Solar Energy and
Weather
“Forecast for tonight: dark.”
- George Carlin
“A day without laughter is like a day
without sunshine, and a day without
sunshine is like, you know, night.”
- Steve Martin
Heat
 Thermal energy is the energy of
motion of particles – such as atoms,
ions, and molecules – in a substance.
 Heat is defined as thermal energy
transferred from one object to another.
 The three mechanisms of heat transfer
are conduction, convection, and
radiation.
Conduction
 Conduction is the mechanism of heat
transfer in which highly energetic atoms
or molecules collide with less energetic
atoms or molecules, giving them energy.
All of the atoms remain in their own
place, however, only the
energy transfers.
Convection
 Convection is the mechanism of heat
transfer in which highly energetic
molecules move from one place to
another.
Radiation
 Radiation is the
mechanism of heat
transfer in which atoms or
molecules emit
electromagnetic waves.
These waves carry the
energy through space and
deposit it only when they
interact with some form of
matter.
Solar Radiation
 Radiant energy takes the form of
electromagnetic waves. The electromagnetic
waves that carry radiant energy from the sun to
the earth fall mostly within a very narrow range
of wavelengths.
Solar Radiation
Radiant Energy Reaching Earth
 Because space contains very little
matter, the solar energy that arrives at
Earth’s outer atmosphere is essentially
unchanged from when it left the sun.
 The amount of radiant energy that hits
one square meter of earth’s outer
atmosphere every second is called the
solar constant and its value is:
1367 J/m2s
Direction of Sun’s Rays
 Since the amount of energy differs depending
on the direction of incoming rays, the solar
constant is defined for the situation in which the
Sun’s rays arrive perpendicular to the surface of
the earth.
The Energy Budget Diagram
 Two different reactions
occur when solar energy
penetrates the earth’s
atmosphere.
 Some of the energy is
reflected back into space
unchanged and the rest is
absorbed, either by the
atmosphere or Earth’s
surface.
Emission of Light
 Earth, the Moon,
and other planets
do not emit visible
light like the Sun
and other stars do.
You see the Moon
in the night sky
because of the
Sun’s light being
reflected off of it.
Emission of Light
 Although the Moon and other planets do
not emit visible light, it doesn’t mean that
they do not emit electromagnetic
radiation.
 Objects cooler than 727oC emit radiation
with wavelengths longer than that of
visible light.
 Earth’s radiation is in the Infrared Range
of the spectrum.
Earth’s Constant Temperature
 Earth maintains an energy balance and
temperature by radiating as much
energy out into space as it absorbs from
the Sun.
 The energy transformations that occur
between the time solar radiation is
absorbed and the time it is re-emitted as
infrared radiation are the transformations
that drive weather systems.
What is the only way for energy
to travel from the Sun to Earth?
Explain why.
 Answer:

The only way for energy to travel from the
Sun to Earth is by radiation. Convection
and conduction require atoms, but there is
nearly a complete vacuum between the
Earth and the Sun.
Name the categories of
electromagnetic waves that
make up radiant enrgy from the
Sun.
 Answer:

Radiant energy from the Sun is
concentrated in the infrared, visible, and
ultraviolet parts of the spectrum.
Define the term “solar
constant”.
 Answer:

The solar constant is the amount of radiant
energy from the Sun that hits one square
metre of Earth’s atmosphere per second,
with the square metre held perpendicular
to the direction of the Sun’s rays (that is,
so that an object held on that square metre
would not cast a shadow).
How does Earth maintain it’s
relatively constant
temperature?
 Answer:

Earth maintains a temperature balance by
absorbing 70 percent of the sunlight falling
on the hemisphere facing the Sun. It
reflects 30 percent of the light and emits
infrared (heat) radiation from its entire
surface at all times. The atmosphere traps
some of this heat and slows the cooling so
that the night and daytime temperatures
are fairly constant to within about 10
percent.