1. Understanding Air Pressure

2. WARM UP Silently study vocabulary for 10 minutes

3. Air Pressure 1.One of the basic weather elements and is an important factor in _weather forcasting_ 2.Air pressure- presure exerted by the weight of air above a. exerted in all directions b. air pressure pushing down = air pressure pushing up c. air pressure at sea level is 1 kg per square cm

4. B. Measuring Air pressure 1.Unit- millibar 2.Describe by using the phrase “inches of mercury” (dates from 1643) 3.Barometer-used for measuring air pressure bar= pressure metron= measuring instrument A. When air pressure _______, the mercury in the tube ____; you fill in the rest!

5. Factors affecting Wind A.Wind- result of horizontal differences in air pressure 1. air flow from areas of higher pressure to areas of lower pressure 2. nature’s way of balancing inequalities in air pressure 3. Ultimate energy source for most wind- solar radiation

6. 3 factors that affect wind 1.Pressure differences 2.Coriolis effect 3.friction

7. Pressure Differences 1.Variation in air pressure are determined from barometric reading from hundreds of weather stations 2.Isobars- lines on a map that connect places of equal pressure ** spacing of isobars indicates amount of pressure change occuring over time

8. 3. Pressure Gradient Pressure change expressed by space between isobars a.steep- high winds, strong pressure gradient, isobars close b.Less steep- light winds, weak pressure gradient, isobars widely spaced

9. Coriolis effect Describes how the Earth’s rotation affects moving objects especially wind In the northern hemisphere wind is deflected to the right of it’s path In the southern hemisphere they are deflected to the left

10. C. Friction 1.Acts to slow air movement which changes wind direction 2.Smooth terrain- low friction and angle of air flow is small rough terrain- higher friction, winds move more slowly 3. Jet stream- most prominent airflow high above the friction layer

11. Measuring wind Anemometer- used to measure wind speed

12. GLOBAL WINDS A.Non-rotating Earth Model 1.Heated air at the equator would rise until reaching the troposphere then the troposphere would deflect air sending it to the poles B. Rotating Earth Model 1. Trade winds- 2 belts of wind that blow constantly from easterly air Located between subtropical and equator

13. Influence of Continents 1. Monsoons- seasonal changes in wind direction – 1. warm months-rainy warm air- summer monsoons Winter monsoon- dominated by dry continental air

14. Assignment Page 534 1.Which pressure cell, high or low, has the fastest wind speed? 2.Which area of the country is experiencing the fastest wind speed? 3.Which pressure system, high or low, has the steepest isobar? 4. Complete the reviewing concepts questions on page 536.