Wind is caused by differences in air pressure and moves from high to low pressure areas. The circulation of air on Earth is affected by unequal heating and the planet's rotation. This causes trade winds between 0-30° latitude and prevailing westerlies between 30-60° N latitude. Monsoon winds reverse direction with the seasons, bringing moisture over land in summer. Deserts form due to lack of precipitation and various climatic and geographic factors. They are characterized by sand dunes and features like oases and dry lake beds, and are home to plants and animals adapted to arid conditions.

1. Chapter 14

2. Wind. Refers to a current of air that naturally moves
along or parallel to the ground. Air moves because
of the differences in air pressure; wind moves from
an area of high pressure to an area of low pressure.

3. Circulation of air on Earth
- Unequal heating on the
earth and the planet’s
rotation affect the
circulation of air.
- Coriolis force causes the
winds to deflect to the
right in the Northern
Hemisphere and to the left
in the Southern
Hemisphere.
- Intertropical
Convergence Zone
(ITCZ). A narrow zone
near the equator which
has calm and light variable
wind.

4. Between 0° to 30° latitude are the trade winds which
constantly blow from the northeast.
Around 30° latitude, airflow begins to subside in
subtropical high-pressure belts, this area is known as
Horse Latitude.
Between 30° and 60° N latitude, the winds blow from the
southeast and are called the prevailing westerlies.
Along 0° and 60° latitude lines is where the air is rising.
The 30 ° and 90 ° latitudes are regions where the air is
sinking which create an area of higher pressure and drier
air.

6. Monsoon Wind. The term
monsoon is derived from an
Arabic word meaning season.
It is a system of winds that
reverses direction with the
seasons.
Heavy seasonal rainfall, is
caused by the discrepancy in
temperature.
Summer monsoon is
considered as large-scale sea
breeze wherein it brings
moisture from the sea as the
land heats and draws in air
from the ocean.

7. Agent of Erosion
Wind. Is considered as an
agent of erosion by:
 Deflation. Involves the
lifting and removal of fine,
dry particles of silt, soil,
and sand by the wind.
 Abrasion. Is the
mechanical wearing and
grinding of rock surfaces
by friction and impact.
The wind deposit
characterized by mounds
and ridges of sand is called
dunes or sand dunes.

8. Types of Sand Dunes
different types based on the
size and shape:
1. Barchan dunes. Are
crescent-shaped dunes.
2. Parabolic Dunes. Are
“U”-shaped dunes.
3. Transverse dunes.
Consist of ridges of sand
that resemble sand
ripples on a large area.
4. Linear dunes. Are long
straight dunes.
5. Star dunes. As the
name implies are dunes
with several arms.

9. Desert. Is also known as rigid land is a landscape or region
characterized by extremely low amount of precipitation.

10. Desertification. Is the
process which involves
the transformation of
arable land to desert
because of climatic
changes, changing
positions of the
continents, or changes in
ocean and air circulation
patterns.
Other factors are human
activities such as
overgrazing, draining of
land, and lowering of the
groundwater table.

11. Origin of deserts
1. Subtropical deserts.
Formed due to dry,
subtropical air into mid-
latitudes. Examples,
Sahara of N Africa,
Kalhari of S Africa, and
the Great Australian
Desert.
2. Continental deserts.
Are found in the
continental interiors
where hot summers and
cold winters prevail.
Examples, Gobi and
Takla Makan.

12. Rainshadow deserts. Are
formed in mountainous
regions where air rises
and condenses, and drops
the moisture as it passes
over the mountains.
Examples, Sierra Nevada
Mts., California and
Nevada, East of the
Cascades of Oregon and
Washington, and East of
the Andes Mts. in South
America.

13. 4. Coastal deserts. Are
formed in areas where
cold upwelling seawater
cools the air and
decreases its ability to
hold moisture. Examples,
Atacama desert of coastal
Peru, and Namib Desert
of coastal South Africa.
5. Polar deserts. Are
formed due to cold dry
air that prevails and
moisture that remains
frozen throughout the
entire year. Example,
Polar regions.

14. Desert Features
Includes:
1. Oases. Are vegetated
areas moistened by
springs, wells, or by
irrigation.
2. Alluvial fans. Are
sedimentary deposits
found at the mouth of a
mountain canyon.

15. 3. Ephemeral stream. Is
formed by intense rain
in the desert. Desert
rain forms the streams
that flows to desert
lakes.
Dry Lake is called Playa
where salt, sand, and
mud are deposited.

16. Plants and Animals
in the Desert
Some animals that live
in the desert are
kangaroo rat, coyote,
jack rabbit, and many
lizards.

17. Xerocoles, are animals
that become adapted
in deserts.
Xerophytes, are plants
that are drought or
salt-tolerant.