12.2 NOTES: Weather Systems

1. 12.2 NOTES:Weather Systems

2. Main Idea 1 • Convection, driven by uneven heating & the diurnal cycle, assures that equilibrium will never be reached, thus weather will always change!

3. Pole Surface Air • Temperature: Cold • Pressure: High • Air flow Air sinks, creating a high-pressure zone below that moves toward the equator in an attempt to reach equilibrium.

4. Equator Surface Air • Temperature: warm • Pressure: low • Air flow: Air rises, creating a high-pressure zone above that moves toward the poles in an attempt to reach equilibrium.

5. Main idea 2 • Earth’s rotation “drags” the atmosphere; results in the Coriolis effect. The CoriolisEffect causes massive variation in global airflow patterns.

6. CoriolisEffect results in convection cells • Describe: Earth’s rotation causes N. Hemisphere winds to diverge to the right of original path. In the S.Hemisphere, winds bend to the left. Creates convection cells.

7. Each hemisphere has 3 cells in which air circulates through the entire depth of the troposphere: -Polar Cells -Ferrel Cells -Hadley Cells

8. Polar Cells • Describe: • Air rises & travels towards Poles (due to CE). Once over Poles, air cools more & sinks, forming the polar highs. At the surface, air diverges outward from the polar highs. Surface winds in the polar cell are called Polar Easterlies. Polar cells form a band around the planet near the N & S Poles.

9. Ferrel Cells • Describe: A mid-latitude cell where the air flows towards poles & eastward near the surface & towards equator & westward at higher levels.The FerrelCells form a band around the planet between Poles & Horse Latitudes. (FYI: Horse latitudes (30o N & S of Equator) are generally areas of high pressure marked by calm, subsiding air that gets heated during descent. It is said that Spanish sailors ferrying horses to the West Indies were usually stuck for months in these calm waters and had to throw their horses into the water to conserve drinking water for themselves. This led to the term 'horse latitudes'.)

10. Hadley Cells • Describe: As warm air moves towards poles, it bends b/c of CoriolisEffect. It cools, loses its push, & heads back towards Equator. The Hadley Cells form a band around the planet b/w Equator & Horse Lats.

11. Major Wind Systems Skip main idea #3 • Defined by: Wind is always defined based on the direction from which it is coming.

12. Polar Easterlies • Describe: The ground winds of the Polar Cell that blow from Polar regions to SubpolarLows. They are deflected by CoriolisEffect towards the west.

13. Westerlies • Describe: The ground winds of FerrelCells that blow from the horse latitudes to the sub polar lows. They are deflected by CoriolisEffect, but bend toward the east b/c they start blowing in the opposite direction.

14. Trade Winds (named for trade shipping) • Describe: Ground winds of Hadley Cells that blow from horse latitudes towards Equator & are deflected by Coriolis Effect toward the west.

15. Doldrums (“Dull”-don’t get stuck here!) • (intertropical convergence zone) • Describe: The quiet, still region near Equator where the trade winds converge & air is rising.

16. When wind systems collide • Effects: Powerful air movements can be created!!! WAAA HAAA HAAAA

17. Polar Jet stream • Describe: A river of fast moving W to E air, high above the surface of Earth (along the polar front). • Temperature Change effects: Jet stream moves faster in the winter b/c temperature differences are much greater b/w the warm Westerlies & Polar Air.

18. Subtropical Jet Stream • (intertropical convergence zone) • Describe: Weaker than Polar Jet Stream & roughly follows the horse latitudes (30 degrees N & 30 degrees S)