Energy and the Atmosphere

 

Note: Remember you are responsible for graphs, charts and other items that form part of the overall summary of this topic.

 

I) Sunlight – energy source for Earth

A) Energy in a sunbeam

1) Cannot be measure directly

2) Need to measure the effect energy has on an object’s temperature

(a) Calorie

(1) The amount of energy needed to raise the temperature of 1 g of water by 1º Celsius

B) Sunlight striking the Earth is affected by several factors

1) Latitude and longitude

(a) Sunlight strikes the Earth at many angles

2) Seasons

(a) Earth’s tilt

3) Time of Day

C) Sunlight in the atmosphere

1) Atmosphere absorbs ultraviolet radiation

(a) Heats the thermosphere and upper stratosphere

(b) Ozone layer

2) Gas and clouds in troposphere also absorb some sunlight energy

3) Clouds reflect light energy back to space and down to Earth’s surface

D) Sunlight at Earth’s surface

1) Reflected back to atmosphere

2) Absorbed by the surface

II) The atmosphere’s energy sources

A) Conduction

1) Movement of heat energy from molecule to molecule

(a) Transfers heat from the Earth to the atmosphere

B) Convection

1) Movement of heat by warm and cold currents

C) Latent heat

1) Energy stored in molecules through evaporation

D) Radiation

1) Release and transfer of energy in wavelengths of heat and light

E) Greenhouse effect

1) Ability of the atmosphere to let energy in and prevent it from escaping back into space

F) Energy budget

1) Sum of all energy gains and losses

Reflection, scattering and absorption of incoming sunlight

  • sun radiates mostly in the visible band, but also in the ultraviolet (shorter wavelength)

  • 51% of the solar radiation striking the earth and its atmosphere is absorbed at the surface

  • 19% absorbed by the atmosphere

  • 30% reflected back into space

  • shortest wavelengths of solar radiation (most dangerous to life) are absorbed by molecules in the upper and middle atmosphere

  • ozone (O3) selectively absorbs ultraviolet radiation while allowing visible radiation to pass through relatively unhindered

  • reflection significantly affects the solar radiation  that reaches the ground (reflection off air molecules, clouds or ground; light colored or shiny objects reflect more radiation than dark objects; energy that is reflected cannot be absorbed or transmitted through an object)

  • Earth's surface, atmosphere and clouds emit radiation in the infrared band and near-infrared band

  • outgoing infrared (IR) radiation from the Earth's surface (terrestrial radiation) is absorbed by water vapor and carbon dioxide (greenhouse gases); this emits IR in all directions, including back to the Earth's surface.  This re-emission to the Earth's surface maintains a higher temperature on our planet than what would be possible without the atmosphere.

  • condensed water is also an efficient absorber and emitter of IR radiation

The Annual Mean Global Energy Budget

  • when averaged over a year, the incoming energy in both the Earth and its atmosphere equals the outgoing energy

  • considering the entire Earth-atmosphere system, the amount of radiation entering the system must equal the amount leaving, or the system would continually heat or cool

  • not all of this energy is radiative energy; some is latent heat

  • considering the atmosphere alone, we find that the atmosphere experiences radiative cooling (the atmosphere is kept from a net cooling by the addition of energy by latent heat)

  • the atmosphere has a warming effect on Earth's surface (Atmospheric greenhouse effect)

  • if Earth had no atmosphere, the globally averaged surface temperature would be -18 degrees Celsius; since Earth has an atmosphere, the average surface temperature actually is 15 degrees Celsius

  • the atmosphere acts as a greenhouse because of gases that selectively allow solar radiation to pass through but absorb and then re-emit terrestrial radiation

  • the greenhouse gases (water vapor, CO2, O2, NO, and methane (CH4)) are selective as to which wavelengths they absorb; O3 absorbs shortwave ultraviolet radiation while water vapor absorbs IR radiation

 

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