Title: Global Circulation
1Global Circulation
- Geog. 1, Week 4, 19 March 2002
- Chapter 6 of Christopherson
- Need to know
- Major Wind Patterns
- High and Low Pressure Systems
2Start From Highly Simplified Model
- Pressure differences
- Equator/Pole air movement
- Add in upper troposphere cooling
- Add in rotation of Earth
- Coriolis Force
- Effects of land mass
3Basic Air Movement Caused by Pressure Differences
- Air moves from high pressure to low pressure
region - If air is heated, density drops and so pressure
drops, e.g. sea breeze
High 1025hPa
Average Pressure 1013hPa
Low 995hPa
Air movement
4High to Low Air Flow Causes Vertical Movement as
Well
Falling air above a high
Rising air above a low
Low air flow in at ground
High air flow out at ground
5Equator to Pole Air Movement
- This model is too simple to be useful
Equator
South Pole
North Pole
Heating
6Equator to Pole Air Movement
Loses heat by radiation
Polar Front
Hadley cell
L
L
H
H
South Pole
Equator
30o S
60o S
Heating
730oN
Equator
30oS
From Christopherson, p. 149
8Now Add In a Rotating Earth
- Apparent change in direction referred to as the
Coriolis Effect
- Coriolis Force
- Northern Hemisphere
- Clockwise round high
- Anticlockwise round low
- Southern Hemisphere
- Anticlockwise round high
- Clockwise round low
9Southern Hemisphere
- This clockwise/anticlockwise air movement around
lows and highs defines the synoptic wind
direction for Tasmania as these systems move past
the State
H
L
10Christopherson p.150
11Friday 8 March 2002 (Mercury Newspaper)
Hobart cool, early drizzle, light to moderate
southerly winds
12C
13northeasterly winds developing
14Strong northerlies, very warm
15Ocean Currents
- Similar general pattern except, obviously,
restricted to the oceans - Surface currents driven by prevailing winds
- Deep currents driven by changes in water density
(e.g. cold Arctic water sinking and moving south
through Atlantic ocean) - Movement slower than air (1000 years for full
cycle)
16Christopherson p.162
17Christopherson p. 164
18Summary
- Large scale atmospheric movement of air due to
uneven heating and cooling plus effect of Earths
rotation and position of continents. This moves
heat (energy) from equator towards poles. - Ocean currents driven by wind and uneven
heating/cooling of oceans. Slower than wind but
large amounts of heat carried from equator
towards poles.
19Equator movement of warm moist air into upper
troposphere
20Subtropical Highs around 30oS e.g. Byron Bay
21Storms at polar convergence about 60oS
22Next Week
- The importance of evaporation and condensation of
water in the atmosphere - Chapter 7 of Christopherson