Geoscience Reference
In-Depth Information
The Asian Monsoon
Like many geographic processes, the Asian monsoon is easy
to visualize in animation. Go to the
Geo Media Library
and
select
The Asian Monsoon
. This animation clearly illustrates
the movement of pressure systems over the course of the year
and shows how they contribute to precipitation patterns. After
you view this animation, be sure to answer the questions at
the end to test your understanding of this concept.
Remember, however, that the ITCZ is not the only large
pressure system that moves seasonally.
All of them do
. This mi-
gration occurs because the pressure systems maintain a more
or less consistent distance from one another across the surface
of Earth. Thus, when the ITCZ migrates, all the systems move
(see Figure 6.22). You will discover in Chapter 9 that this sea-
sonal migration of pressure systems influences the distribution
of global climates in a major way.
because this is where the greatest seasonal fluctuation of the
ITCZ occurs.
In order to understand the monsoon, let's compare the
geographic variability that exists with respect to the seasonal
migration of the ITCZ (Figure 6.23). Beginning first with the
Americas, notice that the ITCZ is located in South America
throughout the year and migrates from the central part of the
continent in January to the northern part of the continent in
July. In other words, the ITCZ shifts across approximately 20°
of latitude in South America over the course of the year. How
does this migration range compare with Asia? Figure 6.23
shows that the position of the ITCZ varies dramatically in
Asia, ranging from northern Australia in January to northern
Monsoonal Winds
One of the most important outcomes of
the seasonal migration of air pressure systems is the
monsoon
.
The monsoon is a cyclical shift of the prevailing wind direc-
tion that occurs at a subcontinental scale over the course of a
year. This process is a good example of how closely geographic
variables are integrated because it is related both to the seasonal
migration of the ITCZ and the maritime vs. continental effect
described in Chapter 5. Although a form of monsoon occurs
in many subtropical places around Earth, including the south-
western United States, it is most pronounced in Southeast Asia
Monsoon
The seasonal change in wind direction that occurs
in subtropical locations due to the migration of the Intertropical
Convergence Zone (ITCZ) and Subtropical High (STH) Pres-
sure System.
Farthest north, 25
°
N
23.5
°
N
Tropic of Cancer
23.5
°
N
ITCZ in July
ITCZ in January
23.5
°
S
Tropic of Capricorn
23.5
°
S
0
1,500
3,000 km
Farthest south, 20
°
S
0
1,000
3,000 mi
Figure 6.23 Position of ITCZ during the solstices.
The red line marks the position of the
ITCZ in January (bottom line) and the blue line indicates its position in July (top line). Note
the extent of seasonal migration in Asia as compared to South America.
