18 atmosphere climate_forstudents

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18 atmosphere climate_forstudents

  1. 1. Chapter 20Atmosphere and Climate
  2. 2. Chapter 20Outline• Atmosphere-what is it?-Composition, coloration, P-T-density relationships-Relative humidity, latent heat, troposphere• Circulation-Gradients and energy input-Movement, prevailing winds, high winds (jet streams)• Weather-Air masses, fronts, clouds and precipitation-Storms (thunderstorms, tornadoes, hurricanes)• Climate-Controls, belts, variability (El Nino example)Chapter 20
  3. 3. Chapter 20Introduction• Earth has a well-developed atmosphere (atm).•  gas mixture called• Density & pressure variations cause air motion• Atmosphere governs physical conditions of weather• Temperature (T).• Pressure (P).• Moisture content.• Wind velocity.• Wind direction.• Climate is long term weather behavior
  4. 4. Chapter 20Atmospheric Components• Present atmosphere comprised of a gas mix:• Nitrogen 78%• Oxygen 21%• Other gases 1%• Aerosols – tiny suspended particles• Liquid droplets solid dust particles
  5. 5. Chapter 20Atmospheric Coloration• Color due to light energy dispersion• Light scattered passing through atm• Some light returns to space• Why is the sky blue?• When the Sun is overhead..• Gases scatter blue light• Why is the sky red?• Setting Sun passes through thickeratmosphere• Only red is left, blue scattered to space
  6. 6. Chapter 20Pressure and Density• Air pressure – force due to weight of overlying air• Greatest near surface• Decreases upward• 14.7 psi (1 atm) at sea level.• Air density – mass of air/vol• Maximum at sea level• Decreases upward
  7. 7. Chapter 20P and T Relations• P & T conditions change with elevation• P - higher near surface; lower above• When air moves from higher to lower P, it…• Expands & cools.• Moving from lower to higher P, it…• Sinks, shrinks, and warms• Called adiabatic cooling and heating
  8. 8. Chapter 20Relative Humidity• Air has varying water amounts:• Dry (desert) 0.3%• Humid (tropical rainforest) 4.0%• Water content described by relative humidity• Ratio (%) of measured water content to max possible• Dry air –low relative humidty• Humid air – high relative humidity• 100% relative humidity air is saturated• Under-saturated air has <100% relative humidity
  9. 9. Chapter 20Relative Humidity• Moisture content changes with T.• Cold air holds less; warm air more.• Warm, under-saturated air becomes saturated as it cools.• Saturation T is the dewpoint• Below dewpoint…• Water forms dew or frost
  10. 10. Chapter 20Relative Humidity• Rising air cools (adiabatically) to form tiny water droplets• Common phenomena -> form clouds• Clouds can dissipate by adiabatic heating
  11. 11. Chapter 20Latent Heat• Water in air can change its state• Liquid >gas or visa versa• With state changes, air T also changes• T change is not due to external energy; hence, “latent.”• Instead, derives from state change alone• Evaporating water absorbs heat, cools air• Condensing water releases heat, warms air
  12. 12. Chapter 20Atmospheric Layers• Atmosphere is thermally layered.• Troposphere (0 - 9 to 12 km).• Mixing layer.• All weather is here.
  13. 13. Chapter 20Outline• Atmosphere-what is it?-Composition, coloration, P-T-density relationships-Relative humidity, latent heat, troposphere• Circulation-Gradients and energy input-Movement, prevailing winds, high winds (jet streams)• Weather-Air masses, fronts, clouds and precipitation-Storms (thunderstorms, tornadoes, hurricanes)• Climate-Controls, belts, variability (El Nino example)Chapter 20
  14. 14. Chapter 20Atmospheric Circulation• Troposphere experiences constant motion (wind)• Wind velocities vary from 0 to >100 km/hr• Wind circulation has both local and global aspects• Local –.operates• Global –
  15. 15. Chapter 20Pressure Gradients• Lateral pressure differences drive horizontal winds• Pressures mapped by isobars-line of equal P• Isobars cannot cross• Air flows from high to low P perpendicular to isobars• Steeper the gradient, faster the airflow
  16. 16. Chapter 20Energy Input• Air circulation is result of heat movement• Warm air expands, becomes less dense> rises• This air is replaced by sinking, colder, denser air• Convection driven by differential solar heating (insolation)•  Solar energy = insolation, or incoming solar radiation
  17. 17. Chapter 20Energy Input• Solar energy bathing Earth is not evenly disturbuted• Vertical Sun rays have more energy• Oblique rays• Tropics (vertical rays) receive• Poles (oblique rays) receive
  18. 18. Chapter 20Seasons• Seasons due to 23.5 tilt to Earths rotation axis• Earth orbits Sun, vertical rays• More north• More south
  19. 19. Chapter 20Seasons – January vs. July
  20. 20. Chapter 20Atmospheric Movement• Troposphere divided into 6 N-S motion cells• Hadley cells – low latitude• Ferrel cells – mid latitude• Polar cells – high latitude• Hadley cell – Risingequatorial air creates low P,cools and rains
  21. 21. Chapter 20• Rotation (via Coriolis effect), complicates N-S flow• Cell airflow is deflected E or W depending on flow direction• Forms convergent and divergent zones• Cooling air sinks, warm air risesAtmospheric Movement
  22. 22. Chapter 20Prevailing Winds• Result is regular wind directions• Called prevailing winds• May be locally modified
  23. 23. Chapter 20High Winds• Troposphere thickness changes with latitude• Warm equatorial air expands it• Cold polar air thins it• At given altitude, equatorial pressure will be higher• Causes equatorial high-altitude air to flow towards poles• Air atop Hadley cells spill over top of Ferrel cells.• Coriolis deflects these winds too!
  24. 24. Chapter 20High Winds• High-altitude pressure gradient• Over• High-altitude westerlies can• Called
  25. 25. Chapter 20Outline• Atmosphere-what is it?-Composition, coloration, P-T-density relationships-Relative humidity, latent heat, troposphere• Circulation-Gradients and energy input-Movement, prevailing winds, high winds (jet streams)• Weather-Air masses, fronts, clouds and precipitation-Storms (thunderstorms, tornadoes, hurricanes)• Climate-Controls, belts, variability (El Nino example)Chapter 20
  26. 26. Chapter 20Weather• Local-scale conditions of T,P wind speed, humidity• Reflects prevailing winds plus local variations• Variation in topography and vegetation• Land vs. sea.• A weather system affects a region for a short time
  27. 27. Chapter 20Air Masses• Air packages with unique recognizable properties• >1,500 km across, they flow over a region for days• Characteristics reflect origin and changes• Weather changes dramatically when air masses changes
  28. 28. Chapter 20Fronts• Fronts – boundaries between air masses• Curved surfaces that lead air masses• Cold fronts:• Steep T and P gradients –move fast• Flow beneath warm air masses• Pushes up warm, humid air, and creates storms
  29. 29. Chapter 20Fronts• Warm front:• More gradual P and T gradient – move slow• Warm air climbs up over colder air• Pushes cold air into wedge• Incline reflects less steep T/P gradients• Warm air rising up the front causes broad cloud cover/precip
  30. 30. Chapter 20Clouds and Precipitation• Water vapor in saturated air changes states by..• Condensing as water droplets• Precipitating as ice crystals• Condensation nuclei help initiate this change• Microscopic solid or liquid particles
  31. 31. Chapter 20Clouds and Precipitation• Several air-lifting mechanisms.• Convective lifting – warmed air rises• Frontal lifting – air is carried upward along fronts• Convergence lifting – converging windds force air upward• Orographic lifting – air must raise to pass over mountains
  32. 32. Chapter 20Clouds and Precipitation• Rain, snow, sleet form in 2 ways,• Collison & coalescence – small droplets collide/merge• Drops fall when too large to suspend• Typical raindrops are 2mm• Drops >5 mm break up• Cold air near ground turns rain to sleet
  33. 33. Chapter 20Cloud Types• Clouds form in troposphere, controlled by:• Air stability• Elevation at which moisture condenses• Wind conditions
  34. 34. Chapter 20Cloud Types• Clouds described by shape:• Cirrus – wipsy, thin, feathery• Cumulus – puffy, cottony• Stratus – stable, layered• Prefixes narrow cloud types.• Cirro – high altitude• Alto – mid altitude• Nimbo – rain producing
  35. 35. Chapter 20Storms• Storms develop along• Centered by• Fueled by• Result:
  36. 36. Chapter 20Thunderstorms• Local pulses of• Rising air forms• Latent heat released by• Cumulus clouds• Anvil head• Heavy rains
  37. 37. Chapter 20Thunderstorms• Lightning is• Scientists do not• Cloud bases develop a• Result: buildup of• Air is a good insulator; prevents• Eventually, charge imbalance
  38. 38. Chapter 20Thunderstorms• Lightning leader advances from• Return stroke starts• Connect to form• Thunder is a• Bolt heats air• Air expands explosively.
  39. 39. Chapter 20Tornadoes• Near-vertical• Air moves with• Local winds up to• Extremely
  40. 40. Chapter 20Tornadoes• Tornadoes develop along• Strong W winds• Strong SE surface winds• Shear initiates• Drafts tip the rotating
  41. 41. Chapter 20Tornadoes• Tornadoes prevalent in• Proper conditions;• Cold polar air from• Warm moist air pushed• Tornado-prone region called
  42. 42. Chapter 20Hurricanes• Huge low-P cyclonic storms from tropical Atlantic.• Defined by• Fueled by• Originate in• Do not form near
  43. 43. Chapter 20Hurricanes• Hurricanes develop in summer & late fall.• Form over warm tropical ocean waters• Cyclonic low-P “tropical disturbances”• Air rises, cools, condenses;• Heat buoys air, creates• Over time, storm gains• Size range –• Strength –
  44. 44. Chapter 20Hurricanes• Storm “named” when winds exceed• Named in• Alternating male/female with• Hurricane tracks move• Landfall removes
  45. 45. Chapter 20Hurricanes• Hurricane-like storms outside the Atlantic are called…• Typhoons –• Cyclones –
  46. 46. Chapter 20Hurricanes• Intensity is ranked • Category 1: Wind speed > 119 km/h; pressure > 980 mbars• Category 5: Wind speed > 250 km/h; pressure < 920 mbars
  47. 47. Chapter 20Hurricanes• 2005 hurricane season set records:• Most named storms (26) – previous record 21 in 1933.• Most hurricanes (13) – Previous record 12 in 1969.• Most category 5s (3) – Previous record 2 in 1960 and 61.• Most major hurricanes (Cat. 3 or higher - 7).• Most major hurricanes in the U.S. (4). Increased stormy trend likely reflects climate change.
  48. 48. Chapter 20Outline• Atmosphere-what is it?-Composition, coloration, P-T-density relationships-Relative humidity, latent heat, troposphere• Circulation-Gradients and energy input-Movement, prevailing winds, high winds (jet streams)• Weather-Air masses, fronts, clouds and precipitation-Storms (thunderstorms, tornadoes, hurricanes)• Climate-Controls, belts, variability (El Nino example)Chapter 20
  49. 49. Chapter 20Climate• “climate” refers to• Long-term• Trends include
  50. 50. Chapter 20Climate Controls• Climatic conditions governed by:• Latitude – N or S position.• Determines• Hotter near• Colder near• Seasonally• Altitude – Height above SL.• Elevation linked to• For same latitude:• Lower elevations• Higher elevations• ~6oC/km lapse rate.
  51. 51. Chapter 20Climate Controls• Climatic conditions governed by:• Proximity to• Land heats & cools faster than• Near oceans have less
  52. 52. Chapter 20Climate Controls• Climatic conditions governed by:• Proximity to ocean currents• Warm currents produce
  53. 53. Chapter 20Climate Controls• Climatic conditions governed by:• Proximity to• Mountains alter air flow -• Mountains modify• Heavy precipitation on• Rain shadow
  54. 54. Chapter 20Climate Controls• Climatic conditions governed by:• Proximity to• Latitudinally• Govern• Directly control
  55. 55. Chapter 20Climate Belts• Climatic belts classified by
  56. 56. Chapter 20Climate Variability• Climate can change in cyclic patterns.• Example: El Niño – Oscillation (ENSO) -> air/water circulationoff Peru.Normal circulation is:• Easterlies push Peru• Upwelling deep, cold,• Rain in
  57. 57. Chapter 20Climate Variability• During El Niño, atmosphere-ocean circulation changes:• Westerlies develop• Low P zone moves• Suppresses Peru• Drought in

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