Geoscience Reference
In-Depth Information
Surface Temperature
Here is a chance to examine the factors that affect temper-
ature more closely. To do so, view the animation
Surface
Temperature
. This animation allows you to observe how the
variables insolation, net radiation, and time of day influence
temperature. The focus of this feature is a hypothetical loca-
tion at 45° N latitude, one that lies deep within a continent.
As you watch this animation, observe how air temperature
near the Earth's surface changes over the course of the day
on June 21, which is the Summer Solstice in the Northern
Hemisphere. In particular, notice the lag that exists with
respect to increases and decreases in insolation and tempera-
ture over the course of the day. After you complete the anima-
tion, be sure to answer the questions at the end to test your
understanding of this concept.
Why does this temperature variation occur? The main rea-
son is the maritime vs. continental effect (Figure 5.7). Large
bodies of water, such as the Pacific Ocean, store tremendous
amounts of thermal energy, primarily because water has a high
specific heat; that is, water absorbs a relatively large amount
of energy before its temperature rises. In addition, solar radia-
tion can penetrate to great depths in the ocean, heating wa-
ter below the surface. The ocean currents constantly mix this
warm water with the cooler water not exposed to sunlight. As
a result, large water bodies maintain a more or less constant
temperature for most of the year (Figure 5.8). This effect can
be enhanced if the ocean current that flows along the coast is a
cold or warm current. Such currents will be described further
in Chapter 6.
As water evaporates from the ocean, energy is transferred to
the atmosphere in the form of latent heat that, in turn, moderates
the air temperature of coastal places such as San Francisco.
This moderating effect is magnified on the west coast of North
America because the prevailing winds are westerly; that is,
they blow from west to east. This circulatory pattern will be
discussed in more detail in Chapter 6, but for now it is sufficient
to know that these westerly winds blow relatively mild, moist
air off the ocean into the continental interior. In this way, San
Francisco maintains a moderate air temperature all year round.
Insolation
Insolation
Water
Land
