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UNIT 2 Chapter 1: Inquiring about Weather Unit 2: Weather Dynamics Section 1.2: The Causes of Weather Science 10 Mrs. Purba UNIT 2 Chapter 1: Inquiring about Weather Section 1.2 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. 1. Earth’s curved surface 2. Earth’s tilt on its axis 3. Earth’s orbit UNIT 2 Chapter 1: Inquiring about Weather Section 1.2 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 2 Chapter 1: Inquiring about Weather Section 1.2 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 2 Chapter 1: Inquiring about Weather 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? Section 1.2 UNIT 2 Chapter 1: Inquiring about Weather 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? Section 1.2 UNIT 2 Chapter 1: Inquiring about Weather Air Masses What other air masses can you see? How do they affect other parts of North America? Section 1.2 UNIT 2 Chapter 1: Inquiring about Weather Section 1.2 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. • Earth's rotation causes wind to travel in a clockwise direction around a high pressure centre (H). How does wind form in this process? UNIT 2 Chapter 1: Inquiring about Weather Section 1.2 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. • Earth's rotation causes wind to travel in a counterclockwise direction around a high pressure centre (L). What kind of weather is expected when there is a low pressure system? UNIT 2 Chapter 1: Inquiring about Weather 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. Section 1.2 UNIT 2 Chapter 1: Inquiring about Weather Section 1.2 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? UNIT 2 Chapter 1: Inquiring about Weather Global Wind Systems Section 1.2 UNIT 2 Chapter 1: Inquiring about Weather Section 1.2 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 2 Chapter 1: Inquiring about Weather Section 1.2 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 2 Chapter 1: Inquiring about Weather Fronts Why does an approaching front signal a change in weather? Section 1.2 UNIT 2 Chapter 1: Inquiring about Weather Section 1.2 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 2 Chapter 1: Inquiring about Weather Section 1.2 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? UNIT 2 Chapter 1: Inquiring about Weather Section 1.2 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 (the period when the oceans store the greatest amount of thermal energy). UNIT 2 Chapter 1: Inquiring about Weather 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? Section 1.2 UNIT 2 Chapter 1: Inquiring about Weather Section 1.2 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.