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 counter-

clockwise 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

HL

What are some local winds?

Valley Breeze Mountain Breeze

H L

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. FrictionFriction 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?

Doldrums

Horse Latitudes

Draw in the red andblue arrows