Earth Science
Chapter 16
Section 3
A. What Causes Wind:
Wind is the horizontal movement of air from an area of high
pressure to an area of low pressure.
All winds are caused by differences in air pressure.
B. Measuring Wind:
Winds are described by their direction and speed.
Wind direction is determined by a wind vane.
Winds are named by the direction from which the wind
comes. A wind from the North is called a North wind.
Wind speed is measured with an anemometer.
Wind blowing over your skin removes heat from your body.
The increased cooling that a wind can cause is called the
wind-chill factor.
C. Local Wind:
Local Winds are winds that blow over a short distance.
Local winds are caused by unequal heating of Earth’s surface
within a small area.
Examples of local wind caused by unequal heating:
1. Sea breeze- A wind that blows from an ocean or lake onto
the land. Warm air on the land rises and is replaced by
cooler air moving in from the water to take its’ place.
2. Land breeze- A wind that blows from the land onto a
body of water. Warm air over the water rises and is
replaced by cooler air from the land.
3. Monsoons- Sea and land breezes over a large region that
changes direction with the seasons. Occur in south and
southeast Asia.
During the summer months the land remains warmer than
the water and a continuous sea breeze occurs. This is the
rainy season.
During the winter months the water remain warmer than
the land and a continuous land breeze occurs. This is the
dry season.
D. Global Winds:
Winds that blow steadily from specific directions over
long distances are called global winds.
Global winds are created by the unequal heating of the
Earth’s surface.
1. Warm air rises at the equator and sinks at the poles in
global convection currents.
The movement of air between the equator and the poles
produces the global winds.
2. The Coriolis effectIf the Earth did not rotate, wind would blow in straight
lines from the poles to the equator.
Because the Earth is rotating the winds do not blow in
straight lines.
Winds in the Northern hemisphere are deflected to the
right.
Winds in the southern hemisphere are deflected to the
left.
E. Global Pressure Belts:
1. Doldrums- An area of low pressure located at the
equator where air rises.
2. Horse latitudes- Areas of high pressure located at 30 N
and 30 S latitude. Air sinks.
3. Subpolar lows- Areas of low pressure located at 60 N
and 60 S latitude. Air rises.
4. Polar highs- Areas of high pressure located at 90 N and
90 S latitude. Air sinks.
F. Global Wind Belts:
1. Trade winds- Blow from the horse latitude to the
doldrums.
2. Prevailing Westerlies- Blow from the horse latitudes
to the subpolar lows.
3. Polar Easterlies- Blow from the polar highs to the
subpolar lows.
Jet Stream- A band of high-speed winds at about 10 Km
above the earth’s surface.
-Jet streams blow from west to east. Speeds
of 200-400 km/hr
-100’s of Km wide and a few Km deep
-Wander north and south along a wavy path