Transcript Regional Wind Systems

Warm Up 3/25
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 high
b. tropical high
d. tropical low
3) Centers of low pressure are called ____.
a. air masses
c. anticyclones
b. jet streams
d. cyclones
Answers: 1) c. 2) a. 3) d.
1)
Regional Wind
Systems
Chapter 19, Section 3
Local Winds
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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
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What type of local wind can form in the Grand
Canyon at night?
Mountain breeze
How Wind is Measured
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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
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Toward which direction does a SE wind blow?
NW (north-west)
El Niño
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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
Normal Conditions
El Niño
El Niño
Concept Check
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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
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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
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Areas dominated by the convergent Trade winds
(equatorial low) have mainly rain forests and
abundant precipitation
Areas dominated by the subtropical highpressure 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
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What two factors mainly influence global
precipitation?
Moisture content of air and distribution of land
and water.
Assignment
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Read Chapter 19 (pg. 532-549)
Do Chapter 19 Assessment #1-29 (pg. 553-554)
Study for Chapter 19 Quiz