1. THE EARTH’S ATMOSPHERE Overview of the Earth’s atmosphere Other planetary atmospheres Vertical structure of the atmosphere Weather and climate

2. OVERVIEW OF THE EARTH’S ATMOSPHERE The atmosphere, when scaled to the size of an apple, is no thicker than the skin on an apple. The atmosphere is a gas. The atmosphere is a fluid. There is a surface but no “top” – the atmosphere gradually thins out with increasing altitude

3. THICKNESS OF THE ATMOSPHERE Approximately 80% of the atmosphere occurs in the lowest 20km above the Earth. Radius of the Earth is over 6,000 km Atmosphere is a thin shell covering the Earth.

5. Structure of the Atmosphere Observed lapse rate. The temperature decreases approximately 6.5 O C for each km of alitude (3.5 O F/1,000 ft) Inversion When a layer of the atmosphere increases with altitude. Troposphere The layer of the atmosphere from the surface of the Earth up to where it stops decreasing in temperature. Up to a height of about 11 km (6.7 mi) Air is constantly mixed due to denser air being above less dense air.

6. On the average, the temperature decreases about 6.5 O C/1,000 km, which is known as the observed lapse rate. An inversion is a layer of air in which the temperature increases with height.

7. Tropopause The upper boundary of the Troposphere The temperature remains constant with increasing altitude Stratosphere Temperature begins to increase with height. Very stable as denser air is below less dense air. Up to about 48 km (30 mi) Temperature increases as a result of interactions between high energy UV radiation and ozone (O 3 )

8. TEMPERATURE LAYERS OF THE ATMOSPHERE: TROPOSPHERE Lower part of the atmosphere Energy source is heating of the earth’s surface by the sun. Temperature generally decreases with height. Air circulations (weather) take place mainly here. Troposphere goes from surface to about 30,000 ft. (10 km).

9. Above 50 km, very little ozone, so no solar heating Air continues to cool with height in mesosphere Mesosphere extends from about 50 km to 90 km above the surface http://www.bath.ac.uk/pr/releases/images/antarctic/noctilucent-clouds.jpg TEMPERATURE LAYERS OF THE ATMOSPHERE: MESOSPHERE

10. TEMPERATURE LAYERS OF THE ATMOSPHERE: THERMOSPHERE Above 90 km, residual atmospheric molecules absorb solar wind of nuclear particles, x-rays and gamma rays. Absorbed energy causes increase of temperature with height. Air molecules are moving fast, but the pressure is very low at these heights.

11. IMPORTANCE OF STRATOSPHERE, MESOSPHERE AND THERMOSPHERE Solar nuclear particles, x-rays, gamma rays, and ultraviolet light can damage living cells. Thermosphere, mesosphere and stratosphere shield life on Earth from these damaging rays.

12. Exosphere Outermost layer of the atmosphere where molecules merge with the vacuum of space. The high kinetic energy of the molecules at this height are significant enough to cause them to be able to escape into space. Ionosphere Alternative name for the thermosphere and upper mesosphere. Due to the occurrence of free electrons and ions. It is the electrons and ions in this layer that cause radio waves to be able to be reflected around the world.

13. The structure of the atmosphere based on temperature differences. Note that the "pauses" are actually not lines, but are broad regions that merge.

14. Fig. 1-4, p. 5

15. TEMPERATURE LAYERS OF THE ATMOSPHERE: STRATOSPHERE Sun’s ultraviolet light is absorbed by ozone, heating the air. Heating causes increase of temperature with height. Boundary between troposphere and stratosphere is the tropopause. Stratosphere goes from about 10 to 50 km above the surface.

16. 5.2 THE OZONE LAYER In the 1970s, scientists noticed that the ozone layer in the stratosphere above Antarctica was thinning.

17. VARIABLE GASES – OZONE (O 3 ) Near the surface, ozone concentrations about 0.04-0.15 ppm In the upper atmosphere ozone concentration can reach ~15 ppm Upper atmospheric ozone is vital to blocking harmful radiation Ozone near the surface, however, harmful to life Chlorofluorocarbons (CFCs) are believed to be depleting upper atmospheric ozone Satellite images showing depletion of ozone.

18. 5.2 CHLOROFLUOROCARBONS AND THE OZONE LAYER A group of chemicals called chlorofluorocarbons (or CFCs) were once commonly used in air conditioners, in aerosol spray cans, and for cleaning machine parts. In the London Agreement of 1991, more than 90 countries banned the production and use of CFCs except for limited medical uses.

19. 5.2 CHLOROFLUOROCARBONS AND THE OZONE LAYER The ozone layer absorbs the Sun’s high-energy ultraviolet (UV) radiation and protects the Earth.

20. 5.2 CHLOROFLUOROCARBONS AND THE OZONE LAYER In the stratosphere, the CFCs break down and release chlorine. The chlorine reacts with ozone molecules, which normally block incoming ultraviolet radiation.

22. Stratopause Where the temperature reaches a maximum of 10 O C (50 O F) Ozone shield A layer of ozone that absorbs much of the ultraviolet radiation that enter the atmosphere. Provides a significant shield to the Earth below from damging UV radiation

23. COMPOSITION OF THE ATMOSPHERE permanent gases variable gases trace gases aerosols roles of nitrogen, oxygen and argonroles of nitrogen, oxygen and argon role of water vaporrole of water vapor carbon dioxide, methane, ozone, CFCs, et al.carbon dioxide, methane, ozone, CFCs, et al.

24. COMPOSITION OF THE ATMOSPHERE The “dry atmosphere”: 78% N 2, 21% O 2, 1% Ar N 2 is primordial – it’s been part of the atmosphere as long as there’s been an atmosphere O 2 has been rising from none at all about 2.2 Gya – comes from photosynthesis Ar 40 /Ar 36 tells us that the atmosphere has been outgassed from volcanoes

25. COMPOSITION OF THE ATMOSPHERE Water Vapor: H 2 O 0-4% H 2 0 can exist in all three phases at the surface of the Earth – solid, liquid and gas Liquid or solid H 2 O can be suspended by atmospheric winds (clouds) or fall to the surface (precipitation) VERY powerful greenhouse gas (both in vapor form and as clouds)

26. COMPOSITION OF THE ATMOSPHERE The Hydrological Cycle

27. Table 1-1, p. 3

28. COMPOSITION OF THE ATMOSPHERE Carbon dioxide 390 ppm (by mass) and counting… Natural and anthropogenic sources/sinks Strong greenhouse gas (GHG) CO 2 is neither the strongest atmospheric GHG pound-for- pound nor molecule-for-molecule… Why the fuss? CO 2 is a product of the reaction that allows modern civilization to exist: combustion.

29. COMPOSITION OF THE ATMOSPHERE The Global Carbon Cycle

30. COMPOSITION OF THE ATMOSPHERE Methane CH 4 concentration: 1.8 ppmv anthropogenic and natural sources/sinks too powerful greenhouse gas oxidizes rapidly, hence low concentrations Large concentrations proposed to explain greenhouse warming of early Earth

31. COMPOSITION OF THE ATMOSPHERE Ozone, CFCs and NO x Ozone (O 3 ) shields the surface from UV rays produced by reaction with NO x and sunlight near the surface CFC’s (Chlorofluorocarbons) destroy stratospheric ozone chlorine is a catalyst: it destroys one O 3 molecule and then is free to find another Ozone at high altitudes (stratosphere) is “good”; ozone at low altitudes (troposphere) is “bad.”Ozone at high altitudes (stratosphere) is “good”; ozone at low altitudes (troposphere) is “bad.”

32. COMPOSITION OF THE ATMOSPHERE Aerosols Dust Sea-spray Microbes Suspended particles in the atmosphere are responsible for cloud formation: water drops nucleate on them Cloud Condensation Nuclei (CCN)

33. Earth's atmosphere has a unique composition of gases when compared to that of the other planets in the solar system.

34. Atmospheric Pressure The atmosphere exerts pressure on the Earth that decreases with increasing altitude This is due to the fact that with increasing altitude, there is a decrease in the column of gases above the Earth’s surface Hydrostatics considers the pressure that is exerted by a fluid that is at rest. Using this as a frame of reference the atmospheric pressure is viewed as a result of the mass of the column of gases above the Earth. Using a molecular frame of reference, the atmospheric pressure is viewed as a result of the kinetic energy of molecules and the force with which they strike an object. Atmospheric pressure is actually a result of the interaction between these two factors.

35. At greater altitudes, the same volume contains fewer molecules of the gases that make up the air. This means that the density of air decreases with increasing altitude.

36. VARIABLE GASES - WATER VAPOR Water Vapor ImageVisible Image Water vapor is invisible – don’t confuse it with cloud droplets Less than 0.25% of total atmosphere Surface percentages vary between <<1% in desserts to 4% in tropics Typical mid-latitude value is about 1-2% Some satellites sensors can detect actual water vapor in atmosphere

37. VARIABLE GASES – METHANE (CH 4 ) Concentrations of about 1.7 ppm Extremely potent green house gas - 21 times more powerful by weight than carbon dioxide Has varied cyclically on a 23,000 year cycle Pattern broken in past 5,000 years with unexpected increase – more abundant now than in last 400,000 years Increase attributed to agriculture, bio-mass burning, fossil fuel extraction, some industry and ruminant out-gassing (cow/sheep burps) Methane growth and sources (From EPA)

38. AEROSOLS (OR PARTICULATES) Small (or “tiny”) solid particles or liquid droplets (excluding clouds and rain) Aerosols can be man-made (anthropogenic) or naturally occurring (like ocean salt, dust, plant emissions) Aerosols are not synonymous with pollution Some aerosols are very beneficial and, in fact, are required for precipitation processes to occur.

39. DENSITY AND PRESSURE WITH HEIGHT Because of compression, the atmosphere is more dense near the surface. Density decreases with altitude

40. STATE VARIABLES TEMPERATURE Air molecules are moving all around us, bouncing off each other and us. When the air molecules have greater kinetic energy (energy of motion), they are moving faster. The temperature of the air molecules is a measure of the average speed of the molecules per standard volume

41. TEMPERATURE SCALES F = 9/5°C + 32 C = 5/9(°F – 32) K = °C +273.16

42. TEMPERATURE CHANGE W/ALTITUDE As a parcel of air rises, it expands due to lower pressure. Work done by molecules to expand causes temperature to decrease (cools) As air sinks, the parcel experiences compression due to higher pressure Air molecules have work done on them, temperature increases (warms)

43. WEATHER BASICS Atmospheric Temperature Areas separating colder and warmer air on a weather map are represented by fronts Cold Fronts (blue – pointed barbs) indicate the movement of a cold air mass into a warmer region Warm Fronts (red – rounded barbs) indicate movement a warm air mass into a colder region Cold FrontWarm Front

44. WEATHER BASICS Atmospheric Humidity Relative Humidity provides a measure of the amount of water vapor in the air relative the maximum possible for a given temperature Dew Point Temperature is the temperature the air must be cooled to for condensation to occur. Much more on these concepts in later chapters

45. The earth's atmosphere thins rapidly with increasing altitude and is much closer to the earth than most people realize.

46. The mercury barometer measures the atmospheric pressure from the balance between the pressure exerted by the weight of the mercury in a tube and the pressure exerted by the atmosphere. As atmospheric pressure increases and decreases, the mercury rises and falls. This sketch shows the average height of the column at sea level.

47. Warming the Atmosphere The temperature of an object is actually a measure of the kinetic energy of the molecules that make up the object. Any object that contains any kinetic energy at all (i.e. has a temperature above absolute 0K gives off radiant energy. Solar constant When the sunlight is perpendicular to the outer edge and the Earth is at an average distance from the Sun it produces about 1,370 watts per m 2. This quantity is believed to remain constant.

48. On the average, the earth's surface absorbs only 51 percent of the incoming solar radiation after it is filtered, absorbed, and reflected. This does not include the radiation emitted back to the surface from the greenhouse effect, which is equivalent to 93 units if the percentages in this figure are considered as units of energy.

49. Mesosphere Temperature again begins to decrease due to a decrease in gas molecules to absorb radiation Thermosphere Temperature again begins to rise due to the presence of molecular fragments which absorb radiation from space. Temperature is extremely high here due to the average kinetic energy of the molecules. Very little energy transfers, however, due to the lack of molecules (very few molecules to collide with objects)

50. THE EARLY ATMOSPHERE reduced primitive atmosphere(H, He, CH 4, NH 3 ) outgassing and the second atmosphere (N 2, Ar – still no oxygen!) The evolution of life and the atmosphere are closely linked – life produced the oxygen (photosynthesis) and cycles the carbon (e.g. limestone) Oxidized modern atmosphere (N 2, O 2, CO 2, etc.)

51. OTHER ATMOSPHERES YESNO EarthThe Moon Marsall the other satellites VenusMercury Jupiterasteroids Saturn Uranus Neptune Pluto Triton (Neptune’s moon) Titan (Saturn’s moon) The Sun

52. OTHER ATMOSPHERES PlanetCompositionTemperaturePressure VenusCO 2 96.5%, N 2 3.5% 750 K90000 mb EarthN 2 78%, O 2 21%, Ar 1% 290K1000 mb MarsCO 2 95%, N 2 2.7%, Ar 1.6% 220K10 mb

53. VERTICAL STRUCTURE OF THE EARTH’S ATMOSPHERE

54. A BRIEF LOOK AT AIR PRESSURE AND AIR DENSITY air density (ρ pronounced “row”) air pressure (p) sea-level pressure (p s ) Baseballs travel farther in higher-altitude air (Denver) than they do in lower-altitude air.Baseballs travel farther in higher-altitude air (Denver) than they do in lower-altitude air.

55. Fig. 1-7, p. 8

56. Fig. 1-8, p. 9

57. LAYERS OF THE ATMOSPHERE vertical temperature (T) profile troposphere stratosphere mesosphere thermosphere Temperatures, winds, humidity and pressures high above the ground are measured twice-daily by radiosonde.Temperatures, winds, humidity and pressures high above the ground are measured twice-daily by radiosonde.

58. WEATHER AND CLIMATE (Chalkboard)

59. ELEMENTS OF WEATHER air temperature air pressure humidity clouds precipitation visibility wind Certain weather elements, like clouds, visibility and wind, are of particular interest to pilots.Certain weather elements, like clouds, visibility and wind, are of particular interest to pilots.

60. CLIMATE average weather time-average regional (spatial) average extremes trends

61. WEATHER VS. CLIMATE Weather is the dynamical way in which the atmosphere maintains the equilibrium climate.

62. A SATELLITE’S VIEW OF THE WEATHER geostationary satellites Atmospheric observation from satellites was an important technological development in meteorology. Other important developments include computers, internet, and Doppler radar.Atmospheric observation from satellites was an important technological development in meteorology. Other important developments include computers, internet, and Doppler radar.

63. STORMS OF ALL SIZES midlatitude cyclonic storms hurricanes and tropical storms thunderstorms tornadoes Storms are very exciting, but they also play an important role in moving heat and moisture around throughout the atmosphere.Storms are very exciting, but they also play an important role in moving heat and moisture around throughout the atmosphere.

64. A LOOK AT A WEATHER MAP wind speed and direction cyclones and anticyclones fronts Wind direction is defined in the opposite way as ocean currents: a southerly current means water is moving towards the south.Wind direction is defined in the opposite way as ocean currents: a southerly current means water is moving towards the south.

65. Fig. 1-13, p. 17

66. Water and the Atmosphere

67. Water exists in three states on the Earth. Liquid when the temperature is above 0 O C (32 O F) Solid when the temperature is below 0 O C (32 O F) A gas when the temperature is above 100 O C (212 O F)

68. Evaporation and Condensation Humidity The amount of water vapor in the air Absolute humidity is a measure of the amount of water vapor present at a given time. Relative humidity is a measure of the amount of water vapor present in the air relative to the amount that the air could hold at that temperature.

69. The maximum amount of water vapor that can be in the air at different temperatures. The amount of water vapor in the air at a particular temperature is called the absolute humidity.

70. The Rate of Evaporation depends on: surface area of the exposed liquid. Air and water temperature Relative humidity The Rate of Condensation depends on: relative humidity Kinetic energy of the gas molecules in the air.

71. Evaporation and condensation are occurring all the time. If the number of molecules leaving the liquid state exceeds the number returning, the water is evaporating. If the number of molecules returning to the liquid state exceeds the number leaving, the water vapor is condensing. If both rates are equal, the air is saturated; that is, the relative humidity is 100 percent.

72. Dew point temperature Temperature at which the relative humidity and the absolute humidity are the same (saturated air) Dew begins to accumulate on surfaces. Form on C nights: Clear Calm Cool

73. Fans like this one are used to mix the warmer, upper layers of air with the cooling air in the orchard on nights when frost is likely to form.

74. Condensation nuclei Gives condensing moisture in the atmosphere something to condense on. Necessary for the production of moisture in the atmosphere (rain, snow). As condensation continues, eventually there will be a point where enough water molecules have condensed on the nuclei that it can no longer remain air borne. It will then fall in the form of rain, snow, etc…

75. This figure compares the size of the condensation nuclei to the size of typical condensation droplets. Note that 1 micron is 1/1,000 mm.

76. Fog and Clouds Both of these are water droplets which have been condensed from the atmosphere. An upward movement of air keeps them from falling Clouds are identified according to whether they are: Cirrus – curly Cumulus – piled up Stratus – spread out

77. (A)An early morning aerial view of fog between mountain at top and river below that developed close to the ground in cool, moist air on a clear, calm night. (B) Fog forms over the ocean where air moves from a warm current over a cool current, and the fog often moves inland.

78. (A)Cumulus clouds. (B) Stratus and stratocumulus. Note the small stratocumulus clouds forming from increased convection over each of the three small islands. (C) An aerial view between the patchy cumulus clouds below and the cirrus and cirrostratus above (the patches on the ground are clear-cut forests). (D) Altocumulus. (E) A rain shower at the base of a cumulonimbus. (F) Stratocumulus.

79. The Winds

80. Local Wind Patterns Due to: The relationship between air temperature and air density. Relationship between air pressure and the movement of air. Upward and downward movement of air leads to: The upward movement has a lifting effect on the surface that creates areas of low pressure The downward movement of air has a piling up effect resulting in areas of high pressure.

81. A model of the relationships between differential heating, the movement of air, and pressure difference in a convective cell. Cool air pushes the less dense, warm air upward, reducing the surface pressure. As the uplifted air cools and becomes more dense, it sinks, increasing the surface pressure.

82. Adjacent areas on the surface of the Earth can have very different temperatures due to differences in heating and cooling rates. This difference is usually greatest between bodies of water and adjacent land masses due to: Water has a high specific heat. Water is easily mixed, which keeps water cooler that adjacent land masses Water cools by evaporation which also keeps a body of water at a lower temperature. This results in a sea breeze since the denser, cooler air from the body of water will move in under the less dense air over the land.

83. The land warms and cools more rapidly than an adjacent large body of water. During the day, the land is warmer, and air over the land expands and is buoyed up by cooler, more dense air from over the water. During the night, the land cools more rapidly than the water, and the direction of the breeze is reversed.

84. Incoming solar radiation falls more directly on the side of a mountain, which results in differential heating. The same amount of sunlight falls on the areas shown in this illustration, with the valley floor receiving a more spread-out distribution of energy per unit area. The overall result is an upslope mountain breeze during the day. During the night, dense cool air flows downslope for a reverse wind pattern.

85. Global Wind Patterns Hot air rises over the equator due to the fact that it is less dense. This is called the intertropical convergence zone. This rising air cools adiabatically as it rises resulting in high precipitation The cooled air descends to reach the surface at about 30 O N and 30 O S of the equator. This forms a high pressure area The great deserts of the world are located in this high pressure area

86. Toward the poles from this high pressure area atmospheric circulation is controlled by a powerful belt of wind near the top of the troposphere called the jet stream. The jet stream is a loop of winds that extend all the way around the globe. Generally move from west in both hemispheres Warm air masses move toward the poles ahead of this trough and cool air masses move toward the equator behind this trough.

87. On a global, yearly basis, the equatorial region of the earth receives more direct incoming solar radiation than the higher latitudes. As a result, average temperatures are higher in the equatorial region and decrease with latitude toward both poles. This sets the stage for worldwide patterns of prevailing winds, high and low areas of atmospheric pressure, and climatic patterns.

88. Part of the generalized global circulation pattern of the earth's atmosphere. The scale of upward movement of air above the intertropical convergence zone is exaggerated for clarity. The troposphere over the equator is thicker than elsewhere, reaching a height of about 20 km (about 12 mi).