1. Structure of the Atmosphere

2. Atmospheric Composition
The atmosphere mostly consists of nitrogen (78%), oxygen (21%), and argon.
99% composed of
Nitrogen and Oxygen
Remaining 1% made up of
small amounts of other gases

3. Atmospheric Thermodynamics
Why does the temperature change from one layer to the next?

4. Troposphere Closest to Earth Altitude 0-10 km
Contains most of the mass of the atmosphere
Weather occurs here, pollution collects
Upper limit called tropopause
Tropopause is where gradual decrease in temperature stops

5. Stratosphere -Above troposphere -Altitude 10-50 km
-Contains mostly ozone
-Ozone absorbs more UV radiation, so this layer is heated
-Upper limit called stratopause
-Stratopause is where gradual increase in temperature stops

6. Mesosphere Above stratosphere Altitude 50-80 km
No concentrated ozone here, so temperature drops again
Upper limit called mesopause
Mesopause is where gradual decrease in temperature stops

7. Thermosphere Above mesosphere
Altitude 80 km and above until outermost boundary of atmosphere
Contains a small part of the atmosphere’s mass
Little air that is in this layer increases in temperature again to greater than 1000C

8. The Ionosphere
The thermosphere can be identified in two parts- the ionosphere and the exosphere.
Ionosphere: 80 km-640 (about 400 miles = 640 km).
It contains many ions and free electrons (plasma).
Auroras occur in the ionosphere.

9. Meteorology

10. Wind
Air moves in response to density imbalances created by the unequal heating and cooling of Earth’s surface.
These imbalances, in turn, create areas of high and low pressure.
Wind can be thought of as air moving from an area of high pressure to an area of low pressure.

11. Humidity Humidity-amount of water vapor in air.
Relative humidity - ratio of water that air contains and the maximum amount of water the air could contain.
Warm air is more capable of holding more moisture that cold air.
Do we usually ever complain of humidity in winter?

12. Clouds
Dew point-temperature at which air must be cooled to reach saturation.
Condensation-phase change from gas to liquid; only occurs at saturation.
Lifted Condensation Level-LCL; point at which condensation occurs.

13. Adiabatic Lapse Rate

14. Cloud Formation Air masses of different temperatures collide.
The less dense, warmer air mass rises over the more dense, colder air mass.
As the warm air rises, it cools, and once it reaches the LCL, water vapor will condense around condensation nuclei to become a cloud, if the density of condensation nuclei is great enough.
Condensation nuclei-particles in the air around which cloud droplets can form.

15. Latent Heat

17. Precipitiation
Coalescence-occurs when cloud droplets collide and join together to form a larger droplet.
When the droplet becomes too heavy to be held aloft, gravity takes over and it falls to Earth as precipitation.
Forms of precipitation: rain, snow, sleet, & hail

18. Another Method of Cloud Formation
Orographic Lifting-air mass is forced to lift due to topography, cooling down quickly in the process, causing condensation and cloud formation.

19. Meteorology
Weather is a specific event or condition that happens over a period of hours or days. For example, a thunderstorm, a snowstorm, and today’s temperature all describe the weather.
Climate refers to the average weather conditions in a place over many years (usually at least 30 years, to account for the range of natural variations from one year to the next).

20. Warm Cold Moist Dry Air Masses Temperature Humidity
A large body of air with similar
TEMPERATURE
HUMIDITY
Warm
Cold
Temperature
Moist
Dry
Humidity

21. Air Mass Air Mass Air Masses’ Characteristics Source Regions
Over land: drier.
Over water: more moist.

22. Maritime: (m) moist (marina/water)
Types of Air Masses
DESCRIPTION CONDITION LOCATION FORMED
Maritime: (m) moist (marina/water)
Continental:(c) dry (continents/land)
Tropical: (T) warm (tropics)
Polar: (P) cold (poles)

23. Maritime Tropical (mT)
Types of Air Masses
Maritime Tropical (mT)
Continental Tropical (cT)
Maritime Polar (mP)
Continental Polar (cP)
If we combine a temperature and humidity characteristic we can make
4 different types of air
masses.

24. Mr. Fetch's Earth Science Class
Types of Air Masses
cP Continental Polar
Dry, cold air to central and eastern US.
mP Maritime Polar
Moist, cold air to east areas of the Canada
mP Maritime Polar
Moist, cold air to west coast of the US.
mT Maritime Tropical
Moist, warm air to west coast of the Mexico.
mT Maritime Tropical
Moist, warm air to south east coast of the US.
cT Continental Tropical
Dry, warm to Desert SW
Mr. Fetch's Earth Science Class
Mr. Fetch’s Earth Science Classroom

25. Air Mass Modification mP Maritime Polar
Air masses move be prevailing winds. The winds cause the air masses to move over land and water. As the air masses move, they change. This is called air mass modification. The air masses becomes more like the area it is moving over…
….. And
At the same time, the area the air mass is moving over becomes more like the mass.
mP Maritime Polar
Moist, cold air to west coast of the US.
Mr. Fetch’s Earth Science Classroom

26. Classification of Air Mass

27. Air Masses Characteristics
Temperature and moisture characteristics of air masses.
Air Mass Type
Winter Characteristics
Summer Characteristics
continental polar cP
Very cold and dry
Cool and dry
maritime polar mP
Mild and humid
continental tropical cT
warm and dry
very hot and dry
maritime tropical mT
Warm and humid
arctic A
Bitter cold and dry

28. Coriolis Effect In the northern hemisphere, a path that would be a
straight line over a stationary earth instead is curved
to the right.
In the Southern
hemisphere the
curvature is to the left.
This effect creates a global wind system that transports air masses.

29. Three Types of Wind Systems
Trade winds
Prevailing westerlies
Polar easterlies

30. Trade Winds Move between equator and 30° N and S latitude.
Air sinks, warms, and returns to equator in westerly direction.

31. Prevailing Westerlies
Occurs between 30° and 60° latitude
Moves in opposite direction of trade winds
Moves weather across U.S.

32. Polar Easterlies
Occur between 60° and poles
Cold air

34. Fronts COLD FRONTS WARM FRONTS STATIONARY FRONT OCCLUDED FRONT
A boundary between two air masses:
COLD FRONTS
WARM FRONTS
STATIONARY FRONT
OCCLUDED FRONT

35. Mr. Fetch's Earth Science Class
When air masses meet…
mP Maritime Polar
Moist, cold air to west coast of the US.
mT Maritime Tropical
Moist, warm air to south east coast of the US.
Mr. Fetch's Earth Science Class
Mr. Fetch’s Earth Science Classroom

36. Steep Slope Cold Fronts
When cold air advances on warm air. - Warm air is forced violently up. - Rising air creates clouds, rain, and storms.
Heavy precipitation for a short period of time likely. Cold Front Animation
Steep Slope
Mr. Fetch’s Earth Science Classroom

37. Cold Fronts
“COLD FRONT” … umm its gets colder , duh!

38. Gentle Slope Warm Fronts
When warm hits cold air. - Warm air gently glides up over the cold air. - Rising air creates clouds and showers. (Less Violent).
Light precipitation for a longer period of time likely.
Warm Front Animation
Gentle Slope
Mr. Fetch’s Earth Science Classroom

39. Warm Fronts
“WARM FRONT”… right, it gets warmer, good.

40. Stationary Front
When a warm or cold front stops moving. - Usually several days of clouds and showers.
The air flows parallel to the front

41. Occluded Front Occluded front occurs when cold front wraps
around warm front.

42. Occluded Front

43. Weather Front Symbols

44. Weather Front Map

45. Weather Fronts

46. Temperature Map

47. National Doppler Radar

48. Atmospheric Pressure The atmosphere has pressure.
The air in a 1 inch square column that goes from the Earth's surface all the way up through the atmosphere exerts a pressure of 14.7 pounds per square inch at sea level.

49. Mr. Fetch's Earth Science Class
SYSTEM TYPES
LOW PRESSURE: cyclones
form along fronts (Unstable)
rising air.
winds rotate counter-clockwise around low pressure systems.
Rainy, stormy weather
Mr. Fetch's Earth Science Class

50. Mr. Fetch's Earth Science Class
The high’s and low’s of weather…
HIGH PRESSURE: anticyclones
sinking air (Stable)
The sinking air stops clouds from forming.
winds rotate clockwise around high pressure systems.
Sunny, clear weather
Mr. Fetch's Earth Science Class

51. Atmospheric Pressure

52. Isobar Maps
Points of equal pressure are connected

53. Weather Station Model

54. Severe Weather

55. Thunderstorms

56. How Thunderstorms Form
For a thunderstorm to form, three conditions must exist.
Abundant source of moisture
2. Mechanism to lift air so that the moisture can condense and release latent heat.
3. Instability in the atmosphere

57. Limit of Thunderstorm Growth
The air in a thunderstorm will keep rising until:
1. Stable air is reached that it cannot overcome
2. Rate of condensation is not able to generate enough latent heat to keep the cloud warmer than the surrounding air

58. Three Types of Thunderstorms
1) air mass thunderstorm-results from air rising due to unequal heating in an air mass.
2) sea breeze thunderstorms-results from extreme temperature differences air over land and water.
3) frontal thunderstorms-results from advancing cold fronts.

59. Stages of Thunderstorm Development
Three Stages
1) Cumulus
2) Mature
3) Dissipation
Flash

60. Cumulus Stage Air rises vertically.
Moisture condenses into visible cloud.
Coalescence occurs.

61. Mature Stage
Precipitation falls, cooling the air surrounding it and creating a downdraft.
The updraft and downdraft creates a convection cell.
Equal amount of updraft and downdraft creates a cumulonimbus cloud.

63. Dissipation Stage Warm air is gone, cooled by downdraft.
Updraft ceases.
Lingering downdraft persists.

64. Supercells
Severe thunderstorm that contain updrafts that rotate about a vertical axis.
They often produce damaging wind, large hail, and tornadoes, and most strong to violent tornadoes are associated with them.

65. Supercells

66. Tornadoes
A tornado is a violent, whirling column of air in contact with the ground.
Before touching ground it is called a funnel cloud.
75% occur in US predominately in Tornado Alley

67. Tornado Alley

68. Tornadoes Tornadoes are visible due to dust, debris, and condensation.
Created when wind speed and direction change suddenly with height, a process called wind shear.
Air pressure inside funnel is usually much lower than outside

69. Enhanced Fujita Scale

70. Tropical Cyclones
Tropical cyclones are large, rotating, low-pressure storms that form over water during summer and fall in the tropics.
Two things to form:
Abundance of warm water
Disturbance to lift air and keep it rising

72. Tropical Cyclone
Most tropical cyclones begin as a disturbance, or a low pressure system that occurs close to the surface of tropical ocean.
Once the low pressure system acquires a cyclonic rotation, it is known as a tropical depression.

73. Forms of Tropical Cyclones
0-65 km/hr-tropical depression
km/hr-tropical storm
120 km/hr +-hurricane
Saffir-Simpson hurricane scale classifies hurricanes from Category 1 to Category 5, Category 5 having the strongest win speeds
Flash

75. Hurricanes Eye-calm center of the storm
Eyewall-band immediately surrounding the eye that contains the strongest winds in a hurricane.
A hurricane will last until it can no longer produce enough energy to sustain itself. This usually happens when:
1) Hurricane runs over land.
2) Hurricane runs into colder water

76. Hurricanes
The Saffir-Simpson Hurricane Scale classifies hurricanes according to wind speed, air pressure in the center, and potential for property damage.
It ranges from Category 1 hurricanes to Category 5 storms, which can have winds in excess of 155 mph.

77. Saffir-Simpson Hurricane Scale

78. Tropical Cyclones Hurricanes in the Atlantic Ocean
Typhoons in the Pacific ocean
Cyclones in the Indians ocean

79. Hurricanes Hazards Violent wind – 74 mph or greater
Storm surge – a mound of ocean water towards coastal area
Floods