Solar Radiation and Insolation

Incoming solar radiation: The output of electromagnetic energy emitted from the Sun that is received by the Earth.

Intensity of radiation = The rate at which energy is radiated.

X = wavelengthY = temperature

Inverse relationship: The higher the

temperature the shorter the

wavelength of radiation.

X

YInsolation is the

portion of the Sun’s energy that is

received by the Earth.

The intensity of insolation from the

Sun on a specific area of Earth is dependent

on a number of factors.

Effects of Earth’s Atmosphere on Insolation

Ozone

Ozone

Nearly all ultraviolet (short wave) radiation is

ABSORBED by ozone (O3 gas) in Earth’s upper

atmosphere.

H20 vapor, methane and CO2 can ABSORB infrared (long wave)radiation.

Much of the incoming solar radiation is REFLECTED or SCATTERED back into space, into the atmosphere or to Earth.

Aerosols --solids and liquids in the atmosphere – ie: pollutants, dust , ice, ash, water droplets, etc.. cause this scattering of radiation.

Balance of Energy from Insolation and Earth’s

Surface Radiation

Nearly 50% of insolation reaches Earth’s surface.

Nearly 50% of insolation is absorbed or reflected by the atmosphere.

Insolation received by the Earth’s surface is changed to heat energy. The Earth’s radiates this heat energy back into the atmosphere.

The amount of energy absorbed from insolation = Earth’s surface

radiation.

DYNAMIC EQUILIBRIUM

Factors Affecting Absorption and Reflection of Insolation

Angle of IncidenceThe angle of incidence is the

angle at which insolation strikes the Earth’s surface.

The higher the angle of incidence = The more insolation absorbed.

The lower the angle of incidence = The more likely the insolation will be scattered or reflected.

Sun is high in the sky Sun is low in the sky

Factors Affecting Absorption and Reflection of Insolation

Surface Characteristics The texture and color of features on the Earth’s surface can affect

the absorption of insolation.

Rough, uneven surfaces and/or dark surfaces

absorb more insolation.

Light and smooth surfaces tend to

reflect rather absorb insolation.

Factors Affecting Absorption and Reflection of Insolation

Change of State and Transpiration

Insolation may cause a change in phase

for water.

Insolation may fuel plant growth and increase the rate of

transpiration -- the process whereby a plant releases water

vapor into the atmosphere.

In both cases, insolation is neither reflected or absorbed, but transforms into potential energy.

Land vs. Water Heating

Equal areas of land and water do not heat up and/or cool off at the same

rate.Water heats and cools more slowly than land for a number or reasons:

Water is transparent and allows a greater

area for insolation to penetrate

compared to a land surface.

Water has a higher specific heat than

the land.

Convection currents in water allow for the distribution of energy absorbed

through insolation over a large

volume.

Some of the insolation striking the water may lead to a phase change

(evaporation). The energy from insolation is transformed to potential

energy.

The Greenhouse Effect

1. Short wave insolation that reaches the Earth’s surface is

absorbed.

2. The Earth’s surface reradiates the energy absorbed from insolation. However, the energy radiated has a longer

wavelength (infrared radiation).

3. “Greenhouse gases” in the atmosphere (ie: CO2,

H2O vapor, etc…)absorb the infrared radiation emitted

from the Earth .

4. The absorption of this radiation in the

atmosphere warms our planet.

1.

2.

3.

4.

The Greenhouse Effect

Modern history has shown an increase in the amount of “greenhouse gases” in the

atmosphere.

This increase is due primarily to human activity, such as the

burning of fossil fuels and emission of pollutants in to atmosphere.

The increase in “greenhouse gases” has led to an increase in

the amount of radiation absorbed from the Earth. This, in turn, has led to an increase in

average global temperatures. Result? Melting ice caps!!