Electromagnetic Spectrum

Paul Adams

Fort Hays State University

What drives the system?

• What do we know about the sun?

What do we want to know?

Energy Transfer

• Conduction –molecule to molecule within a substance

• Convection (and advection) –mass movement of a fluid

• Radiation –absorption of electromagnetic waves

3 mechanisms of energy transport

A view

Some Radiation Basics

• Electromagnetic Wave – Alternating electric and magnetic waves

• Wavelength – length of wave from peak to peak

• Photons – packets of electromagnetic energy

A view

Detecting EM Radiation

• How can you detect the radiation and show your students it is there?

• Using the provided equipment: (UV, Cell phone,spectrometer, radar gun, IRTs, UV beads)

• A) What is a question you have?

• B) How will you test it?

• C) What did you find?

Radiation Interactions with Matter

• Emission – release of electromagnetic waves

• Absorption – receiving of electromagnetic waves

• Scattering – deflection of electromagnetic waves in all directions

• Reflection – deflection of electromagnetic waves into the backwards direction

Interactions with the Atmosphere

Why is the sky blue?

Why is the sunset red?

                                   

           

                                         

         

What is the greenhouse effect?

• Certain gases are transparent to visible light but absorb infrared– Called “greenhouse gases”– Include water vapor (H2O), carbon dioxide (CO2),

methane (CH4)• Greenhouse gases allow sunlight to pass through and

warm the surface• When the Earth emits infrared, it is absorbed and

reemitted (“trapped”) by the greenhouse gases• Without the greenhouse effect, Earth’s surface would be

30° colder than it is• Venus has a much thicker CO2 atmosphere, and a much

stronger greenhouse effect (surface temperature 490 °C)

Src: J. Heinrichs, Turning up the heat on the future: Global Warming and its Consequences

Schematic diagram of the greenhouse effect

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Greenhouse gases over the past millenium

• Exponential increase over the past 1000 years in CO2, CH4, and N2O is clear

• CO2 concentrations have increased by about 35% since pre-industrial times

• Methane concentrations have more than doubled

Source: 2001 IPCC report

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The global instrumental temperature record

• Quality instrument measurements begin about 1850

• Global record shows approximately 1 °C increase over past 150 years

• Note “Dust Bowl” peak around 1940

• Warming is greater in Northern Hemisphere than Southern

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Seasonal temperature trends

• Temperature increase has been greater in winter than any other season – key “smoking gun”

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Seasonal temperature trends

• Temperature increase has been greater in winter than any other season – key “smoking gun”

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• Key findings:– Cold nights and

days are decreasing, warm nights and days increasing

– Decreases in cold nights, increases in warm nights are much greater than corresponding changes during daytime

– Consistent with warming caused by enhanced greenhouse effect

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Temperature change by 2100 with CO2 stabilization at 450 ppm

Source: IPCC, 2001 Src

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Global mean surface temperature under different scenarios

Source: IPCC, 2001

Predicted precipitation changes

• Overall increase in precipitation

• Some areas (Arctic, Sahara, Antarctic) become wetter

• Other areas become drierAnnual mean precipitation change: 2071 to 2100 Relative to 1990

Source: IPCC, 2001

Sea ice will continue to decline dramatically

Sea level rise

• Global sea level will rise between 0.3 and 0.9 meters, depending on scenario

• Causes: melting polar ice, thermal expansion of water

Source: IPCC, 2001

EM Spectrum

EM WaveWavelengthFrequency

Human UsesPros and Cons