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.
Y
X
X = wavelength
Y = temperature
Inverse relationship:
The higher the
temperature the
shorter the
wavelength of
radiation.
Insolation 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
H20 vapor, methane
and CO2 can ABSORB
infrared (long
wave)radiation.
Ozone
Much of the incoming solar radiation
is REFLECTED or SCATTERED back into
space, into the atmosphere or to
Earth.
Ozone
Nearly all ultraviolet (short
wave) radiation is
ABSORBED by ozone (O3
gas) in Earth’s upper
atmosphere.
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.
The amount of energy absorbed
from insolation = Earth’s surface
radiation.
DYNAMIC EQUILIBRIUM
Insolation received
by the Earth’s
surface is changed
to heat energy. The
Earth’s radiates this
heat energy back
into the
atmosphere.
Factors Affecting Absorption and Reflection of Insolation
Angle of Incidence
The higher the angle of incidence = The more
insolation absorbed.
Sun is high in the sky
The angle of incidence is the
angle at which insolation
strikes the Earth’s surface.
The lower the angle of incidence = The more
likely the insolation will be scattered or
reflected.
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).
1.
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.
3.
2.
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!!