Phys. 102: Introduction to Astronomy
advertisement
SOAR 2005 Ocean Circulation and Heat Transport 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 Energy Transfer Convection – hot stuff moves Conduction – hot stuff heats neighbors Radiation – heat moves as IR radiation Properties of Water General properties Stable (hard to tear apart) Versatile solvent (universal solvent) Polar properties Give rise to surface tension Capillary action Responds to electric fields Solid floats in the liquid Ponds freeze on top, ice insulates water! Water most dense as liquid at 4C Heat Properties of Water High latent heats 1 calorie = 4.186 Joules High Heat Capacity High energy gain/loss to change temperature Energy Transfer by Water Specific Heat Energy absorbed or released to change temp. Raising 1 kg of water 1°C absorbs 4,168 Joules 1 kg 10 cm square cube of water Substance Specific Heat (Joule/K/kg) Air (50C) 1050 Iron or Steel 460 Lead 130 Glass 840 Quartz 762 Granite 804 Sandstone 1088 Shale 712 Soil (average) 1050 Wood (average) 1680 Ice 2100 Steam 2050 Water 4168 4000 Joules ≈ energy to lift 400 kg or 900 lb 1 m Energy Transfer by Water Latent Heat Specific Heat (Joule/kg) Energy absorbed or Substance released to change phase vaporization Evaporating 1 kg of water absorbs 2,257,000Joules 1 kg fusion Alcohol 879,000 109,000 Water 2,257,000 333,500 10 cm square cube of water 2,257,000 Joules ≈ energy to lift 225,700 kg or 507,000 lb 1 m Energy Transfer by Water Latent heat effects weather Evaporating water absorbs energy from water, cooling it. Condensing water releases energy to air, heating it. Energy Budget Insolation Sun’s incident energy drives air motions (energy from deep interior adds a tiny bit) Distribution of Sunlight Reflection from clouds, landscape Absorption by atmosphere Absorption by surface Albedo = ratio of sunlight reflected Earth: 0.367 Moon: 0.113 Mars: 0.15 Venus: 0.84 Insolation: 1,373 W/m2 Most solar energy comes in as light (shortwave radiation) 30% Reflected by atmosphere 20% Absorbed by atmosphere 50% Absorbed by Earth’s surface Energy Flow from Surface 7% conducted to air 23% transferred by water 20% radiated as IR (longwave) % of total insolation Energy Absorbed by Atmosphere % of total insolation 20% from Sun 7% conducted from surface 23% transferred by water 8% radiated by surface Complete Energy Budget Temperature Controls 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 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 Moist air rising stormy Dry air falling Arid Moist air rising stormy Dry air falling Arid Pressure Zones Pressure Zones: air motion is vertical so there is little wind! 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 Oceans’ Impact on Climate Most common compound on Earth Covers 71% of surface area Land area on Earth = surface on Mars 1.36 billion km3 (326 million mk3) 70% of us by weight Major constituent of most plants & animals Originated from Outgasing of Volcanos (continues) Bombardment by comets (much reduced) Present volume established 2 by ago Quantity in equilibrium Location of Water Southern Hemisphere Moderates climate Westerlies Easterlies Earth closest to sun in January (southern summer) Antarctica surrounded Strong winds, currents Isolates Antarctic High within “polar vortex” Traps CFC’s, Destroys ozone Pacific Ocean Covers ½ the Earth Navigated by Polynesians and Chinese in ancient times? Mosaic of Antarctica from Galileo spacecraft Location of Water Oceans 97.22% Pacific Atlantic Indian Arctic 48% 28% 20% 4% 4280 km 3930 3960 1205 Percentage of freshwater (14 kft) deep (13 kft) (13 kft) ( 4 kft) Percentage of surface water Properties of Water Present as solid, liquid, gas on Earth Gas & solid on Mars & most places Solid and liquid (?) on Europa Polar molecule H2O Oxygen 8 p+, 8 no, 8e- Hydrogen 1 p+, 1 e- e- tend to hang around Oxygen Making that side negative Surface Currents Mapped by rubber duckies, bottles World Surface Currents Driven by wind, Coriolis, continents Distribute heat from equator toward poles Surface Currents: Pacific Some flow into arctic ocean Oya Siwo: cold current soutward past Asia North Pacific Drift brings warm water eastward California current brings cold water south Kuro Siwo warm current to north Cold Peruvian current brings fish toward shore East Australian warm current to south West Wind Drift circles Antarctcia Surface Currents: Atlantic COLD Labrador current drives subsurface currents COLD Canaries current past Africa West Wind Drift dominates south Atlantic currents Gulf Stream feeds North Atlantic Drift, dominates north Atlantic currents Brazilian & Benguela currents circle south Atlantic Gyres: Circular Currents North Atlantic Gyre Turning and turning in the widening gyre The falcon cannot hear the falconer; Things fall apart; the centre cannot hold; William Butler Yeats, The Second Coming Gyres Circular currents Eckman transport “mounds” water pushes water to surface current Coriolis deflection balances gravity Sea Level isn’t level! Sea Level Sea level varies due to changes in local gravity (subsurface structure) currents (Eckman transport) Mean Sea Level Monitored by satellites Low Residuals = departure from normal High Click for Quicktime Movie of Sea surface height and temperature. Regional Surface Currents Equatorial Currents Drive upwelling in east, spreading in west Water deflects N & S due to continents & Coriolis Currents driven by trade winds Water leaving shore pulls water up from below: upwelling Regional Current Variations ENSO – El Niño Southern Oscillation Trade winds & equatorial currents slacken Normal trade winds push warm surface water to Asia allowing upwelling of cold, nutrient-rich, water near South America Slackened trade winds allow warm water to slosh east, stopping upwelling of nutrientrich water Currents & Ocean Life Nutrients compounds of nitrogen, silicon, phosphorous minerals carried by upwelling cold water Phytoplankton Fish food (bottom of the food chain) CO2 sink (absorb ½ Earth’s CO2) Some toxic (algae blooms, “red tides”) Fish Prefer living in warmer water Best fishing where cold & warm water meet! eg. The Outer Banks Trigger unknown Sea Surface Temperature monitored for signs of building El Niño 1997-98 El Niño building fading …… ENSO Regional Current Variations PDO – Pacific Decadal Oscillation Discovered in 1996 by Steven Hare researching connection between Alaska Salmon & Pacific climate Warm (+) = Warm equatorial waters In positive phase since April 2001 Cool (-) = Warm water at high latitudes Regional Current Variations PDO – Pacific Decadal Oscillation Currently in Positive phase (since April 2001) Fisheries in northeast pacific very productive Regional Current Variations Gulf Stream Keeps Europe warm!! Drives worldwide currents Deep Ocean Currents Thermohaline circulation Density of sea water increases with salinity decreases with temperature Cold, salty water sinks to bottom. Evaporation decreases water surface temperature increases salinity Gulf Stream Warm surface water gets colder and saltier than subsurface water. warm surface water evaporates in N. Atlantic cools, increases salinity ⇒ sinks to bottom North Atlantic Downwelling Gulf Stream Bring warm water north … keep Europe warm! Cools, salinates, sinks, pulling more north North Atlantic Downwelling Gulf stream waters sink to bottom Flow South along ocean bottom Drives Deep water circulation Deep Ocean Circulation Great Conveyor Belt moving HEAT circuit takes about 2000 years Deep Ocean Circulation Great Conveyor Belt moving HEAT circuit takes about 2000 years Deep Ocean Circulation Great Conveyor Belt moving HEAT circuit takes about 2000 years Ocean Conveyor Belt Can shut Down with too much fresh water Thermohaline Shutdown? 13,400 years ago Lake Iroquois drained through lake Champlain and Hudson Valley into Atlantic Jeffrey Donnelly, WHOI, December 2004, “Catastrophic Flooding from Ancient Lake May Have Triggered Cold Period ” Thermohaline Shutdown? 13,300 years ago Lake Candona formed from remnant of Lake Iroquois Jeffrey Donnelly, WHOI, December 2004, “Catastrophic Flooding from Ancient Lake May Have Triggered Cold Period ” Thermohaline Shutdown? 13,100 years ago Lake Candona increases as glacier continues retreating Jeffrey Donnelly, WHOI, December 2004, “Catastrophic Flooding from Ancient Lake May Have Triggered Cold Period ” Thermohaline Shutdown? 13,000 years ago Lake Candona drains through St. Lawrence Valley, seawater intrudes as Champlain Sea Jeffrey Donnelly, WHOI, December 2004, “Catastrophic Flooding from Ancient Lake May Have Triggered Cold Period ” Thermohaline Shutdown Gulf Stream stops warming Europe Europe cools dramatically Lake Iroquois draining through Hudson Valley: Intra-Alleroid Cold Period Lake Candona draining through St. Lawrence Valley: Younger Dryas Ocean Changes Temperature rising Cause of more and more powerful hurricanes? The oceans have absorbed about 30 times more heat than the atmosphere since 1955 Oceans Atmosphere 18.2 x 1022 J 6.6 x 1021 J Curry, WHOI, OCCI Ocean Changes Salinity Decreasing in north Atlantic cf. Curry, WHOI, OCCI Salinity Ocean Changes Decreasing at high latitude Increasing at low latitude “ … deep waters have become less salty in critical North Atlantic locations, where salty, dense waters sink to drive the global ocean circulation system... ” Salinity Ocean Changes Decreasing at high latitude Increasing at low latitude “Global warming may be intensifying evaporation, adding more fresh water vapor to the atmosphere and leaving tropical oceans relatively saltier.”
