The Science of Flight Chapter 1-1

1. The Science of FlightChapter 1-1 The Atmosphere

2. Overview • What is the Atmosphere • Describe the Atmosphere • Roles of Water and Particulate Matter • Atmosphere in Motion

3. What is the Atmosphere • An ocean of air that surrounds the Earth • There is not distinct line between the atmosphere and space • There is a gradual increase in the distance between the molecules that make up the atmosphere

4. Describing the Atmosphere • A complex arrangement of molecules and atoms • There are three major ways to look at atmospheric composition: • Atmospheric elements • Atmospheric regions • Atmospheric pressure

5. Atmospheric Elements • The Earth’s atmosphere is a mixture of gases, suspended solids, and liquids • 78% Nitrogen • 21% Oxygen • 1% Other gases • The atmosphere absorbs energy, recycles water, and works with electrical and magnetic forces to provide a moderate temperature

6. Atmospheric Regions • The atmosphere can be divided into four layers based on temperature: • Troposphere and Tropopause: the region in which most of us live work and play

7. Atmospheric Regions • Troposphere/Tropopause: Contains 78% of the gases of the atmosphere • Zone were clouds and rain occur • Temperatures decrease as height increases • The Tropopause acts as a ceiling to the weather zone; contains the Jet Stream

8. Atmospheric Regions • The Stratosphere and Stratopause: • Contains a layer of ozone • The ozone keeps most of the UV radiation from the Sun from reaching the surface

9. Atmospheric Regions • The Mesophere and Mesopause: • The coldest zone of the atmosphere • Extends 50 miles high past the Stratopause • Temperatures decrease to near -90 C

10. Atmospheric Regions • The Thermosphere and Thermopause: • Extends from 80-600K above the Earth • Includes the ionosphere and exosphere • Temps increase rapidly

11. Atmospheric Regions • The Thermosphere and Thermopause: • The ionosphere occurs at about 80K and is electrically charged • Charged particles from the Sun are concentrated into radiation layers in the exosphere; called the Van Allen Belt

12. Atmospheric Pressure • At high altitudes, the atoms and molecules are very far apart • The force of air, or air pressure, is measured with a barometer • Atmospheric pressure is defined as “the downward pressure exerted by the weight of the overlying atmosphere.”

13. Atmospheric Pressure • Changes in atmospheric pressure play a significant role in weather • Low pressure regions experience more stormy weather • High pressure regions are more likely to be associate with clear skies, lower humidity, and more stable conditions • Winds blow because of differences in air pressure

14. Roles of Water and Particulate Matter • Water • Mostly restricted to the Troposphere • Goes through a cycle from vapor to condensation to precipitation

15. Roles of Water and Particulate Matter • Water • If there is a lot of water vapor in the air we say it is humid • The amount of water vapor that can exist in the air increases when the temperature rises

16. Roles of Water and Particulate Matter • Evaporation: • The air is constantly gaining and losing water; water gets into the air through evaporation • A simple example is water boiling and becoming vapor • Evaporation on a global scale happens in a similar manner; a process called solar radiation

17. Roles of Water and Particulate Matter • Humidity: • The term that indicates the amount of water vapor in the air • The actual water vapor in the air at a given time is referred to as absolute humidity • Relative humidity is the amount of water vapor that can still enter the air mass before it becomes saturated • The ratio of absolute humidity to the saturation point equals the relative humidity

18. Roles of Water and Particulate Matter • Condensation and Precipitation: • When part of the water vapor in the air returns to a liquid or solid form • Happens due to lower temperatures • Lower temperatures cause the saturation point to change

19. Roles of Water and Particulate Matter • Dew Point Temperature: • The key factor in condensation and precipitation • The temperature at or below which water vapor will condense

20. Roles of Water and Particulate Matter • Particulate Matter: • Dust and other very small particles play an important role in the water cycle • The serve as condensation nuclei • Very small; two millionths of an inch

21. Atmosphere in Motion

22. Atmosphere in Motion • Radiation: • The heat energy of the Sun reaches the Earth as radiation or solar energy. Radiation transfers heat by means of heat waves. • Radiation that reaches the Earth is absorbed by land and water surfaces. Surface features influence the amount of radiation absorbed by the Earth.

23. Atmosphere in Motion • Conduction • The passage of energy through something, particularly heat and electricity. • Heated molecules move more rapidly than cold molecules. Heat is transferred from fast moving molecules to slow moving molecules until all are moving at the same speed. • A good example of conduction is a stove heating a pan.

24. Atmosphere in Motion • Convection: • The most efficient method of heating the atmosphere. Air is first heated by radiation and conduction. • The air absorbs the heat energy. Warm air is forced upward as cold air flows in displacing the warm air.

25. Atmosphere in Motion • Convection • Convection currents cause a constant exchange of cold air for warm air until heat is distributed evenly. • Convection also determines the movement of large air masses above the Earth, the action of the winds, rainfall, ocean currents, and the transfer of heat from the interiors of the Sun to its surface.

26. Atmosphere in Motion • Advection • The horizontal transfer of a property such as heat, caused by air movement. • When the wind blows, it is simply movement by or within the local air mass. Advection is an important factor in the global circulation of air.

27. Atmosphere in Motion • Insolation: • The rate at which the Earth’s surface is heated by solar radiation. • The amount received at any point on the Earth’s surface is dependent on the angle that the Sun’s rays make with the horizon, the distance of the Earth from the Sun, and the amount of radiation absorbed by the atmosphere. • Greater in the equatorial zone than anywhere else on the Earth’s surface due to the angle of incidence.

28. Atmosphere in Motion • Heat Balance: • If there was no balance of heat among the Earth, its atmosphere, and space, the Earth would become increasingly warmer. • Of all the solar radiation arriving at the top of the atmosphere, 42 percent is reflected into space by clouds and atmospheric dust; 15 percent is absorbed directly into the atmosphere; and 43 percent reaches the Earth directly.

29. Atmosphere in Motion • Heat Balance: • Of the 15 percent absorbed directly into the atmosphere, 4 percent eventually reaches the Earth as diffused sky radiation. Thus, a total of about 47 percent of the incident solar radiation finally reaches the Earth and heats it. • The heating process that tends to maintain the Earth's heat balance is also primarily responsible for worldwide weather.

30. Atmosphere in Motion • Wind: • When air is heated, it rises. This occurs because the heat applied to it has decreased its density to the point where it is lighter in weight than the surrounding air. The surrounding cooler air pushes the lighter, heated air upward.

31. Atmosphere in Motion • Wind: • When the heated air rises, cooler, higher pressure air flows laterally to fill the lower pressure area created. This lateral movement is referred to as wind. • Other factors that affect the circulation of the air are: • Gravity • Friction • Centrifugal force

32. Atmosphere in Motion • Coriolis Effect: • The Earth rotates on its axis in such a way that an observer in space over the North Pole would see the Earth turning in a counterclockwise direction. (Clockwise in the Southern Hemisphere.)

33. Atmosphere in Motion • The Pressure Gradient: • The atmosphere is a constantly changing landscape of invisible mountains and valleys. Some of the influences that cause this are: • Irregular distribution of oceans and continents. • Heat-transferring qualities of different Earth surfaces. • Daily temperature variations.

34. Atmosphere in Motion • The Pressure Gradient: • The high-pressure areas of the atmosphere are the mountains, and the low-pressure areas are the valleys. The wind flows from these high-pressure mountains into the low-pressure valleys.

35. Atmosphere in Motion • The Pressure Gradient: • The slope of the high-pressure mountain is called the pressure gradient. • On weather maps lines called isobars show the degree of steepness. • Isobars are drawn through points of equal sea-level atmospheric pressure. • Isobars identify five different types of pressure patterns.

36. Atmosphere in Motion • Local and Surface Air Movements: • The general circulation of air is complicated by the irregular distribution of land and water areas. • Different types of surfaces differ in the rate at which they absorb heat from the Sun and transfer heat to the atmosphere. • In some regions local low-pressure areas form over hot land surfaces and over warmer water surfaces in the winter.

37. Atmosphere in Motion • Local and Surface Air Movements: • Convection currents are formed along shorelines. These currents cause the wind to flow from the water over the land during the day. During the night, they cause the wind to blow from the land toward the water. • Local air circulation of limited scope is caused by variations in the Earth’s surface.

38. Atmosphere in Motion • Local and Surface Air Movements: • Some surfaces give off or reflect a great amount of heat. • Sand • Rocks • Plowed areas • Barren land • Other surfaces tend to retain heat. • Meadows • Planted fields • Water

39. Atmosphere in Motion • Local and Surface Air Movements: • Rising air currents are encountered by aircraft flying over sand, rock, and other surfaces that give off considerable heat. • Descending air currents are encountered over surfaces that retain heat.

40. Atmosphere in Motion • Local and Surface Air Movements: • Moving air flowing around obstructions tends to break into eddies. • On the leeward side of the mountain there are descending air currents. Such conditions cause turbulent air. The stronger the wind, the greater the descending air currents and turbulence. • Aviators flying into the wind toward mountainous terrain should place enough distance between their aircraft and the mountain tops to avoid dangerous descending air currents.

41. Atmosphere in Motion • The Jet Stream: • The jet stream is a narrow current of air, which moves around the Earth in wavelike patterns. It is like a “river” of wind moving at a high rate of speed. • The jet stream varies from about 100 to 400 miles wide and 1 to 3 miles thick. • Winds usually have a speed of 150 to 300 mph, but speeds of 450 mph have been recorded. Its general motion is from west to east.

42. Atmosphere in Motion • The Jet Stream: • The jet stream shifts positions frequently and actually migrates with the seasons. Sometimes two streams flow across the United States, one along the northern border and the other well toward the south. • The cruising range of aircraft flying downwind within the jet stream is greatly increased. Pilots anticipating high-altitude or long-range flights attempt to discover the location of the jet stream and use it to their advantage.

43. Summary • What is the Atmosphere • Describe the Atmosphere • Roles of Water and Particulate Matter • Atmosphere in Motion

44. What’s Next