Transcript Chapter 23.2

Ch. 23.2 Solar Energy and
the Atmosphere
Radiation
 Radiation—all forms of energy that travel
through space as waves.
 Includes visible light, x-rays, radio waves,
uv radiation, and more.
 The difference in types of radiation is their
wavelength.
 The electromagnetic spectrum is made
up of electromagnetic waves of all
different wavelengths.
 Almost all energy from the sun reaches
earth as electromagnetic waves (some is in
particle form).
 Solar radiation must pass through the
atmosphere before reaching the earth’s
surface.
Atmosphere’s possible effect on
solar radiation:
 Shorter wavelengths absorbed by oxygen
and nitrogen in upper atmosphere
(mesosphere and thermosphere).
 UV rays absorbed by oxygen in stratosphere
to form ozone.
 Longer wavelengths (visible and infrared)
reach lower atmosphere.
 Most infrared radiation is absorbed by
carbon dioxide and water vapor in
troposphere.
 Very little visible light absorbed.
Scattering
 Gas and particles in the atmosphere reflect
and bend light waves in all directions,
without changing their wavelengths.
 Some radiation scattered back into space.
 Because of scattering, sunlight reaches
earth from all directions.
 Short wavelengths (blue) are most easily
scattered, so sky appears blue.
 When sun is low on horizon, more blue than
red is scattered (more blue wavelength
photons eventually end up being scattered
back into space), so more red light
wavelengths reach the surface, so the sun
appears red.
Reflection
 Only 20% of solar radiation is absorbed by
the atmosphere.
 30% is scattered back to space or
reflected by clouds, or the earth’s surface.
 Remaining 50% is absorbed by earth’s
surface. Dark colored surfaces absorb
more…Light colors reflect more. (Table
23.1)
 Since 30% of solar radiation that reaches
the earth is reflected or scattered back to
space, earth has an average reflectivity of
30%.
 The albedo of earth is 0.3.
 Albedo of the moon is 0.7 (70% of light is
reflected).
Absorption and Infrared Energy
 Radiation absorbed by earth’s surface is reemitted as longer wavelength infrared rays.
 Some gases in the lower atmosphere
absorb the longer infrared rays, thus
trapping heat and warming the air.
 The process of trapping and warming is
known as the Greenhouse Effect.
 Concern that excessive release of
greenhouse gases by humans may lead to
global warming.
Variations in Temperature
 Radiation heats the earth unequally,
depending on several factors…
 Latitude
 Elevation
 Nearness to bodies of water.
 Influence of wind patterns.
 Daily and seasonal delays (2.00 p.m., and
late July).
Conduction and Convection
 In conduction, the energy and movement
of atoms or molecules is transferred to
adjacent atoms or molecules, which
transfers heat.
 Solids are good conductors, but not
gases, because gas molecules are much
further apart.
 Lower atmosphere is heated through
conduction by contact with the warm
surface.
 Convection is the transfer of heat by the
movement of liquids or gases..
 In the atmosphere, uneven heating results in
warm air rising, and cold air sinking.
 Rising warm air creates low pressure;
sinking cold air creates high pressure.
 Air always moves from high to low pressure,
creating wind.