Global Circulation and Winds (Stewart Cap. 4)

Outline Atmospheric pressure Winds Global circulation patterns Ocean circulation patterns

1. Atmospheric Pressure

Atmospheric Pressure Density of the atmosphere decreases with altitude Earth

Atmospheric Pressure: Force exerted by the atmospheric per unit area

Measuring Atmospheric Pressure At sea level: 101,320 Pascals (101 kPa) 1013.2 millibars 76 cm Hg (30 in Hg)

Atmospheric Pressure

Atmospheric Pressure Isobar map

Differences in atmospheric pressure cause air to move … 820 830 840 850 860 820 830 840 850 860 870 880 890 weak pressure gradient strong pressure gradient

Winds are named for the direction they originate from

Local winds Land – sea breezes Daytime: sea breeze Night time: land breeze

3. Global circulation patterns http://www.bergonia.org/History/Hist-maps/columbusmap.gif

Cold High Pressure Solar radiation creates variation in heating / atmospheric pressure 0o 30oN 60oN 30oS 60oS 90oN SUN Warm Low Pressure Earth

L Warm air rises at equator and flows towards the poles 90oN 60oN 30oN 30oS 60oS 90oN L

H L H Cold air sinks at 30o N and S latitude creating high pressure 30oS 60oS 90oN H L H

Low pressure at 0o , 60o latitude high pressure at 30o , 90o latitude Doldrums: strong vertical uplift, little horizontal wind Hadley cells: well developed low pressure cells in the tropics

H 0o 30oN 60oN 30oS 60oS 90oN L Pressure gradients influence development of global wind patterns H L H L H

H L H Easterly winds (trade winds) Westerly winds Easterly winds 90oN 30oS 60oS 90oN Easterly winds Westerly winds H Easterly winds (trade winds) L H

4. Ocean circulation patterns

Ocean currents large continuously moving loops (gyres) produced by winds, Coriolis effect and land masses

Ocean circulation exposes east coasts of continents to warm currents, west coasts to cold currents

Ocean upwelling

Summary Variation in heating causes variation in atmospheric pressure conditions Variation in atmospheric pressure causes air to move (H  L) Local-scale wind patterns occur with variation in heating, pressure

Summary (continued) Direction of air movement affected by pressure gradient, Coriolis effect, and friction In No. Hemisphere L pressure systems (cyclones) circulate counterclockwise in, H pressures systems (anticyclones) circulate clockwise out

Summary (continued) Global variation in heating produces L pressure at 0o and 60o, H pressure at 30o and 90o H and L pressure systems drive global wind patterns (easterlies between 30o N and 30o S; westerlies between 30-60o N and S)

Summary (continued) Ocean currents influenced by winds, Coriolis effect and land masses Ocean circulation exposes east coasts of continents to warm currents, west coasts to cold currents