Transcript Understanding Our Environment

Air, Weather, and Climate
Chapter 17
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Outline:
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Composition and Structure of the Atmosphere
Weather Engine
 Solar Radiation
Weather
 Jet Streams
 Cyclonic Storms
Climate
 El Nino
 Climate Change
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
COMPOSITION AND STRUCTURE OF THE
ATMOSPHERE
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Weather - A description of physical conditions
of the atmosphere.
Climate - A description of the long-term
weather pattern in a particular area.
 Weather and climate are primary
determinants of biomes and ecosystem
distribution.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Past and Present Composition
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Many geochemists believe the earth’s
earliest atmosphere was made up of mainly
hydrogen and helium.
 Volcanic emissions have added carbon,
nitrogen, oxygen, and sulfur.
 Virtually all oxygen was produced by
photosynthesis.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
A Layered Envelope
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Troposphere
 Ranges in depth from 12.5 km over the
equator to 8.0 km over the poles.
- All weather occurs here.
- Composition is relatively uniform.
- Air temperature drops rapidly with
increasing altitude.
 Tropopause - Transition boundary that
limits mixing between the troposphere
and upper zones.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
A Layered Envelope
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Stratosphere
 Extends from troposphere to about 45 km.
- Air temperature is stable, or increases
with altitude.
 Fraction of water vapor is 1000x less
and ozone is 1000x more than in the
troposphere.
- Relatively calm
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
A Layered Envelope
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Mesosphere
 Middle Layer.
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- Minimum temperature is about - 80 C.
Thermosphere
 Extends to about 1,600 km.
- Ionized gases and high temperatures.
 Ionosphere - Lower Thermosphere
 Aurora borealis (northern lights)
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
THE GREAT WEATHER ENGINE
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Solar Radiation
 Incoming solar energy at the top of the
atmosphere averages about 1,330 watts/m3.
- About half is reflected or absorbed by
atmosphere.
 Amount reaching earth’s surface is at
least 10,000 times greater than all
installed electric capacity in the world.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Solar Radiation
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Visible light passes through atmosphere
undiminished.
Ultraviolet light is absorbed by ozone in the
stratosphere.
Infrared radiation is absorbed by carbon
dioxide and water in the troposphere.
 Albedo - Reflectivity
- Fresh clean snow
90%
- Dark soil
3%
- Net average of earth
30%
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Solar Radiation
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Solar Radiation
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Most solar energy reaching the earth is
visible light.
 Energy reemitted by the earth is mainly
infrared radiation (heat energy).
- Longer wavelengths are absorbed in the
lower atmosphere, trapping heat close to
the earth’s surface.
 Greenhouse Effect
 Increasing atmospheric CO2 due to
human activities appears to be
causing global warming.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Convection Currents and Latent Heat
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Lighter air rises and is replaced by cooler,
heavier air, resulting in vertical convection
currents.
 Transport energy and redistribute heat.
Much of solar energy absorbed by the earth
is used to evaporate water.
 Energy stored in water vapor as latent
heat.
- If condensation nuclei are present, or if
temperatures are low enough,
condensation will lead to precipitation.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Convection Currents
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Releasing latent heat causes air to rise, cool,
and lose more water vapor.
 Rising, expanding air creates an area of
relatively high pressure at the top of the
convection column.
- Air flows out of high-pressure zone
towards areas of low-pressure, where
cool, dry air is subsiding.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Convection Currents
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Subsiding air is compressed as it
approaches the earth’s surface where it piles
up and creates an area of high pressure at
the surface.
 Air flows out of this region back towards
low pressure, closing the cycle.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Convection Currents
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
WEATHER
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Energy Balance
 Solar energy is unevenly distributed.
- Sun strikes the equator directly all year.
- Earth’s axis is tilted.
 Energy imbalance is evened out by
movement of air and water vapor in the
atmosphere and by liquid water in rivers
and ocean currents.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Convection Cells and Prevailing Winds
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As air warms at the equator, rises, and
moves northward, it sinks and rises in
several intermediate bands, forming
circulation cells.
 Surface flows do not move straight North
and South, but are deflected due to
Coriolis Effect.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Convection Cells and Prevailing Winds
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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.
- Winds directly under regions of
subsiding air are often light and variable.
 Horse latitudes
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Convection Cells and Prevailing Winds
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Jet Streams
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Jet Streams - Large-scale upper air flows.
 Generally 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.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Jet Streams
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Usually (2) main jet streams over NA:
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 Subtropical - (30 ) north
 Northern - Circumpolar vortex
- During winter, the Northern Hemisphere
tilts away from the sun and the
atmosphere cools, pushing cold polar air
farther south.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Circumpolar Vortex
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Frontal Weather
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Cold Front - Boundary formed when cooler
air displaces warmer air.
 Cold air is more dense, thus hugs ground
and pushes under warm air.
- Warm air cooled adiabatically.
Warm Front - Boundary formed when warm
air displaces cooler air.
 Warm air is less dense and slides over
cool air, creating a long wedge-shaped
band of clouds.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Frontal Weather
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Cyclonic Storms
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When rising air is laden with water vapor,
latent energy released by condensation
intensifies convection currents and draws up
more warm air and water vapor.
 Storm cell will exist as long as temperature
differential exists.
- Hurricanes (Atlantic)
- Typhoons (Western Pacific)
- Cyclones (Indian Ocean)
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Cyclonic Storms
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Tornadoes - Swirling funnel clouds.
 Rotation not generated by Coriolis forces.
 Generated by “supercell” frontal systems
where strong dry cold fronts collide with
warm humid air.
- Greater air temperature differences in
Spring thus more tornadoes.
 Spinning - Rolling vortex tubes
 Downbursts - Disorganized supercells
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Tornadoes
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Seasonal Winds
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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.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
CLIMATE
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Driving Forces and Patterns
 Periodic weather cycles detected.
- Solar magnetic cycles
- Milankovitch Cycles - Periodic shifts in
earth’s orbit and tilt.
 Change distribution and intensity of
sunlight reaching the earth.
 Ice cores show drastic changes
may have occurred over short
periods of time (decades).
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
El Nino Southern Oscillation
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Large pool of warm surface water in Pacific
Ocean moves back and forth between
Indonesia and South America.
 Most years, the pool is held in western
Pacific by steady equatorial trade winds.
- Every three-five years the Indonesian
low collapses and the mass of warm
surface water surges back east.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
El Nino Southern Oscillation
During an El Nino year, the northern jet
stream pulls moist air from the Pacific over
the US.
- Intense storms and heavy rains.
 During intervening La Nina years, hot,
dry weather is often present.
 Pacific Decadal Oscillation - Very large
pool of warm water moving back and forth
across the North Pacific every 30 years.

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
El Nino Southern Oscillation
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Human-Caused Global Climate Change
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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.
- Precipitation rates also increased.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Greenhouse Gases
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Carbon Dioxide - Fossil-fuel burning.
- Atmospheric levels increasing steadily.
Methane - Ruminants, Coal-mines
- Absorbs more infrared than CO2.
Chlorofluorocarbons (CFC’s) - Refrigerants
- Declined in recent years
Nitrous Oxide - Burning organic material
Sulfur Hexafluoride - Electrical insulation
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Aerosol Effects
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Aerosols 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 to cool
global climate about 1o C for nearly a year.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Effects of Climate Change
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Artic sea ice thinning
Alpine glaciers retreating
Wild plants and animals may be forced to
alter migration patterns, or abandon current
ranges.
 Coral reefs bleaching.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Winners and Losers
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Residents of extreme northern areas would
enjoy warmer temperatures and longer
growing-seasons.
Plant growth patterns may be altered.
One-third of population living in areas likely
flooded by rising seas.
More evaporation may cause severe storms.
 Infectious disease likely to spread faster.
 Circulation patterns may cause more
snowfall at poles - New ice age ?
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
International Climate Negotiations
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Kyoto Protocol (1997)
 160 nations agreed to roll back carbon
dioxide, methane, and nitrous oxide
emissions about 5% below 1990 levels by
2012.
- Sets different limits for different
countries, depending on prior output.
 Developing countries exempted.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Summary:
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Composition and Structure of the Atmosphere
Weather Engine
 Solar Radiation
Weather
 Jet Streams
 Cyclonic Storms
Climate
 El Nino
 Climate Change
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.