Earth's Atmosphere: A Comprehensive Overview

1. Chapter 15 Air, Weather & Climate

2. Outline • The Atmosphere and Climate • Convection Currents • Greenhouse Effect • Weather • Winds • Frontal Systems • Cyclonic Storms • Climate • ENSO • Climate Change • Kyoto Protocol

3. The Atmosphere and Climate • Atmosphere– the air surrounding the earth which extends upwards 500km (300 miles) • Weather - daily temperature and moisture conditions in a specific place • Climate - a description of the long-term weather pattern in a particular area (30+ years)

4. Earth’s First Atmosphere • Composition - Probably H2, He (common in space) • These gases are relatively rare on Earth and were probably lost to space early in Earth's history due to: • Earth's gravity was not strong enough to hold lighter gases • Earth still did not have a differentiated core (solid inner/liquid outer core) which created Earth's magnetic field (magnetosphere = Van Allen Belt) which deflects solar winds. • Once the core differentiated the heavier gases could be retained

5. Earth’s Second Atmosphere • Produced by volcanic out gassing. • Gases produced were probably similar to those created by modern volcanoes (H2O, CO2, SO2, CO, S2, Cl2, N2, H2) and NH3 (ammonia) and CH4 (methane) • No free O2 at this time (not part of volcanic gases). • Ocean Formation - As the Earth cooled, H2O produced by out gassing could exist as liquid in the Early Achaean, allowing oceans to form.

6. The Atmosphere Today

7. Atmospheric Aerosols • AEROSOLS: Aerosols are minute particles or droplets suspended in the atmosphere which can affect climate. • Reflect & scatter sunlight • Cause chemical reactions in the atmosphere • ie: ozone depletion • 3 sources of Aerosols • 1. Volcanic activity (dust, SO2) • 2. Desert dust • 3. Anthropogenic (burning forests/fuels)

8. Selected Properties of Earth’s Atmosphere

9. Layers of the Atmosphere • “Spheres” are layers of air • “Pauses” mark boundaries between two “spheres” • Due to temperature variations the air in the layers do not mix

10. Troposphere • Densest layer (nearest the earth) • Contains 75-80% of all gas molecules • All weather occurs here • Convection currents circulate the air (mix heat & moisture) • Highest air pressure • (sea level = 14.7 lbs/in2)

11. Stratosphere – “Global Sunscreen” • Contains majority of atmospheric ozone • Ozone is produced when O2 interacts with UV radiation. • O2 + UV  O3 • Ozone blocks UV rays allowing life to survive • Little mixing of air so aerosols stay many years • Commercial jets fly here – avoid turbulence

12. Mesosphere • Temperatures drop rapidly in this layer • Coldest temps on earth -90°C (-130° F) • Least studied due to its position • (above weather balloons & aircraft and below orbiting spacecraft)

13. Thermosphere • Extremely hot from suns radiation • Contains highly ionized (charged) gas molecules • When solar radiation hits these ionized molecules they glow – “Aurora borealis” concentrated above Earth’s magnetic pole • https://vimeo.com/16917950

14. Sun’s Energy • INSOLATION (incoming solar radiation) • About 25% is reflected by clouds and the atmosphere. • Another 25% is absorbed by carbon dioxide, water vapor, ozone, aerosols and a few other gases. • About 50% reaches the earth’s surface. • Insolation is greatest at equator, decreasing toward higher latitudes (the poles) • Insolation is short wave radiation (light) which becomes long-wave (infrared/heat) after absorption by surface/clouds/gases.

15. Energy Balance

16. Effects of Albedo (Reflectivity) • Surfaces that reflect energy have a highalbedo. • Fresh clean snow 80-85% • Dense clouds 70-90% • White sand 20-30% • Surfaces that absorb energy have low albedo. • Forests 5-10% • Water (sun overhead) 5% • Dark soil/Pavement 3% • Absorbed energy causes water to evaporate and allows for photosynthesis. • Absorbed energy is released as heat.

17. Energy and the Greenhouse Effect • Most insolation reaching the Earth is high energy light (a.k.a. near infrared) of short wavelength. • Energy reradiated (reemitted) by earth is heat (a.k.a. far infrared) of long wavelength. • Longer wavelengths are absorbed in the lower atmosphere, trapping heat close to the earth’s surface. • GREENHOUSE EFFECT: The atmosphere transmits sunlight while trapping heat.

18. GREENHOUSE EFFECT Earth’s average temp. today is 58.30F. Without the greenhouse effect the temp. would be 330F cooler!!! (250F)

19. Contributing Factors to the Greenhouse Effect • Gases in the atmosphere, especially carbon dioxide, methane and water vapor, are the substances that retain heat. • Burning fossil fuels releases carbon dioxide and particulate aerosols. • Cows, melting permafrost, landfills and production of fuels releases methane • Increased heat increases evaporation of water • Deforestation destroys carbon sinks (absorbers). And, MUCH MORE TO COME .....

20. Arctic Sea Ice • Positive feedback loop - poles covered with ice reflect solar radiation back into space. Now that ice is melting, open water is absorbing more heat, which in turn is melting more ice, leading to more warming. • (there is no balance – only forward momentum) • Arctic Sea Ice Extent http://svs.gsfc.nasa.gov/vis/a000000/a003800/a003893/seaIceArea_2011_Wdate.mp4

21. WEATHER:short term physical conditions of the atmosphere in a specific place

22. Uneven Heating of the Earth • Insolation is not equal around the earth. • Much of solar energy absorbed by the Earth is used to evaporate water. • When water evaporates it absorbs energy. (580 calories per gram) • Energy stored in water vapor is LATENT HEAT. • When water vapor (gas) cools & condenses (turns to liquid), heat energy is released. • Heat and water move from warmer areas near the equator towards cooler areas at poles. Heat redistribution prevents extreme temperature fluctuation.

23. Uneven Heating of the Earth • 3 causes of unequal heating: • 1. insolation strikes earth at different angles • 2. insolation travels through more/less atmosphere where it is absorbed • 3. effect of albedo on different surfaces

24. Earth’s Tilt • Earth’s tilt causes seasonal variations • Tropics receive more direct insolation than poles

25. Convection Currents • Releasing latent heat causes air to rise, cool, and lose more water vapor as precipitation. • Warm air close to equator vs. cold air at poles also produces pressure differences that cause weather. • Air near surface warms and becomes less dense than the air above it; rises above cool air creating vertical convection currents. • Low pressure - air is rising • High pressure - air is sinking • Pressure differences cause winds. Winds move from High to Low

26. Circulation Patterns

27. 4 PROPERTIES OF AIR 1. DENSITY: mass of all molecules in a given volume less dense air rises, more dense air sinks 2. CAPACITY TO HOLD WATER VAPOR: warm air holds more water vapor than cold air SATURATION POINT: the maximum amount of water vapor air can hold at a given temp. 3. LATENT HEAT RELEASE: Whenever water vapor condenses, the air becomes warmer and rises

28. 4 PROPERTIES OF AIR 4. EFFECTS OF CHANGE IN PRESSURE: ADIABATIC COOLING: the cooling effect of reduced pressure on air as it rises in the atmosphere and expands ADIABATIC HEATING: the heating effect of increased pressure on air as it sinks toward the surface of Earth and decreases in volume

30. CONVECTION CURRENTS 1. Insolation reaches Earth’s surface 2. Energy is absorbed and the surface warms 3. Surrounding air warms via conduction 4. Warmer air rises carrying heat upward 5. As air rises, it cools and becomes denser 6. This “new” air displaces other air & spreads 7. Cooled air begins to sink 8. Cool/dry air returns to the surface & warms

31. Convection Currents

32. Weather Happens • WEATHER – short-term, physical conditions in the atmosphere (humidity, temperature, air pressure, wind and precipitation) • RAIN/PRECIPITATION: • Air cools as it rises, and water condenses as air cools. • Cooling occurs because pressure decreases as air rises. • CONDENSATION NUCLEI (tiny particles/aerosols) must also be present to have precipitation. Water vapor collects/condenses on them!

33. Weather Happens • WIND: • Movement of large air masses • Air moves from areas of high pressure to areas of low pressure • Winds are deflected by the Coriolis effec • HUMIDITY: • The amount of water vapor in the air • Relative humidity, expressed as a percent, measures the current absolute humidityrelative to the maximum for that temperature.

34. CORIOLIS EFFECT • Surface air flows do not move straight north and south, but are deflected due to the CORIOLIS EFFECT. • The curving pattern results from the rotation of earth in an eastward direction as winds move above it. • Winds are deflected because earth’s rotation at the equator is faster than its rotation at the poles. • Therefore – air at the equator is moving faster than air at higher latitudes

35. Winds and currents move clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.

36. JET STREAMS • JET STREAMS - hurricane force winds at the top of the troposphere which follow an undulating path

37. RAIN SHADOW EFFECT • Warm moist air rises, adiabatically cools and precipitation forms on windward side of mountain. Dry, desert-like conditions are found on the leeward side of the mountain.

38. Ocean Currents • Ocean currents are affected by several factors: • Temperature, salinity, continents, Coriolis effect, gravity, & surface winds • Ocean currents strongly influence the climate conditions on adjacent land. • As surface water moves, deep water wells up to replace it. Upwelling brings huge amounts of nutrients from the ocean bottom which supports large amounts of producers which in turn support large populations of fish. Most upwelling occurs on the west coasts of continents

39. Ocean Currents • Temperature: warm water rises, cold water sinks as water warms, it expands. (tropical water is actually a few inches higher than subtropical water) • Gravity: the force of gravity allows the tropical water to flow to higher latitudes • Salinity: salty water is denser and sinks • Coriolis Effect: like the air masses, water is also defected due to the rotation of the earth. • Continents: create barriers that shape currents • Surface Winds: create water movement on the surface of oceans called GYRES.

40. OCEAN CURRENTS & GYRES • GYRES: circular surface currents that move between continents

41. THERMOHALINE CIRCULATION • Ocean circulation is also driven by differences in water density due to temperature and salinity of the water – referred to as the Global Conveyer Belt

42. CHANGES TO THE THC • Lake Agassiz – 11,000 years ago, an ice dam broke and the lake drained into the N. Atlantic. Stopping the THC and created a mini-ice age in Europe. • Vast melting of Greenland ice sheets could have similar effects.

43. Seasonal Winds and Monsoons • Monsoon - seasonal reversal of wind patterns caused by differential heating and cooling rates of oceans and continents • Most prevalent in subtropical and tropical areas. • Tilt of Earth’s axis changes location where the Sun is most intense over the course of the year. Places where the Sun shines most directly have evaporation and convection currents which bring thunderstorms. • Seasonal rains support tropical forests and fill great rivers such as the Ganges and Amazon.

44. Summer Monsoons in India Summer cycle: (Monsoon season) Winds from the ocean carry warm, moist air causing rain on land Winter cycle: Winds come from the land are dry and cool, rains occur over the oceans

45. Frontal Weather • COLD FRONT- boundary formed when cooler air displaces warmer air • Cold air is more dense and pushes warm air up. • Creates strong, short-lived storms

46. Frontal Weather • WARM FRONT- boundary formed when warm air displaces cooler air • Warm air is less dense and slides over cool air, creating a long wedge-shaped band of clouds and precipitation.

47. Cyclonic Storms • When rising air is laden with water vapor, latent heat energy released by condensation intensifies convection currents and draws up more warm air and water vapor. (___________ feedback) • HURRICANES (Atlantic) • (Form off W Coast of Africa) • TYPHOONS (Western Pacific) • CYCLONES (Indian Ocean) • These storms are usually very large and generate high winds. Cause severe wind and flood damage • Winds are highest in the center

48. Hurricane Classification Hurricane Katrina – Category 5 Hurricane Matthew – Category 4 Hurricane Sandy – Category 3

49. Cyclonic Storms • TORNADOES - swirling funnel clouds • Rotation not generated by Coriolis forces • Generated by a “supercell” frontal systems where strong dry cold fronts collide with warm humid air • Common in midwest

50. Tornado Intensity