Download Atmospheric Pressure and Wind

Atmospheric Pressure and
Wind
Chapter 15 Section 3
Why Air Moves
• Wind is created by differences in air pressure
• Warm air is less dense and creates areas of
low pressure
• Warm air rises
• Cold air is more dense and creates areas of
high pressure
• Cold air sinks
• Surface winds blow from polar high-pressure
areas to equatorial low-pressure areas
Why Air Moves
• The uneven heating of the Earth produces
pressure belt, this happens in increments of 30
degrees latitude
• Air doesn’t move in one large circular pattern
from the poles to the equator
• At 30 degrees N & S the warm air from the
equator cools and sinks
• At the poles the cold air sinks and starts to warm
and become less dense at 60 degrees N & S and
rise
• The curving of moving objects, such as wind, by
the Earth’s rotation is called the Coriolis effect
Types of Winds
• There are two types of winds; local & global
winds
• Global winds are part of a pattern of air
circulation that moves across the Earth
• These winds travel longer distances
• The winds that blow from 30 degrees latitude to
the equator in the north & south hemisphere is
called trade winds
• The area of low pressure at the equator is
known as the Doldrums
Types of Winds
• The Westerlies are wind belts found in both the
Northern and Southern Hemispheres between
30 and 60 degrees latitude
• The polar easterlies are wind belts that extend
from the poles to 60 degrees latitude in both
hemispheres
• The jet streams are narrow belts of high-speed
winds that blow in the upper troposphere &
lower stratosphere
Types of Winds
• Local winds are influenced by the geography of
an area
• As air warms and becomes less dense it rises
and produces lower pressure
• Colder air becomes more dense and sinks
producing areas of high pressure
• A land breeze is produced by an area of low
pressure over the water
• The water hold stays warmer than the land
does at night causing the air to warm and rise
pulling the cooler land air out to the sea
Types of Winds
• A sea breeze occurs when a land mass heats
the air above it, the warmer less dense air rises
and is replace by cooler more dense from the
sea
• A mountain breeze occurs when the mountains
cool quicker than the valley below, the cool
mountain air is more dense and sinks into the
valley
• A valley breeze occurs when the valley air
heats up during the day, the warmer less dense
air moves up the mountains face