1. The Atmosphere in Motion Chapter 19 Sec. 1, 2, & 4 300

2. Air Pressure & Wind sec. 1 What is wind? –horizontal movement of air What does wind do? –helps moderate surface temperatures –distributes moisture –helps to “clean” atmosphere (w/ precipitation)

3. What is Air Pressure? What is air pressure? –weight of air pushing on Earth’s surface @ sea level =14.7 pounds per square inch (psi) Why don’t we feel air pressure? –b/c it’s exerted in all directions

4. Measuring Air Pressure How do we measure air pressure? –with barometer at sea level –29.92 inches –1013.2 millibars (mb)

5. Why Does Air Pressure Change? There are three things that affect air pressure. –Humidity –Altitude –Temperature

6. As humidity increases, what happens to air pressure? –Decreases Why? –b/c H 2 0 molecules have less mass than N 2 & O 2 molecules that are being displaced Why Does Air Pressure Change?

7. As altitude increases, what happens to air pressure? –decreases Why? –b/c less air above

8. How does temperature affect air pressure? –warm air  low pressure Why? –b/c air expands »less air per square inch –cold air  high pressure Why? –b/c air compresses »more air per square inch Why Does Air Pressure Change?

9. How Do Meteorologists Analyze Air Pressure? by plotting isobars on weather map –What is an isobar? line on which all points have equal barometric pressure

10. Wind What causes winds? –differences in air pressure (pressure gradient) due to unequal heating of Earth’s surface How is pressure gradient calculated? –change in pressure over change in distance 1020 mb – 1016 mb = 4 mb = 0.04 mb 100 km 100 km 1 km

11. How Do Winds Blow in Relation to Pressure? always from high to low pressure

12. How Do Isobars Portray the Pressure Gradient? What do isobars that are close together represent? –steep gradient, quick pressure change, fast winds What do isobars that are far apart represent? –gentle gradient, slow pressure change, slow winds

13. anticyclone High-Pressure Area As move toward center of a set of closed isobars & the pressure steadily increases: –a.k.a “high” or “anticyclone” air circulates clockwise –“right hand rule” air diverges fair weather & cooler & drier air

14. cyclone Low-Pressure Area As move toward center of a set of closed isobars & the pressure steadily decreases: –a.k.a “low” or “cyclone” air circulates clockwise –“right hand rule” Air converges stormy weather, warmer & more humid air, rain/snow

15. Measuring Surface Wind Direction & Speed What instrument do we use to tell the direction from which wind is coming? –wind vane Arrowhead points into wind (where wind is blowing from) How are winds named? –for direction from which wind is blowing Ex. westerly wind blowing FROM west westerly wind

16. Measuring Surface Wind Direction & Speed How is wind speed measured? –anemometer –Beaufort Scale

17. Factors Affecting Winds sec. 2 What is the Coriolis effect? –apparent curve of an object’s path What causes the Coriolis effect? –Earth’s rotation How does it affect winds in the: –Northern Hemisphere? curve to right –Southern Hemisphere? curve to left Coriolis Effect Animation Coriolis Effect & Wind Direction Visualization

18. How do seasons & continents affect winds? –direction of winds change seasonally  monsoons winter  cold, dry winds summer  warm, moist winds & heavy rains –most dramatic in S. Asia Continental & Local Winds Sec. 4

19. When & How Does a Sea Breeze Develop? less dense more dense LOW pressure HIGH pressure

20. When & How Does a Land Breeze Develop? less dense more dense LOW pressure HIGH pressure

21. When & How Does a Valley Breeze Develop? Slope heats up quickly & air becomes less dense, causing low pressure Valley stays cooler & air is more dense, causing high pressure

22. When & How Does a Mountain Breeze Develop?