1. Atmospheric Circulation
Geography “Physical Geography of the World’s Oceans”
Atmospheric Circulation
air moves because of pressure differences
large scale air motion is influenced by Coriolis effect
horizontal air motion drives ocean circulation
atmosphere and ocean circulation have similarities
Go slow, explain everything, reiterate big picture

2. greatest solar heating is in equatorial region
more reflection at high latitudes
Earth’s radius = km
atmosphere’s thickness ~100 km
so figure not to scale
longer path through atmosphere
at high latitudes

3. solar radiation at Earth’s surface (W m-2)

4. cumulonimbus cloud
density, rising air, condensation

5. mean sea surface T & S

6. Coriolis Effect (summary)
Motions in a rotating frame will appear deflected to the right in the northern hemisphere
Motions in a rotating frame will appear deflected to the left in the southern hemisphere
Motions are not deflected on the equator, greatest deflection at poles, varies with latitude

7. vertical structure of atmosphere
air temperature cools with height in troposphere

8. fluid motion is driven by spatial pressure differences

9. atmospheric circulation in its simplest form
solar heating maximum at equator decreases air density
light moist air rises decreasing atmospheric mass, thus lowering pressure
rising air cools adiabatically
cooling causes condensation, rain and increases density
air moves poleward cooling and increasing density
heavy, cool, dry, air increases atmospheric mass, thus increasing pressure
pressure difference gives rise to Hadley circulation

10. Ferrel’s three-cell model of atmospheric circulation
low pressure (warm/wet) at equator
high pressure (cold/dry) at poles

11. Ferrel’s three-cell model of atmospheric circulation
addition of Coriolis Effect gives global winds

12. global atmospheric circulation
tropical

13. vertical air velocity (July average)
rising air
sinking air
Hadley circulation is not zonally uniform

14. intertropical convergence zone (ITCZ)

15. more realistic global atmospheric circulation has meandering subpolar fronts
tropical

16. Rossby waves dominate at midlatitudes
warm and cold conditions can migrate at mid-latitudes greatly influencing weather patterns, especially in the United States

17. global pressure and winds
July
January

18. Geostrophic Flow
For large scale motion, pressure and Coriolis are roughly in balance. This is referred to as geostrophic balance and gives rise to geostrophic flow.
Stated another way, geostrophic flow arises from a balance of pressure and Coriolis “forces”.
Geostrophic flow is along lines of constant pressure and its magnitude is proportional to the pressure gradient.

19. global winds and pressure; why we live in the west
July
January

20. atmospheric circulation over North America map shows both pressure contours and wind vectors
clockwise or anti-cyclonic rotation around a high in the northern hemisphere

21. atmospheric circulation over North America map shows both pressure contours and wind vectors
counter-clockwise or cyclonic rotation around a low in the northern hemisphere

22. Sea Breeze – another mechanism for (local) winds

23. global winds and pressure
July
January

24. Indian Monsoons
Monsoon winds are not in geostrophic balance because winds are not along lines of constant pressure. Thus, pressure and Coriolis are not in balance.
Northeast or Winter Monsoon
Southwest or Summer Monsoon

25. wind C P

27. Northeast - The system that brought the rain and snow across the Northeast yesterday will continue to do so today, but precipitation should generally be lighter than it was on Tuesday.
West - Warm temperatures are expected again across the West with an upper level ridge continuing to be the dominant weather feature in the region. An upper level trough will begin to move into the West Coast tomorrow night and Friday, breaking down the ridge that's been in place.

29. Midterm on Wednesday 5 Nov 2008
Readings (Ocean and Atmosphere):
Text Chapter 8 (pgs 138 – 151 and )
Reader pgs
Reader Maps pgs
HW #2 assigned; Due Friday 31 Oct 2008
Midterm on Wednesday 5 Nov 2008