Chapter 2: Atmosphere: Origin, Composition, and Structure

Key Terms

• Atmosphere – a thin envelope of gases that encircles the earth and other particles (aerosols)

• Weather – the state of the atmosphere at a specific place and time

• Meteorology – the study of the atmosphere and the processes that cause weather

• Climate – weather conditions at some place averaged over a specific time period

• Climatology – the study of the climate

Computer Forecast Models

• Scientific Model – an approximate representation of a real system (Earth-Atmosphere System)– Conceptual– Graphical – weather map– Physical– Numerical – run by computers (used to predict

weather)• All models simulate reality and are subject to

error. More at: http://www.crh.noaa.gov/news/display_cmsstory.php?wfo=lmk&storyid=106486&source=0

Modern Atmosphere

• Homosphere – lowest 80km of the atmosphere where principal gas ratios remain relatively constant

• Heterosphere – above 80km where concentrations of heavier gases decrease more rapidly

Important Gases

• Nitrogen (N2) ~ 78%• Oxygen (O2) ~ 21%• Argon (Ar) ~ 1%• Greenhouse Gases – trace amounts but important role on Earth

– Water Vapor (H2O) ~ 0-4%– Carbon Dioxide (CO2)– Ozone (O3)– Methane (CH4)

Aerosols

• Tiny solid and liquid particles suspended in the atmosphere– Wind erosion of soil– Ocean spray– Forest fires– Volcanic eruptions– Agricultural and industrial activities

Pollution

• Air Pollutant – gas or aerosol that at a certain concentration adversely affects organisms and the environment– Natural pollutant: carbon monoxide– Non-natural pollutant: benzene

• Primary – harmful immediately upon emission into atmosphere (car exhaust)

• Secondary – results of chemical reactions between primary pollutants (smog)

Monitoring the Atmosphere

• Surface Observations– First done in 1800’s by Army Medical Corps - now run by

the National Weather Service (NWS)– Automated Surface Observing System (ASOS)

• About 1700 across the US• Fully automated year round

– NWS Cooperative Observer Network• About 8000 across the US• Monitored by volunteers with equipment supplied by

NWS– Doppler Radar

• About 113 operated by the NWS• Others operated by television stations, military, private

companies

Monitoring the Atmosphere

• Surface observations, continued– Army monitored weather to compare with troop health– Mid-1800s – national network of volunteer observers– 1849 – telegraph companies transmitted weather conditions

free of charge– 1860s – loss of ships in Great Lakes• Government took a greater role in forecasting

– 1870 – President Ulysses S. Grant established 24 stations under the auspices of the U.S. Army Signal Corps

– 1891 – transferred from military to civilian hands• New weather bureau under U.S. Department of

Agriculture

Monitoring the Atmosphere

• Surface observations, continued– Transferred to Commerce Department in 1940– 1965, Weather Bureau reorganized into the National

Weather Service (NWS)• Under Environmental Science Services Administration

(ESSA), which became National Oceanic and Atmospheric Administration (NOAA)

– 1990s – NWS modernized and expanded• Today,123 NWS Forecast Offices (see next slide)• Added Automated Surface Observing Systems (ASOS)

NWS Forecast Offices

Monitoring the Atmosphere

Automated Surface Observing System

(ASOS)

Cooperative Observer Network– Member stations record daily

precipitation and max/min temperatures for hydrologic, agricultural, and climatic purposes

Monitoring the Atmosphere

• Upper Air Observations– Radiosonde – measuring device carried through the atmosphere

by a weather balloon• Transmit data immediately• Balloons are launched simultaneously at 0000 and 1200 UTC• Data transmitted (temperature, pressure, dewpoint, wind) are

plotted on a chart creating a sounding– Dropwindsonde – same thing except dropped by an airplane

instead of launched by a balloon– Satellites

Monitoring the Atmosphere

Radiosonde

Launching a

Radiosonde

Upper Air Observations

Locations of radiosonde observation

stations

Data from radiosonde shown in a Stüve

diagram

Remote Sensing

• Measurement of environmental conditions by processing signals that are either emitted by an object or reflected back to a signal source– Radar– Satellites

Atmospheric Setup

The atmosphere is divided into several different concentric layers. This plot shows the variation in average air temperature with height.

Characteristics of Air Masses & Fronts

Pressure decreases exponentially with height. This means that the majority of the molecules that make up the atmosphere are in the lower layers. About 50% of the atmosphere's mass is within 6km of the surface and 99.9% is within 50km.

Layers of the Atmosphere

• Troposphere– Layer at the surface– Layer where weather occurs (except some high clouds)– About 6km high at the poles and 20km at the equator– Temperature generally decreases with height due to sunlight

heating the Earth’s surface and warms air above it.– Tropopause – boundary between troposphere and

stratosphere (average height near 12km)– Tropopause varies in height across the globe.

Layers of the Atmosphere

• Stratosphere– About 40km thick (extends to an altitude near

50km)– Layer where airplanes fly (location of jet stream)– Layer where ozone is present– Temperature generally increases with height (Ozone absorbing solar radiation followed by a release of energy, which warms the stratosphere)– Stratopause – boundary between stratosphere

and mesosphere

Why do I want to fly here?• Get to places faster• It’s a fairly stable layer (most weather occurs in the

troposphere), less turbulence

Layers of the Atmosphere

• Mesosphere– Base is about 50km above the surface– Temperature again decreases with height– Coldest layer of the atmosphere (little ozone)– Atmospheric pressure at around 1 mb– 99% of atmospheric mass located below– Without proper breathing equipment, brain would become oxygen starved– Extends to the mesopause which is about 80km (50 miles) above the surface of the

earth

• Thermosphere– Extremely thin air (particles range from 1-10km apart)– Increasing temperature because first particles to receive sun’s energy (solar radiation)– Estimated top is about 500km– May be 10 km between molecules– Heat shield

• Exosphere (outer space)

Ionosphere

• Primarily located in the thermosphere• Home to a high concentration of ions and

electrons• Location of the Aurora Borealis• Caused by the solar wind, in which Earth’s

magnetic field deflects

The Ionosphere and the Aurora

• The magnetosphere is caused by the deflection of the solar wind by Earth’s magnetic field

• Solar wind = Stream of charged particles let go from the upper atmosphere of the sun

Aurora borealis

Review

Air Temperature and Altitudinal Relationships in the Atmosphere