PowerPoint PresentationSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39III. Circulation of the AtmosphereA. Atmosphere, Weather and Climate Some history: All cultures recognize impacts of climate, and want to predict and influence the weather.Formal study of the atmosphere goes back tothe Greeks. Aristotle’s treatiseMeteorologica, “discourse on things above”.III. Circulation of the AtmosphereA.Atmosphere, Weather and ClimateSome history: Initially humans most interested in extremes of weather: drought, flood, violent storms.More recently, we are interested in how industrial activity influences weather and human health.III. Circulation of the AtmosphereA.Atmosphere, Weather and ClimateSome historical examples:Dec. 1952 London fogLos Angeles in the late 1950sIII. Circulation of the AtmosphereA.Atmosphere, Weather and ClimateSome historical examples:Local problems: original solutions…….• Time release of pollutants with storms• Build taller smokestacksEffective locally, but using the atmosphere as an infinite sewer led to regional problems: acid rain, GHG, ozone depletion.To understand how human activity might influence the atmosphere, weather and climate, we need to understand not only its structure, but why and how it moves.III. Circulation of the AtmosphereA. Atmosphere, Weather and ClimateAtmosphere: Gaseous layer from Earth’s surface to the “edge of space”.For us: Troposphere, Tropopause, StratosphereWeather:Climate:State of the atmosphere at a particular place or region, for a short period of time.Average weather (for a place or region). Usually average of last 30 years.III. Circulation of the AtmosphereA. Atmosphere, Weather and ClimateB. Origin of the AtmosphereEarth’s early atmosphere very different than today’s….. Dense (10% of Earth’s mass) and composed of CO, H2S, N2, H2, H20.All was lost to the intense solar wind during earliest episode in Earth’s history.Present atmosphere: Derived from outgassing of Earth’s hot interior. Initially different in composition from the modern atmosphere.Solar wind removes initial atmosphereIII. Circulation of the AtmosphereA. Atmosphere, Weather and ClimateB. Origin of the AtmosphereWhy doesn’t the atmosphere just drift off into space?Some of it does….but its only the lightest gases….hydrogen (H2) and helium (He2).The rest is held in place by gravity.III. Circulation of the AtmosphereA. Atmosphere, Weather and ClimateB. Origin of the AtmosphereC. State of the Atmospherea. Composition (nearly constant)b. Temperature, Pressure, Humidityc. WindsIII. Circulation of the AtmosphereD. Movement of air1. Vertical motion2. Horizontal motionIV. Circulation of the AtmosphereD. Movement of air1. Vertical motion: buoyancy (density). 2. Horizontal motion: Air moves horizontally because of differences in pressure. Air always moves from high pressure to low pressure.Rate of movement (wind speed) depends on the pressure gradient.III. Circulation of the AtmosphereD. Movement of air1. Vertical motion: buoyancy (density). 2. Horizontal motion: differences in pressure. 3. The Heat Enginea) Sea Breeze, a simple heat engine.b) The Earth as a heat engine.Flux of solar radiation less at higher latitudes; max. at equatorEarthSunIII. Circulation of the AtmosphereD. Movement of air4. The Coriolis Effect: Tendency for fluids (air or water, or anything moving in them) moving across Earth’s surface to be deflected from a straight line path.Not a real forceIII. Circulation of the AtmosphereD. Movement of air4. The Coriolis Effect: Coriolis Rules of thumb• NH to right; SH to left• Effect is small (cannot impact draining bathtub, etc) • Biggest effect is on large objects.• Impact increases as speed of object increases.• Coriolis Effect is zero at the equator.III. Circulation of the Atmosphere5. General Circulation of the Atmospherea. Hadley Cell: 0 to 30° on either side of the equator.b. Ferrel Cell: Indirect, 30 to 60° on either side of the equator.c. Polar High (or Polar Easterlies): 60-90°ITCZ: Inter-Tropical Convergence ZoneDoldrumsHorse LatitudesTropical EasterliesMid-latitude Westerlies, Polar EasterliesIV. Circulation of the Atmosphere5. General Circulation of the Atmosphered. Consequences of large-scale circulationDistribution of major deserts, dustDistribution of rainfallAverage zonal winds (Trades, Westerlies)III. Circulation of the Atmosphere6. Seasonal contrasts:• Because Earth’s axis is tilted relative to its orbit around the Sun, we have seasons.III. Circulation of the Atmosphere6. Seasonal contrasts:Maximum flux of solar radiation shifts north and south of the equator over the annual cycle. This exerts a powerful influence on atmospheric circulation, imparting a strong seasonal cycle over the large-scale patterns of atmospheric motion.III. Circulation of the Atmosphere6. Seasonal phenomenaa. TemperatureTied to the different properties of land vs ocean (just like our sea breeze analogy).•••AlbedoHeat capacityConvection (water) vs Conduction (solids) (Continentality: range of temperature during a seasonal cycle)III. Circulation of the Atmosphere 6. Seasonal phenomenaa. Temperature (Continentality: range of temperature during a seasonal cycle)Tropical regions and maritime regions (coastal) have low continentality.Mid-latitude large continents have high continentality.Poles are lower.III. Circulation of the Atmosphere6. Seasonal phenomenab. Hurricanes They are all the same thing(Atlantic)Typhoons in the PacificCyclones in the Southern HemisphereSAFFIR/SIMPSON DAMAGE POTENTIAL SCALECATEGORY WINDSPEED (MPH) PRESSURE (MB) SURGE (FT)1 74 – 95 > 980 4 - 52 96 – 110 965 – 979 6 - 83 111 - 130 945 – 964 9 - 124 131 - 155 920 - 944 13 - 185 > 155 < 920 > 18500 km15 kmIV. Circulation of the Atmosphere6. Seasonal phenomenab. Atlantic HurricanesHow and where do they start?IV. Circulation of the Atmosphere6. Seasonal contrastsb. Atlantic HurricanesStart: As small low pressure disturbances off AfricaRequire: •••Warm water (>26 °C)(High evaporation rates)Stable troposphere(to develop the spiral)Track that keeps them over warm waterTo provide “fuel” through the release of latent heat of condensationEvaporation