Unit 2 Lesson 1 Influences on Weather

1. Unit 2 Lesson 1 Influences on Weather

2. Unit 2Lesson 1 Influences on Weather How does the water cycle affect weather? • Weatheris the condition of Earth’s atmosphere at a certain time and place. • The water cycle is the continuous movement of water among the atmosphere, land, oceans, and living things. • Evaporation, condensation, and precipitation in the water cycle are also parts of weather. • Weather is described by factors such as temperature, humidity, precipitation, air pressure, wind, and visibility.

3. Unit 2Lesson 1 Influences on Weather What is humidity and how is it measured? • Humidityis the amount of water vapor in the air. As more water evaporates, humidity of the air increases. • Relative humidityis the amount of water vapor in the air compared to the amount of water vapor needed to reach saturation. It is measured with a psychrometer. • When air is saturated, the rates of evaporation and condensation are equal.

5. Unit 2Lesson 1 Influences on Weather What is humidity and how is it measured? • Dew point is the temperature at which more condensation than evaporation occurs. • When air temperature drops below the dew point, water vapor condenses to form dew, fog, and clouds. • When an object’s temperature drops below the air surrounding it, dew will form on the object.

7. Unit 2Lesson 1 Influences on Weather What is precipitation? • Precipitationis any form of water that falls to Earth’s surface from the clouds. It includes rain, snow, hail, and sleet. • Inside a cloud, water droplets collide forming larger droplets. When they become too heavy, they fall as rain. • Snow forms when air temperatures are low enough to turn water vapor directly into ice in the clouds. • When balls or lumps of ice fall from clouds during thunderstorms, it is called hail. • Sleet forms when rain falls through a layer of freezing air, producing falling ice.

8. Unit 2Lesson 1 Influences on Weather What is air pressure? • Airpressureis the force of air molecules pushing on an area. • A barometer is used to measure air pressure. • Air pressure and density decrease with altitude. • Air pressure and density will also increase with cooler air and decrease with warmer air.

10. Unit 2Lesson 1 Influences on Weather What is air pressure? • Why do mountain climbers sometimes need extra oxygen to breathe at the top of a mountain?

11. Unit 2Lesson 1 Influences on Weather What is wind and how is it measured? • Windis air that moves horizontally, or parallel to the ground. • Differences in air pressure sets air in motion. Over a short distances, air moves from higher pressure to lower pressure. This is felt as wind. • An anemometer is used to measure wind speed. • A wind vane or wind sock is used to measure wind direction.

12. Unit 2Lesson 1 Influences on Weather What are pressure systems and how do they interact? • Areas of different air pressure cause changes in the weather. • In a high-pressure system, air slowly sinks down and spreads outward. • In a low-pressure system, air rises and cools.

14. Unit 4Lesson 3 What Influences Weather? What are pressure systems and how do they interact? • A high-pressure system can form a low-pressure system. .

15. Unit 2Lesson 1 Influences on Weather How do different pressure systems affect us? • Sinking air in a high-pressure system generally produces clear skies and calm air or gentle breezes. • Rising air in a low-pressure system generally produces clouds and rain.

16. Unit 2Lesson 1 Influences on Weather How do air masses affect weather? • An air massis a large volume of air in which temperature and moisture content are nearly the same throughout. • An air mass forms when air remains over a region for many days and takes on the temperature and humidity of the land below it.

18. Unit 2Lesson 1 Influences on Weather Where do fronts form? • A boundary, called a front, forms between air masses with differing densities. • Fronts cause a change in weather as they pass. • The temperature and moisture content of the air masses that meet and their movement relative to each other determine the type of front formed.

19. Unit 2Lesson 1 Influences on Weather Where do fronts form? • Cold fronts form as a cold air mass pushes an existing warm air mass up.

20. Unit 2Lesson 1 Influences on Weather Where do fronts form? • Warm fronts form as a warm air mass slides up over a retreating cold air mass.

21. Unit 2Lesson 1 Influences on Weather Where do fronts form? • Stationary fronts form when a cold air mass and a warm air mass remain in one place.

24. Unit 2Lesson 1 Influences on Weather How do global wind patterns affect local weather? • Winds are caused by changes in pressure, which is due to unequal heating. • Wind speed and direction are affected by local winds. Globally, there is an overall movement of surface air from the poles toward the equator. • Winds bring different air masses to a region, which affects the weather.

26. Unit 2Lesson 1 Influences on Weather How do jet streams affect weather? • Jet streams are long-distance winds that travel above global winds for thousands of kilometers. • A jet stream affects temperatures and precipitation patterns. • The polar jet stream travels further south in the winter and further north in the summer.

27. Unit 2Lesson 1 Influences on Weather How do jet streams affect weather? • Each hemisphere usually has two main jet streams.

28. Unit 2Lesson 1 Influences on Weather Ocean Effects How do ocean currents influence weather? • Surface currents in the ocean are caused by wind. • Energy is transferred to the atmosphere by the movement of warm and cold currents. • Hurricanes and monsoons are affected by ocean currents.

29. Unit 2Lesson 1 Influences on Weather How do ocean currents influence weather? • As currents flow, they warm or cool the atmosphere above, affecting local temperatures. • Coastal areas may have lower summer temperatures than inland areas because of cold-water currents. • Coastal areas may have higher winter temperatures than inland areas because of warm-water currents.

31. Unit 2Lesson 1 Influences on Weather How do ocean currents influence weather? • Why is San Diego cooler than El Centro in the summer?

32. Unit 2Lesson 1 Influences on Weather How do ocean currents influence weather? • Why is Lillehammer colder than Bergen in the winter months?