Lecture 3

7 types of radiation

1. AM radio waves wavelength 100 2. Television waves wavelength 1 - shorter waves 3. Microwaves wavelength 10(-3) - shorter waves as well, the shorter the wave the more energy is carrying along the wave. The shorter the wave length the warmer the object; the warmer the object the more radiation is emitted 4. Infrared waves 10(-6) - red wave, also known is micrometer 5. Visible light wavelength 5x10(-7) - have different colors along the waves 6. Ultraviolet waves 10(-7) - invisible waves, it has carried energy but we can not see it 7. X rays wavelength 10(-9) - the shortest wave, powerful waves, carry a lot of energy

how much of the Sun's energy does the Earth get?

1. Scattered (reflected away) Scattering happens when solar radiation is reflected by Gases, aerosols (very small, solid (dust, salt, smoke) or liquid), or clouds in the atmosphere and Earth's surface 2. Absorbed (not reflected) Absorption of solar radiation occurs by gases and clouds in the atmosphere and Earth's surface 3. Transmitted - happens when solar radiation passes through the atmosphere to the surface, where it will be absorbed or reflected

Greenhouse Effect sequence of steps:

1. Solar (shortwave) radiation is absorbed by Earth's surface. 2. Earth emits infrared (longwave) radiation. 3. Greenhouse gases absorb most of Earth's outgoing infrared radiation. 4. Greenhouse gases emit infrared radiation in all directions. 5. Earth absorbs downward directed infrared radiation Result: warmer surface temperature

If the amount of clouds were to increase by 10%, correspondingly increasing the albedo, how would that

1.Affect the amount of solar radiation reflected back to space will increase 2. Affect the amount of solar radiation absorbed at the Earth's surface will decrease

Absorption of Radiation

Absorption of shortwave radiation by atmospheric gas molecules is fairly weak --> atmosphere is transparent to solar radiation Most absorption of shortwave radiation occurs at the Earth's surface Most atmospheric gases do not interact strongly with longwave radiation. However... Greenhouse gas molecules absorb certain wavelengths of Earth's emitted longwave (infrared) radiation

What emits radiation?

All objects with a temperature greater than 0 K emit some type of radiation. As long is molecule is moving, it will emit some form of radiation. Examples: Human, sun, Earth Radiation laws: Warmer objects emit more intensely (more radiation emits) than cold objects. (Stefan-Boltzmann Law) Warmer objects emit a higher proportion of their energy at short wavelengths than cold objects. (Wien's Law) --> the larger proportion will be the shorter waves will be --> the warmer the object the lower, shorter average wave length

Energy Balance

Assume that the Earth's surface is in thermodynamic equilibrium: - Upward radiation emitted by the surface equals the downward radiation absorbed by the surface The surface absorbs two types of radiation infrared and solar Average surface temperature = 15°C

Energy

Classical Definition: The ability to do work Alternative Definition: The capacity to change environmental conditions - for example, temperature of a substance

There are three modes of energy transfer in the atmosphere

Conduction: the transfer of energy by collisions between neighboring molecules without any net external motion. Conduction does occur in the atmosphere, but is very inefficient because of the distance between air molecules. Conduction is much more important in solid substances, such as associated with heat transfer in soil. Example candles, holding the pin above the flame of candle. The transmission of heat from one end of the pin to the other, and from the pin to your finger, occurs by conduction. Heat transferred in this fashion always flows from warmer to colder regions. The greater temperature difference the more rapid heat transfer. The molecules inside of the pin is consider are good conductors of heat versa air which is very poor conductor of the heat. Convection: The transfer of heat by the mass movement of a fluid (such as water and air) is called convection Convection occurs both in the atmosphere and ocean. For example turbulence in the atmosphere is a very efficient means of vertical transfer of heat. The term ADVECTION (applied to atmosphere or ocean) refers to horizontal "convection" transferring energy heat from one place to another via movement air (wind) Example of convection is the spot of paragliding is dependent on thermals, also the birds use the rising thermal. Hawks, for example, seek out rising thermals and ride them up into the air as they scan the landscape for prey. Radiation: the propagation of electromagnetic waves through space.

Earth's Energy Balance

Energy entering top of atmosphere = Energy leaving top of atmosphere Energy gained by atmosphere = Energy lost by atmosphere The atmosphere of Earth is very thin Energy gained by Earth's surface = Energy lost by Earth's surface

How long does it take sunlight to reach Earth?

It takes 8 minutes

Terrestrial or Longwave Radiation

Planets mainly emit - infrared radiation Radiation emitted by planets occurs mainly at wavelengths than those contained in solar radiation Solar Radiation ("Shortwave") Terrestrial Radiation ("Longwave")

Sudden Removal of all Greenhouse Gases

Removal of greenhouse gases would decrease downward directed radiation; now upward emitted radiation from surface is greater than downward energy absorbed by surface Thus, average surface temperature starts to decrease. As surface cools, radiation emitted by surface (upward) decreases until balance is restored. At this point, cooling stops Average surface temperature = -18°C

Most reflective surfaces

Snow (fresh) - 80% Snow (old) - 60% The older snow becomes slighter darker, grey color, dirt with some material and lower albedo Clouds cumulus and stratus are very bright from space, and reflect a lot of sunlight Cirrus cloud are high cloud and altostratus cloud is more middle cloud are also reflect but not as much as cumulus Asphalt and forrest, liquid water (dark ocean from the space) and soil, dark wet are absorb most of incoming sunlight Ice cube have low albedo as well around 35%. Snow is more transparent than ice cube. Deserts are high albedo , example. North Africa, Saudia Arabia

Solar radiation

Sunlight's peak radiation intensities per wavelength are in the visible spectrum! Overall, sunlight is primarily made up of the following: Visible Light - has a maximum emission 0.5, brightest day, 0.4 - 0.7, 44% Infrared Radiation - near visible light, 0.7 - 1.5 micrometers 48% (37+11) Ultraviolet Radiation - can cause of skincare, sunburns 7%

Electromagnetic Radiation

The main way energy is transferred between the Sun and Earth. "The interaction between electromagnetic radiation and gases in the Earth's atmosphere is the basis of the so-called greenhouse effect. Therefore, an exposition on...electromagnetic radiation is necessary before embarking on an explanation of the greenhouse effect." Radiation is the transfer of energy by particle waves Particles are also called photons, meaning packets of energy. The most important general characteristic is its wavelength (), defined as the crest-to-crest distance. Radiation travels through space at the speed of light in a vacuum - 3 x 108 meters per second (186,000 miles per second)

Absorption of Radiation by gases in the Earth's Atmosphere

The strongest absorbers of infrared radiation are water vapor and carbon dioxide, and poor absorbers of visible solar radiation. Nitrous oxide, methane, and ozone, which is most abundant in the stratosphere absorb infrared radiation emitted from the earth's surface, they gain kinetic energy. The gas molecules share this energy by colliding with neighboring air molecules, such as oxygen and nitrogen (both of which are poor absorbers of infrared radiation). These collisions increase the average kinetic energy of the air, which results in an increase in temperature. Thus, most of the infrared radiation emitted from the earth's surface keeps the lower atmosphere warm Look again at Fig 2.11 and observe that, in the bottom diagram, there is a region between about 8 and 11 micrometers where neither water vapor nor carbon dioxide readily absorbs infrared radiation. Because these wavelengths of emitted radiation pass upward through the atmosphere and out into space, this wavelength range is known as the atmospheric window. Clouds can enhance the atmospheric greenhouse effect. Tiny liquid droplets are selective absorbers in that they are good absorbers of infrared radiation but poor absorbers of solar radiation. Clouds even absorb the wavelengths between 8 and 11 micrometers, which are otherwise "passed up" by water vapor and carbon dioxide. Thus, they have the effect of enhancing the atmospheric greenhouse effect by closing the atmospheric window.

Solar vs. Terrestrial Radiation

The sun is much hotter than planets; therefore, solar radiation consists primarily of shorter wavelengths than terrestrial radiation Terrestrial radiation - longwave radiation example Earth 288K, majority radiation on Earth between 5 and 20 micrometers. Shortwave radiation example sun 6000K, sun emits higher intensity radiation Human emit infrared type of radiation right now.

Earth's Greenhouse Effect

Without the greenhouse effect, the surface temperature of Earth would be Very Cold (-18°C/0°F) Greenhouse gases play an important role in shaping climate. More GHGs - warmer climate --> more ongoing radiation is going be absorb trapped --> heat up and meet radiation in both directions Less GHGs - cooler climate