Warm - Up

1. Warm - Up What are centers of low pressure called? Describe the location and direction of flow of the three global wind belts. In a high pressure system are isobars located closer or farther apart?

2. Regional Wind Systems Chapter 19, Section 3

3. Local Winds • The local winds are caused either by topographic effects or by variations in surface composition—land and water—in the immediate area • During warm summer months, coastal land is heated more intensely than the water, producing an area of low pressure which the cooler ocean air moves into fill, creating a breeze in the afternoon (sea breeze); at night the reverse may take place (land breeze) • The same happens in the mountains, with the air from the valley coming up to replace the air from the mountain slopes (valley breeze); at night the reverse takes place (mountain breeze)

4. Sea and Land Breezes

5. Valley and Mountain Breezes

6. How Wind is Measured • Two basic wind measurements—direction and speed—are especially important to the meteorologist • Winds are always labeled by the direction from which they blow • The wind vane is the instrument used to determine wind direction • Prevailing Wind – when wind consistently blows more often from one direction than from any other • In the United States, the westerlies consistently move weather from west to east across the continent • Within this general eastward flow are cells of high and low pressure with the characteristic clockwise and counterclockwise motion which cause the westerlies to vary considerably from day to day and place to place • Anemometer – device to measure wind speed

7. How Wind is Measured

8. El Niño • At irregular intervals of three to seven years, the warm countercurrents, along the coasts of Peru and Ecuador, become unusually strong and replace normally cold offshore waters with warm equatorial waters – El Niño • The warm waters block the nutrients from reaching the surface waters, causing many fish to die off, and greatly affects the fishing industries of Peru and Ecuador • Some inland areas that are normally arid get an abnormal amount of rain, increasing their crop production • These episodes mostly effect the eastern tropical Pacific, but is a part of the global circulation and affects the weather all over the world

9. Normal Conditions

10. El Niño

12. El Niño

13. La Niña • The opposite of El Niño is an atmospheric phenomenon known as La Niña • Researchers have come to recognize that when surface temperatures in the eastern Pacific are colder than average, a La Niña event is triggered that has a distinctive set of weather patterns • A typical La Niña winter blows colder than normal air over the Pacific Northwest (with more precipitation) and the Northern Great Plains • It warms much of the rest of the United States

14. La Niña

15. Global Distribution of Precipitation • Areas dominated by the convergent Trade winds (equatorial low) have mainly rain forests and abundant precipitation • Areas dominated by the subtropical high-pressure cells are regions of extensive deserts • The interiors of large land masses commonly experience decreased precipitation • You will be able to explain much about global precipitation through your knowledge of global winds and pressure systems

16. Global Distribution of Precipitation

17. Assignment • Read Chapter 19, Section 3 (pg. 543-548) • Do Section 19.3 Assessment #1-6 (pg. 548) • Study for Chapter 19 Quiz on Monday!!