2 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.
3 Where is pressure greater, at top of a mountain or at sea level?
4 So …. Atmospheric pressure is greatest near Earth’s surface Decreases as you move out to spaceCan vary from locations at the same level due to the density of the air
5 Cold Air vs. Warm AirCold air is denser than warm air so has a higher pressureWarm is less dense so has a low pressureThese masses of warm/cold air used to predict weather
6 BarometerMeasures air pressureMeasured in millibars
7 Movement of AirWindThe movement of air molecules from an area of high pressure to an area of low pressureTemperature differences on Earth’s surface create areas of different pressure and the winds that circulate our planet
8 Causes of temperature difference Earth is curved rather than flat so more solar radiation is received at the equatorAir 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)
9 The Coriolis Effect Due to Earth’s rotation Causes air masses moving south in Northern Hemisphere to be turned westward from their original pathsThese wind patterns determine the weather and also when ships/planes can travel
10 Review ….. What 2 things determine our wind patterns on Earth ? Differences in heatingCoriolis effect
11 Global Wind SystemsTrade windsWesterliesEasterliesDoldrums
12 Jet Streams Located near top of troposphere Flow west to east 2 jet streams in each hemisphereResemble fast moving riversAverage speed between km/hTheir positions in altitude and latitude from day to day / season to season