1. The AtmosphereSection 3 Fronts and Severe Weather 〉 How do fronts affect the weather? 〉 When fronts move through an area, the result is usually precipitation and a change in wind direction and temperature. air mass: a large body of air where temperature and moisture content are similar throughout front: the boundary between air masses of different densities and usually different temperatures

2. The AtmosphereSection 3 Fronts and Severe Weather, continued Interactions between air masses have predictable effects on the weather in a given location. Clouds, rain, and sometimes snow can occur at fronts. Front types include warm fronts cold fronts stationary fronts

3. The AtmosphereSection 3 Fronts and Severe Weather, continued Lightning is a discharge of atmospheric electrical energy. –Water droplets and ice crystals in thunderclouds build up electrical charges. –Lightning is a big spark that jumps between clouds or between clouds and Earth to equalize the charge. Lightning heats the air so fast that the air expands faster than the speed of sound. –The shockwave created is thunder.

4. The AtmosphereSection 3 Fronts and Severe Weather, continued Tornadoes are funnels of high-speed wind. –Tornado winds are the most violent winds on Earth. Wind speeds may reach up to 500 km/h. –Tornadoes typically form along a front between cool, dry air and warm, humid air. –funnel cloud: a column of water droplets Tornadoes are fast moving and unpredictable.

5. The AtmosphereSection 3 Tornado

6. The AtmosphereSection 3 Fronts and Severe Weather, continued Hurricanes are large, rotating tropical storm systems. These storms are called –hurricanes in North America and the Caribbean –cyclones in the Indian Ocean –typhoons in the western Pacific tropical depressions: intense low-pressure areas that can become hurricanes

7. The AtmosphereSection 3 Fronts and Severe Weather, continued Hurricanes are powered by energy released as water vapor condenses to form clouds. The center of a hurricane is called the eye. The eye is usually calm. Hurricane winds can reach speeds greater than 250 km/h.

8. The AtmosphereSection 3 Climate 〉 How is climate different from weather? 〉 Weather changes from day to day, but climate does not change as quickly. climate: the average weather conditions in an area over a long period of time

9. The AtmosphereSection 3 Climate, continued Temperatures tend to be higher close to the equator. –Sunlight strikes the earth more directly close to the equator. –The sun’s rays are less concentrated at the poles, and do not warm the atmosphere as much.

10. The AtmosphereSection 3 Climate, continued Earth’s tilt and rotation account for our seasons. –When the North Pole is tilted toward the sun, the Northern Hemisphere experiences summer. There is more daylight, and the temperature increases. Earth is farthest from the sun on July 4. When the South Pole is tilted toward the sun, the Southern Hemisphere experiences summer.

11. The AtmosphereSection 3 Climate, continued Earth’s surface features affect climate. topography: the size and shape of the land surface features of a region, including its relief –Variations in topography affect the climate of a region. Mountains can trap moisture on one side. –Deserts may form on the dry side of a mountain. Broad flat surfaces allow winds to merge on the plains. –Thunderstorms and tornados may form.

12. The AtmosphereSection 3 Climate, continued Global climate changes over long periods of time. Many factors produce changes in Earth’s climate, such as: eruptions of volcanoes shift of the continents changes in Earth’s tilt Many scientists think that increases in human-made greenhouse gases have caused the recent increase in global average temperature.