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Download Phys. 102: Introduction to Astronomy
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SOAR 2007 Earth’s Atmosphere and Wind Course Outline Course Outline Atmospheric structure, pressure & wind Oceanic Circulation Energy transfer & circulation Past Climates Global Climate Change Origin of Planets Coalescence of matter in circumsolar cloud Many Craters Collisions heat! Molten interior Interior layered Denser materials sink to center Core mostly Iron (Fe) & Nickle (Ni) Crust mostly rocky (CaCO3, SiO2, etc) Planetary Atmospheres Form from Gases from planet’s interior (volcanoes) Gases from impacts (planets) Terrestrial Planets Mercury – none Venus CO2 with H2SO4 clouds Mars – CO2 with H2O clouds Earth – N2 with O2 Jupiter & Saturn – H with NH3 clouds Galilean moons – traces Titan – N2 with CH4 Uranus & Neptune – H with CH4 clouds Planetary Atmospheres Escape Velocity R from center Molecular Speed & Temp 1 2 3 mvavg kT 2 2 3kT v m avg k 1.381023J Radius (kg) (km) lb m/s 1000 mph SOL 2E+30 695990 4196 617439 1,381 MERCURY 3E+23 2440 57 4248 9.5 VENUS 5E+24 6052 136 10358 23 EARTH 6E+24 6378 150 11174 25 Luna 7E+22 1737 25 2376 5.3 MARS 6E+23 3397 57 5017 11 JUPITER 2E+27 71492 380 59524 133 Io 9E+22 1820 28 2557 5.7 Europa 5E+22 1570 20 2034 4.6 Ganymede 1E+23 2630 22 2749 6.1 Callisto 1E+23 2400 19 2450 5.5 SATURN 6E+26 60268 160 35473 79 Titan 1E+23 2670 19 2597 5.8 NAME 2GM planet vescape or Mass Weight of 150 lb person K Boltzmann' s Constant Escape Speed Planetary Atmospheres Presence & size due to combination of Temperature = Distance from Sol Size of world = escape velocity Large worlds Keep atmospheres even close to Sol Small worlds Only have atmospheres far from Sol Composition due to Size of world 2 GM world mmolecule TEscape 3 R world k Large worlds keep small molecules (H) Small worlds keep large molecules (N2, O2, CO2) Mercury Inner Planets Small, hot no atmosphere stays Venus Large, hot thick atmosphere NO WATER H2O H2 + O that binds with C, S, etc CO2 + H2S04 Clouds Run-away greenhouse effect Mars Small, cool thin atmosphere & thinning Evidence of ancient oceans but water now present only as solid and gas CO2 + H2O Clouds, fogs Mars & Venus Both primarily CO2 but very different! Mars 95.3% CO2 Venus 96.5% CO2 250K – 273K = -23ºC = -10ºF 750K – 273K = 477ºC = 890ºF Venus: Greenhouse gone wild! Interaction with Sunlight Sky is blue because blue scatters, red doesn’t Earth Complex atmospheric evolution Primordial Atmosphere Lost to space H & He very light molecules, escape easily Initially like Venus & Mars: mostly CO2 THEN Water condensed into oceans Oceans absorbed CO2 Locked it into rocks (CaCO3 = limestone) Life flourished in oceans Released free oxygen Sedimentary rocks turned red Ozone layer formed Evolution of Earth’s Atmosphere Oxygen content created, maintained by life. Atmospheric Structure Layers (from surface) due to Density (Pressure) Radiation Environment Temperature Atmospheric Structure Layers (from surface) Troposphere – sphere of weather Stratosphere – sphere of ozone (O3) Mesosphere Ionosphere – sphere of ions Atmospheric Structure Layers By Function Ozonosphere (O3 layer) Upper portion of Stratosphere Absorbs UV (0.1-0.3 nm), radiates IR Ozone constantly created Warmest layer in & destroyed by UV, atmosphere CFC’s increase destruction Harmed by CFC’s Cl + 2O3 Cl + 3O2 … and Cl is free to kill again! Hole in the ozone layer over Antarctica Atmospheric Structure Layers By Function Ionosphere Thermosphere & Mesosphere Ionized particles (UV + atoms ions + e- + energy Absorbs -rays, x-rays, UV, cosmic rays Reflects AM radio waves Importance of Wind Arises due to differences in pressure Force Newtons Pascal Pa P 2 Area (meter ) Distributes heat moisture dust pollutants microscopic life Air Pressure Pressure is force/area = weight of air column 1 in2 column weight = 14.7 lb 1 m2 column weight = 10 tonnes 1 tonne = 1000 kg = 2204 lb Why doesn’t the air pressure crush you when you lie down? Air Pressure Standard Atmosphere 760 mm Hg 29.92 in Hg 33.9 ft. H2O 1013 millibars (mb) 1013 hPa hectopascals Weight of Hg = Weight of Air Hg(tube area)(column height) = (air presure)(bowl area) Weight of column of Hg Weight of column of air Varies with Air Pressure altitude (in Pa, H in m) H log10 P 5 15500 air motion rising air = low pressure subsiding air = high pressure moving air is at lower pressure than still (or slower moving air … wind pulls curtains against window screen & airplane wings up! Air Motion Updrafts – upward motion of air Downdrafts – downward motion of air Wind Horizontal motion of air across Earth’s surface (advection) Measured by anemometers 1 knot = 1 nautical mile/hour = (1 minute of latitude)/hour = 1.852 kph = 1.15 mph Speed and Direction recorded Driving Forces Gravitational Force Earth’s gravity holds atmosphere TEscape 2 GMworld mmolecule 3 Rworld k Pressure Gradient force isobar = line of constant pressure Pressure Gradient force acts perpendicular Importance of Wind Only a difference in pressure makes air move. Driving Forces Pressure Gradient force Indicated by density of isobars Driving Forces Pressure Gradient force Indicated by of isobars 18 hPa across density ~400 km North America & Greenland, February 6, 18Z (1 pm EST) Driving forces Pressure Gradient force from high pressure to low pressure Driving Forces Coriolis Force Acts ONLY ON MOVINGr objects r proportional to velocity ( F v ) perpendicular to velocity acts over large distances force velocity Does not determine direction water spins down a drain! The rolling ball follows a straight path seen from above, a curved path seen from the rotating reference frame (riding on the merry-go-round). Different latitudes “orbit” axis at different speeds. Projectile carries small speed, falls behind high speed equator. Coriolis Force Coriolis Force All moving objects are deflected to their right in northern hemisphere to their left in southern hemisphere Coriolis force deflects velocity no matter what the original direction of the velocity! Coriolis Force: All moving objects are deflected to their right in northern hemisphere to their left in southern hemisphere Coriolis Force Northern Hemisphere Southern Hemisphere Moving objects deflected to their own right. Moving objects deflected to their own left. Tropical Cyclone Olyvia L L Hurricane Isabel Storms rotate counterclockwise Storms rotate clockwise Cyclones & Anticyclones Cyclone – circulation around low pressure CCW in northern hemisphere CW in southern hemispere Anticyclone – circ. around high pressure CW in northern hemisphere CCW in southern hemisphere http://www.usatoday.com/weather/tg/whighlow/whighlow.htm Driving Forces Friction Friction with ground slows wind Extends upward ~ 500 m Varies with surface, time Surface air slows air aloft Friction with ground slows wind Geostrophic Winds Pressure Gradient Force creates wind ⊥ to isobars Coriolis Force deflects motion to right in N. hemisphere ⇒ deflects Coriolis force! Forces Wind deflects due to Balance Isobars Coriolis force Pressure Coriolis Gradient force Coriolis force acts perpendicular to new force wind direction wind velocity wind along isobar Geostrophic Winds Pressure Gradient Force creates wind ⊥ to isobars Coriolis Force deflects motion to its right in N. hemisphere to its left in S. hemisphere aligns wind with isobars Surface Winds: Not Geostrophic Friction slows winds at surface Reduces Coriolis force Pressure Gradient force dominates Convection Cells Sunlight heats land, water, air Land warms, heats air Air circulates Convection cells warms -> expands -> rises cools -> contracts -> sinks Water circulates Currents driven by wind & Earth rotation Water temperature increases SLOWLY Large energy change needed for small temp. change Convection Cells Hot surface heats air Air expands, becomes less dense than surroundings rises, spreads out at top Air aloft cools, becomes more dense than surroundings sinks, spreads out on surface Atmospheric Circulaton Rising Air Cools Water vapor condenses (usually) results in clouds Lowers surface pressure Atmospheric Circulaton Falling Air Warms DRY (lost mosture rising) Increases surface pressure Atmospheric Circulation Sunlight heats ground Ground heats air , drives convection from subsolar latitude Subsolar latitude is 0º on the equinoxes Maximum Insolation Subsolar latitude is 23.5º N/S on the solstices Atmospheric Circulaton Air rises from subsolar latitude, clouds form & precipitate, air aloft moves N & S, cools, dries & sinks at about 30º N &S Driven by heating near equator Dry air falling Arid Moist air rising humid Air spreads N & S on surface Air aloft cools until it sinks Atmospheric Circulaton Cold, dry air falling Arid Air warms and moistens along surface Air from aloft sinks near poles, moves N & S along surface Driven by cooling near poles Surface flows converge, rise Dry air falling Arid Moist air rising humid Moist air rising stormy Dry air falling Arid Moist air rising stormy Dry air falling Arid InterTropical Convergence Zone Rising Air: Low Pressure Pressure Zones Pressure Zones Falling Air: High Pressure Pressure Zones Pressure Zones: air motion is vertical so there is little wind! Wind Zones Winds: Falling air spreads North & South along surface. But the winds don’t go straight! Winds named for direction they are from Windless zones names vary Wind Zones Easterlies Polar Front Westerlies Horse Latitudes NE Trades Doldrums SE Trades Horse Latitudes Westerlies Polar Front Easterlies General Atmospheric Circulation ITCZ STHPC Polar High Polar Easterlies Doldrums Polar Front Horse Latitudes Cross sectional view Westerlies Easterly Trades World Pressure Cells: January North American High H Aleutian Low Islandic Low Siberian High Parallel isobars over (low friction) ocean ⇒ rippin’ winds!!! World Pressure Cells: July Hurricane Azores High paths! Tibetan Low Monsoon Winds Parallel isobars over (low friction) ocean ⇒ rippin’ winds!!! Upper Atmospheric Winds Jet Streams: Fast Winds Aloft Polar Jet Stream Above Polar Front (midlatitude air meets polar) Rossby waves move loops north & south 7,600 – 10,700 m (25-35 kf) speeds up to 300 kph (190 mph) Upper Atmospheric Winds Jet Streams: Fast Winds Aloft Subtropical Jet Stream above Subtropical highs (tropical air meets midlatitude) 9,100 – 13,700 m (30-35 thousand feet) speeds less than Polar Jet Stream Polar Jet Stream Determines N.Am. winter weather Strong west wind monitored by weather balloons Check out PBS’s explanation!: www.pbs.org/wgbh/nova/vanished/jetstream.html Polar Jet Stream Determines N.Am. winter weather Rossby waves bring cold air south
