1. CH. 19: Air Pressure & Wind Air Pressure=the pressure exerted by the weight of air above. Air pressure is very important factor in predicting the weather! Air pressure at sea level is 14.7 lbs per square inch.

2. Barometer=instrument used to measure air pressure. 2 TYPES: 1. Aneroidcanister like device, pressure changes on the spring move the arrow 2. Mercuryliquid device, pressure changes make the liquid go up(high) & go down(low)

3. What causes wind? Wind is the horizontal movement of air. Wind is caused by the horizontal differences in air pressure. The differences in air pressure are in turn caused by differences in temperature(solar radiation)

4. 3 Factors Affecting Wind: 1. Pressure Differencesgreater the difference the greater the wind. Air moves from high to low pressures Isobars=lines of equal pressure Closely packed = windy Widely spaced = not as windy Pressure Gradient=steep means windy Pressure Gradient=weak/not steep means Not windy

5. 2. Coriolis EffectEarths rotation affects moving objects --Free moving objects move to the right in the northern hemisphere & to the left in the southern. 3. Frictiononly important near Earth. Friction slows wind & can change wind direction. JET STREAMS=high up & fast moving!

6. 19.2 Pressure Centers & Wind Pressure Centershelp 2 predict weather (2) Low (Cyclones) = air is unstable & rises, cools, condenses, clouds = stormy, cloudy, air moves ccw in N. hemisphere, winds move inward (?) Pressure decreases toward center High (Anti-Cyclones) = air is stable & descends, warms, evaporates, clear/fair, air moves cw in N. hemisphere, winds move outward (?) Pressure increases toward center

7. GLOBAL WINDS (read pgs 540-542) 0 degrees = equatorial low 30 degrees = subtropical high 60 degrees = subpolar low 90 degrees = polar high

8. Trade Winds = belt between 0 & 30 Prevailing Westerlies=belt between 30 & 60 Polar Easterlies=belt between 60 & 90 What is the polar front? Page 541 What are monsoons? Page 542

9. 19.3 Regional Wind Systems Local Windssmall-scale winds are produced by a locally generated pressure gradient. Local Windsare caused by 2 things: 1. by topographic effects (mtns. Etc.) 2. by variations in surface composition (land or water, etc.)

10. 4 Types of Local Winds: 1. Sea Breezehappens during the day, land heats up quicker & causes air to rise allowing cooler air to come from the sea. 2. Land Breezehappens during the night, land cools of quicker & causes the warmer air over the sea to rise allowing cooler air to come from the land.

11. 3. Valley Breezeoccurs during the day, air rises from valley floors. 4. Mountain Breezeoccurs at night, air sinks from the mountain tops toward the valley floor.

12. MEASURING WIND Wind Directionwind vane, wind direction is given by the direction the wind is coming FROM, (N,S,E,or W) or sometimes given in degrees! Wind Speedanemometer. Wind Sockssee them at airports measure wind speed & direction!

13. El Nino & La Nina Read about these phenomena carefully! When do they occur? Why do they occur? What global/local affects occur? Global ppt. Distribution? Read page 548Why does it rain in some places more than others?