Ch. 23.2 Solar Energy and Ch. 23.2 Solar Energy and the Atmospherethe Atmosphere

RadiationRadiation

RadiationRadiation—all forms of energy that travel —all forms of energy that travel through space as waves.through space as waves.

Includes visible light, x-rays, radio waves, Includes visible light, x-rays, radio waves, uv radiation, and more.uv radiation, and more.

The difference in types of radiation is their The difference in types of radiation is their wavelengthwavelength..

The The electromagnetic spectrumelectromagnetic spectrum is made is made up of electromagnetic waves of all up of electromagnetic waves of all different wavelengths.different wavelengths.

Almost all energy from the sun reaches Almost all energy from the sun reaches earth as electromagnetic waves (some is in earth as electromagnetic waves (some is in particle form).particle form).

Solar radiation must pass through the Solar radiation must pass through the atmosphere before reaching the earth’s atmosphere before reaching the earth’s surface.surface.

Atmosphere’s possible effect on Atmosphere’s possible effect on solar radiation:solar radiation:

Shorter wavelengths absorbed by oxygen Shorter wavelengths absorbed by oxygen and nitrogen in upper atmosphere and nitrogen in upper atmosphere (mesosphere and thermosphere).(mesosphere and thermosphere).

UV rays absorbed by oxygen in UV rays absorbed by oxygen in stratosphere to form ozone.stratosphere to form ozone.

Longer wavelengths (visible and infrared) Longer wavelengths (visible and infrared) reach lower atmosphere.reach lower atmosphere.

Most infrared radiation is absorbed by Most infrared radiation is absorbed by carbon dioxide and water vapor in carbon dioxide and water vapor in troposphere.troposphere.

Very little visible light absorbed.Very little visible light absorbed.

ScatteringScattering

Gas and particles in the atmosphere reflect Gas and particles in the atmosphere reflect and bend light waves in all directions, and bend light waves in all directions, without changing their wavelengths.without changing their wavelengths.

Some radiation scattered back into space.Some radiation scattered back into space. Because of scattering, sunlight reaches Because of scattering, sunlight reaches

earth from all directions.earth from all directions. Short wavelengths (blue) are most easily Short wavelengths (blue) are most easily

scattered, so sky appears blue.scattered, so sky appears blue.

When sun is low on horizon, more blue than When sun is low on horizon, more blue than red is scattered (more blue wavelength red is scattered (more blue wavelength photons eventually end up being scattered photons eventually end up being scattered back into space), so more red light back into space), so more red light wavelengths reach the surface, so the sun wavelengths reach the surface, so the sun appears red.appears red.

ReflectionReflection

Only 20% of solar radiation is absorbed Only 20% of solar radiation is absorbed by the atmosphere.by the atmosphere.

30% is scattered back to space or 30% is scattered back to space or reflected by clouds, or the earth’s surface.reflected by clouds, or the earth’s surface.

Remaining 50% is Remaining 50% is absorbedabsorbed by earth’s by earth’s surface. Dark colored surfaces absorb surface. Dark colored surfaces absorb more…Light colors reflect more. (Table more…Light colors reflect more. (Table 23.1)23.1)

Since 30% of solar radiation that reaches Since 30% of solar radiation that reaches the earth is reflected or scattered back to the earth is reflected or scattered back to space, earth has an average reflectivity of space, earth has an average reflectivity of 30%.30%.

The The albedo albedo of earth is 0.3.of earth is 0.3. Albedo of the moon is 0.7 (Albedo of the moon is 0.7 (70%70% of light is of light is

reflected).reflected).

Absorption and Infrared EnergyAbsorption and Infrared Energy

Radiation absorbed by earth’s surface is re-Radiation absorbed by earth’s surface is re-emitted as longer wavelength infrared rays.emitted as longer wavelength infrared rays.

Some gases in the lower atmosphere Some gases in the lower atmosphere absorb the longer infrared rays, thus absorb the longer infrared rays, thus trapping heat and warming the air.trapping heat and warming the air.

The process of trapping and warming is The process of trapping and warming is known as the known as the Greenhouse Effect.Greenhouse Effect.

Concern that excessive release of Concern that excessive release of greenhouse gasesgreenhouse gases by humans may lead to by humans may lead to global warming.global warming.

Variations in TemperatureVariations in Temperature

Radiation heats the earth unequally, Radiation heats the earth unequally, depending on several factors…depending on several factors…

LatitudeLatitude ElevationElevation Nearness to bodies of water.Nearness to bodies of water. Influence of wind patterns.Influence of wind patterns. Daily and seasonal delays (2.00 p.m., and Daily and seasonal delays (2.00 p.m., and

late July).late July).

Conduction and ConvectionConduction and Convection

In In conductionconduction, the energy and movement , the energy and movement of atoms or molecules is transferred to of atoms or molecules is transferred to adjacent atoms or molecules, which adjacent atoms or molecules, which transfers heat.transfers heat.

Solids are good conductors, but not Solids are good conductors, but not gases, because gas molecules are much gases, because gas molecules are much further apart.further apart.

Lower atmosphere is heated through Lower atmosphere is heated through conduction by contact with the warm conduction by contact with the warm surface.surface.

ConvectionConvection is the transfer of heat by the is the transfer of heat by the movement of liquids or gases..movement of liquids or gases..

In the atmosphere, uneven heating results in In the atmosphere, uneven heating results in warm air rising, and cold air sinking.warm air rising, and cold air sinking.

Rising warm air creates low pressure; Rising warm air creates low pressure; sinking cold air creates high pressure.sinking cold air creates high pressure.

Air always moves from high to low pressure, Air always moves from high to low pressure, creating wind.creating wind.