The Atmosphere

1. The Atmosphere

2. Origin of Modern Atmosphere • original atmosphere surrounded the homogenous planet Earth and probably was composed of H and He • second atmosphere evolved from gases from molten Earth • H2O, CO2, SO2, CO, S2, Cl2, N2, H2, NH3, and CH4 • allowed formation of oceans and earliest life • modern Atmosphere • evolved after Cyanobacteria started photosynthesizing • oxygen produced did not reach modern levels until about 400 million years ago ♦compared to the size of the Earth (10,400 km), the atmosphere is a thin shell (120 km).

3. The Atmosphere • The atmosphere is the thin layer of gas surrounding earth. Half of the mass of the atmosphere is below a height of 5.5 km, 90% is below 16.5 km, and 99% is below 30 km.

4. This is what the atmosphere looks like viewed edge on from space. The image is of a small cross-sectional area, note the small curvature of the surface, yet the atmosphere is a small part of the whole. Looking closely, you can see tall thunderstorm clouds silhouetted against an orange layer of atmospheric gases backlit by the sun just below the horizon. Above this layer is the clear blue of the stratosphere and the blackness of space. From NASA Space Shuttle Flight 6 on 4 April 1983

5. AtmosphereLayers • Exosphere • Thermosphere • (Ionosphere) • Mesosphere • Stratosphere • Troposphere

6. Troposphere • 8 to 14.5 kilometers high (5 to 9 miles) • most dense • the temperature drops from about 17 to -52 degrees Celsius • almost all weather is in this region

7. Stratosphere • extends to 50 kilometers (31 miles) high • dry and less dense • temperature in this region increases gradually to -3 degrees Celsius, due to the absorption of ultraviolet radiation • ozone layer absorbs and scatters the solar ultraviolet radiation • ninety-nine percent of "air" is located in first two layers • every 1000-m 11% less air pressure

8. Ozone Layer • The ozone layer is a layer in Earth's atmosphere which contains relatively high concentrations of ozone (O3). • This layer absorbs 93-99% of the sun's high frequency ultraviolet light, which is potentially damaging to life on earth. • Over 91% of ozone in earth's atmosphere is present here. • Concentration of Ozone is relatively high in the stratosphere. "Relatively high" means a few parts per million—much higher than the concentrations in the lower atmosphere but still small compared to the main components of the atmosphere. • It is mainly located in the lower portion of the stratosphere from approximately 10 km to 50 km above Earth's surface, though the thickness varies seasonally and geographically

9. The Mesosphere • Above the stratosphere is the mesosphere • 1.The region between the ionosphere and the exosphere, extending from about 250–650 mi. (400–1050 km) above the surface of the Earth. • 2. The region between the stratosphere and the thermosphere, extending from about 20–50 mi. (32–80 km) above the surface of the Earth.

10. The Ionosphere • Also called thermosphere • many atoms are ionized (have gained or lost electrons so they have a net electrical charge). • The ionosphere is responsible for absorbing the most energetic photons from the Sun, and for reflecting radio waves, thereby making long-distance radio communication possible.

11. The Exosphere • The exosphere is the uppermost layer of the atmosphere. On Earth, its lower boundary at the edge of the thermosphere is estimated to be 500 km to 1000 km above the Earth's surface, and its upper boundary at about 10,000 km. It is only from the exosphere that atmospheric gases, atoms, and molecules can, to any appreciable extent, escape into space. The main gases within the exosphere are the lightest gases, mainly hydrogen, with some helium, carbon dioxide, and atomic oxygen near the exobase. The exosphere is the last layer before space.

12. Composition • Nitrogen (N2, 78.08% ) • Oxygen (O2, 20.95% ) • Argon (Ar, 0.93% ) • Neon (Ne, 0.002% ) myriad other very influential components are also present which include: • Water (H2O, 0 - 7%), • "greenhouse" gases or Ozone (O3, 0 - 0.01%), • Carbon Dioxide (CO2, 0.038% ),

13. Composition • It would seem that the composition of the atmosphere would be stratified with different chemical composition at different heights. In fact, mixing in the atmosphere causes the composition to be nearly uniform up to about 80 km.

14. Structure • The density and pressure of the atmosphere drop nearly exponentially with height up to a height of 100 km. • Temperature decreases with height in the troposphere up to a height of 10-15 km, then it increases with height in the stratosphere. • The stratosphere is defined as that region above the troposphere where temperature increases with height. Because temperature increases with height, the layer is stable and stratified, hence the name. The stratosphere is heated from above by the absorption of solar ultraviolet radiation by ozone in the stratosphere.

15. Temperature Gradient

16. Temperature Inversion • Inversion in the atmosphere above San Diego, red curve. The air at a height of one kilometer is more than 5° C warmer than the air at the surface. There is also a much weaker, and shallower inversion above Dallas. • Inversions strongly influence atmospheric pollution. Inversions inhibit vertical convection, trapping pollutants close to the surface. Strong, persistent, inversions over urban areas lead to much greater concentrations of pollutants in the urban air.

17. Inversions • Inversions: • Limit vertical mixing. This traps pollutants close to the ground. • Limit cloud formation. This leads to more sunlight, which drives chemical reactions in the polluted air. • Limits precipitation. This increases the lifetime of the pollutants in the atmosphere.

18. Inversions • Inversions are common along west coasts of continents. • There winds blowing toward the equator cause water at the ocean's surface to move away from the coast. • The water is replaced by colder water upwelled from deeper in the ocean. • The cold water cools the lower kilometer of the atmosphere, producing the inversion. • Strong inversions are common along the California coast. They are responsible for the warm, dry, cool climate of Los Angeles, San Francisco, and San Diego. They are also responsible for smog commonly found in these cities, especially Los Angeles.

19. Inversions • Inversions also occur above inland lakes and rivers on days when the water is cooler than the air, and winds are weak, and in valleys at night when colder air drains off surrounding hills. • Sea-surface temperature along the US west coast on 16-18 July 2006 measured by the Advanced High Resolution Radiometer AVHRR on the NOAA polar-orbiting, meteorological satellites. The cold (blue) areas are upwelled water caused by north winds offshore of the coast.

20. Atmospheric Density

21. Ozone • Ozone is a very important trace gas in the atmosphere. It exits in two places: • In the stratosphere at heights around 20-30 km. This is good ozone. It protects all life on earth from dangerous solar ultraviolet radiation (energy). • Close to the surface due to pollution. It is produced from nitrogen oxides and volatile carbon-based compounds when there is intense solar radiation (energy), above all in the spring and summer. This is bad ozone. It causes respiratory illness; it damages plants; and it attacks rubber. • Remember "Good Up high, Bad Nearby"

22. Ozone • This is what the smog in Los Angeles looks like from the ground, a thick brown or slightly orange haze with a strong smell of ozone. In this scene, the inversion is below the top of the highest buildings. The exhaust from more than a million cars driven in the morning rush hour is trapped below this level.

23. Seasonal Changes • Occur because the earth’s axis is tilted • Creates opposite seasons in the northern and southern hemisphere • Factor that determines global air circulation patterns

24. Ocean Currents

25. Ocean Currents • Sea-surface temperature influences air temperature as the ocean exchanges heat with the overlying atmosphere. • It also influences evaporation rates which are generally higher where sea-surface temperature is higher

27. Ocean Currents • There are two type of Ocean Currents: • 1. Surface Currents--Surface Circulation • These waters make up about 10% of all the water in the ocean. • These waters are the upper 400 meters of the ocean.

28. Ocean Currents • 2. Deep Water Currents • These waters make up the other 90% of the ocean • These waters move around the ocean basins by density driven forces and gravity. • The density difference is a function of different temperatures and salinity • These deep waters sink into the deep ocean basins at high latitudes where the temperatures are cold enough to cause the density to increase.

29. Ocean Currents Ocean Currents are influenced by two types of forces 1. Primary Forces--start the water moving 1. Solar Heating 2. Winds 3. Gravity 4. Coriolis 2. Secondary Forces--influence where the currents flow

31. Air Temperature • As solar energy reaches the Earth, equatorial regions heat up more than the poles. • Warm air and water at the equator travel poleward while cold air and water at the poles travel equatorward in an attempt to equalize this temperature contrast. • It is the atmosphere's continual struggle for temperature balance that brings us our changing weather.

32. http://www.usatoday.com/weather/tg/wglobale/wglobale.htm

33. Coriolis Effect • The Earth is a spinning globe where a point at the equator is traveling at around 1100 km/hour, but a point at the poles is not moved by the rotation. • This fact means that projectiles moving across the Earth's surface are subject to Coriolis forces that cause apparent deflection of the motion.

34. Coriolis Effect • Since winds are just molecules of air, they are also subject to Coriolis forces. • Winds are basically driven by Solar heating. • Solar heating on the Earth has the effect of producing three major convection zones in each hemisphere. • If solar heating were the only thing influencing the weather, we would then expect the prevailing winds along the Earth's surface to either be from the North or the South, depending on the latitude. • However, the Coriolis force deflects these wind flows to the right in the Northern hemisphere and to the left in the Southern hemisphere.

37. A Little Review a for a You • What is the definition of the atmosphere? A thin layer of air that forms a protective layer around the planet!

38. A Little Review a for a You • In what ways does our atmosphere protect us? 1 – Keeps out the extreme hot or cold 2 – Keeps out Cosmic Rays 3 – Helps protect us from small space debris

39. Where is the Cosmic radiation absorbed? (two places) F Match the terms to their places Mesosphere Troposphere Outer Space/Exosphere E Thermosphere Stratosphere Ozone Layer D C B A

40. Climate • Average long term weather of an area • Seasonal variations and weather extremes averaged over a long period (at least 30 years) • 2 Main factors • Temperature • Precipitation • amount • distribution

41. Air Pressure • air pressure is caused by the weight of the air pressing down on the Earth, the ocean and on the air below • the pressure depends on the amount of air above the measuring point and falls as you go higher • air pressure changes with weather

42. Weather

43. Weather • air in a high pressure area compresses and warms as it descends • the warming inhibits the formation of clouds, meaning the sky is normally sunny in high-pressure areas • haze and fog might form • the opposite occurs in an area of low pressure

45. Humidity • relative humidity is the amount of water vapor in the air compared with the potential amount at the air's current temperature • expressed as a percentage • depends on air temperature, air pressure, and water availability • the Earth has about 326 million cubic miles of water • only about 3,100 cubic miles of this water is in the air as water vapor > clouds > precipitation

47. Cloud cover • moisture in the atmosphere forms clouds which cover an average of 40% of the Earth at any given time • a cloudless Earth would absorb nearly 20 percent more heat from the sun • clouds cool the planet by reflecting sunlight back into space. This is known as Albedo However • clouds reduce the amount of heat that radiates into space by absorbing the heat radiating from the surface and reradiating some of it back down • the process traps heat like a blanket

48. Precipitation • Air containing water vapor cools in atmosphere and therefore condenses to form droplets of liquid water • Rain: liquid, falls, d >0.5 mm (sphere) • Freezing Rain: occurs when drop touches frozen surface • Sleet: ice pellets, d < 0,5 mm, begins as rain but enters air below freezing • Snow: water deposits in hexagonal nuclei below freezing • Snow Pellets: grains of ice, d = 2-5 mm • Hail: 5-190 mm in diameter, concentric rings of ice

49. Winds • horizontal wind moves from areas of high to low pressure • vertical wind moves from low to high pressure • speed is determined by differences in pressure • Coriolis effect causes winds to spiral from high pressure zones and into low pressure zones

50. Winds • wind speed is detected by a anemometer and direction by a weather vane • wind direction is based on where the wind is coming from: an wind from the east is an easterly • Beaufort Wind Speed Scale is has a range from 0 for calm to 12 for a hurricane with waves greater than 37 feet