Part 1. Energy and Mass Chapter 1. Composition and Structure of the Atmosphere.
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Transcript of Part 1. Energy and Mass Chapter 1. Composition and Structure of the Atmosphere.
Part 1. Energy and Mass
Chapter 1.
Composition and Structure of the Atmosphere
MeteorologyThe study of the atmosphere and the processes that cause “weather”
ClimatologyExamines weather elements over long time periods
IntroductionThe Atmosphere
A mixture of gas molecules, suspended particles, and falling precipitation
The atmosphere strongly affects our day-to-day lives
The Thickness of the AtmosphereDensity decreases rapidly with height • The top of the atmosphere is undefined• Majority of mass is compressed near the
surface
Gases and particles are exchanged between the surface and atmosphere
A gas molecule that is input slowly into the atmosphere has a long average residence time.
A gas molecule that is input rapidly into the atmosphere has a short average residence time. Average residence time of CO2 is about 100
years.
Evolution of the AtmosphereEarly atmosphere = hydrogen (H2) and helium (He) -- 4 billion years ago
Secondary atmosphere formed from volcanic outgassing (produced CO2 rich atmosphere) -- 4 to 3 billion years ago
CO2 replaced by O2 through photosynthesis (by life!) and dissolution in water -- by 3.4 billion years ago; significant free O2 by 2.5 billion years ago
N2 (inert) slowly grew to present day levels
Composition of the Atmosphere
Variable Gases
Water VaporMost abundant variable gas
Added/ removed to air through the hydrologic cycle
Concentrations = nearly 0% to nearly 4% (by volume)
Important to energy balance and many atmospheric processes (it is a greenhouse gas)
Water vapor image showingbroader distribution of moisture than the image of actual clouds (below)
Water vapor image
Cloud image
Dry air
Moist air
Carbon DioxideA trace gas
• 0.038% of atmosphere’s mass• Important to Earth’s energy balance (it is a
greenhouse gas)
Added through biologic respiration, volcanic activity, decay, and natural and human-related combustion
Removed through photosynthesis
Increasing at a rate of 1.8 ppm/year
Temporal increases due to human activities
Seasonal variations related to biological activity
2006 value: about 380 ppm
MethaneA variable gas in small but recently increasing concentrations
Increases from burning of fossil fuels, livestock digestion, and agriculture cultivation (esp. rice)
Effective absorber of terrestrial radiation (it is a greenhouse gas)• Plays a role in near-surface warming
The annual increases in atmospheric methane
Aerosols (particulates)Any solid and/or liquid particle, other than water
Both natural (sea spray, dust, combustion) and human (combustion) sources
Long residence times for some types
Acts as condensation nuclei
Will cool atmosphere if emitted in large amounts (such as volcanic eruptions)
Vertical Structure of the AtmosphereDensity
Mass (kg) per unit volume (m3)• Sea level average = 1.2
kg/m3
Near surface air is more dense
• Compressibility of air • Mean free path (of an air
molecule)– At surface = 0.0001 mm– At 150 km = 10 m
Elevationin the atmosphere
Higher density
Lower density
Thermal Layers of the AtmosphereFour distinct atmospheric layers • Troposphere• Stratosphere• Mesosphere• Thermosphere
Each has particular temperature characteristics with height.
Troposphere Lowest layer
Steady temperature decrease with height • -6.5oC/km (-3.6oF/1000ft)
Virtually all weather processes• Contains 80% of atmospheric mass
Tropopause = top of troposphere
Violent updrafts maypenetrate cloud tops into the stratosphere. The flattenedtop of this cumulonimbus cloud is in the stratosphere.
StratosphereLittle actual “weather”
Temperature inversion
• Caused by absorption of UV radiation by O3
(ozone) in the ozone layer
Stratopause = top of stratosphere
Ozone Tri-atomic form of oxygen
Absorbs ultraviolet radiation
Chlorofluorocarbons (CFCs) destroy ozone Destruction peaks over southern hemisphere
Antarctic circumpolar vortex limits latitudinal mixing
• Leads to an O3 “hole”
The reduction of ozone over Antarcticaover time. Area in redindicates the “ozone hole.”
MesosphereDecreasing temperatures with height
Coldest layer
ThermosphereSlowly merges into space
Increasing temperatures with height• “Temperature” = molecular kinetic energy
Combined Mesosphere and Thermosphere = 0.1% of total mass of atmosphere
IonosphereA layer of electrically charged particles (ions)• In the meso- and thermosphere• D-, E-, and F-layers with increasing height
Interactions with subatomic solar particles cause • The aurora borealis (northern lights) • The aurora australis (southern lights)
The ionosphere reflects radio waves, allowing radio transmissions over long distances around the Earth.
TemperatureEnergy of the atmosphere, measured in degrees (Fahrenheit, Celsius or Kelvin)
HumidityWater content of the atmosphere, often expressed as relative humidity
PressureForce of the atmosphere, measured in millibars (mb) or kilopascals (kPa)
Weather Measurements and Units
A Brief History of Meteorology
GalileoPrototype thermometer in 1593• Fahrenheit (1714) and Celsius (1736)
temperature scales
Torricelli Barometer (1643)
Instruments to measure water vapor introduced in late 1700s