Radiation understanding by Muhammad Fahad Ansari 12IEEM14

Radiation Understanding

•Muhammad Fahad Ansari

12IEEM14

15 Lecture Material for Introduction of Environmental Physics

Class 12 EE Batch1. Sound and Light

2. Radiation Understanding

3. Global Warming

4. Terrestrial Environment

5. Extra-Terrestrial Environment

6. Natural and Man made radiation

7. Universe understanding

8. Understanding water

9. Cloud formation

10.Climate

11. Climate change

Radiation Understanding

1. EATRH’S ATMOSPHERE

2. STRUCTURE

3. SUN’S ELECTROMAGNETIC SPECTRUM

4. Energy from the Sun

5. Atmospheric Greenhouse Effects

Radiation and Earth’s Atmosphere• The earth’s global average surface temperature in present

climate is 15C (59F). Without the atmosphere, it would be -18C (-0.4F),

• About 33C or 59.4F colder! Atmosphere is the most important component of the earth’s climate.

• Radiation vs. other heat sources:• Total energy enter the earth’s atmosphere: 174 petawatts or

174X1015 Watts• Solar: 99.978%, Geothermal: 0.013%, waste and fossil fuel:

0.007%, tidal: 0.002%

Earth’s Atmosphere

1. What is it?

A thin gaseous envelope around the planet.

2. Composition Today’s atmosphere: nitrogen (78%), oxygen

(21%), other (1%) – trace gases!

Nitrogen, oxygen, argon, water vapor, carbon dioxide, methane, and most other gases are invisible.

Clouds are not gas, but condensed vapor in the form of liquid droplets or ice particles.

Ground based smog, which is visible, contains reactants of nitrogen and ozone.

3. Structure Four layers: Troposphere

(overturning)

Stratosphere (stratified)

From surface to 8-18 km

From troposphere top to 50 kmMesosphere

Thermosphere

Blue sky!

The Structure of Earth’s Atmosphere

1. Four layers defined by

temperature

2. Importance to climate and climate change

Troposphere:

Troposphere:Stratosphere:Mesosphere:Thermosphere:

T decreases with elevationT increases with elevationT decreases with elevationT increases with elevation

80% of Earth’s gases

Most of Earth’s weather happens

Most of the measurements

Stratosphere:

19.9% of Earth’s gases

Ozone layer:

Blocking Sun’s ultraviolet radiation

Energy from the Sun

1. Characteristics

Travels through space (vacuum) in a speed of light

3. Importance to climate and climate change

In the form of waves:

In stream of particles

Electromagnetic waves

(Photons)

Primary driving force of Earth’s climate engine

2. Electromagnetic spectrum

From short wavelength, high energy, gamma rays to long wavelength, low energy, radio waves

Releases heat when absorbed

Ultraviolet, Visible, Infrared

Sun’s Electromagnetic Spectrum

Solar radiation has peak intensities in the shorter wavelengths, dominant in the region we know as visible, thus shortwave radiation

Longwave & Shortwave Radiation

The hot sun radiates at shorter wavelengths that carry more energy, and the fraction absorbed by the cooler earth is then re-radiated at longer wavelengths.

Atmospheric Greenhouse Effects

T= 15°C (59°F)

T= –18°C (0°F)

Greenhouse effects make Earth’s surface warmer!

Surface Temperature With the Atmosphere

Surface Temperature Without the Atmosphere

Water vapor accounts for 60% of the atmospheric greenhouse effect, CO2 26%, and the remaining greenhouse gases 14%.

Greenhouse Gases

Water vapor (H2O)

Carbon dioxide (CO2) Methane (CH4)

Nitrous oxide (N2O)Ozone (O3)Chlorofluorocarbons

(CFC’s)

What are they?

CO2 contributes most (55-60%) to the anthropogenic greenhouse effect, and methane is a distant second (16%).

CFCs cause the strongest greenhouse warming on a molecule-for-molecule basis.

Atmospheric Absorption

Solar radiation passes rather freely through Earth's atmosphere.

Earth emits longwave energy, which either leaks through a narrow window or

is absorbed by greenhouse gases and radiated back to Earth.

Wavelength

Abs

orpt

ion

(100

%)

Nitrous Oxide

Methane

Ozone

Water Vapor

Carbon Dioxide

Total Atmo

IR

UV

Solar Intensity and Latitude

Solar intensity, defined as the energy per area, is different at different latitude.

A sunlight beam that strikes at an angle is spread across a greater surface area, and is a less intense heat source than a beam impinging directly.

Unequal Radiation on a Sphere

Insolation is stronger in the tropics (low latitudes) than in in the polar regions (high latitudes).

Pole-to-Equator Heating Imbalances

What controls the elevation of the Sun above the horizon?

Earth’s Tilt Primarily Determines Season

Earth's Annual Energy Balance

The balance is achieved locally at only two lines of latitude.

A global balance is maintained by excess heat from the equatorial region transferring toward the poles.

Incoming Solar Radiation

Outgoing Longwave Radiation

Unequal heating of tropics and poles

The Global Energy Budget: Driver of Atmospheric Motion

However, the tilt of theEarth means this balanceis not maintained for eachlatitude

A balance exists between the incoming solar andoutgoing longwave energy averaged over the globe and the year

DEFICITSURPLUS

Questions:

• What is the current global mean surface temperature?

• Why it is 33C or 59F warmer than it would be without the atmosphere?

• Why is climate dominated by the radiation balance of the atmosphere?

• What are the main greenhouse gases in the earth’s atmosphere?

• In what latitudes the earth’s gain and lost radiative energy (heat), respectively?

Questions:

• What is the current global mean surface temperature? – 15C or 59F

• Why it is 33C or 59F warmer than it would be without the atmosphere?– Because of greenhouse effect of the atmosphere

• Why is climate dominated by the radiation balance of the atmosphere?– It contributes to 99.978% of total heat flux into the atmosphere

• What are the main greenhouse gases in the earth’s atmosphere?– H2O, CO2, CH4, O3, CFCs, NO2

• In what latitudes the earth’s gain and lost radiative energy (heat), respectively? – Gain heat in the tropics or 40S-40N, loss heat in high latitudes

(50S-50N)

Interested in more questions? Try these questions:

• Can you name one or more main causes of glacier and interglacier climate change?

• What is the most important greenhouse gases for modern climate change? What is the fastest growing greenhouse gas?

• Earth’s climate has been much colder and warmer than that of today. Do you know in what ways the earth’s radiation balance was altered?