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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 earth’s 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 earth’s 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 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.

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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

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).

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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 world’s 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 (CFC’s) - 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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