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/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.

InsolationThe 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.

Radiation Laws• All objects emit radiation.

• Hot objects emit more radiation (per unit area) than cold objects.

less radiationmore radiation

Rad

iati

on

Law

s(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:

Energy pathways and

principles• Transmission

• Scattering

• Reflection

• Absorption

• Refraction

Transmission

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

Direct radiation

Direct radiation

Scattering

• Energy “bounces off” particles in the atmosphere.

Backscattering (albedo)Scattering

(diffuse radiation)

ScatteringRayleigh 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.

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.

distance , scatter

• result?

Scattering & light

short , scatter

• result?

Reflection

• Energy is bounced directly back out to space (energy loss to Earth’s system)

Albedo ()

• reflective quality of a surface

Light color high

Dark color low

Absorption

• Energy is absorbed by the atmosphere or the surface

• Thermal (heat) energy created.

• ozone

• oxygen

• carbon dioxide

• water vapor

• liquid water / clouds

Refraction• Change in direction

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

RefractionChange in direction

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

• Conduction

• Convection

• Adiabatic Cooling and Warming

• Latent Heat in Phase Changes of H2O

Four Heat Transfer Mechanisms

Molecule to molecule energy transfer

When molecules collide, higher energy molecules excite lower temperature molecules, thereby transferring kinetic (heat) energy.

Conduction

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.

Convection

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

Adiabatic Cooling and Warming

Ice80 calories/gram

Water

585 calories/gram

Water Vapor

Phase Changes (Latent Heat)

Rele

ase

s En

erg

ySto

res E

nerg

y

Freezing

Condensation

Melting

Evaporation

Su

bli

mat

ion S

ub

lima tio n

30 Units

64 Units Longwave

22 Latent Heat

6 Units

48 Units

64 Units

14 Units Greenhouse

6 Units Conduction/Convection

19 direct absorb

3 Ozone

100 Units

100 Units Outgoing

Key Points• Electromagnetic radiation and spectrum

• Radiation laws and solar radiation

• Energy pathways and transfer principles

• Earth energy budget