Air Pressure

Weight of the atmosphere per unit area.

Atmosphere is made of gas molecules moving equally in all directions

What causes air pressure to change?

Why Does Air Pressure Change?

1.Constant Temperature Change

Warm Air = Low Pressure

Cold Air = High Pressure

2. Changing Humidity Water vapor is less than 1% of air Weighs less than N or O Humid Air = Low Pressure

COLD AIR WARM AIR

High Pressure Low Pressure

Air Pressure Units

Millibar

Isobars: Lines that join areas of equal pressure at the same timeMILLIBAR

ISOBAR

Highs & Lows Pressure Gradients

Pressure Gradient

Strong Pressure Gradient: Isobars are located close together Strong Wind

Weak Pressure Gradient: Isobars are far apart Weak Wind

What Causes Winds?

Wind results from differences in air pressure High Pressure= Lots of air Low Pressure= Not a lot of air

Wind: movement of air from high to low pressure

Sea Breezes Occur during the day Land heats up faster than the ocean High Pressure on Ocean, Low pressure on

Land The air moves from the high pressure (ocean)

to the low pressure (land)

SEA BREEZE

Land Breeze Usually at night Land cools faster, making it colder than the sea High Pressure on Land, Low above Ocean This makes the air move from high pressure

(land) to low pressure (ocean)

Land Breeze

The Coriolis Effect

Global Wind Belts Unequal heating creates a giant transfer system. Moves warm air towards high altitudes and cool

air towards the equator.

Creating Wind Belts!

Measuring Winds Wind Vein: Determines wind direction Anemometer: Speed is determined by the rotation of

the cups on the anemometer Knot: the unit used to measure wind speed

1 Knot = 1.15 miles or 1.85 Kilometers