2. UNIT 1: Weather Dynamics Chapter 1: Inquiring about Weather 1.2 - The Causes of Weather Chapter 2: Weather Forecasting

3. 1.2 The Causes of Weather The amount of solar energy that Earth receives every year is the same amount that Earth radiates back into space. The distribution of this energy is not equal throughout Earth. Three factors affect the distribution of solar energy on Earth. Earth’s curved surface Earth’s tilt on its axis Earth’s orbit UNIT 1 Chapter 1: Inquiring about Weather Section 1.2 TO PREVIOUS SLIDE

4. How Earth’s Curved Surface Affects Weather The amount of solar energy that reaches different regions of Earth varies because of Earth’s curved surface. The concentration of light that warms Earth’s surface is unequally distributed. UNIT 1 Chapter 1: Inquiring about Weather Section 1.2 TO PREVIOUS SLIDE

5. How Earth’s Tilt Affects Weather Earth’s tilt causes the yearly pattern of changes called seasons. As Earth orbits the Sun, the northern hemisphere is sometimes tilted toward the Sun and at other times it is tilted away. Describe how the tilt of the Earth affects temperatures in the Northern Hemisphere. UNIT 1 Chapter 1: Inquiring about Weather Section 1.2 TO PREVIOUS SLIDE

6. How Earth’s Orbit Affects Weather The shape of Earth’s orbit affects how much solar energy it receives. When Earth’s orbit is more oval, Earth gets much more solar energy when it is nearest the Sun than when it is farthest from the Sun. When the orbit is circular, solar energy is more evenly balanced during the year. How long does it take Earth to cycle from an oval orbit to a circular orbit? UNIT 1 Chapter 1: Inquiring about Weather Section 1.2 TO PREVIOUS SLIDE

7. Air Masses UNIT 1 Chapter 1: Inquiring about Weather Section 1.2 TO PREVIOUS SLIDE 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?

8. Air Masses UNIT 1 Chapter 1: Inquiring about Weather Section 1.2 TO PREVIOUS SLIDE What other air masses can you see? How do they affect other parts of North America?

9. 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? UNIT 1 Chapter 1: Inquiring about Weather Section 1.2 TO PREVIOUS SLIDE

10. Low Pressure Systems UNIT 1 Chapter 1: Inquiring about Weather Section 1.2 TO PREVIOUS SLIDE 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?

11. The Coriolis Effect and Wind UNIT 1 Chapter 1: Inquiring about Weather Section 1.2 TO PREVIOUS SLIDE 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.

12. Global Wind Systems UNIT 1 Chapter 1: Inquiring about Weather Section 1.2 TO PREVIOUS SLIDE 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?

13. 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? UNIT 1 Chapter 1: Inquiring about Weather Section 1.2 TO PREVIOUS SLIDE

14. 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. UNIT 1 Chapter 1: Inquiring about Weather Section 1.2 TO PREVIOUS SLIDE Continued …

15. Fronts UNIT 1 Chapter 1: Inquiring about Weather Section 1.2 TO PREVIOUS SLIDE Why does an approaching front signal a change in weather?

16. 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? UNIT 1 Chapter 1: Inquiring about Weather Section 1.2 TO PREVIOUS SLIDE Continued …

17. Extreme Weather UNIT 1 Chapter 1: Inquiring about Weather Section 1.2 TO PREVIOUS SLIDE 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? Continued …

18. Extreme Weather UNIT 1 Chapter 1: Inquiring about Weather Section 1.2 TO PREVIOUS SLIDE Continued… 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.

19. Extreme Weather UNIT 1 Chapter 1: Inquiring about Weather Section 1.2 TO PREVIOUS SLIDE 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?

20. Section 1.2 Review UNIT 1 Chapter 1: Inquiring about Weather Section 1.2 TO PREVIOUS SLIDE 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.