Download Pressure Centers and Winds

Warm-Up
What is the device used for mearsuring air
pressure called?
 What is the ultimate energy source for
most winds?
 What is a Jet Stream?
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Pressure Centers
and Winds
Chapter 19, Section 2
Highs and Lows
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
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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
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Cyclonic and Anticyclonic winds
Airflow Associated with Cyclones
and Anticyclones
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
Global Winds on a Rotating Earth
When the effect of rotation is added into the
system, the two-cell 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)
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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
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Global Winds on a Rotating Earth
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, Section 2 (pg. 537-542)
 Do Section 19.2 Assessment #1-7 (pg. 542)
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