Section 12.2 Weather Systems

Transcription

1 Section 12.2 Weather Systems Weather results when air masses with different pressures and temperatures move, change, and collide as a result of uneven heating of the Earth combined with the Earth s rotation.

2 I can I can describe the Coriolis Effect; it causes and effects. 2. I can identify the major global wind systems. 3. I can describe the Inter Tropical Convergence Zone (ITCZ) 4. I can locate the Horse Latitudes and explain their existence. 5. I can identify the four types of fronts. 6. I can describe the characteristics of Low and High Pressure Systems, including direction of air movement, direction of rotation, and distinctive weather for each. 7. I can identify the one major difference affecting pressure systems in the northern hemisphere as opposed to the southern hemisphere.

3 Global Wind Systems If the Earth did not rotate, wind patterns would look like this. Cold, dense air would sink at the poles Warm, less dense air would rise at the equator.

4 But, Earth does rotate This results in fluids and objects moving in an apparent curved path rather than a straight line. Northern Hemisphere air curves to the right Southern Hemisphere air curves to the left. Coriolis Effect

5 Here's Why, pt 1 Air is always rising at the equator because it gets the most solar radiation. Wind is blowing towards the equator because the equator is a low pressure area.

6 Here's Why, pt 2 The equator spins faster than any other point on Earth. As one moves towards the poles, the distance traveled in 24hrs (ie speed) decreases

7 What does this mean? Trade Winds move from Northeast and Southeast towards the equator. Since they had a slower initial speed, they are deflected westward as the equator races beneath them.

8 What does this mean? Cont. Prevailing Westerlies begin at the Horse Latitudes. They move faster than latitudes to the north. So, these winds will move from SW to NE Westerlies come from the west.

9 What does this mean? Cont. Polar Easterlies sinking air at the poles has very little speed. So, it is deflected from NE to SW. Polar Easterlies originate from the poles and move in an easterly direction, from the east.

10 Inter Tropical Convergence Zone Trade Winds move towards the equator. Solar heating of the earth causes warmed air to rise. Air with moisture cools and condenses providing precipitation for Rainforests. Note the seasonal shifts ITCZ

11 Horse Latitudes Dry air sinks and undergoes compressional warming at ~30 N and S latitudes Note correlation with Desert Biomes in NA, SA, Africa, Asia and Australia

12 Jet Streams Air high in the atmosphere keeps it momentum. Meaning that it moves faster than the ground far below it. Occur at boundaries between wind zones. Speeds can reach 185 km/h from 10.7 to 12.2km above Earth. Weather systems generally follow the path of Jet Streams. Jet streams can move air masses and effect weather.

13 Fronts Boundaries between air masses are called Fronts Remember Convergence of air masses and clouds There are 4 types of fronts which depend on how the air masses are moving Cold Warm Occluded Stationary

14 Cold Front Cold Front Cold air mass pushes up a warm air mass Intense precipitation and Thunderstorms Blue line w/ triangles indicate direction

15 Warm Front Warm Front Warm air slides over a departing cold air mass Gradual Slope Cirrus clouds form and precipitation is light and steady Red line with semicircles indicate direction.

16 Stationary Front Stationary Front Small pressure differences cause a front to stop moving, could stay for several days, light wind and precipitation across an entire region Shown by alternating blue triangles and red semicircles, opposite directions

17 Occluded Front Occluded Front Cold air mass overtakes a warm front; warm air forced up, Results in strong winds and precipitation Alternating purple triangles and semicircles, same direction.

18 Low Pressure Systems Air rises, spirals inward CCW in the Northern Hemisphere, Associated with cloudy weather and precipitation. Think Hurricanes. Opposite in Southern Hemisphere thanks to the coriolis effect. Right Hand Rule applies

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20 High Pressure Systems Air sinks spirals outward CW in the Northern Hemisphere, Associated with fair weather and possible drought. Again it is the opposite in the Southern Hemisphere thanks to the coriolis effect.

21 1. Summarize information about the four types of fronts. Explain how they form and lead to changes in weather. Your answers should reflect the information provided on page 322. Be sure to know the symbols used to represent each type of front. As well as their colors or color combination.

22 2. Distinguish among the three main wind systems Trade Winds 30N or 30S towards the Equator from the Northeast and Southeast respectively. Prevailing Westerlies Middle Latitudes. From the Southwest to the Northeast in Northern Hemisphere. Responsible for most of the Weather in the United States. From the Northwest to the Southeast in the Southern Hemisphere. Polar Easterlies Occur near the poles. Move from east to west.

23 3. Describe the Coriolis effect. The apparent deflection of wind to the west caused by the rotation of the Earth. Because Earth is a sphere, latitudes have different circumferences, and therefore, different eastward speeds. The greatest eastward speed is at the equator. Air rising at the equator and moving towards the poles appears to curve east because it is moving faster than the part of the Earth over which is moving. The smallest circumferences are at the poles. Air moving from the poles towards the equator appears to curve west because it is moving slower than the part of the Earth over which it is moving.

24 4. Explain why most tropical rainforests are located near the equator. The Inter Tropical Convergence Zone (ITCZ) is located near the equator and creates an area of low pressure as air rises. The rising air cools, condenses, and coalesces to produce precipitation for rainforests.

25 5. Describe how a Jetstream affects the movement of air masses. Surface weather systems that move air masses travel along the Jetstream. The intensity and movement of weather is determined by the Jetstream.

26 6. Compare and contrast high pressure and low pressure systems High Pressure Sinking Air Rotates CW in the Northern Hemisphere Moves outward Symbolized by a H Results in clear skies Extended -- Drought Low Pressure Rising Air Rotates CCW in Northern Hemisphere Moves inward Symbolized by a L Results in rain, overcast Extended -- Flooding

27 7. Analyze why most of the world s deserts are located between the latitudes 10N to 30N and 10S to 30S. Air sinks, dries, and warms by compression in these areas, creating hot and dry conditions over large portions of landmasses.