OCE 1001 Quiz 4 2 15 Lecture 18 Air Sea Interaction Recently satellites have been used successfully to measure the sea surface This requires detecting a signal of several cm s from a platform as much as displacement 1000km away Rings and Eddies o Dramatic examples of ocean storms o All major current systems o Move water biota salt heat o Long lived up to 3 years o Several types exist Subsurface lenses 10 000 in NA alone El Ni o o Subsurface eddies are possibly the dominant form of ocean variability o Global short term climate anomaly centered in Pacific o World wide effects on precipitation wildlife population temperatures increased forest fires in Indonesia o Societal problems caused by drought and flooding and collapse of food based industries Ex 1532 Incas and Pizarro o Examples of Economic Impact of El Ni o events Peru Anchovy fishery lost 90 of its catch Sea bird population plummeted guano production fell off These coupled with flooding caused considerable economic hardship in Peru Anchovy fish meal animal feed replaced by soybeans Soybean prices went up Meat chicken prices went up all over the world Philippines Drought conditions led to collapse of coconut industry Coconut prices went up Price of hand soap detergent went up o El Ni o is the oceanographic part of a coupled ocean atmosphere perturbation referred to as ENSO El Ni o southern oscillation La Nina o Trades excessive o Sea Surface extremes are enhanced Local Peru Conditions o Ekman transport seaward southern hemisphere o Upwelling North Atlantic Oscillation Offshore upper layer Ekman transport sets up an upwelling of deeper nutrient rich cool waters o El Ni o conditions Hot water cold water shift depressed thermocline Upwelling no longer brings up nutrients Food chain collapses El Ni o depression of thermocline can move along continent disrupt California fisheries weather o The dominant mode of winter climate variability in the North Atlantic region ranging from central North America to Europe and much into Northern Asia o Positive NAO index Shows a stronger than usual subtropical high pressure center and a deeper than normal Icelandic low The increased pressure difference results in more and stronger winter storms crossing the Atlantic Ocean on a more northerly track This results in warm and wet winters in Europe and in cold and dry winters in northern Canada and Greenland The eastern US experiences mild and wet winter conditions o Negative NAO index Shows a weak subtropical high and a weak Icelandic low The reduced pressure gradient results in fewer and weaker winter storms crossing on a more west east pathway They bring moist air into the Mediterranean and cold air to northern Europe The US east coast experiences more cold air outbreaks and hence snowy weather conditions Greenland will have milder winter temperatures Lecture 19 Tides What Causes tides o Caused by combination of Gravity of Moon and Sun Orbital motion o If earth had no continents and a deep ocean of uniform depth there would be two bulges of high tide one of each side o But why two Orbits are mutual o Moon and Earth orbit around a common point Barycenter o Closer to Earth s center because Earth is more massive Gravitational force of moon o Gravity is stronger closer to the moon zenith o Gravity is weaker farther from the Moon nadir o Centripetal center seeking force required to keep orbit stable is constant o At most points on Earth Moon s gravity does not equal the force required for orbit o Resultant force is the difference between these o Across the whole earth they balance each other So the orbit stays stable o But at individual points they create tides o Tide generating forces are the components of the resultant force which are parallel to Earth s surface o This pushes water toward the zenith and nadir and creates a tidal bulge on each side Tides from the Sun and Moon o Tidal bulge from moon is bigger o But the sun creates a bulge too o These interact to produce different tide strengths o Full or new moon Sun earth and moon aligned syzygy Tidal bulges add up Stronger cycle o Quarter moon Sun earth and moon at right angles quadrature Tidal bulges partially cancel Weaker cycle o The Earth is tilted Sun and moon are not directly above the equator Angle of tilt declination Tilt means that tidal bulge is at an angle Very high tides alternate with moderately high tides o Orbits are elliptical Tides are stronger when Earth is closer to the Moon or Sun o Tides are extreme shallow water waves meaning that their length is much longer than the ocean is deep o This means they can t move fast enough to keep up with Earth s rotation o Even if the oceans were deep enough tides would still be slowed by friction and blocked by continents So the tidal bulges don t literally exist They are instead broken into smaller cells In each cell tide waves rotate around an amphidromic point This rotation is usually o Counterclockwise in N hemisphere o Clockwise in S hemisphere In summary tides are complex o Tides are influenced by about 400 different factors o Cannot be predicted purely mathematically o Observations are necessary to model them Effect of Continents o Two main factors of continents influence tides Coastline shape Offshore depth o Shallower waters amplify tides Tidal Patterns o Diurnal Common in shallow inland marginal seas e g Gulf of Mexico o Semidiurnal Common along Atlantic coast of North America o Mixed Most common Coastal Tidal Currents o Rotary currents Move in a circle in a tidal cell In open ocean little friction In restricted channels where there is friction these produce o Reversing currents Flood current Water rushes into a bay or river or estuary before high tide Ebb current Water rushes out before low tide Tidal Bores Whirlpools o In extreme cases flood currents are very sudden o Occur in narrow straits between two bodies of water with different Fish that breed on beaches using tides tidal cycles o Grunion Tides as a Renewable Energy Source o Dams with turbines o Underwater windmills o Disadvantages Only run a few times a day Disturb wildlife Tides Summary o Idealized Tidal Bulges Moon and sun s gravity creates two tidal bulges on each side of Earth Moon s effect is stronger Earth s tilt places the tidal bulges at an angle Elliptical orbits cause variations in tidal strength During full or new moons tidal bulges from moon and sun line up creating stronger tides spring tides During half quarter moons tidal bulges from moon and sun are at
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