Go With the Flow From High to Low Investigating Isobars

Transcription

1 Go With the Flow From High to Low Investigating Isobars Science 10 Mrs. Purba

2 Air Masses The air over a warm surface can be heated, causing it to rise above more dense air. The result is the formation of an air mass a very large mass of air that has the same properties, such as humidity and temperature, as the area over which the air mass forms. Which air mass is shown nearest Nova Scotia, and what are the characteristics of it?

3 Air Masses What other air masses can you see? How do they affect other parts of North America?

4 High Pressure Systems When an air mass cools over an ocean or a cold region of land, a high pressure system forms. As the air mass cools, the air mass becomes more dense. When the air mass contracts, it draws in surrounding air from the upper atmosphere. How does wind form in this process?

5 Low Pressure Systems Air masses that travel over warm land or oceans may develop into low pressure systems. When an air mass warms, it expands and rises. As it rises, it cools. Water vapour in the air may condense, producing clouds or precipitation. What kind of weather is expected when there is a low pressure system?

6 UNIT 2 Investigating Isobars Section 1.2 What is an Isobar? line showing a weather pattern a line drawn on a weather map that connects places with equal atmospheric pressure. Isobars are often used collectively to indicate the movement or formation of weather systems. Isobar lines may never cross or touch. Isobar lines may only pass through pressures of 1000+/- 4. In other words, allowable lines are 992, 996, 1000, 1004, 1008, and so on.

7 UNIT 2 Investigating Isobars Section 1.2 Drawing Isobars You will use a black colored pencil to lightly draw lines connecting identical values of sea level pressure. Remember, these lines, called isobars, do not cross each other. Isobars are usually drawn for every four millibars, using 1000 millibars as the starting point. Therefore, these lines will have values of 1000, 1004, 1008, 1012, 1016, 1020, 1024, etc., or 996, 992, 988, 984, 980, etc. You will then identify a high pressure center and a low pressure center. You will predict the location of fair weather and stormy weather. You will identify the direction of spin around a high pressure center and a low pressure center.

8 UNIT 2 Investigating Isobars Section 1.2 Begin drawing from the 1024 millibars station pressure over Salt Lake City, Utah (highlighted in gray). Draw a line to the next 1024 value located to the northeast (upper right). Without lifting your pencil draw a line to the next 1024 value located to the south, then to the one located southwest, finally returning to the Salt Lake City value. Now connect the pressure areas that are 1020 millibars. Complete the map.

9 UNIT 2 Investigating Isobars Section 1.2

10 UNIT 2 Investigating Isobars Section 1.2 Labelling Highs & Lows Isobars can be used to identify "Highs" and "Lows." The pressure in a high is greater than the surrounding air. The pressure in a low is lower than the surrounding air. Label the center of the high pressure area with a large blue "H". Label the center of the low pressure area with a large red "L".

11 UNIT 2 Investigating Isobars Section 1.1

12 UNIT 2 Investigating Isobars Section 1.2 Adding Weather High pressure regions are usually associated with dry weather because as the air sinks it warms and the moisture evaporates. Low pressure regions usually bring precipitation because when the air rises it cools and the water vapor condenses. Shade, in green, the state(s) where you would expect to see rain or snow. Shade, in yellow, the state(s) where you would expect to see clear skies. Isobars can be used to identify "Highs" and "Lows."

13 UNIT 2 Investigating Isobars Section 1.2 Weather Rhyme When pressure is low, expect rain or snow. When pressure is high, look for a blue sky.

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15 UNIT 2 Investigating Isobars Section 1.2 Put A Spin On It In the northern hemisphere the wind blows clockwise around centers of high pressure. The wind blows counterclockwise around lows. Draw arrows around the "H" on your map to indicate the wind direction. Draw arrows around the "L" on your map to indicate the wind direction.

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17 The Coriolis Effect and Wind The Coriolis effect is a change in the direction of moving air, water, or any objects on Earth s surface due to Earth s rotation. As Earth rotates, any location at the equator travels much faster than a location near either of the poles. Explain in your own words why the actual path of wind is curved in the northern and southern hemispheres.

18 Global Wind Systems Wind systems are wide zones of prevailing winds. There are three major wind systems, which occur in both hemispheres. Trade Winds Prevailing Westerlies Polar Easterlies How does the air circulation of the trade winds compare with the air circulation of the prevailing westerlies?

19 Jet Streams A large temperature gradient in upper-level air, combined with the Coriolis effect, results in strong westerly winds called jet streams. A jet stream is a narrow band of fast-moving wind. A jet stream can have a speed up to 300 km/h or greater at altitudes of 10 km to 12 km. Storms form along jet streams and generate large-scale weather systems. What do the jet stream and seasons have in common?

20 Fronts A front is a zone that develops as a result of the meeting of two air masses with different characteristics. Each air mass has its own temperature and pressure. An approaching front means a change in the weather, and the extent of the change depends on the difference between conditions in the air masses. Fronts usually bring precipitation.

21 Fronts Why does an approaching front signal a change in weather?

22 Extreme Weather Thunderstorms are extreme weather events that include lightning, thunder, strong winds, and hail or rain. A tornado is a violent, funnel-shaped column of rotating air that touches the ground. When tornados form over water, waterspouts occur. What causes a thunderstorm?

23 Extreme Weather When strong horizontal winds hit the rapidly rising air in a thunderhead, funnel clouds can result. Strong winds tilt the funnel cloud (A). The funnel cloud becomes vertical and touches the ground (B). A tornado forms as the funnel cloud travels along the ground. (C). What characteristic of a tornado makes it so dangerous?

24 Extreme Weather The tropics, the regions closest to the equator, are the ideal location for the formation of intense storms called tropical cyclones to occur. Wind speeds of tropical cyclones may reach 240 km/h. Tropical cyclones are also called cyclones, typhoons, or hurricanes. Hurricane season extends from late summer to early fall.

25 Extreme Weather This is a cross-section of a hurricane (A) and a satellite image of a hurricane (B). Why do tropical cyclones originate in the tropics?

26 Section 1.2 Review Earth s shape, tilt, and orbit affect weather. Five main air masses affect North America. The cooling and warming of air masses creates high and low pressure systems, respectively. Fronts form where two air masses meet. The Coriolis effect and differences in atmospheric pressure create global wind systems. Rapidly rising warm air results in extreme weather such as tropical cyclones, thunderstorms, and tornadoes.