer to this layer informally as airWe refer to this layer informally as air
The majority of the energy that drives theThe majority of the energy that drives theatmosphere is from the Sun.atmosphere is from the Sun.
The atmosphere receives most of this energyThe atmosphere receives most of this energy
from the surface.from the surface. Imbalances of energy drive the winds.Imbalances of energy drive the winds.
Eventually, all energy degrades down to friction.Eventually, all energy degrades down to friction.
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Origin of the AtmosphereOrigin of the Atmosphere
Volcanoes release HVolcanoes release H22, CO, CO22, H, H22OOvv, N, N22, NH, NH33,,CHCH44
No ONo O22 or Oor O33, so no land organisms!, so no land organisms!
OneOne--celled aquatic organisms release COcelled aquatic organisms release CO22to atmosphere when breaking down foodto atmosphere when breaking down foodthrough fermentationthrough fermentation
Simple aquatic plants took in COSimple aquatic plants took in CO22 andandreleased Oreleased O22 to atmosphere viato atmosphere viaphotosynthesisphotosynthesis
OO33 formed from the Oformed from the O22
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State of the AtmosphereState of the Atmosphere
We commonly express the state of theWe commonly express the state of theatmosphere by measuring it using theatmosphere by measuring it using thefollowing variables:following variables:
PressurePressure
TemperatureTemperature
WindWind
HumidityHumidity
Cloud coverCloud cover
Precipitation type and amountPrecipitation type and amount
Visibility (distance one can see horizontally)Visibility (distance one can see horizontally)
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Types of MeasurementsTypes of Measurements
Contact MeasurementsContact Measurements Also calledAlso calledinin--situ measurements; Asitu measurements; Ameasurement that is conducted bymeasurement that is conducted by
sticking a probe into the mediumsticking a probe into the mediumbeing measured (thermometer).being measured (thermometer).
Remote SensingRemote Sensing A measurementA measurement
conducted by remote means and notconducted by remote means and notfrom directly within the mediumfrom directly within the mediumbeing measured (satellites).being measured (satellites).
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The Relationship Between AirThe Relationship Between Air
Pressure and AltitudePressure and Altitude Pressure decreasesPressure decreases
as you go up inas you go up inheight.height.
The change inThe change inpressure is notpressure is notconstant. Theconstant. Thepressure decreasespressure decreasesexponentiallyexponentially withwithincreasing height.increasing height.
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Pressure & DensityPressure & Density
Gravity pullsGravity pullsgases towardgases toward
earth's surface,earth's surface,
and the wholeand the whole
column of gasescolumn of gases
exerts a pressureexerts a pressure
of 1000of 1000
hectopascalhectopascal((hPahPa) at sea level.) at sea level.
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Pressure and DensityPressure and Density
Decrease with HeightDecrease with Height
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WeatherWeather
Weather is the state of theWeather is the state of theatmosphere at a particular time andatmosphere at a particular time and
a particular place.a particular place. An example of weather informationAn example of weather information
would be the temperature in Manilawould be the temperature in Manilatoday at 7 p.m.today at 7 p.m.
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ClimateClimate
Climate is the longClimate is the long--term state of theterm state of theatmosphere at a particular location.atmosphere at a particular location.
Can be expressed as averages andCan be expressed as averages and
extremes.extremes. Normal conditions is simply a 30Normal conditions is simply a 30--yearyear
average of that particular variable.average of that particular variable.
Examples of climate information would be:Examples of climate information would be:
The normal high in Palawan on August 1 is 83The normal high in Palawan on August 1 is 83degrees.degrees.
The record amount of precipitation in PalawanThe record amount of precipitation in Palawanon August 1 is 2.55 inches back in 1961.on August 1 is 2.55 inches back in 1961.
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More DefinitionsMore Definitions
Meteorology is the study of theMeteorology is the study of theEarths atmosphere, its motions andEarths atmosphere, its motions andbehaviorbehavior
Climatology is the study of theClimatology is the study of theEarths climate, its past and futureEarths climate, its past and future
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Atmospheric CompositionAtmospheric Composition
Dry air (neglecting water vapor) isDry air (neglecting water vapor) iscomposed of the following gases:composed of the following gases:
Nitrogen (NNitrogen (N22)) = 78%= 78%
Oxygen (OOxygen (O22)) = 21%= 21%
Argon (Ar)Argon (Ar) = 1%= 1%
Trace GasesTrace GasesDust, bacteria, and other particulatesDust, bacteria, and other particulates
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Atmospheric MoleculesAtmospheric Molecules
Note that the Oxygen, Nitrogen, andNote that the Oxygen, Nitrogen, andHydrogen that we breathe are notHydrogen that we breathe are notsingle atoms of that gas, but insteadsingle atoms of that gas, but insteadare two atoms of that gas bondedare two atoms of that gas bondedtogether in what is called a diatomictogether in what is called a diatomicmolecule.molecule.
Ozone is an example of a triatomicOzone is an example of a triatomicmolecule with three oxygen atoms.molecule with three oxygen atoms.
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Atmospheric CompositionAtmospheric Composition
The dry air components in the air are wellThe dry air components in the air are well--mixed, meaning they do not vary widelymixed, meaning they do not vary widelywith location or time at the surface.with location or time at the surface.
Water vapor (HWater vapor (H22O) is a variable gas. YouO) is a variable gas. Youwill see it depends on temperature andwill see it depends on temperature andthe availability of liquid water. A volumethe availability of liquid water. A volume
of air can have between 0% and 4% waterof air can have between 0% and 4% watervapor, and this varies both in time andvapor, and this varies both in time andspace.space.
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Vertical Layers of the AtmosphereVertical Layers of the Atmosphere
The Earths atmosphere has 4 distinctThe Earths atmosphere has 4 distinctlayers that are identified by the waylayers that are identified by the waytemperature changes with height.temperature changes with height.These layers are:These layers are:
-- TroposphereTroposphere
-- StratosphereStratosphere
-- MesosphereMesosphere
-- ThermosphereThermosphere
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Atmospheric LayersAtmospheric Layers
8 layers are8 layers are
defined bydefined by
constant trendsconstant trends
in average airin average airtemperaturetemperature
(which changes(which changes
with pressurewith pressure
and radiation),and radiation),
where the outerwhere the outerexosphere isexosphere is
not shown.not shown.
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TroposphereTroposphere
This is the layer closest to the EarthsThis is the layer closest to the Earthssurfacesurface
Almost all the weather phenomenonAlmost all the weather phenomenonwe know of occurs in this layer.we know of occurs in this layer.
The depth of the troposphere variesThe depth of the troposphere variesby the season (deeper in summer)by the season (deeper in summer)
Temperature on average decreasesTemperature on average decreaseswith height.with height.
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StratosphereStratosphere
The next layer above the troposphereThe next layer above the troposphere
The boundary between the stratosphereThe boundary between the stratosphereand troposphere is called the tropopause.and troposphere is called the tropopause.
The ozone layer is found hereThe ozone layer is found here
Some clouds can form here near the polesSome clouds can form here near the poles
Temperature increases with heightTemperature increases with height
Very little mixing occurs between theVery little mixing occurs between thetroposphere and stratosphere.troposphere and stratosphere.
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Mesosphere/ThermosphereMesosphere/Thermosphere
The mesosphere is the next layer above theThe mesosphere is the next layer above thestratosphere.stratosphere.
Clouds (noctilucent) are rare in the mesosphere.Clouds (noctilucent) are rare in the mesosphere.
The thermosphere rests above the mesosphere,The thermosphere rests above the mesosphere,and no clouds exist.and no clouds exist.
Temperature decreases with height in theTemperature decreases with height in themesosphere and increases with height in themesosphere and increases with height in thethermosphere.thermosphere.
The highest temperatures for the atmosphereThe highest temperatures for the atmosphereoccur in the thermosphere, but it doesnt feel hotoccur in the thermosphere, but it doesnt feel hotbecause the atmosphere is so thin up there.because the atmosphere is so thin up there.
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Atmospheric DensityAtmospheric Density
Density and pressure in theDensity and pressure in theatmosphere decrease exponentiallyatmosphere decrease exponentiallywith heightwith height
Approximately 75% of the totalApproximately 75% of the totalatmosphere is in the troposphereatmosphere is in the troposphere
Approximately 99% of theApproximately 99% of theatmosphere is the troposphere andatmosphere is the troposphere andstratospherestratosphere
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Biogeochemical CyclesBiogeochemical Cycles
The following are contributoriesThe following are contributoriesto the composition of theto the composition of the
atmosphere:atmosphere: Nitrogen CycleNitrogen Cycle
Carbon Dioxide CycleCarbon Dioxide Cycle
Oxygen CycleOxygen Cycle
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Nitrogen CycleNitrogen Cycle
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Carbon CycleCarbon Cycle
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Oxygen CycleOxygen Cycle
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Heat Transfers in the AtmosphereHeat Transfers in the Atmosphere
Heat transfersHeat transfersfrom high tofrom high tolow temps.low temps.
There areThere arethree means:three means:
ConductionConduction
ConvectionConvection RadiationRadiation
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Heat TransferHeat Transfer -- ConductionConduction
Conduction occurs whenConduction occurs whenheat is transferredheat is transferredmolecule to moleculemolecule to molecule
Solids including wet soilSolids including wet soil
are good conductorsare good conductors CalmCalm air is a poorair is a poor
conductor; the heat hardlyconductor; the heat hardlytravels by conduction a fewtravels by conduction a fewcentimeters from surfacecentimeters from surfacein into the atmosphere.in into the atmosphere.
But we know heat fromBut we know heat fromsurface can reachsurface can reachkilometers high.kilometers high.
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Heat TransferHeat Transfer -- ConvectionConvection
It is because the atmosphere is seldomIt is because the atmosphere is seldomcalm; rather it often moves up and down.calm; rather it often moves up and down.
Mass movement in vertical caries heatMass movement in vertical caries heatwith itwith it
Heated air is less dense, expands, andHeated air is less dense, expands, andrisesrises starts thermals.starts thermals.
Cooler, denser air sinks to replace warmCooler, denser air sinks to replace warmairair completes convective cycle.completes convective cycle.
This vertical heat transfer is known asThis vertical heat transfer is known asconvection.convection.
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RadiationRadiation
What is radiation? It is the energy inWhat is radiation? It is the energy intransient and is also called radiant energy.transient and is also called radiant energy.
Recall we also said radiation is a meansRecall we also said radiation is a means
of energy transfer in parallel toof energy transfer in parallel toconduction and convection.conduction and convection.
Radiation is also viewed as stream ofRadiation is also viewed as stream ofparticle called photons that carries energy.particle called photons that carries energy.
As a means of transfer, radiation travels inAs a means of transfer, radiation travels inelectromagnetic waves.electromagnetic waves.