Atmospheric Pressure and Winds Chapter 19

Air Pressure The weight of the atmosphere per unit area. –1kg per cm² at sea level –14.7 lbs/in² at sea level Directed equally in all directions Barometer – 76cm / 30in at sea level – given in metric unit of millibars (mb)

Barometer Instrument that measures air pressure Mercury Barometer –Requires a tall column of mercury Aneroid Barometer –Uses no liquid

Mercury Barometer

Air Pressure Records

Why Air Pressure Changes Temperature Changes – warm air is lighter than cold air Changing Humidity – the more water vapor, the lighter the air – water vapor pushes out heavier O 2 and N 2 of the dry air

What Makes Wind Blow Pressure Gradient Force – the difference in air pressures that cause winds Local Winds – Sea Breeze: daytime wind from sea, land heats faster than water and causes air to rise – Land Breeze: nighttime wind from land to sea, water is warmer than land

Local Winds: Sea Breeze

Local Winds: Land Breeze

Earth’s Rotation and Weather Systems Coriolis Effect –Turns wind to the right Clockwise –Out of HIGH pressure Counterclockwise –Into LOW pressure

High Pressure Center

Low Pressure Center

Global Air Currents

Air Masses and Fronts Chapter 20

Air Masses Huge section of air that has the same weather throughout Take on the characteristics of the area they originated over maritime tropical – mT continental tropical – cT maritime polar – mP continental polar - cP

Air Mass Source Regions

Fronts Boundary between 2 air masses Causes warm air to rise –Where temperatures and humidity change

Warm Front: Map View Slow moving Long lasting rain Cirrus to stratus clouds, then nimbostratus

Warm Front: Side View

Cold Front: Map View Fast moving Unstable air Cumulus – cumulonimbus clouds Thunderstorms Clears quickly and leaves clear skies

Cold Front

Occluded Front: Map View When a cold front overtakes a warm front Form low pressure systems

Occluded Front: Side View Warm Air Cold Air