Radiation Insolation and Energy Transfer Solar Radiation Sun

Radiation, Insolation, and Energy Transfer

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/cm 2/minute

Classifying Radiation • Classified based on wavelength,

The Electromagnetic Spectrum Micrometers or microns (µ) = 1/1 000 or 0. 000 001 or 10 -6 Hence Microwaves are about 1 mm - 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% Insolation 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.

Radiation Laws • All objects emit radiation. more radiation less radiation • Hot objects emit more radiation (per unit area) than cold objects.

Radiation Laws (Wein’s Law) The hotter the radiating body, the shorter the wavelength of maximum radiation. Sun: 6000ºC (11, 000ºF) Earth: 15ºC (60ºF)

Getting through the atmosphere: • • • Transmission Scattering Reflection Absorption Refraction Energy pathways and principles

Direct radiation Transmission Direct radiation • Energy is passed through the atmosphere • Energy/heat provided to the Earth system

Scattering (diffuse radiation) Backscattering (albedo) • Energy “bounces off” particles in the atmosphere.

Scattering Rayleigh Scattering: selective scattering if dust is about 1/10 the wavelength of light (. 5 micron) VIB G YOR 4 x 1 x Scattering & light short , scatter • result? 1. sun appears yellow as VIB is scattered out. 2. sky is blue: VIB is down-scattered and becomes prominent. Mie Scattering: white scattering, non- selective, occurs with bigger particles, about 30 x the wavelengths of light. 1. salt crystals: things whiter at distance 2. bluer sky at high elevation - less white 3. white clouds. distance , scatter • result?

Albedo ( ) Reflection • reflective quality of a surface Light color high Dark color low • Energy is bounced directly back out to space (energy loss to Earth’s system)

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 of radiation, by wavelength, in response to change in density of medium.

Refraction Change in 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 H 2 O

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.

Adiabatic Cooling and Warming

Phase Changes (Latent Heat) Ice Evaporation 585 calories/gram Water Vapor Releases Energy Water Freezing Condensation Sublimation Melting Stores Energy Sublimation 80 calories/gram

100 Units Outgoing 100 Units 30 Units 64 Units Longwave 3 Ozone 19 direct absorb 48 Units 6 Units Conduction/ Convection 22 Latent Heat 14 Units Greenhouse

Key Points • • Electromagnetic radiation and spectrum Radiation laws and solar radiation Energy pathways and transfer principles Earth energy budget