1. 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
The force exerted by the weight of the air above is called ____.
a. convergence c. air pressure
b. the Coriolis effect d. divergence
Which force generates winds?
a. gravity c. pressure differences
b. friction d. the Coriolis effect
Answers: 1) a. 2) c. 3) c.

2. Pressure Centers and Winds
Chapter 19, Section 2

3. 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
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

4. Cyclonic and Anticyclonic winds

5. Airflow Associated with Cyclones and Anticyclones

6. Concept Check With what type of weather is rising air associated?
Cloud formation and precipitation

7. Global Winds on a Non-Rotating Earth
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

8. Global Winds on a Non-Rotating Earth

9. 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.

10. 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)
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

11. Global Winds on a Rotating Earth

12. Concept Check What is the polar front?
The stormy belt where subpolar westerlies and polar easterlies meet.

13. Global Winds – Influence of Continents
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

14. Global Winds – Influence of Continents

15. Global Winds – Influence of Continents

16. Assignment Read Chapter 19 (pg. 532-549)
Do Chapter 19 Assessment #1-29 (pg )