Solar Radiation: Sun to Earth • Speed of light: 300,000 km/second (186,000 miles/sec.) • Distance to Earth: 150 million km (93 million miles) • Radiation reaches us in about 8.3 minutes
Radiation • Radiation: energy transferred in the form of electromagnetic waves • no transfer of matter • no material medium needed Solar Constant = 2 calories/cm2/minute
Classifying Radiation • Classified based on wavelength,
The Electromagnetic Spectrum Micrometers or microns (µ) = 1/1 000 000 or 0.000 001 or 10-6 Hence Microwaves are about 1mm - long.Radio waves are about a meter to 1000 meters long.
The sun’s energy distribution: • UV and shorter = 7% • Visible light = 50% • Infrared (IR) = 43% • Thermal Infrared, the longest infrared, = heat. • Microwaves(1 mm – 30 cm) are used for long distance communications. • Radar is portion of microwave. Microwave cooking discovered on Navy ships. Takes 1/2 the energy of conduction or convection ovens - more efficient. • Why doesn’t microwave pass through window of oven? • Gamma - used for food safety. Discovered after nuclear blasts. Insolation
Radiation Laws • All objects emit radiation. • Hot objects emit more radiation (per unit area) than cold objects. more radiation less radiation
Radiation Laws Sun: 6000ºC (11,000ºF) Earth: 15ºC (60ºF) (Wein’s Law) The hotter the radiating body, the shorter the wavelength of maximum radiation.
Getting through the atmosphere:Energy pathways and principles • Transmission • Scattering • Reflection • Absorption • Refraction
Transmission Direct radiation Direct radiation • Energy is passed through the atmosphere • Energy/heat provided to the Earth system
Scattering • Energy “bounces off” particles in the atmosphere. Backscattering (albedo) Scattering (diffuse radiation)
Scattering & light • short , scatter • result? Scattering Rayleigh Scattering:selective scattering if dust is about 1/10 the wavelength of light (.5 micron) VIB G YOR 4x 1x 1. sun appears yellow as VIB is scattered out. 2. sky is blue: VIB is down-scattered and becomes prominent. • distance , scatter • result? Mie Scattering:white scattering, non-selective, occurs with bigger particles, about 30x the wavelengths of light. 1. salt crystals: things whiter at distance2. bluer sky at high elevation - less white 3. white clouds.
Albedo () • reflective quality of a surface Reflection • Energy is bounced directly back out to space (energy loss to Earth’s system) Light color high Dark color low
Absorption • ozone • oxygen • carbon dioxide • water vapor • liquid water / clouds • Energy is absorbed by the atmosphere or the surface • Thermal (heat) energy created.
Refraction • Change in direction direction of radiation, by wavelength, in response to change in density of medium.
Refraction Change in direction direction of radiation, by wavelength, in response to change in density of medium.
Four Heat Transfer Mechanisms • Conduction • Convection • Adiabatic Cooling and Warming • Latent Heat in Phase Changes of H2O
Conduction Molecule to molecule energy transfer When molecules collide, higher energy molecules excite lower temperature molecules, thereby transferring kinetic (heat) energy.
Convection Heat is transferred by the movement, from place to place, of a gas or liquid. The principal motion is vertical. All heated gases and liquids experience this kind of “mixing” heat exchange.
Adiabatic Cooling and Warming When air rises it expands and cools as its pressure is decreased. Thus, when it descends, it is warmed, as pressure increases. This change takes place without the addition or subtraction of energy from another source.
Phase Changes (Latent Heat) Ice 80 calories/gram Water 585 calories/gram Water Vapor Freezing Melting Sublimation Releases Energy Stores Energy Sublimation Evaporation Condensation
100 Units Outgoing 100Units 6Units 30Units 64Units 64Units Longwave 6Units Conduction/Convection 22 Latent Heat 14Units Greenhouse 3 Ozone 19 direct absorb 48Units
Key Points • Electromagnetic radiation and spectrum • Radiation laws and solar radiation • Energy pathways and transfer principles • Earth energy budget