1. Chapter 7: Atmospheric Circulations
By the end of this chapter you should:
Understand the scales of motion
Be able to give an example of an eddy
Have an understanding of the general circulation of the atmosphere

2. Scales of Atmospheric Motions
Scales of motion – different sizes of circulation
Microscale – smallest scale of motion. 2 meters or less and last seconds to minutes
Mesoscale – circulation around a city (20 km). Can last minutes to hours
Synoptic scale – Circulations around highs and lows (2,000 km). Can last many days
Fig 7.1
Planetary scale – Circulations around the entire Earth.

3. Scales of Atmospheric Motions
Fig 7.1

4. Scales of Atmospheric Motions
Fig 7.1

5. Eddies - Big and Small
Eddy – a circulation formed downwind from an object (examples?)
Rotor – rotation formed downwind from a mountain wave
Wind shear –
change of wind
speed or
direction with
height

6. Thermal Circulations Thermal circulations Circulations brought
on by changes in air
Temperature.

7. Sea and Land Breezes Types of thermal circulations
Sea breeze (scale of motion?)
Land breeze
Sea breeze front – leading
edge of the sea breeze
Florida sea breezes can have huge walls of clouds. Make for great gliding due to vertical movement

8. Sea and Land Breezes

9. Seasonally Changing Winds - the Monsoon
Monsoon wind system – “monsoon” means seasonal
Asian monsoon – in winter the land is much colder than ocean. In summer, opposite is true

10. Seasonally Changing Winds - the Monsoon

11. Mountain and Valley Breezes
Valley breeze – explain this
Mountain breeze – explain this

12. Katabatic Winds
Katabatic winds – in general, any wind that flows downhill
Perfect scenario is elevated plateau with mountains around
Bora – katabatic
wind in the Adriatic
Sea

13. Chinook (Foehn) Winds
Chinook winds – fierce wind that flows on the eastern slope of the Rockies.
Compressional heating – main source of the heat from the Chinook. Air descends very rapidly and warms
Chinook wall cloud – a bank of clouds forming over the mountains

14. Santa Ana Winds Santa Ana wind Warm, dry wind that originates from the
Desert. Usually needs
a high in the Great
Basin
Compressional heating
Fans huge wildfires

15. Desert Winds
Dust storms – formed by surface winds that form from surface heating. Wind picks up dust
Dust devils – Formed from combination of surface heating, unstable atmosphere, and an obstacle in the way

16. General Circulation of the Atmosphere
General circulation only represents the average circulation
Why are the prevailing winds in Hawaii northeasterly and in san Jose northwesterly?
Cause: unequal heating of the earth’s surface
Effect: atmospheric heat transport

17. Single-cell Model Basic assumptions Covered with water
Sun is always over equator
Earth does not rotate
Hadley cell
Heat at the equator creates a low that brings heat to the poles aloft

18. Single-cell Model Why is the single-cell model wrong?
Earth has the Coriolis force. In this model, all winds would be easterly. We know that is wrong
So let’s spin
the planet.

19. Three-cell Model
Model for a rotating earth - keep first two assumptions
Hadley cell is still apparent
Doldrums – equatorial region where winds are light. Warm air rises, condenses and moves laterally towards the poles
Subtropical highs – convergence of air aloft creates highs at 30 degrees. Major deserts and horse latitudes.
Trade winds – some of the surface air from the Subtropical highs move back to the equator and deflect due to the Coriolis force.
Intertropical convergence zone – converge of the trade winds from both hemisphere to get rising air and thunderstorms

20. Three-cell Model
Westerlies – some of the air from the Subtropical highs move towards the poles and deflect towards the east
Polar front – the boundary between the mild air towards the equator and the cold air near the pole (Subpolar lows)
Polar easterlies – air behind the polar front that is deflected to the west by the Coriolis force

21. Figure 7.21: The idealized wind and surface-pressure distribution over a uniformly water-covered rotating earth.
Watch this Active Figure on ThomsonNow website at
Fig. 7-21, p. 185

22. Average Surface Winds and Pressure: The Real World
Semipermanent highs and lows – two areas of highs and lows per hemisphere
Bermuda high & Pacific high
Icelandic low & Aleutian low
Siberian high

23. Figure 7.22: Average sea-level pressure distribution and surface wind-flow patterns for January (a) and for July (b). The heavy dashed line represents the position of the ITCZ.
Fig. 7-22a, p. 188

24. Fig. 7-22b, p. 189

25. The General Circulation and Precipitation Patterns
Where would you expect regions of high and low precipitation?
Heavy precipitation
Regions close to ITCZ, polar fronts, subpolar lows

26. Westerly Winds and the Jet Stream
Jet streams – regions of very fast-moving air in the upper atmosphere due to high pressure at the equator and low pressure near the poles

27. Winds and Upwelling Upwelling – rising of cold water from below
Wind flow parallel to the coastline is deflected to the right by what force? Cold water replaces this

28. El Niño and the Southern Oscillation
El Niño – a natural event that occurs around Christmas. Upwelling weakens along the west coast of South America. Major events can cause great hardship
Southern Oscillation – seasaw pattern of high and low pressures switching on opposite sides of the Pacific Ocean
La Niña – cold water episodes opposite El Niño

29. El Niño and the Southern Oscillation

31. Other Atmosphere-Ocean Interactions
North Atlantic Oscillation
Arctic Oscillation
Pacific Decadal Oscillation