APES U2 L3 atmosphere

AP Environmental

ScienceUnit 2

Part 3: The Atmosphere

Past and Present Atmospheric Past and Present Atmospheric CompositionComposition

• Hydrogen and helium were the primary components of the earliest atmosphere

• H and He lost to outer space and replaced by:– Volcanic emissions have added carbon, nitrogen,

oxygen, and sulfur– Oxygen - majority produced by photosynthesis

• Modern atmosphere:N2 78% He 0.0005%

O2 21% CH4 0.00015%

Ar 0.9% H2 0.00005%

CO2 0.03% H2O 0-4%

TroposphereTroposphere• Ranges in depth from 18 km over the equator to

8.0 km over the poles (Troposphere diagram)• All weather occurs here• Composition is relatively uniform; this layer is well

mixed across the planet• Air temperature drops rapidly with increasing

altitude• Contains ~ 75% of the mass of the atmosphere• Tropopause - Transition boundary that limits

mixing between the troposphere and upper zones; created by an abrupt transition in temperature

Atmospheric diagram

StratosphereStratosphere

• Extends from troposphere to about 50 km• Air temperature is initially stable and then

increases with altitude• Similar composition to troposphere

– Exceptions:• 1000x less H2O vapor• Ozone is 1000x greater

• Ozone produced when lightning or solar radiation strike O2 molecules

Atmospheric diagram

Ozone – the basicsOzone – the basics

• Ozone produced when lightning or solar radiation strike O2 molecules (formation diagram)

• Stratospheric Ozone = “good” ozone• Tropospheric Ozone = “bad” ozone which we will

discuss later• Ozone Formation

– Dynamic process (Diagram)• UV strikes O2 and ozone is created• Another UV wave strikes O3, which destroys

the O3• “Cycle” then repeats

Uppermost layersUppermost layers• Mesosphere - Middle Layer

• Region of declining temperature• Minimum temperature is ~ - 80o C

• Thermosphere– Extends to about 1,600 km– Ionized gases and high temperatures– However, the density of the atmosphere is so

low in this region that the actual temperature is low

– Aurora borealis (northern lights)

Atmospheric diagram

Uppermost layersUppermost layersTransition out of the atmosphere and into space is

gradual• No sharp delineation point• Referred to by some as the “exosphere”

Atmospheric diagram

The Great Weather EngineThe Great Weather Engine

• The weather and climate of Earth are driven by incoming energy from the Sun

• Incoming solar energy at the top of the atmosphere averages about 1,330 watts/m3

• Amount reaching earth’s surface is at least 10,000 times greater than all installed electric capacity in the world

• Solar Flux Movie

Determining Earth’s Solar Energy BudgetDetermining Earth’s Solar Energy Budget

• Radiative forcing– The difference between incoming and outgoing

solar radiation– Differences can result from differing amounts of

insolation (incoming radiation) or quantities of radiatively active compounds in the atmosphere

• Characteristics of electromagnetic spectrum (EM spectrum diagram)

– As wavelength (λ) decreases the amount of energy in the wave increases

– Quality versus quantity• Quality – mix of λ present in the light• Quantity – amount of each λ present


• Greenhouse Effect – Longer λ are absorbed in the lower atmosphere, trapping heat close to the surface of the planet– On Earth the Greenhouse has produced a planet-

wide climate that is “just right” (Thank you, Goldilocks) for the existence of life

– While on a planet like Venus, the Greenhouse Effect is “out of control” and has led to an average surface temperature of 461oC (~860oF)


• Incoming Radiation– Visible light passes through atmosphere

unchanged or reduced in quality or quantity– UV light is absorbed by stratospheric ozone


• Outgoing Radiation– Significant portion of energy is reflected (~30%)

• Albedo – surface reflectivity–Fresh clean snow and ice – 90% –dark soil – 3% –water 5-10%–Net albedo for Earth 30%–Our moon’s albedo is 12%–Net albedo for Venus is 65%


• Outgoing Radiation– Light energy that strikes the surface is absorbed

and then emitted as infrared (IR) radiation– IR radiation is absorbed by tropospheric CO2,

H2O, and other greenhouse gases – In the long term, all incoming radiation becomes

outgoing radiation– Therefore, a planet will need constant supplies of

energy from a sun to maintain a suitable surface temperature (at the minimum, since Earth also needs solar energy to drive photosynthesis)

• Solar energy budget diagram

Greenhouse Gases – The good, the bad and Greenhouse Gases – The good, the bad and the uglythe ugly

• We need greenhouse gases! • The above statement sometimes gets lost in the

debate• Without greenhouse gases Earth would be a

frozen (surface at least) lifeless rock• However, too much of a good thing can (and

usually is) a bad thing

Greenhouse Gases – The good, the bad and Greenhouse Gases – The good, the bad and the uglythe ugly

• Not all greenhouse gases are created equal– Length of life in atmosphere

(production/destruction cycle)– Ability to absorb radiation in terms of both λ and

the quantity absorbed (absorption diagram)– Contribution to radiative forcing (radiative forcing

diagram)

Greenhouse Gases Greenhouse Gases

• H2O

– Potent greenhouse gas– Responsible for 36-70% of the greenhouse

effect (depending on location and not including clouds)

Greenhouse Gases Greenhouse Gases • Carbon Dioxide

– Causes 9-26% of greenhouse effect– By-product of natural (i.e., no human

involvement) reactions:• End product of biological metabolism • Inorganic reactions such as chemical

weathering of rocks– Produced through fossil-fuel burning (human

caused)– Atmospheric levels increasing steadily

Greenhouse GasesGreenhouse Gases

• Methane (CH4)

– Another by-product of biology• Prokaryotic metabolism (Ruminants and rice

paddies are two significant human enhanced releases of CH4)

– CH4 is a more potent greenhouse gas than CO2

– Responsible for 4-9 % of greenhouse effect

Greenhouse GasesGreenhouse Gases• Ozone and Oxygen

– Responsible for 3-7% of the greenhouse effect• Chlorofluorocarbons (CFCs)

– Human made, exclusively. Used in refrigerants– Use and therefore atmospheric [ ] have declined

in recent years• Nitrous Oxide - Burning organic material• Sulfur Hexafluoride - Electrical insulation

What is the difference between weather and climate?

• WeatherWeather - A description of the current physical conditions of the atmosphere– Humidity, temperature, pressure, wind, and

precipitation– Varies on a short time scale (minutes, hours,

days, weeks)• ClimateClimate - A description of the long-term weather

pattern in a particular area– Much longer time scale (weeks, months, years,

decades)

Energy and WeatherEnergy and Weather

• Energy Balance– Solar energy is unevenly distributed

• Sun strikes the equator directly all year• Earth’s axis is tilted

– Energy in motion• Energy imbalance is evened out by

movement of air and water vapor in the atmosphere and by liquid water in rivers and ocean currents.

Convection Currents and Latent Convection Currents and Latent HeatHeat

• Lighter air rises and is replaced by cooler, heavier air, resulting in vertical convection currents.– Transport energy and redistribute heat.

• A significant amount of solar energy absorbed by the earth is used to evaporate water.– Energy stored in water vapor is known as latent

heat.– If condensation nuclei are present, or if

temperatures are low enough, condensation will lead to precipitation.

Convection CurrentsConvection Currents1. Air travels across a moist surface that is sun warmed2. Air then moves in an area of low pressure at the

surface3. Rising, expanding air creates an area of high pressure

at the top of the convection column4. At the top of the column, latent heat is released to

space; the higher the air rises the greater the latent energy lost

5. Condensation occurs and water rains out6. Air flows out of high-pressure zone towards areas of

low-pressure, where cool, dry air is subsiding7. Subsiding air is compressed and warmed in ground

level high pressure zones8. Air then flows back into ground level low pressure air

and repeats the cycleAtmospheric convection cycle diagram

Convection Cells and Prevailing WindsConvection Cells and Prevailing Winds• Air warms at the equator, rises, and moves

poleward, it sinks and rises in several intermediate bands, forming circulation cells.– Surface air flows do not move straight North or

South, but are deflected due to the Coriolis Effect• Major zones of subsidence occur at about 30o

north and south latitude.– Where dry, subsiding air falls on continents, it

creates broad, subtropical desert regions

Convection cells and prevailing winds diagram

Jet StreamsJet Streams• Jet Streams - Large-scale upper air flows.

– Typically, follow meandering paths from west to east (6-12 km above surface)

– Wind speeds are often 200 km/hr– Number, flow speed, location, and size all vary on

a daily basis• Usually two main jet streams over North America:

– Subtropical - 30o North– Northern - Circumpolar vortex (diagram)

• During winter, the Northern Hemisphere tilts away from the sun and the atmosphere cools, pushing cold polar air farther south

Seasonal WindsSeasonal Winds• Monsoon - Seasonal reversal of wind patterns

caused by differential heating and cooling rates of oceans and continents.– Most prevalent in tropical countries where large

land area is cut off from continental air masses by mountain ranges and surrounded by a large volume of water

– Countries around the Indian Ocean are most prone to monsoon weather

ClimateClimate

• The long term pattern of weather in an area• Climate is primary determinant in the location of

biomes and ecosystem on Earth• Distribution of biomes has changed radically over

the course of Earth’s history• Climate variability is influenced by a variety of

factors, some natural and at least one that is not

Solar intensitySolar intensity

• Changes in the distribution and intensity of sunlight reaching the earth– Solar magnetic cycles – changes amount of

light falling on Earth– Milankovitch Cycles - periodic shifts in earth’s

orbit and tilt • Eccentricity• Precession of the equinoxes• Axial tilt

Aerosol EffectsAerosol Effects

• Aerosols and other particles in the atmosphere have a tendency to reflect sunlight and cool surface air temperatures.– Short-lived, thus effects are temporary.– Mt. Pinatubo erupted in 1991 and ejected

enough ash and sulfate particles• Cooled global climate ~1o C for nearly a

year– Similar phenomena (exchange meteor strike

for volcanic eruption) is thought to have contributed to extinction of dinosaurs

Human-Caused Global Climate ChangeHuman-Caused Global Climate Change• Anthropogenic Greenhouse Effect

– Accelerated atmospheric warming due to human emissions of CO2 and other greenhouse gases

• Intergovernmental Panel on Climate Change (IPCC) estimates average global temperature will increase over the next century by 1.4 - 5.8o C (2.5 - 10.4o F).– Difference between current temperature and the

last ice age is only 5o C.– Every year of the 1990’s was among the 15 hottest

of the past millennium.– Night temperatures generally increased more than

daytime (Urban Heat Island Effect).– Precipitation rates also increased in certain regions

The dynamic ozone “cycle”

Electromagnetic spectrum

http://upload.wikimedia.org/wikipedia/commons/7/7c/Atmospheric_Transmission.png

Solar Radiation Budget for EarthSolar Radiation Budget for Earth

Convection currents and latent energyConvection currents and latent energy

Convection Cells and Prevailing WindsConvection Cells and Prevailing Winds

Circumpolar Vortex

Circumpolar Vortex

Milankovitch Cycles - EccentricityMilankovitch Cycles - Eccentricity

Milankovitch Cycles - PrecessionMilankovitch Cycles - Precession

Milankovitch Cycles – Axial TiltMilankovitch Cycles – Axial Tilt

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APES U2 L3 atmosphere