The Water Cycle Evaporation, Condensation and Precipitation

1. The Water Cycle Evaporation, Condensation and Precipitation The _________evaporates water from lakes and _______. As the air rises, it cools. The water vapor ____________ into tiny droplets of . The droplets crowd together and form a ________Wind blows the towards the land. The tiny droplets join together and fall as _____________ to the land . The water soaks into the ground and collects in oceans and rivers . The cycle that never ends has started again!

2. Understanding weather Chapter 7 Notes

3. Water in the Air • Weather is the condition of the atmosphere at a certain time and place. • The condition is affected by the amount of water in the air.

4. The Water Cycle • Water is constantly being recycled through the water cycle.

6. Humidity • As water evaporates from lakes oceans and plants it becomes water vapor. • The amount of water vapor in the air is called humidity. As the temperature increases, the amount of water vapor the air can hold increases.

7. Relative Humidity • Relative Humidity is the amount of water vapor in the air compared with the maximum amount of water vapor that the air can hold at a certain temperature

8. Factors that affect Relative Humidity Amount of Water Vapor Temperature The relative humidity decreases as the temperature rises and increases as the temperature drops • The more water vapor in the air the higher the relative humidity. • The water vapor drops the relative humidity drops.

9. Measuring Relative Humidity • A psychrometer is an instrument that is used to measure relative humidity. • It consists of two thermometers: one wet bulb thermometer and one dry bulb thermometer. • The difference in the temperature readings between the two thermometers indicates the amount of humidity.

10. Measuring Relative Humidity

11. Dew Point • Dew point: the temperature at which a gas condenses into a liquid. • Air is saturated at dew point

12. Condensation • Condensation: the process by which a gas, such as water vapor, becomes a liquid. • Condensation occurs when saturated air (air full of humidity) cools.

13. Explain how water condenses on this glass.

14. The ice in the glass of water causes the air surrounding the glass to cool to its dew point. Water vapor then condenses on the outside of the glass. How would you explain dew on grass in the morning?

16. Clouds • A cloud is a collection of millions of tiny water droplets or ice crystals. • Clouds form as warm air rises and cools ( condensation)

17. Clouds

19. Cumulus Clouds • Puffy, white clouds that tend to have flat bottoms • Form when warm air rises • Indicate fair weather • When they get larger they produce thunderstorms – cumulonimbus clouds (AKA Thunderheads) • Clouds with nimbus or nimbo will produce precipitation

20. Cumulus Clouds Cumulonimbus Cloud 

21. Stratus Clouds • Stratus Clouds form in layers • Cover large areas and often block out the sun • Caused by a gentle lifting of a large body of air. • Nimbostratus clouds are dark stratus clouds that produce continuous rain. • Fog is a stratus cloud found near the ground.

22. Stratus Clouds

23. Cirrus Clouds • Cirrus Clouds are thin feathery white clouds found at high altitudes • Cirrus clouds form when the wind is strong • They can indicate a change in weather.

24. Cirrus Clouds

26. Clouds and Altitude • Clouds are classified by the altitude that they form

27. Cloud Classification • Low clouds – have no prefix • Ex. Cumulus, Stratus • Middle clouds – Have the prefix alto • Ex. Altocumulus, Altostratus • High clouds – Have the prefix Cirro • Ex. Cirrostratus, Cirrus

28. 1 2 4 3 5

29. Precipitation • Precipitation is water in solid or liquid form that falls from the air to the Earth • There are four major forms • Rain • Snow • Sleet • Hail

30. Rain • The most common form of precipitation. • Rain is produced when the water droplets in a cloud become a certain size.

31. Sleet and Snow • Sleet forms when rain falls through a layer of freezing air. • Snow forms when temperatures are so cold that water vapor changes directly to a solid.

32. Hail • Hail are balls or lumps of ice that fall from clouds. • Hail forms in cumulonimbus cloudsdue to updrafts freezing the water droplets.

33. Match the correct definition with the correct term. • a.precipitation • b.condensation • c.weather • d.humidity • a.relative humidity • b.cloud • 1.amount of water vapor in the air compared to the maximum it can hold • 2.process in which water vapor cools and turns to liquid • 3.collection of water droplets suspended in the air • 4.amount of water vapor in the air • 5.water that falls to the Earth’s surface as rain, snow, sleet, or hail • 6.condition of the atmosphere at a certain time and place

34. 7. What role does runoff play in the water cycle? • a. It is the process in which liquid turns to water vapor. • b. It carries water from precipitation into oceans. • c. It takes water out of the water cycle. • D. It is not part of the water cycle. • 8. What happens when air reaches its dew point? • a.Condensation occurs. • b. Relative humidity is 100%. • c. The humidity decreases. • D Clouds form. • 9. How does sleet differ from snow? • a. It is not a form of precipitation. • b. It is liquid and not ice. • c. It starts as rain and freezes in the air. • d. It starts as water vapor and changes to a solid.

35. Air Masses and Fronts • Changes in weather are caused by the movement and interaction of air masses. • An air mass is a large body of air where temperature and moisture content are similar throughout .

36. Air Masses • Air Masses are characterized by their moisture content and temperature which is determined by the area over which the air mass forms(Source Region)

37. Types of air masses • Maritime (m) Forms over water; wet • Continental ( c ) Forms over land; dry • Polar ( P) Forms over polar regions; cold • Tropical (T) develops over the tropics: warm

38. The first letter represents the moisture content. The second letter represents the temperature that is a characteristic of the air mass.

39. Cold Air Masses • Most of our cold weather comes from the three polar air masses. If it forms over land it is cold and dry. If is forms over the ocean it is cold and wet. • In the winter this means rain or snow. • In the summer it is cool and foggy.

40. Warm Air Masses • There are four warm air masses that influence weather in the U.S. • they bring hot, humid weather in the summer. • They can also produce hurricanes and thunderstorms. • In the winter they bring mild, cloudy weather.

41. Fronts • When two air masses meet, the air within them does not easily mix. That is to say that the air in one air mass will not easily mix with the air from another air mass. Instead, the air stays within its own air mass. Because of this phenomena, a border forms between two clashing air masses as they rub together. This border is called a front.

42. Fronts • The term ‘front’ was first used by Norwegian scientists who compared two air masses colliding to two armies as they clash on the battle front. Just like one army taking over another in a battle, one air mass ultimately takes over, pushing the other one out the away. • Fronts should not be thought of as a vertical wall. This is because they are actually sloped, like a hill. Often the slope of a front can be extremely gradual, taking hundreds of miles across the surface of the Earth to reach an altitude of just one mile.

43. Fronts • Front: the boundary between air masses of different densities and usually different temperatures • Four kinds of fronts • Cold front • Warm front • Occluded front • Stationary front

44. Cold Fronts • Cold fronts move faster than warm fronts. This causes the cold air mass to push the warm air mass up quickly. • The fast movement of a cold front bringsthunderstorms, heavy rain, or snow followed by cooler weather.

46. Warm Fronts • A warm front forms where warm air moves upward above colder denser air • The warm air gradually rises it cools and the water vapor condensates. • Warm fronts bring light rain followed by warmer weather

48. Occluded Front • An occluded frontforms when a warm air mass is caught between two colder air masses • This produces cold temperatures and large amounts of rain or snow.

49. Stationary Fronts • Stationary fronts form when a cold air mass meets a warm air mass and neither displaces the other. This may happen because there is not enough wind to keep the air masses pushing against each other. • Brings many days of cloudy wet weather.