Geoscience Reference
In-Depth Information
Geography of Köppen Climates
of air. Thus, average monthly precipitation drops below 6 cm
(2.5 in.) for a month or two. Nevertheless, this slightly re-
duced season precipitation is not sufficient to change the
nature of the vegetation, which is also rainforest in these
regions.
The tropical monsoon climate (
Am
) is directly related to
the onshore flow of mT air that occurs in places like Southeast
Asia and southwest India (Figure 9.2), which was discussed
in detail in Chapter 6. This onshore flow occurs in summer
when the ITCZ is overhead and reverses in winter when the
landmass cools. Because the onshore monsoon winds are
southwesterly, the climate is largely associated with the west
coasts of landmasses. The tropical monsoon climate (
Am
) also
occurs on the eastern side of landmasses in some places, such
as the northeast coast of South America (Figure 9.2), where
northeast trade winds bring humid air into the region on a sea-
sonal basis.
The third subdivision of the tropical
A
climates is the
tropical savanna climate (
Aw
). This climate region is poleward
of the tropical rainforest climate (
Af
) in both hemispheres and
is found over large regions of the world (Figure 9.2). The pri-
mary difference between this climate zone and the tropical
rainforest (
Af
) and tropical monsoon (
Am
) climates is that
the tropical savanna climate (
Aw
) has very distinct wet and
dry seasons. As you might imagine, this cycle is distinctly re-
lated to the impact of Earth-Sun geometry on the migration
of large-scale atmospheric pressure systems. The wet season
occurs during the summer months because the ITCZ is over-
head due to the high Sun angle that time of year. In contrast,
the dry season occurs during the winter months because the
ITCZ is in the opposite hemisphere during that time of year
and is replaced by the STH. As a result of this distinct wet/dry
cycle, the vegetation is a mix of grass and trees known as
sa-
vanna
(Figure 9.4).
This section of the chapter focuses on the global geography
of Köppen climates. The discussion begins with the climates
found in tropical latitudes and progresses to those occurring in
very cold regions of the world. As you work your way through
this discussion, refer frequently to the global map of Köppen
regions in Figure 9.2 to improve your understanding of climate
geography. You should also go to the Geo Media Library at the
end of this discussion to view the climograph for each region.
This site also includes a selection of photographs of each area to
give you a better idea of the landscape and, in some cases, how
people interact with it.
Tropical (
A
) Climates
Tropical
A
climates are the climates found at low latitudes that
straddle the Equator, extending to approximately 25° latitude
in both the Northern and Southern Hemispheres (Figure 9.2).
A
climates are warm in that the average monthly temperature
exceeds 18°C (64°F). This climate region is further divided into
three subcategories on the basis of precipitation.
The tropical rainforest climate (
Af
) occurs at very low
latitudes and is most closely associated with consistently
high amounts of monthly solar radiation and the strong influ-
ence of the ITCZ. As a result, the relative humidity is always
very high, abundant rainfall occurs every month due to after-
noon convection, and vegetation consists of dense rainforest
(Figure 9.3).
The tropical monsoon climate (
Am
) is very closely re-
lated to the tropical rainforest climate (
Af
) because it also
receives abundant precipitation. This climate region differs,
however, because it has a more prominent seasonal pattern
that is associated with a migrating Sun position and the flow
Figure 9.3 The tropical rainforest climate (
Af
).
Tropical rain-
forest in the African Congo. Due to the very warm temperatures,
high humidity, and persistent rainfall in this region, the vegetation
is very dense.
Figure 9.4 The tropical savanna climate (
Aw
).
Tropical sa-
vanna in northern Australia consists of a mix of trees and grass
due to the seasonal wet and dry cycle associated with the tropical
savanna climate.
