Geoscience Reference
In-Depth Information
VISUAL CONCEPT CHECK
9.1
This satellite image focuses on the Middle East, including
northern Saudi Arabia, Iraq, Jordan, and Israel. The land
bodies are tan-colored because they are deserts with very
little vegetation. Which of the following statements best
explains the presence of deserts in northern Saudi Arabia
and southern Iraq? (
Hint:
The latitude of Baghdad is 33° N.)
a)
The region is predominantly influenced by the ITCZ.
b)
The region is influenced largely by low-pressure
systems.
c)
The region is dominated by the STH Pressure System.
d)
The region lies on the windward side of a major
mountain range.
Mesothermal (
C
) Climates
Now that the tropical and desert climates of Earth have been dis-
cussed, let's turn our attention to the climate regions character-
ized by a somewhat more seasonal temperature pattern. These
temperature zones are known as mesothermal (
C
) climates be-
cause they have both a warm and cool season, with fairly abun-
dant precipitation. Mesothermal (
C
) climates are situated in the
midlatitudes, typically between about 20° and 60° N and S lati-
tude (Figure 9.2). Most people live in this climate zone.
If you look again at the global climate map in Figure 9.2,
notice that the distribution of
C
climates varies noticeably be-
tween the Northern and Southern Hemispheres. (
How can this
variability be related to the hemispheric land-water differen-
tial that exists?
) In the Southern Hemisphere,
C
climates extend
across much of the South American landmass south of 40° S
latitude; this occurs because the continent is narrow. North of
the Equator, in contrast, the east-west belt of
C
climate is inter-
rupted by a zone of arid climate in the lee of the Rocky Moun-
tains in North America and by the Himalayas in Asia. These
breaks occur in the Northern Hemisphere because the conti-
nents in that part of the world are very large, which limits the
amount of oceanic-derived moisture that can reach the interior.
Three broad mesothermal climate zones occur on Earth. The
most humid of these climate regions are the humid subtropical
hot-summer climates (
Cfa
,
Cwa
), which are found on the east-
ern side of continents between about 20° to 35° N and S latitude
(Figure 9.2). The distinction between
Cfa
and
Cwa
is based on the
fact that
Cwa
climate regions have a distinct winter dry period—
hence, the
w
designation. Otherwise, the two regions are climati-
cally similar because they have a hot and humid summer season.
Cfa
regions are humid, with average annual precipitation
ranging from 100 cm to 200 cm (40 in.-80 in.). This humid cli-
mate arises because these regions are affected by mT air masses
on the western side of the adjoining ocean's subtropical high-
pressure zone. A good example of this geographical pattern oc-
curs in the southeastern United States, ranging from the Caroli-
nas to east Texas (Figure 9.2). During a typical summer, a strong
subtropical high-pressure system known as the “Bermuda High”
develops off the southeast coast of the United States. Because of
the anticyclonic circulation of the system, it pumps warm, moist
air from the Atlantic into the
Cfa
region, where it falls as con-
vectional rain due to land heating. Winter precipitation is caused
by frontal systems associated with strong midlatitude cyclones.
(
Why is it logical that in the winter midlatitude cyclones bring
precipitation to the American Southeast, whereas they do not
in summer
?) Total annual rainfall is about 162 cm (63 in.), with
ample precipitation every month. Although winters are mild, a
distinct annual high-temperature cycle is present, ranging from
16°C (62°F) in January to 33°C (91°F) in July.
Vegetation in
Cfa
regions is largely characterized by dense for-
ests of broadleaf deciduous trees (like oak and elm) that drop their
leaves during extended cold or dry periods. In particularly warm
places, such as southern China and the Gulf Coast of the United
States, the native forest consists of broadleaf evergreen trees that
remain green throughout the year (see Figure 9.7 as an example).
The second climate within the
C
classification is the Mediter-
ranean dry-summer climate (
Csa
,
Csb
). In contrast to the humid
subtropical hot-summer climates (
Cfa
,
Cwa
),
Cs
climates are lo-
cated along the west coast of continents, at an average latitude of
about 35° N and S (Figure 9.2). The difference between the
Csa
and
Csb
climate zone is that the former has a hotter summer than
the latter, with the warmest month having an average temperature
>
22°C (71.6°F). Otherwise, they are climatically very similar be-
cause the wet season occurs in the winter, as opposed to the sum-
mer when the air is dry. This pattern occurs because in the winter
strong midlatitude cyclones bring moisture into the region from
the nearby ocean to the west. During the summer months, how-
ever, the midlatitude storm track migrates north and is replaced by
the STH Pressure System due to the high Sun angle. The amount
of rainfall any particular
Cs
region receives is essentially related
