Air, Weather, and Climate

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Air, Weather, and Climate
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Outline

• The Atmosphere and Climate
• Greenhouse Effect
• Convection Currents
• Weather
• Coriolis Effect
• Cyclonic Storms
• Climate
• El Nino
• Climate Change

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THE ATMOSPHERE AND CLIMATE

• 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.

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The Atmosphere and Climate

• Troposphere
• Ranges in depth from 18 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.

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The Atmosphere and Climate

• Stratosphere
• Extends from troposphere to about 50 km.
• Air temperature is stable, or increases with
  altitude.
• Has almost no water vapor and ozone is 1000x more
  than in the troposphere.
• Relatively calm

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The Atmosphere and Climate

• Mesosphere
• Middle Layer
• Thermosphere
• Begins at 80 km.
• Ionized gases and high temperatures.
• Lower Thermosphere
• Aurora borealis (northern lights)

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Energy and the Greenhouse Effect

• Of the solar energy that reaches the outer
  atmosphere
• About one-quarter is reflected by clouds and the
  atmosphere.
• Another quarter is absorbed by carbon dioxide,
  water vapor, ozone and a few other gases.
• About half reaches the earths surface.

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Energy Balance
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Energy and the Greenhouse Effect

• Surfaces that reflect energy have a high albedo
  (Reflectivity).
• Fresh clean snow 80-85
• Dark soil 3
• Net average of earth 30

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Energy and the Greenhouse Effect

• 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 earths
  surface.
• Greenhouse Effect
• Increasing atmospheric CO2 due to human
  activities appears to be causing global warming.

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Convection and Atmospheric Pressure

• 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.

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Convection Currents

• 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.

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Convection Currents

• Subsiding air is compressed as it approaches the
  earths 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.

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Coriolis Effect

• 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.

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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.
• Winds directly under regions of subsiding air are
  often light and variable.

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Jet Streams

• Jet Streams - Large-scale upper air flows.
• Generally follow undulating paths where Hadley
  and Ferrell cells meet.

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Ocean Currents

• Warm and cold ocean currents strongly influence
  climate conditions on land.
• As surface water moves, deep water wells up to
  replace it.
• Ocean circulation also driven by differences in
  water density.
• Gyres

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Seasonal Winds and Monsoons

• 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.

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Frontal Weather

• 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.

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Cyclonic Storms

• 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)

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Cyclonic Storms

• 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.

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Tornadoes
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CLIMATE

• Driving Forces and Patterns
• Periodic weather cycles detected.
• Solar magnetic cycles
• Milankovitch Cycles - Periodic shifts in earths
  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).

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El Nino Southern Oscillation

• 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.

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El Nino Southern Oscillation

• During an El Nino year, the northern jet stream
  pulls moist air from the Pacific over the U.S..
• 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.

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Human-Caused Global Climate Change

• In 1988, the Intergovernmental Panel on Climate
  Change (IPCC) was formed.
• Released third climate report in February 2001.
• Recent changes in worlds climate have had
  discernable impacts on physical and biological
  systems.
• Human activities must be at least partially
  responsible.

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CO2 Concentrations on Mauna Loa
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Sources of Greenhouse Gases

• Carbon Dioxide - Fossil-fuel burning.
• Atmospheric levels increasing steadily.
• Methane - Ruminants, Coal-mines.
• Absorbs more infrared than CO2.
• Chlorofluorocarbons (CFCs) - Refrigerants
• Declined in recent years.
• Nitrous Oxide - Burning organic material.

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Aerosol Effects

• 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.

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Current Evidence of Climate Change

• Global average surface temperature rose 0.6o C
  during 20th century.
• Droughts are more frequent and widespread.
• Severe weather events have increased
  dramatically.
• Polar regions have warmed much faster than the
  rest of the world.
• Ice shelves on Arctic peninsula are disappearing.
• Many animals breeding earlier and extending their
  ranges.
• Amphibians disappearing.

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Current Evidence of Climate Change

• Retreating alpine glaciers.
• Mt. Kilimanjaro
• Glacier National Park
• Coral reefs are bleaching.
• Northern growing seasons are longer.
• Sea level has risen.
• Arctic sea ice is 40 thinner.

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Winners and Losers

• 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 ?

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Predicted Warming for CO2 Doubling in 2100
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International Climate Negotiations

• 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.
• 126 countries have ratified the Protocol. U.S.
  has not.

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Controlling Greenhouse Emissions

• Reducing carbon dioxide levels.
• Renewable energy sources may offer a better
  solution to climate problems.
• Capturing and storing carbon dioxide.
• Carbon Management
• Planting vegetation
• Emissions trading system
• Deep water injection

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Summary

• The Atmosphere and Climate
• Greenhouse Effect
• Convection Currents
• Weather
• Coriolis Effect
• Cyclonic Storms
• Climate
• El Nino
• Climate Change

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