Warm Up1) If Earth did not rotate, how would air at the

equator move?a. Air would sink and move toward the poles.b. There would be no air movement.c. Air would rise and move toward the poles.d. none of the above

2) Near the equator, rising air is associated with a pressure zone known as the ____.a. equatorial low c. equatorial highb. tropical high d. tropical low

3) Centers of low pressure are called ____.a. air masses c. anticyclonesb. jet streams d. cyclones

Answers: 1) c. 2) a. 3) d.

Regional Wind Systems

Chapter 19, Section 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)

Sea and Land Breezes

Valley and Mountain Breezes

Concept Check

• What type of local wind can form in the Grand Canyon at night?

• Mountain breeze

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

How Wind is Measured

Concept Check

• Toward which direction does a SE wind blow?

• NW (north-west)

El Niño• 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

• 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

Normal Conditions

El Niño

El Niño

Concept Check

• What is an El Niño and what effect does it have on the weather?

• An episode—occurring every three to seven years—of ocean warming that affects the eastern tropical Pacific; warm countercurrents become unusually strong and replace normally cold offshore waters with warm equatorial waters.

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

La Niña

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

Global Distribution of Precipitation

Concept Check

• What two factors mainly influence global precipitation?

• Moisture content of air and distribution of land and water.

Assignment• Read Chapter 19, Section 3 (pg. 543-549)• Do Chapter 19 Assessment #1-29 (pg.

553-554)• For Section 3: #’s 6, 16, 17, 24-27, 29

• For the Multiple Choice (#1-10) write the question and the answer.

• For the rest…Complete Sentences!

• Study for Chapter 19 Quiz!!!