Transcript Global Circulation - University of Tasmania

Global Circulation
Geog. 1, Week 4, 19 March 2002
Chapter 6 of Christopherson
Need to know
Major Wind Patterns
High and Low Pressure Systems
Start From Highly Simplified
Model
1.
2.
3.
4.
5.
6.
Pressure differences
Equator/Pole air movement
Add in upper troposphere cooling
Add in rotation of Earth
Coriolis ‘Force’
Effects of land mass
Basic 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
Air movement
Low
995hPa
High to Low Air Flow Causes
Vertical Movement as Well
• Clouds
WHY?
Rising air
above a low
Low – air flow in at ground
Clear
Falling air
above a high
High – air flow out at ground
Equator to Pole Air Movement
This model is too simple to be useful
South
Pole
Equator
Heating
North
Pole
Equator to Pole Air Movement
More realistic model
Loses heat
by radiation
Polar Front
Hadley cell
L
H
South
Pole
60o
S
30o
H
L
S
Equator
Heating
30oN
Equator
30oS
From Christopherson, p. 149
Now 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
Southern 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
Christopherson p.150
Friday 8 March 2002 (Mercury Newspaper)
Hobart: cool, early drizzle, light to moderate southerly winds
C
northeasterly winds developing
Strong northerlies, very warm
Ocean 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)
Christopherson p.162
Christopherson p. 164
Summary
• Large scale atmospheric movement of air
due to uneven heating and cooling plus effect
of Earth’s 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.
Equator – movement of warm moist air
into upper troposphere
Subtropical Highs – around 30oS
e.g. Byron Bay
Storms at polar convergence about 60oS
Next Week
• The importance of evaporation and
condensation of water in the atmosphere
Chapter 7 of
Christopherson