1. How Does Air Move Around the Globe?

2. Review of last lecture
Thickness of the atmosphere: less than 2% of Earth’s thickness
Definition of temperature. 3 units.
Four layers of the atmosphere, what separate them?
Definition of pressure and its unit.
Definition of pressure gradient. Pressure gradient sets the air in motion.
Equation of state (Relationship between P, ρ, and T)
Vertical Pressure Distribution. How does pressure change with height? What is the hydrostatic equilibrium?

3. Review of last lecture (cont.)
Know 3 Forces that affect wind speed /direction
Especially work on Coriolis force, as this is the hardest to understand. Which direction is air deflected to by Coriolis force?
What is the geostrophic balance? At which level is it valid? Difference between upper level and surface winds
Does cyclones correspond to high or low surface pressure? Is the air moving clockwise or counter-clockwise around them? How about anticyclones?
What are the troughs and ridges?

4. The most common atmospheric circulation structure
Cooling
or No Heating
Heating H L
Imbalance of heating  Imbalance of temperature  Imbalance of pressure  Wind

5. Introduction
Well-defined heating, temperature and pressure patterns exist across the globe
These define the general circulation of the planet
In describing wind motions:
Zonal winds (east-west): flow parallel to lines of latitude
Flowing eastward: Westerly wind
Flowing westward: Easterly wind
Meridional winds (north-south): flow parallel to lines of longitude
Flowing northward: Southerly wind
Flowing southward: Northerly wind

6. Annual mean precipitation (heating)
Extratropical stormtrack
Tropical rainfall

7. Primary Highs and Lows Equatorial low Subtropical high Subpolar low
Polar high

8. Three-cell model Zonal mean circulation
Each hemisphere is divided into 3 distinct cells:
Hadley Cell
Ferrel Cell
Polar Cell

9. Vertical structure and mechanisms
Polar Cell (thermal):
Driven by heating at 50 degree latitude and cooling at the poles
Ferrel Cell (dynamical): Dynamical response to Hadley and polar cells
Hadley Cell (thermal): Heating in tropics  forms surface low and upper level high  air converges equatorward at surface, rises, and diverges poleward aloft  descends in the subtropics
Polar
Hadley

10. Zonal mean structure of temperature
Two characteristics:
Horizontally uniform in the tropics
Steep gradient in the extratropics

11. Vertical structure of zonal wind
Two characteristics:
Westerly winds in the extratropical troposphere (caused by the Coriolis force). Explains why storms move eastward, flight times
Jet streams: local maximum of winds (caused by sharp pressure gradient across the boundary between warm tropical air and cold polar air)

12. The Jet Streams
Caused by steep temperature gradients between cold and warm air masses
Polar front - marks area of contact, steep pressure gradient  polar jet stream
Low latitudes  subtropical jet stream
Stronger in winter, affect daily weather patterns

13. Semipermanent Pressure Cells: NH winter
South Atlantic high
South Indian high
South Pacific high
Low pressure centers: weather and precipitation
High pressure centers: warm, drought and desert

14. Semipermanent Pressure Cells: NH summer
South Pacific high
South Atlantic high
South Indian high

15. General circulation of the oceans
Ocean surface currents – horizontal water motions
Transfer energy and influence overlying atmosphere
Surface currents result from frictional drag caused by wind - Ekman Spiral
Water moves at a 45o angle (right)
in N.H. to prevailing wind direction
Due to influence of Coriolis effect
Greater angle at depth

16. Global surface currents
Surface currents mainly driven by surface winds
North/ South Equatorial Currents pile water westward, create the Equatorial
Countercurrent
western ocean basins –warm poleward moving currents (example: Gulf Stream)
eastern basins –cold currents, directed equatorward

17. Summary Three precipitation (heating) belts. Primary high and lows
Three-cell model. Mechanism for each cell
Two characteristics of zonal mean temperature structure
Two characteristics of zonal mean wind structure. Why does westerly winds prevail in the extratropical troposphere? What cause the jet streams?
Semipermanent pressure cells. Low pressure is associated with clouds and precipitation. High pressure is associated with warm surface temperature, drought, and desert.
What drives the ocean surface currents? In the case of Ekman spiral, what is the direction of surface current relative to surface wind?

18. Works cited Images http://pulleysandgears.weebly.com/gears.html