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Air. Earth’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.
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Air Earth’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 Air • Wind • 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 Systems Trade 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
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