AirEarth’s Atmosphere

Atmospheric Pressure * The weight of the air above you. The more air that is above you the more pressure you will feel.

* Sinking air pushes down more- cold air is usually high pressure.

* Rising air pushes down less- hot air is usually low pressure.

Where is pressure greater, at top of a mountain or at sea level?

Sea level

So …. Atmospheric pressure is greatest near Earth’s surface

Decreases as you move out to space

Can vary from locations at the same level due to the density of the air

Cold Air vs. Warm Air Cold air is denser than warm air so has a higher pressure

Warm is less dense so has a low pressure

These masses of warm/cold air used to predict weather

Barometer Measures air pressure

Measured in millibars

Movement of AirWind

The movement of air molecules from an area of high pressure to an area of low pressure

Temperature differences on Earth’s surface create areas of different pressure and the winds that circulate our planet

Causes of temperature difference Earth is curved rather than flat so

more solar radiation is received at the equator

Air above equator is heated more than any place on Earth … heated air rises (low pressure)

Air above poles receives less radiation so air is cooler … colder air sinks (high pressure)

The Coriolis Effect Due to Earth’s rotation

Causes air masses moving south in Northern Hemisphere to be turned westward from their original paths

These wind patterns determine the weather and also when ships/planes can travel

Review ….. What 2 things determine our wind patterns on Earth ?

Differences in heating Coriolis effect

Global Wind SystemsTrade winds

Westerlies

Easterlies

Doldrums

Jet Streams Located near top of troposphere

Flow west to east

2 jet streams in each hemisphere

Resemble fast moving rivers

Average speed between 97-185 km/h

Their positions in altitude and latitude from day to day / season to season

Jet Stream

Local Wind Systems Land Breezes

Movement of air towards water

Sea Breezes Movement of air towards land

Mountain vs. Valley Breezes During DAY, heated air along mountain slopes rises = Valley Breeze

At NIGHT, cooled air along mountain slopes moves downward = Mountain Breeze