Guided Notes for Weather Systems

Chapter 12, Section 2

1. Because the Earth rotates from west to east, the Coriolis effect causes moving air particles to deflect to the right in the northern hemisphere and to the left in the southern hemisphere.

2. The Coriolis effect combines with imbalances in heat to produce distinct global wind systems that transport colder air to warmer areas and warmer air to colder areas.

3. The trade winds occur at 30 degrees north and south latitude. There, the air sinks, warms, and moves toward the equator in a westerly direction.

4. Near the equator, the trade winds from both hemispheres converge and are forced upward, creating an area of low pressure called the intertropical convergence zone (ITCZ).

5. The ITCZ is characterized by a band of cloudiness and occasional showers that provide moisture for tropical rain forests.This area is also called the doldrums.

6. The prevailing westerlies occur between 30 and 60 degrees north and south latitude in a circulation pattern opposite the trade winds. In this zone, surface winds move toward the poles in an easterly direction.

7. Winds are named for the direction from which they blow. The prevailing westerlies are responsible for the movement of weather systems across the U.S. and Canada.

8. The polar easterlies occur between 60 and 90 degrees latitude. They flow from the northeast to the southwest in the Northern Hemisphere.

9. Narrow bands of fast, high-altitude, westerly winds called jet streams flow at speeds up to 185 km/h at elevations of 10 to 12 km.

10. Disturbances form along jet streams and give rise to large-scale weather systems that transport cold air toward the tropics and warm air toward the poles.

11. A front is the narrow region separating two air masses of different densities. There are four main types of fronts: cold fronts, warm fronts, stationary fronts, and occluded fronts.

Name and describe the 4 types of fronts Cold Front: cold air displaces warm air and

forces it to rise, often creating thunderstorms Warm Front: warm air gradually displaces cold

air, creating clouds and showers Stationary Front: when two air masses meet,

and neither is displaced, causing long periods of rain

Occluded Front: when a cold air mass overtakes a warm front, wedging it upward. This creates precipitation on both sides of the front

13. In a surface high-pressure system, air sinks and spreads away from the center. This air is deflected to the right by the Coriolis effect, making the overall circulation move in a clockwise direction in the northern hemisphere.

14. In surface low-pressure systems, air rises. This air is replaced by air from outside of the system, so the net flow is inward and upward. In the northern hemisphere, air in a low-pressure system moves in a counter-clockwise direction.

15. High-pressure systems are usually associated with fair weather, while low-pressure systems are associated with clouds and precipitation.

16. A wave cyclone is a type of low-pressure system. It usually begins as a stationary front. An imbalance causes part of the front to move south as a cold front and another part to move north as a warm front. This sets up a counter-clockwise, or cyclonic circulation.