BISL 04-Weather and Climate

The Effect of the Andes Mountains

1. 
   

HUMID WINDS

In the mountains, the predominant

winds are moisture-laden and blow in

the direction of the coastal mountains.

T

he mountains are geographical features with a great influence on climate. Winds laden with

moisture collide with these vertical obstacles and have to rise up their slopes to pass over

them. During the ascent, the air discharges water in the form of precipitation on the

windward sides, which are humid and have dense vegetation. The air that reaches the leeward

slopes is dry, and the vegetation usually consists of sparse grazing land.

An Obstacle Course

Mountain

Everest

Aconcagua

Dhaulagiri

Makalu

Nanga Parbat

Kanchenjunga

Ojos del Salado

Kilimanjaro

MAJOR

MOUNTAIN RANGES

HOW OBSTACLES WORK

TYPES OF

OROGRAPHICAL EFFECTS

VEGETATION

Elevation

29,035 feet (8,850 m)

22,834 feet (6,960 m)

26,795 feet (8,167 m)

27,766 feet (8,463 m)

26,660 feet (8,126 m)

28,169 feet (8,586 m)

22,614 feet (6,893 m)

19,340 feet (5,895 m)

13,

(4,000)

10,

(3,000)

6,

(2,000)

3,

(1,000)

0 feet (0 m)

HIGH LEVEL OF

POLLUTION IN

SANTIAGO

Partly because it is

the most urbanized

and industrialized city

of Chile, the capital,

Santiago, faces

serious pollution

problems. In addition,

it is located in a

valley with

characteristics that

do not help disperse

the pollution

produced by vehicles

and factories.

This drawing shows
the coast and the
Andes near Santiago,
Chile, at Uspallata
Pass.

Moist adiabatic

gradient

The temperature

decreases 1° F

(0.6° C) for every

300 feet (100 m).

Dew point, or

condensation point

Dry adiabatic

gradient

The temperature

declines 1.8° F

(1° C) every 300

feet (100 m).

Temperature (in °F [°C])

-40 to -4 (-40 to -20)

-4 to 14 (-20 to -10)

14 to 32 (-10 to 0)

Greater than 32 (0)

Composition

Ice crystals

Supercooled

water

Microdroplets

of water

Drops of

water

IN THE CLOUD

SNOW RAIN

16,

(5,000)

13,

(4,000)

10,

(3,000)

6,

(2,000)

3,

(1,000)

Surface

Height in

feet (m)

24 SURFACE FACTORS

2. 
   

ASCENT AND CONDENSATION

Condensation occurs when a mass of air cools

until it reaches the saturation point (relative

humidity 100 percent). The dew point rises when

the air becomes saturated as it cools and the

pressure is held constant.

3. 
   

PRECIPITATION

A natural barrier forces the

air to ascend and cool. The

result is cloud formation

and precipitation.

4. 
   

DESCENDING

WIND

A natural

barrier forces

the air to

descend and

warm up.

Western slopes

receive most of the moisture, which

leads to the growth of pine and other

trees of coastal mountain ranges.

Eastern slopes

The rays of the Sun fall directly upon

these areas, making them more arid.

There is little or no vegetation.

Obstacles, such as buildings,

trees, and rock formations,

decrease the velocity of the

wind significantly and often

create turbulence around them.

CLASSIC SCHEME

The more humid zone

is at the top.

VERY HIGH

This is produced on

mountains above

16,400 feet (5,000 m)

in height.

The most humid area is

halfway up the slope,

on the windward side.

UNEVEN

MOUNTAINSIDE

The most humid

area is at the top of

the leeward slope.

It runs parallel to the Pacific Ocean,

from Panama to southern Argentina.

It is 4,500 miles (7,240 km) long

and 150 miles (241 km) wide.

19,700 feet

(6,000 m).

ANDES MOUNTAIN RANGE

has altitudes greater than

FRONT VIEW Rotational flow

PLAN VIEW Flow and counterflow

ARGENTINA

CHILE

Drops of super-

cooled water

combine to

form ice crystals.

The crystals

grow in size.

While they are

falling, they combine

with other crystals.

The microdroplets

increase in size and

fall because of

gravity.

When they fall,

these drops collide

with smaller ones.

Successive

collisions increase

the size of the

drops.

90° F

(32° C)

72° F

(22° C)

54° F

(12° C)

36° F

(2° C)

27° F

(-3° C)

18° F

(-8° C)

Viña del

Mar

Santiago,

Chile

Valparaíso

PACIFIC

OCEAN

COASTAL

MOUNTAIN RANGE

INTERMEDIATE

DEPRESSION

Rocky

Mountains

Appalachians

Alps

Urals

Himalayas

Andes

Tundra. Its rate of growth

is slow and only during the

summer.

Taiga. The vegetation is

conifer forest.

Mixed forest. Made up of

deciduous trees and conifers.

Chaparral. Brush with

thick and dry leaves.

Grazing. Thickets

predominate: low, perennial

grazing plants with an

herbaceous appearance.

Area affected by

precipitation

DRY HUMIDS

Winds Winds

WEATHER AND CLIMATE 25