Download Low-Latitude Climates

Low-Latitude Climates
Chapter
9
Overview of Low-Latitude Climates
The low-latitude climates lie for the most part between the
Tropics of Cancer and Capricorn and represent about 50 percent
of Earth’s surface.
They occupy the entire equatorial zone (10° N to 10° S), most of
the
e tropical
op ca zone
o e ((10°
0 to
o 15°
5 Na
and
d S), and
a d part
pa of
o the
e subtropical
sub op ca
zone (25–35° N and S).
Overview of Low-Latitude Climates
The low-latitude climates are characteristically warm throughout
the year, and are sometimes described as lacking any winter
season.
Constant warmth is the distinguishing feature of these climates
climates,
with the 18 °C winter isotherm used to establish their poleward
limits.
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The Wet Equatorial Climate
(Köppen Af)
The wet equatorial climate occurs in areas where the ITCZ
is nearby for most of the year.
This climate is dominated byy warm,, moist maritime
equatorial (mE) and maritime tropical (mT) air masses that
yield heavy convectional rainfall.
The wet equatorial climate is found in the latitude range 10°
N to 10° S.
2
The Wet Equatorial Climate
(Köppen Af)
Precipitation is plentiful in all months, and the annual total
often exceeds 2,500 mm.
There is usually a seasonal pattern to the rainfall
rainfall, with a
somewhat wetter period occurring during the time of year
when the ITCZ migrates into the region.
Mean monthly and mean annual temperatures are typically
close to 27 °C.
The Monsoon and Trade Wind
Coastal Climate (Köppen Am, Af)
The monsoon and trade-wind coastal climate occurs in
latitudes from 5° to 25° N and S.
q
climate,, the monsoon and tradeLike the wet equatorial
wind coastal climate has abundant rainfall.
However, the rainfall in monsoon and trade-wind coastal
regions shows a stronger seasonal pattern (especially
pronounced in monsoon climates).
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The Monsoon and Trade Wind
Coastal Climate (Köppen Am, Af)
The monsoon and trade-wind coastal climate results from
two somewhat different situations.
p
((mT))
On tradewind coasts,, moisture-laden maritime tropical
and maritime equatorial (mE) air masses produce rainfall.
The trade winds move these air masses onshore across
narrow coastal zones backed by highlands.
As the warm, moist air passes over coastal hills and
mountains, the orographic effect produces shower activity.
4
The Monsoon and Trade Wind
Coastal Climate (Köppen Am, Af)
Rainfall is also intensified by easterly waves, which are
more frequent when the ITCZ is nearby.
This trade-wind effect is limited to the east coasts of land
masses because the trade winds blow from east to west.
The monsoon climate occurs anywhere where there is a
seasonal shift in wind direction.
The Monsoon and Trade Wind
Coastal Climate (Köppen Am, Af)
In the monsoon and trade-wind coastal climate, the warmest
temperatures occur in the high-sun season, just before the
arrival of the ITCZ brings clouds and rain.
The seasonall reduction
Th
d ti iin solar
l radiation
di ti caused
db
by th
the h
heavy
cloud cover affects temperature through the summer.
Generally there is no shortage of moisture in the wet equatorial
and monsoon and trade wind coastal climates, and even during
the extended dry periods that occur in the monsoon.
5
The Wet-Dry Tropical Climate
(Köppen Aw, Cwa)
In the monsoon and trade-wind coastal climate, the ITCZ
moves into and away from the region to produce the
seasonal cycles of rainfall and temperature.
These cycles become stronger farther from the equator,
and the monsoon and trade-wind coastal climate grades
into the wet-dry tropical climate.
The Wet-Dry Tropical Climate
(Köppen Aw, Cwa)
The wet-dry tropical climate is distinguished by very dry
conditions during the low-sun season; this alternates with
very wet conditions during the high-sun season.
During the low
low-sun
sun season
season, the ITCZ moves well beyond
the wet-dry tropical climate region, and the dominant air
masses are of the dry continental tropical (cT) type.
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The Wet-Dry Tropical Climate
(Köppen Aw, Cwa)
In the high-sun season, when the ITCZ is nearby, moist mT
and mE air masses dominate.
A characteristic
h
t i ti off the
th tropical
t i l wet-dry
t d climate
li t iis itits llarge
year-to-year variability in precipitation.
7
8
The Dry Tropical Climate (Köppen
BWh, BSh)
The dry tropical climate is associated with the subtropical high
pressure cells.
Here, strong subsidence and adiabatic warming inhibit
condensation.
Rainfall is rare and occurs only when unusual weather conditions
move moist air into the region.
The Dry Tropical Climate (Köppen
BWh, BSh)
Since skies are clear most of the time, the sun heats the surface
intensely, keeping air temperatures high.
During the high-sun
high sun period
period, heat is extreme
extreme.
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The Dry Tropical Climate (Köppen
BWh, BSh)
The driest areas of the dry tropical climate are centred near
the Tropics of Cancer and Capricorn, with rainfall
increasing toward the equator.
Immediately adjacent to the dry tropical regions
regions, recipitation
comes during a short rainy season at the time of the year
when the ITCZ is nearby.
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Highland Climates of Low Latitudes
Highland climates are cool to cold, usually moist, climates that are
associated with mountainous regions and high plateaus (closely
associated with the climate of the surrounding lowlands).
Generally, the higher the location, the colder and wetter is its climate.
Temperatures are lower since air temperatures in the atmosphere
normally decrease with altitude.
Rainfall increases because orographic precipitation tends to be induced
when air masses ascend to higher elevations, especially on windward
slopes.
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A Look Ahead
The next chapter discusses the climates of the mid- and
high latitudes.
The mid- and high-latitude climates are extremely diverse
and include regions
g
that experience
p
very
y wet, very
y dry,
y very
y
hot, and very cold conditions at least at certain times of the
year.
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