Atmospheric Moisture and Cloud Formation

1. Quiz Chapter 24 • Sublimation • Latent heat • Humidity • Saturated • Relative humidity • Psychrometer • Hair hygrometer • Specific humidity • Dew point • Dew

2. Turn to page 482 describe how relative humidity is measured

3. This is due at the end of class Warm up question: How does relative humidity measure humidity Exit: What is a dew point Homework: Questions on page 483 – due 2/4

4. Homework Questions on page 483 – due 2/4 . Essential QuestionDescribe what happens when the temperature of air decreases at or below the dew point

5. Sublimation Latent heat Humidity Saturated Relative humidity Psychrometer Hair hygrometer Specific humidity Dew point Dew Frost Condensation nuclei Convective cooling Adiabatic Advective cooling Stratus clouds Cumulus clouds Cirrus clouds Radiation fog Advection fog Upslope fog Steam fog Chapter 24

6. Chapter 24 • Sleet • Glaze ice • Hail • Coalescence • Supercooling • Freezing nuclei • Cloud seeding • Rain gauge • Video Link • experiments

7. Chapter 24 Section 1 Objectives • Explain how water vapor enters the air. • Explain the meaning of humidity and describe how it is measured. • Describe what happens when the temperature of air decreases at or below the dew point.

8. Atmospheric Moisture Water in the air is called water vapor: it is tasteless, odorless, and invisible gas Water in the air can also be in the form of ice or water droplets Notes chapter 24 section 1

9. Heat energy and water Water in the form of ice is held in a CRYSTALLINE STRUCTURE Evaporation occurs when water molecules rotate and vibrate fast enough to overcome forces of attraction Can ice become vapor without first becoming water? Sublimation: process where water in a solid form (ice) goes directly to a gas phase Notes chapter 24 section 1

10. Heat energy and water Though most water enters atmosphere through EVAPORATION, some water does enter through SUBLIMATION Where does most sublimation occur? (hint: where is there a lot of ice???) Latent Heat: “Hidden” heat Given off during evaporation Taken out during freezing Notes chapter 24 section 1

11. Humidity Humidity: amount of water in the atmosphere When the air CANNOT hold anymore water, the air is considered to be SATURATED The higher the temperature of air – THE MORE WATER IT CAN HOLD As the temperature decreases, so does the ability of air to hold water vapor Notes chapter 24 section 1

12. Relative Humidity Relative Humidity is a RATIO MASS OF WATER IN AIR POTENTIAL MASS OF WATER Potential mass of water that air can hold changes with the temperature of the air Hotter - more water vapor content Colder – less water vapor content Notes chapter 24 section 1

13. Measuring Relative Humidity Wet Bulb – Dry Bulb Method Dry bulb takes temperature of air with the amount of moisture present Wet Bulb takes temperature of air SIMULATING A SATURATED ATMOSPHERE Using both measurements, estimate humidity based on Relative Humidity Chart Tool: PSYCHOMETER Notes chapter 24 section 1

14. Specific Humidity Express the amount of water in the air in g/kg It is not affected by temperature or pressure. Notes chapter 24 section 1

15. Dew point This is the temperature at which air is saturated with water . Below this temperature liquid or solid water forms. Dew may also form on a surface via condensation If the dew point is below freezing frost will form Notes chapter 24 section 1 list the conditions that must exist for a cloud to form

16. Chapter 24 Section 2 Objectives • List the conditions that must exist for a cloud to form. • Identify the types of clouds. • Describe four ways fog may form.

17. Clouds and fog Are visible water droplets in the atmosphere Clouds and fog are the same, altitude is the only difference. Notes chapter 24 section 2 list the conditions that must exist for a cloud to form

18. Cloud formation The water needs something to condense onto, dust. The air must be at or below the dew point to cause cloud formation or saturated. Notes chapter 24 section 2 list the conditions that must exist for a cloud to form

19. Convective cooling As air rises it expands and cools, due to the release of energy. This process of cooling and heating to rising and falling air is called adiabatic Notes chapter 24 section 2 list the conditions that must exist for a cloud to form

20. Convective cooling Warms at a steady rate of 10C for every 100 M the air descends. The cooling is effected by the condensation process and averages .70C per 100 M the air rises. Notes chapter 24 section 2 list the conditions that must exist for a cloud to form

21. Convective cooling The level at which the clouds form is called the condensation level. This starts at the bottom of the cloud and further condensation allow the clouds to form up. Notes chapter 24 section 2 list the conditions that must exist for a cloud to form

22. Forceful Lifting Can be caused by air moving over a mountain range. It can also be caused by warm air pushing over a cold air mass. Notes chapter 24 section 2 list the conditions that must exist for a cloud to form

23. Temperature changes The mixing of two or more moist air masses with different air temperatures may be enough to get below the dew point. Notes chapter 24 section 2 list the conditions that must exist for a cloud to form

24. Advective cooling This is when warm moist air passes over a cold body of water or land mass, the heat is absorbed (dropping below the dew point) and low clouds form or fog. Notes chapter 24 section 2 list the conditions that must exist for a cloud to form

25. Classification of clouds By form and altitude Forms: Stratus, Cumulus and Cirrus. Altitude groups: Low is up to 2,000 M, Middle is 2,000 to 6,000 M and High is above 6,000 M Notes chapter 24 section 2 list the conditions that must exist for a cloud to form

26. Stratus Clouds Are sheet like or layered, they are low to the earth surface and cover large areas of the sky. Formed when warm air is above cool air, give very little rain. Two other types: nimbostratus are dark and give heavy rain or snow, altostratus form at middle latitudes and little rain Notes chapter 24 section 2 list the conditions that must exist for a cloud to form

27. Cumulus Clouds Are the puffy or popcorn clouds, if the form at the middle they are altocumulus and at lower levels are stratocumulus and cumulus. If there are strong rising winds a cumulonimbus forms and can produce thunder, lighting and rain. Notes chapter 24 section 2 list the conditions that must exist for a cloud to form

28. Cirrus Clouds These are the feathery or curly clouds at high altitudes. Normally made of ice crystals, that can cause a halo to form around the sun or moon. Notes chapter 24 section 2 list the conditions that must exist for a cloud to form

29. Fog Radiation fog or ground fog forms close to the ground as it gives off the heat from the day, more common in valleys were the cold air can collect. Advection fog forms when warm moist air pushes over a colder surface. Upslope fog is cause by warm air moving uphill and steam fog is when warm air moves over a colder body of water. Notes chapter 24 section 2 list the conditions that must exist for a cloud to form

30. Chapter 24 section 3 essential questions • Describe the various types of liquid and solid precipitation. • Compare the two processes that cause precipitation • Describe how rain may be produced artificially • Describe how precipitation is measured list the conditions that must exist for a cloud to form

31. Precipitation Moisture that falls from the sky; either as a liquid or solid. ( rain, snow, sleet and hail) Notes chapter 24 section 3 list the conditions that must exist for a cloud to form

32. Forms of precipitation Liquid – rain A drizzle – drops less then .5 mm are close together and fall slowly. Raindrops - .5 mm to 5 mm, can be a mist to heavy rains as in a storm. Notes chapter 24 section 3 list the conditions that must exist for a cloud to form

33. Forms of precipitation Snow – most common solid form. Smaller in size in lower temp because of lack of moisture. Sleet – rain freezes in the air as it falls to the ground. If it freezes when it hits the ground it forms sheet ice or glaze ice. Notes chapter 24 section 3 list the conditions that must exist for a cloud to form

34. Forms of precipitation Hail – lumps of ice that are spherical or irregular in shape. Form in normally in cumulonimbus clouds, rain gets pushed through a freeze layer and wind currents push it up and down several times. Notes chapter 24 section 3 list the conditions that must exist for a cloud to form

35. Causes of precipitation Water droplets are normally small enough to stay in the air. If the size increases 100 times from 20 micrometers, they will begin to fall Notes chapter 24 section 3 list the conditions that must exist for a cloud to form

36. Coalescence Rain drop size is determined by the size of the nuclei. As droplets collide they get larger until it comes down as rain. Coalescences is how rain forms in the tropics. Notes chapter 24 section 3 list the conditions that must exist for a cloud to form

37. Supercooling Water temps may go as low as -100C. They do not freeze unless they have a freezing nuclei to attach to. Once the process starts, crystals form quickly and fall as snow or rain Notes chapter 24 section 3 list the conditions that must exist for a cloud to form

38. Cloud seeding They add freezing nuclei to the cloud like: silver iodine (from flares or burners) or powdered dry ice. Conflicting evidence on effect, it may someday help end droughts and control storms. Notes chapter 24 section 3 list the conditions that must exist for a cloud to form

39. Measuring precipitation Three types: a wide funnel attached to a cylindrical container, one that dumps when it reaches a certain level, and the last weighs the amount of water in the bucket. Only measure in one small area. Snow is measured by depth and water volume, average is 10cm of snow per 1cm of water Notes chapter 24 section 3 list the conditions that must exist for a cloud to form