RADIATION
Insolation in tercepted sol ar radi ation
Earth intercepts of the sun’s radiation
Solar constant amount of radiation received at the top of the atmosphere (on a plane surface perpendicular to sun’s rays) = 1372 Watts/m 2 (reduced by half by the time it reaches surface of earth)
energy per unit area amount of energy received at earth’s surface per unit of area (square meter, square inch, etc.)
surface receives more energy per unit area (more concentrated) when the sun’s rays are vertical (direct) less energy per unit area (less concentrated) when sun’s rays are oblique (slanted)
Electromagnetic Radiation Radiant energy
Earth, sun, everything! radiates energy –tropical zones receive more energy than they radiate –polar zones radiate more energy than they receive –excess heat transfer: ocean currents, winds
Sun’s energy from atomic fusion: hydrogen atoms fused into helium atoms –lost mass converted to energy
Electromagnetic radiation (EMR) –travels at speed of light (93 million miles in 8.5 minutes) –travels in waves Wavelength: size of wave
electromagnetic spectrum “ruler” to measure different types of energy
Solar (Sun) vs. Terrestrial (Earth) Radiation: sun’s SHORTWAVE : –gamma, X-ray, UV, visible, infrared earth’s LONGWAVE : –infrared
Absorption of radiation in the atmosphere: Shortwave absorbers: ozone, water vapor Longwave absorbers: water vapor, carbon dioxide, ozone “The atmosphere is relatively transparent to shortwave radiation and opaque to longwave radiation”
Types of heat energy Sensible heat thermometer Latent heat released or stored in a phase change
First Law of Thermodynamics: energy cannot be created or destroyed, but can be: CONVERTED TRANSFERRED
Energy Transfer Mechanisms: Conduction energy transmitted within a substance by collision of molecules Convection vertical motion of energy from one place to another through physical motion of air
Energy Budget/Balance Exchange of energy between the sun, the earth, and the atmosphere –balance between incoming and outgoing
radiation entering the atmosphere can be: absorbed transformed, re-emitted reflected “albedo” : percentage of incoming radiation that is reflected; earth/atmosphere albedo = 31 %
Incoming solar shortwave radiation
Longwave exchanges between surface, atmosphere, and space:
The Balancing Act = 143 energy leaves surface as: –radiation –latent heat (evaporation) –sensible heat (conduction) losses: = 144
Counterradiation by the atmosphere:
Greenhouse Effect atmosphere admits most shortwave; absorbs and counterradiates longwave allows average surface temperature to be 59 o F rather than - 4 o F
Review of energy balance
Latitudinal differences in net radiation
Seasonal and Diurnal (daily) differences in insolation
Seasonal and Diurnal (daily) differences in net radiation