SOAR 2007 Ocean Circulation Coriolis Force All moving

SOAR 2007 Ocean Circulation

Coriolis Force: All moving objects are deflected to their right in northern hemisphere to their left in southern hemisphere

Coriolis Force üNorthern Hemisphere üSouthern Hemisphere þMoving objects deflected to their own right. þMoving objects deflected to their own left. Tropical Cyclone Olyvia L L Hurricane Isabel Storms rotate counterclockwise Storms rotate clockwise

Temperature Controls ü Sunlight heats land, water, air þ Land warms, heats air þ Air circulates ý Convection cells Ö warms -> expands -> rises Ö cools -> contracts -> sinks þ Water circulates ý Currents driven by wind & Earth rotation ý Water temperature increases SLOWLY Ö Large energy change needed for small temp. change

Atmospheric Circulation üSunlight heats ground üGround 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

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

Wind Zones Nice Pattern … But the continents and oceans mess it up! Easterlies Polar Front Westerlies Horse Latitudes NE Trades Doldrums SE Trades Horse Latitudes Westerlies Polar Front Easterlies

Earth’s Oceans ü Most common compound on Earth þ Covers 71% of surface area ý Land area on Earth = surface on Mars ý 1. 36 billion km 3 (326 million mk 3) þ 70% of us by weight ý Major constituent of most plants & animals ü Originated from þ Outgasing of Volcanos (continues) þ Bombardment by comets (much reduced) þ Present volume established 2 by ago ý Quantity in equilibrium

Location of Water ü Southern Hemisphere þ Moderates climate Westerlies Easterlies ý Earth closest to sun in January (southern summer) þ Antarctica surrounded ý Strong winds, currents ý Isolates Antarctic High Ö within “polar vortex” Ö Traps CFC’s, Destroys ozone ü Pacific Ocean þ Covers ½ the Earth ý Navigated by Polynesians and Chinese in ancient times? Mosaic of Antarctica from Galileo spacecraft

Location of Water ü Oceans 97. 22% þ Pacific þ Atlantic þ Indian þ Arctic 48% 4280 km (14 kft) deep 28% 3930 (13 kft) 20% 3960 (13 kft) 4% 1205 ( 4 kft) Percentage of freshwater Percentage of surface water

Surface Currents Move Heat ü Mapped by rubber duckies, bottles

World Surface Currents ü Driven by wind, Coriolis, continents ü Distribute heat from equator toward poles

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 ü Circular currents ü Eckman transport “mounds” water þ pushes water to surface current þ Coriolis deflection balances gravity Sea Level isn’t level!

Sea Level ü Sea level varies due to þ changes in local gravity (subsurface structure) þ currents (Eckman transport) ü Mean Sea Level þ Monitored by satellites Low Residuals = departure from normal High Click for Quicktime Movie of Sea surface height and temperature.

Surface Currents: Pacific Some flow into arctic ocean Oya Siwo: cold current soutward past Asia North Pacific Drift brings warm water eastward Kuro Siwo warm current to north California current brings cold water south East Australian warm current to south Cold Peruvian current brings fish toward shore 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

Regional Surface Currents ü Equatorial Currents þ 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 ü ENSO – El Niño Southern Oscillation þ 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

Trigger unknown Sea Surface Temperature monitored for signs of building El Niño 1997 -98 El Niño building fading …… ENSO

Currents & Ocean Life ü Nutrients þ compounds of nitrogen, silicon, phosphorous minerals carried by upwelling cold water ü Phytoplankton þ Fish food (bottom of the food chain) þ CO 2 sink (absorb ½ Earth’s CO 2) þ Some toxic (algae blooms, “red tides”) ü Fish þ Prefer living in warmer water ü Best fishing where cold & warm water meet! þ eg. The Outer Banks

Regional Current Variations ü PDO – Pacific Decadal Oscillation þ Discovered in 1996 by Steven Hare researching connection between Alaska Salmon & Pacific climate þ Warm (+) = Warm equatorial waters In positive phase since April 2001 þ Cool (-) = Warm water at high latitudes

Regional Current Variations ü PDO – Pacific Decadal Oscillation þ Currently in Positive phase (since April 2001) ý Fisheries in northeast pacific very productive

Regional Current Variations ü Gulf Stream þ Keeps Europe warm!! þ Drives worldwide currents

Deep Ocean Currents ü Thermohaline circulation þ Density of sea water ý increases with salinity ý decreases with temperature Cold, salty water sinks to bottom. þ Evaporation ý decreases water surface temperature ý increases salinity þ Gulf Stream Warm surface water gets colder and saltier than subsurface water. ý warm surface water evaporates in N. Atlantic cools, increases salinity ⇒ sinks to bottom

North Atlantic Downwelling ü Gulf Stream þ Bring warm water north … keep Europe warm! þ Cools, salinates, sinks, pulling more north

North Atlantic Downwelling ü Gulf stream waters sink to bottom þ Flow South along ocean bottom þ Drives Deep water circulation

Deep Ocean Circulation ü Great Conveyor Belt moving HEAT þ circuit takes about 2000 years

Deep Ocean Circulation ü Great Conveyor Belt moving HEAT þ circuit takes about 2000 years

Ocean Conveyor Belt ü Can shut Down with too much fresh water 100 trillion m 3 = 100 x 1012 m 3 = 1014 m 3 x (1 km/1000 m)3 = 1014 m 3 x (1 km 3/109 m 3) = 105 km 3 100 trillion m 3 = 100, 000 km 3 = 24, 000 mi 3

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 ü Gulf Stream stops warming Europe þ Europe cools dramatically Lake Iroquois draining through Hudson Valley: Intra-Alleroid Cold Period Lake Candona draining through St. Lawrence Valley: Younger Dryas

Ocean Changes ü Temperature rising þ 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 ü Salinity þ Decreasing in north Atlantic cf. Curry, WHOI, OCCI

ü Salinity Ocean Changes þ Decreasing at high latitude þ 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. . . ”

ü Salinity Ocean Changes þ Decreasing at high latitude þ Increasing at low latitude “Global warming may be intensifying evaporation, adding more fresh water vapor to the atmosphere and leaving tropical oceans relatively saltier. ”

Regional Current Variations ü North Atlantic Oscillation þ Known since 19 th Century þ Positive ý strong Gulf Stream ý warm winter & spring in Scandinavia & E. US ý cool along east coast of Canada & west Greenland þ Negative ý dry in E. N. Am ý wet in S. Europe

NAO Mostly positive since mid 1970’s www. jisao. washington. edu

NAO ü Negative Phase mid 1950’s - 1970

NAO ü Mostly positive since mid-70’s

Ocean Variations ü Atlantic Multidecadal Oscillation þ Sea Surface Temperature in North Atlantic

Ocean Variations ü Atlantic Multidecadal Oscillation þ Correlates with numbers of major hurricanes … and southwestern droughts! Not perfect correlation … what else is going on?

Ocean Variations ü Atlantic Hurricanes & ENSO þ Number & Strength of hurricane increases with La Niña

Oceans’ Effects on Climate ü Absorbs & releases heat S L O W L Y þ moderates climates ý Ogdensburg has longer growing season than Potsdam! ý Potsdam has harsher climate than Venice þ moves heat around globe ý moves heat from equator to poles ý moves heat from surface to depths þ transfers heat to atmosphere ý evaporation absorbs heat ý condensation releases heat

Properties of Water ü General properties þ Stable (hard to tear apart) þ Versatile solvent (universal solvent) þ Polar properties ý Give rise to surface tension ý Capillary action ý Responds to electric fields ý Solid floats in the liquid Ö Ponds freeze on top, ice insulates water! Ö Water most dense as liquid at 4 C

Properties of Water ü Present as solid, liquid, gas on Earth þ Gas & solid on Mars & most places þ Solid and liquid (? ) on Europa ü Polar molecule H 2 O þ Oxygen ý 8 p+, 8 no, 8 e- þ Hydrogen ý 1 p+, 1 e - þ e- tend to hang around Oxygen Making that side negative

Heat Properties of Water ü High latent heats þ 1 calorie = 4. 186 Joules ü High Heat Capacity þ High energy gain/loss to change temperature

Energy Transfer by Water ü Specific Heat þ Energy absorbed or released to change temp. Raising 1 kg (1 l) of water 1°C absorbs 4, 168 Joules 1 kg 4000 Joules 10 cm square cube of water Substance Specific Heat (Joule/K/kg) Air (50 C) 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 ≈ energy to lift 400 kg or 900 lb 1 m

Energy Transfer by Water ü Latent Heat Specific Heat (Joule/kg) þ Energy absorbed or Substance released to change phase vaporization Evaporating 1 kg (1 l) of water absorbs 2, 257, 000 Joules 1 kg 2, 257, 000 Joules fusion Alcohol 879, 000 109, 000 Water 2, 257, 000 333, 500 10 cm square cube of water ≈ energy to lift 225, 700 kg or 507, 000 lb 1 m

Energy Transfer by Water ü Latent heat effects weather Evaporating water absorbs energy from water, cooling it. Condensing water releases energy to air, heating it.

Energy Transfer ü Convection – hot stuff moves ü Conduction – hot stuff heats neighbors ü Radiation – heat moves as IR radiation

Source Regions & Climate Prevailing winds over big continent (harsh climate) Prevailing winds over warm ocean (hot & humid) Prevailing winds over cold ocean (mild climate)

Surface Currents: Atlantic Prevailing winds over warm ocean (VERY mild climate) Prevailing winds over continent (harsh climate) Winter winds over BIG continent … dry Summer winds over warm ocean … monsoons! Prevailing winds over warm ocean (rainforest) Potsdam Venice