1. Atmospheric Circulation
Chapter 7

2. Atmospheric circulation
Global – Covers major portions of the earth
Synoptic – covers 100s to 1000s of km2
Mesoscale – covers 10 of km2
Microscale – small exchanges of mater and energy

3. Global Scale Circulation

4. Single cell model George Hadley The earth is warmed at the equator.
Air expands upward and diverges toward the pole
At the pole air cools and flows back toward the equator

5. Single cell model
Because the earth is rotating the wind is shifted to the right (left in SH)

6. Single cell model
Zonal winds – blow east to west or west to east Meridional winds – blow south to north or north to south

7. Single cell model
Not a very realistic model

8. 3-cell model
Each hemisphere is divided into 3 distinct circulation cells

9. 3-cell model Polar cell Ferrel cell Hadley cell
Each cell has associated pressure and wind patterns

10. 3-cell model
ITCZ = Intertropical convergence zone Creates the equatorial low, rainiest regions on earth Little wind – doldrums

11. 3-cell model
Subtropical High – very dry Location of many of the earth’s deserts Little wind – horse latitudes Between NE trade winds

12. 3-cell model
Subpolar low – plenty of rain Mid latitude westerlies Polar high – pretty dry Polar easterlies

13. Global Atmospheric Circulation Model
To view this animation, click “View” and then “Slide Show” on the top navigation bar.

14. 3-cell model
Is OK at explaining some pressure and wind phenomena. Ex ITCZ

15. The “real” world
Not covered by distinct belts that completely encircle the earth
Circulation is dominated by semi-permanent cells of low or high pressure

16. Winter
Weather in the North America is dominated by the Aleutian Low and Icelandic Low

17. Summer
Weather in North America is dominated by the Hawaiian High and the Bermuda-Azores High

18. Seasonal Pressure and Precipitation Patterns
To view this animation, click “View” and then “Slide Show” on the top navigation bar.

19. The jet stream
The pressure gradient force increases with height

20. The jet stream
The Polar front is a boundary between very cold polar air and warmer mid-latitude air Creates an extreme Pressure Gradient force

21. The jet stream
The result is a powerful flow of air, the jet stream, located near the tropopause at the polar front

22. Synoptic scale circulation

23. Ridges and troughs
Ridges – thicker regions of the atmosphere with higher pressure, often associated with surface divergence
Troughs – thinner regions of the atmosphere with lower pressure, often associated with surface convergence

24. Ridges and troughs
Ridge Trough

25. Ridges and troughs Can best be seen on a 500mb map
Troughs point toward the equator
Ridges point toward the pole
500mb map

26. Rossby Waves
The ridges and troughs form long waves, called Rossby waves, which circle each hemisphere. Rossby waves can remain stationary or move west to east Movement of the waves can transport vast amounts of air

27. The Jet Stream and Rossby Waves
To view this animation, click “View” and then “Slide Show” on the top navigation bar.

28. Rossby waves
Groovy web animation

29. Ocean Currents
Large scale movements of surface water that can exchange energy and moisture with the atmosphere

30. Ocean Currents

31. Ocean Circulation
To view this animation, click “View” and then “Slide Show” on the top navigation bar.

32. Foehn winds
Winds that flow down mountain slopes, warm by compression and bring warm dry air to the lowlands
Chinook – formed by air descending the eastern slopes of the Rocky Mountains
Santa Ana – formed by high pressure over the Rockies and Great Basin

33. Chinook

34. Santa Ana

35. Mesoscale circulation

36. Sea / land breezes Sea breeze Land breeze
Land warms faster in the day then water
Causes air to expand, rise, diverge and thus create low pressure
Air moves from the sea to balance the pressure
Land breeze
At night the land cools faster than the water and the situation is reversed

37. Sea / land breezes

38. Mountain / valley breezes
Daytime heating of the mountain causes air to warm, rise and be replaced by
air from the valley
Mountain breeze
At night the mountain cools an air sinks down to the valley

39. Have a great day!