Chapter 21, guest starring Ch. 20, Section 2

Vocabulary 1. Coriolis effect

2. Trade winds

3. Westerlies

4. Easterlies

5. Doldrums

6. Horse latitudes

7. Air mass

8. Continental polar air mass

9. Continental tropical air mass

10. Maritime polar air mass

11. Maritime tropical air mass

12. Cloud

13. Troposphere

14. Advective cooling

15. Stratus clouds

16. Nimbostratus

17. Altostratus

18. Cumulus clouds

19. Cumulonimbus

20. Altocumulus

21. Stratocumulus

22. Cirrus clouds

23. Cirrocumulus

24. Cirrostratus

25. Crepuscular rays

26. Fog

27. Radiation fog

28. Advection fog

29. Upslope fog

30. Steam fog

31. Front

32. Cold front

33. Warm front

34. Squall line

35. Stationary front

36. Occluded front

37. Polar front

38. Midlatitude cyclones

39. Anticyclones

40. Thunderstorm

41. Cumulus stage

42. Mature stage

43. Dissipating stage

44. Lightning

45. Thunder

46. Hurricane

47. Latent heat

48. Storm surge

49. Saffir-Simpson scale

50. Tornado

51. Barometer

52. Anemometer

53. Wind vane

54. Radar

55. Station model

56. Isotherms

57. Isobars

58. Watch

59. Warning

60. Cloud seeding

I. Air Masses A. Air Movement

1. Uneven heating of Earth’s surface causes differences

in air pressure

a. Equator gets more solar energy than poles

b. Heated air rises – creates low-pressure system

c. Cold air sinks – creates high-pressure system

2. Air moves from high-pressure areas to low-pressure

areas

a. So surface air usually moves from poles to equator

b. At high altitudes, air moves from equator to poles

3. Differences in temp & pressure create wind belts

a. 3 wind belts in each hemisphere (Northern & Southern)

i. Trade Winds: 0° - 30°

ii. Westerlies: 30° - 60°

iii. Easterlies: 60° - 90°

b. Wind belts are influenced by the Coriolis effect – Earth’s

rotation causes wind deflection

c. Doldrums: low-pressure zone at equator (0°)

d. Horse latitudes: high-pressure zones at 30° N and S

B. Formation of Air Masses

1. Air mass: large body of air with nearly uniform

conditions of temperature and moisture content

2. Temperature of air masses usually depend on the

climate where they form

a. Polar regions have cold, dry air masses

b. Tropical oceans have warm, wet air masses

C. Types of Air Masses

1. Classified according to where they form

2. Take on characteristics of areas where they form

3. Continental air masses develop over land & usually have low humidity – bring dry conditions when they travel

1. Continental tropical (cT): form over warm, dry areas of land (southwest U.S.)

2. Continental polar (cP): form over cold, dry areas of land (polar Canada)

4. Maritime air masses develop over water & have high humidity – bring precipitation & fog when they travel

1. Maritime tropical (mT): form over warm, wet areas (tropical Pacific & Atlantic)

2. Maritime polar (mP): form over cold, wet areas (polar Pacific & Atlantic)

D. Air Masses in North America

1. Continental air masses

a. Continental tropical develop over deserts in southwest U.S.

i. Bring hot, dry weather in summer; don’t form in winter

b. Continental polar develop over northern Canada where it’s covered with snow/ice & move into the northern U.S.

i. Bring cool, dry weather in summer; very cold weather in winter (polar vortex!)

2. Maritime air masses

a. Maritime tropical develop in warm areas of Atlantic, Caribbean, & Gulf of Mexico, then travel to eastern U.S.

i. Bring hot, humid weather in summer; mild, cloudy weather in winter

b. Maritime polar develop in north Pacific & move into northwest U.S.

i. Bring cool, foggy weather in summer; rain & snow in winter

ii. Sometimes dry out as they move over mountains in western U.S., bringing cool & dry weather to central U.S.

Fronts See Interactive Reading Packet

Clouds (Chapter 20, section 2) A. Cloud: collection of small

water droplets or ice

crystals suspended in the

air; forms when air is

cooled & condensation

occurs

1. Form in troposphere:

lowest layer of the

atmosphere, about 7

miles thick

B. Advective Cooling:

process by which

temperature of an air mass decreases as it moves over a cold surface;

causes air to cool & form clouds

C. Types of Clouds

1. Stratus Clouds: found 0 – 6500 ft. above Earth’s surface

a. Have a flat, uniform base

b. Cover large areas of sky, may block out sun

c. Rarely produce precipitation

d. Nimbostratus: dark gray, produce heavy precipitation

e. Altostratus: type of stratus cloud that occurs at middle altitude;

usually doesn’t produce precipitation

2. Cumulus Clouds: vertical clouds with dark bottoms &

cotton-y looking top

a. Form when warm, moist air rises & cools

b. Height depends on stability of troposphere

a. Tallest clouds form on hot, humid days

c. Cumulonimbus: high, dark storm clouds; produce thunder,

rain, lightning, & other severe weather

d. Altocumulus: mid-altitude cumulus clouds; thunderstorms may

follow

e. Stratocumulus: low-altitude clouds that are combination of

stratus & cumulus

3. Cirrus Clouds: thin, feathery clouds formed above

20,000 ft. above surface

a. Composed of ice crystals

b. Usually indicate fair or pleasant weather

c. Cirrocumulus: high-altitude, small puffy clouds; indicate

upcoming snowfall or rainfall

d. Cirrostratus: long, thin clouds covering most of sky; may cause

halos!

4. Crepuscular rays: rays of sunlight that stream through

gaps in clouds, especially stratocumulus

5. Fog: water vapor condensed near Earth’s surface;

essentially clouds that form on the ground

a. Radiation fog: forms from nightly cooling of earth; thickest in

valleys & low elevations

b. Advection fog: forms when warm, moist air moves across a

cold surface; common along coasts & over oceans

c. Upslope fog: forms by lifting & cooling of air as air rises over

land slopes (hills, mountains, etc.)

d. Steam fog: shallow layer formed when cool air moves over a

warm body of water (rivers)

III. Weather Instruments A. Lower Atmosphere Weather

1. Thermometer: indicates & measures temperature

a. Usually uses mercury or alcohol in a sealed glass tube

b. Rise in temp. causes liquid to expand & fill more of the tube

c. Electric thermometers are based on electrical currents that

increase with temperature

2. Barometer: measures air pressure, can indicate fronts

approaching

3. Anemometer: measures wind speed

a. Small cups are attached to a rotating base -- wind

pushes the cups & causes the base to rotate,

which triggers an electrical signal to register wind

speed

b. Used at airports to determine flight conditions

4. Wind vane: determines wind direction

a. Arrow-shaped device rotates as tail catches the

wind

b. Described using compass directions

B. Upper Atmosphere Weather

1. Radiosonde: group of instruments carried by balloons to measure conditions in the upper atmosphere

a. Sends measurements as radio waves

b. Path of balloon is tracked to determine speed & direction of winds

2. Radar: uses reflected radio waves to determine the velocity & location of objects

a. Can track precipitation & thunderstorms through how radar pulses reflect off of water particles

3. Satellites are used to monitor weather that cannot be tracked from the ground

4. Computers store weather data, solve complex equations about atmospheric tendencies, and provide more reliable forecasts

IV. Forecasting Weather A. Global Weather

1. Monitored by the World Meteorological Organization

a. World Weather Watch enables the rapid exchange of weather

data around the world

b. Helps establish &

improve forecasting

in developing

countries

c. Offers insight about

how weather impacts

human activities

2. Weather Maps

a. Used to communicate a lot information at once

b. Station model: group of symbols indicating weather conditions at a given location

i. Cloud cover, wind speed, wind direction, dew point, temperature, atmospheric pressure, etc.

c. Different types of lines are used on weather maps to indicate conditions

i. Isotherms: connect points of equal temperature

ii. Isobars: connect points of equal atmospheric pressure

3. Forecasts

a. Weather data gathered from radar, satellites, and other instruments are input into computer models to create forecasts

b. Meteorologists compare models to create more reliable predictions

c. Relatively easy to determine temperature, pressure, wind speed & direction, but can be difficult to anticipate precise timing & amount of precipitation

d. Severe weather predictions have different levels:

i. Watch: conditions are ideal for severe weather

ii. Warning: severe weather has been spotted or is expected within 24 hours

4. Controlling Weather

a. Scientists are currently investigating if there are ways to

control rain, hail, and lightning

b. Cloud seeding: produces rain through adding particles to

clouds that cause them to produce precipitation

i. Can be used to prevent more severe precipitation, like

cause rain instead of hail

c. Attempts at hurricane control have been generally

unsuccessful

d. It is possible to generate

artificial lightning, but

there is no conclusive

information about

modifying preexisting

lightning