Geology lecture 18
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Geology lecture 18

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  • Think about main themes- plate tectonics 100 questions- 50 (fourth exam) 50 (fair game) Study like previous exams- smaller amounts of material and think about summary of ideas from the ends of different chapters
  • More extreme changes in weather patterns causes more storms

Geology lecture 18 Geology lecture 18 Presentation Transcript

  • Chapter 20Atmosphere and Climate
  • 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
  • Chapter 20Introduction• Earth has a well-developed atmosphere (atm).•  gas mixture called• Density & pressure variations cause• Atmosphere governs• Temperature (T).• Pressure (P).• Moisture content.• Wind velocity.• Wind direction.• Climate is
  • Chapter 20Atmospheric Components• Present atmosphere comprised of a gas mix:• Nitrogen 78%• Oxygen 21%• Other gases 1%• Aerosols –
  • Chapter 20Atmospheric Coloration• Color due to• Light scattered passing through• Some light returns• Why is the sky blue?• When the Sun is• Gases scatter• Why is the sky red?• Setting Sun passes
  • Chapter 20Pressure and Density• Air pressure –• Greatest near• Decreases• 14.7 psi (1 atm) at sea level.• Air density –• Maximum at• Decreases
  • Chapter 20P and T Relations• P & T conditions change with• P - higher near• When air moves from higher to lower P, it…• Expands & cools.• Moving from lower to higher P, it…• Called
  • Chapter 20Relative Humidity• Air has varying water amounts:• Dry (desert) 0.3%• Humid (tropical rainforest) 4.0%• Water content described by• Ratio (%) of measured• Dry air -• Humid air -• 100% relative humidity air is• Under-saturated air has <100%
  • 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• Below dewpoint…• Water forms
  • Chapter 20Relative Humidity• Rising air cools (adiabatically) to form• Common phenomena ->• Clouds can dissipate by adiabatic
  • Chapter 20Latent Heat• Water in air can• With state changes, air T also• T change is not due to external energy; hence, “latent.”• Instead, derives from• Evaporating water• Condensing water
  • Chapter 20Atmospheric Layers• Atmosphere is thermally layered.• Troposphere (0 - 9 to 12 km).• Mixing layer.• All weather is here.
  • 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
  • Chapter 20Atmospheric Circulation• Troposphere experiences• Wind velocities vary from• Wind circulation has both• Local –.• Global –
  • Chapter 20Pressure Gradients• Lateral pressure differences• Pressures mapped by• Isobars cannot• Air flows from high to low P• Steeper the gradient,
  • Chapter 20Energy Input• Air circulation is result of• Warm air expands,• This air is replaced by• Convection driven by•  Solar energy =
  • Chapter 20Energy Input• Solar energy bathing Earth is not• Vertical Sun rays have• Oblique rays• Tropics (vertical rays) receive• Poles (oblique rays) receive
  • Chapter 20Seasons• Seasons due to• Earth orbits Sun, vertical rays• More north• More south
  • Chapter 20Seasons – January vs. July
  • Chapter 20Atmospheric Movement• Troposphere divided into• Hadley cells –• Ferrel cells –• Polar cells –• Hadley cell – Risingequatorial air creates
  • Chapter 20• Rotation (via Coriolis effect), complicates• Cell airflow is deflected• Forms• Cooling airAtmospheric Movement
  • Chapter 20Prevailing Winds• Result is• Called
  • Chapter 20High Winds• Troposphere thickness changes• Warm equatorial air• Cold polar air• At given altitude, equatorial pressure• Causes equatorial high-altitude air• Air atop Hadley cells spill over top of Ferrel cells.• Coriolis deflects
  • Chapter 20High Winds• High-altitude pressure gradient• Over• High-altitude westerlies can• Called
  • 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
  • Chapter 20Weather• Local-scale conditions of• Reflects• Variation in• Land vs. sea.• A weather system affects
  • Chapter 20Air Masses• Air packages with• >1,500 km across,• Characteristics reflect• Weather changes dramatically when
  • Chapter 20Fronts• Fronts -• Curved surfaces that lead• Cold fronts:• Steep• Flow• Pushes up
  • Chapter 20Fronts• Warm front:• More gradual• Warm air• Pushes• Incline reflects• Warm air rising up the front causes
  • Chapter 20Clouds and Precipitation• Water vapor in saturated air• Condensing as• Precipitating as• Condensation nuclei• Microscopic
  • Chapter 20Clouds and Precipitation• Several air-lifting mechanisms.• Convective lifting –• Frontal lifting –• Convergence lifting –• Orographic lifting –
  • Chapter 20Clouds and Precipitation• Rain, snow, sleet form in 2 ways,• Collison & coalescence –• Drops fall when• Typical raindrops are• Drops >5 mm• Cold air near ground turns rain
  • Chapter 20Cloud Types• Clouds form in troposphere, controlled by:• Air stability• Elevation at which moisture condenses• Wind conditions
  • Chapter 20Cloud Types• Clouds described by shape:• Cirrus – wispy, thin, feathery• Cumulus – puffy, cottony• Stratus – stable, layered• Prefixes narrow cloud types.• Cirro – high-altitude• Alto – mid-altitude• Nimbo – rain-producing
  • Chapter 20Storms• Storms develop along• Centered by low pressure• Fueled by warm, moist air• Result: lightening, wind, rain, hail/sleet/snow
  • Chapter 20Thunderstorms• Local pulses of intense rain, wind, lightning• Rising air forms cumulus clouds• Latent heat released by condensing water warms air• Cumulus clouds build upward• Anvil head develops• Heavy rains ensue
  • Chapter 20Thunderstorms• Lightning is electrical charge separation in clouds• Scientists do not fully understand why this happens• Cloud bases develop a negative charge• Result: buildup of positive group charge• Air is a good insulator; prevents charge dissipation• Eventually, charge imbalance overwhelms air
  • Chapter 20Thunderstorms• Lightning leader advances from cloud base• Return stroke starts from ground• Connect to form the bolt• Thunder is a direct result• Bolt heats air 8K to 30K degrees C• Air expands explosively.
  • Chapter 20Tornadoes• Near-vertical rotating funnel-shaped vortex cloud• Air moves with violent speed about a rotation axis• Local winds up to 500 km/h (300mph)• Extremely destructive
  • Chapter 20Tornadoes• Tornadoes develop along steep P gradients• Strong W winds carry polar air• Strong SE surface winds carry warm moist air• Shear initiates horizontal rotation• Drafts tip the rotating cylinder upright
  • Chapter 20Tornadoes• Tornadoes prevalent in Midwest US• Proper conditions; March to September• Cold polar air from Canada sweeps south• Warm moist air pushed north from Gulf of Mexico• Tornado-prone region called “Tornado Alley”
  • Chapter 20Hurricanes• Huge low-P cyclonic storms from tropical Atlantic.• Defined by sustained winds >119 km/hr (74 mi/hr)• Fueled by warm ocean winds (>27 degrees C)• Originate in low latitudes (<20 degrees N) with warm water• Do not form near equator (insufficient lateral winds)
  • Chapter 20Hurricanes• Hurricanes develop in summer & late fall.• Form over warm tropical ocean waters off W. Africa• Cyclonic low-P “tropical disturbances” pull air inward• Air rises, cools, condenses; releases latent heat• Heat buoys air, creates lower P, pulls in more air• Over time, storm gains size and strength• Size range – 100 to 1500 km• Strength – >250 km/hr
  • Chapter 20Hurricanes• Storm “named” when winds exceed ~60 km/hr• Named in alphabetical order• Alternating male/female with varying national origin• Hurricane tracks move W and N, often crossing land• Landfall removes fuel (warm, moist air)
  • Chapter 20Hurricanes• Hurricane-like storms outside the Atlantic are called…• Typhoons – Western Pacific Ocean• Cyclones – Northern Indian Ocean
  • 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
  • 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.
  • 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
  • Chapter 20Climate• “climate” refers to persistent weather patterns• Long-term (30+ years) regional trends• Trends include maxima, minima, ranges, timing, etc. in:• T,P, humidity, precipitations, wind conditions, storms
  • Chapter 20Climate Controls• Climatic conditions governed by:• Latitude – N or S position.• Determines insolation• Hotter near equator• Colder near poles• Seasonally varies• Altitude – Height above SL.• Elevation linked to T• For same latitude:• Lower elevations warmer• Higher elevations colder• ~6oC/km lapse rate.
  • Chapter 20Climate Controls• Climatic conditions governed by:• Proximity to water- influences T stability• Land heats & cools faster than oceans• Near oceans have less T extremes (smaller T ranges)
  • Chapter 20Climate Controls• Climatic conditions governed by:• Proximity to ocean currents influences T conditions• Warm currents produce warmer climates
  • Chapter 20Climate Controls• Climatic conditions governed by:• Proximity to mountains• Mountains alter air flow – funneling/blocking winds• Mountains modify moisture patterns• Heavy precipitation on windward side• Rain shadow(desert) on leeward side
  • Chapter 20Climate Controls• Climatic conditions governed by:• Proximity to semi-permanent high and low P cells• Latitudinally controlled• Govern prevailing winds• Directly control humidity
  • Chapter 20Climate Belts• Climatic belts classified by T, precipitation, and vegetation
  • Chapter 20Climate Variability• Climate can change in cyclic patterns.• Example: El Niñ o – Oscillation (ENSO) -> air/water circulationoff Peru.Normal circulation is:• Easterlies push Peru coast surface water west• Upwelling deep, cold, nutrient-rich water replaces flow• Rain in west Pacific
  • Chapter 20Climate Variability• During El Niñ o, atmosphere-ocean circulation changes:• Westerlies develop in west Pacific• Low P zone moves out over east Pacific• Suppresses Peru coastal upwelling• Drought in west Pacific