Download Pressure Centers and Winds

Warm Up 3/21/08
The deflection of wind due to the Coriolis effect is
strongest at ____.
a. the poles
c. midnight
b. the equator
d. the midlatitudes
2) The force exerted by the weight of the air above is
called ____.
a. convergence
c. air pressure
b. the Coriolis effect
d. divergence
3) Which force generates winds?
a. gravity
c. pressure differences
b. friction
d. the Coriolis effect
Answers: 1) a. 2) c. 3) c.
1)
Pressure Centers
and Winds
Chapter 19, Section 2
Highs and Lows
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Cyclones – centers of low pressure
Anticyclones – centers of high pressure
In cyclones, pressure decreases from the outer isobars
toward the center
In anticyclones, the values of the isobars increase from
the outside toward the center
When the pressure gradient and the Coriolis effect are
applied to pressure centers in the Northern Hemisphere,
wind blows counterclockwise around a low and
clockwise around a high
In either hemisphere, friction causes a net flow of air
inward around a cyclone and a net flow outward around
an anticyclone
The usual “villain” in weather reports is the low-pressure
center
Cyclonic and Anticyclonic winds
Airflow Associated with Cyclones
and Anticyclones
Concept Check
With what type of weather is rising air
associated?
 Cloud formation and precipitation
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Global Winds on a Non-Rotating Earth
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The underlying cause of wind is the unequal
heating of Earth’s surface
The atmosphere balances these differences by
acting as a giant heat-transfer system
The system (atmosphere) moves warm air toward
high latitudes and cool air toward the equator
On a non-rotating planet, the heated air at the
equator would rise until it reached the tropopause
The tropopause would act as a lid and deflect the
air toward the poles
This upper-level airflow would reach the poles, sink,
spread out in all directions at the surface, and move
back toward the equator
Global Winds on a Non-Rotating Earth
Concept Check
How does the atmosphere balance the
unequal heating of Earth’s surface?
 The atmosphere transfers heat by moving
warm air toward high latitudes and cool air
toward the equator.
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Global Winds on a Rotating Earth
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When the effect of rotation is added into the system, the twocell convection model breaks down into smaller cells
Near the equator, rising air produces a pressure zone known as
the equatorial low (has much precipitation)
At 30 degrees north and south latitude, this air comes down,
producing hot, arid conditions; this is the subtropical high (many
of the world’s deserts are situated around this latitude)
Trade Winds – two belts of winds that blow almost constantly
from easterly directions and are located on the north and south
sides of subtropical highs
Westerlies – dominant west-to-east motion of the atmosphere
that characterizes the regions on the poleward side of the
subtropical highs
Polar Easterlies – winds that blow from the polar high toward
the subpolar low
Polar Front – stormy frontal zone separating cold air masses of
polar origin from warm air masses of tropical origin
Global Winds on a Rotating Earth
Concept Check
What is the polar front?
 The stormy belt where subpolar westerlies
and polar easterlies meet.
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Global Winds – Influence of Continents
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Where landmasses break up the ocean surface,
large seasonal temperature differences disrupt
the global pattern of pressure zones in the
atmosphere
Large landmasses can become cold in the
winter when a seasonal high-pressure system
develops, and the surface airflow will be directed
off the land
Monsoons – seasonal reversals of wind
direction associated with large continents,
especially Asia; in the winter, the wind blows
from land to sea, and in the summer, the wind
blows from sea to land
Global Winds – Influence of Continents
Global Winds – Influence of Continents
Assignment
Read Chapter 19 (pg. 532-549)
 Do Chapter 19 Assessment #1-29 (pg. 553554)
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