Air Pressure and Wind
What is air pressure?
• The weight of the atmosphere as it pushes
down on Earth’s surface.
• It is exerted equally in all directions.
Measuring air pressure
Measured with a barometer.
Mercury
Aneroid
Units of measurement
• Metric units are millibars (1013 sea level)
• English units are inches of mercury (29.92)
What can change air pressure?
• Temperature: Cold air exerts a higher
pressure than warm air.
• Humidity: Dry air exerts a higher pressure
than moist air.
How is pressure shown on a weather
map?
Isobars are lines connecting points of equal air
pressure. They are 4 mbs apart.
1008
1012
1016
How does air pressure affect wind?
Air moves from areas of high pressure to areas
of low pressure.
What are the characteristics of high
and low pressure systems?
•
•
•
•
Cooler air temp
Rising barometer
Clear, nice weather
Wind moves
clockwise and out
•
•
•
•
Warmer air temp
Falling barometer
Poor, humid weather
Wind moves counterclockwise and in
Why do you think air moves out of a High and
into a low?
What do isobars look like on a map?
They usually form loops around the high and
low pressure systems.
How are winds named?
Wind is named by the direction it comes from.
Northeast
Northwest
What are some local winds?
Sea Breeze
Land Breeze
What are some local winds?
Valley Breeze
Mountain Breeze
What affects global wind patterns?
1. Earth’s Rotation
The Coriolis Effect is the tendency of an object
moving over Earth’s surface to follow a curved path.
In the Northern hemisphere, wind and water curve
to the right.
In the Southern hemisphere, wind and water curve
to the left.
Coriolis Effect
Coriolis Effect
How does this
affect water in
the oceans?
What affects global wind patterns?
2. Friction
Friction between air and ground slows the
wind.
So air at high elevation moves faster.
The jet stream is a fast current of air at the top
of the troposphere. It can supply energy to
storms and direct their path.
What are the global winds?
Draw in the
red and
blue arrows
Horse Latitudes
Doldrums