Geoscience Reference
In-Depth Information
as cadmium, mercury, chromium, and lead compounds. These
pollutants can originate from stationary locations, such as fac-
tories and power plants, or mobile sources, such as automo-
biles. When ingested in large concentrations over a long period
of time, these pollutants can accumulate in human tissue and ul-
timately cause cancer, immune disorders, and a variety of neu-
rological, reproductive (e.g., reduced fertility), developmental,
respiratory, and other health problems.
some of it is directly absorbed by various components of
the atmosphere. These various pathways directly influence
climate on Earth and will be discussed thoroughly later in
the chapter.
Heat Transfer
Before exploring the various pathways that solar radiation
follows on Earth, it is useful to first understand how heat is
transferred to Earth's atmosphere, land, and oceans. This dis-
cussion is based on the first law of thermodynamics, which
states that energy cannot be created or destroyed; it can only
change forms. Heat is a form of energy, related to the motion of
atoms and molecules, which is transferred in several different
ways that are easy to imagine (Figure 4.15). This transfer fol-
lows the second law of thermodynamics, which can be stated as
follows: heat can spontaneously flow from a region of higher
temperature to an area of colder temperature, but not the other
way around.
The next time that you are around a campfire, consider
that heat is transferred by
radiation
. This process involves the
creation of electromagnetic waves, either as visible light or
The Flow of solar Radiation
on Earth
Once solar radiation reaches Earth, it flows along several
pathways within the atmosphere and to the surface. Some ra-
diation flows straight from the Sun to the surface of Earth as
insolation
, which is most accurately defined as the amount
of solar radiation measured in watts per square meter (W/m
2
)
that strikes a surface perpendicular to the Sun's incoming
rays. Most solar radiation, however, follows a very indirect
path. Some of it bounces around like a ping-pong ball, while
Electromagnetic
waves (infrared,
visible, ultraviolet)
Cool end,
atoms vibrate
slower
Cooler water
sinks
Cooler water
sinks
Atoms collide
in middle
Fire
Hot end,
atoms vibrate
faster
Hot water
rises
(a)
Conduction
Transfer of heat by
collision of atoms
or molecules
(b)
Convection
Transfer of heat by
movement of fluids
in semicircular
pattern
(c)
Radiation
Transfer of heat by
electromagnetic
radiation
Figure 4.15 mechanisms of heat transfer.
(a) Conduction transfers heat by collisions between fast-vibrating atoms or molecules (hot)
and slower-vibrating atoms or molecules (cool). (b) Convection is the transfer of heat by the large-scale movement of matter. (c) Radiation
is the transfer of heat by electromagnetic radiation, usually in the form of infrared, visible, or UV waves.
Insolation
Amount of solar radiation measured in watts per
square meter (W/m
2
) that strikes a surface perpendicular to the
Sun's incoming rays.
Energy that is transmitted in the form of rays or
Radiation
waves.
