Understanding Cyclones, Anticyclones, and Global Winds: A Meteorological Exploration

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. 553-554)