lecutre16_oceanII - OCEANS II tides and currents GEO 1111...

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OCEANS II – tides and currents GEO 1111 – Introduction to Earth Systems Lecture 16
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Key terms tides spring and neap tides semi-diurnal, diurnal, and mixed tides tidal range tidal currents flood currents bb t ebb currents slack water tidal bore Coriolis force surface and deep-water ocean currents Ekman spiral and transport upwelling and downwelling ENSO (El Niño, La Niña) th h li i l ti ( i t b lt i l ti ) GEO 1111 – Introduction to Earth Systems Lecture 16 thermohaline circulation (giant conveyor belt circulation)
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Outline Today: 1. WAVES (cont’d – Tsunamis) 2. TIDES 3. OCEAN CURRENTS GEO 1111 – Introduction to Earth Systems Lecture 16
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TIDES Is this person safe? GEO 1111 – Introduction to Earth Systems Lecture 16 Mont St-Michel, France
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What are tides and what causes them? O tid it ti l Tides : periodic rise and fall of the ocean Ocean tides gravitational attraction of MOON and SUN Gravitational attraction: • F G 1 / km 2 • Moon tides = 2x Sun tides M d E th 28 d Moon around Earth: 28 days Earth around itself: 24 hours GEO 1111 – Introduction to Earth Systems Lecture 16 - Moon dominates gravitational force over Earth compared to Sun due to closer distance (km^2 is important) -centrifigal force - due to the fact that the earth revolves throughout the day - pulling outwards - closest side has more gravitational forces acting on it
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What are tides and what causes them? tides intensit thro gh a l nar c cle NEAP SPRING TIDES: highest high tides and tides intensity through a lunar cycle lowest low tides ; Sun and Moon _______ (add up) NEAP TIDES: lowest high tide and highest low tide ; Sun and Moon ______ one another SPRING GEO 1111 – Introduction to Earth Systems Lecture 16 * animation 2 crests, 2 troughs - within a period of 28 days - moon cycle maximized tidal range is working against working together - aligned (at 90 degree angle)
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Tides are waves Tides vs. wave classification • Longest T wave; 12h & 24h • SHALLOW- (depth < λ /20) or DEEP-water wave (depth > λ /2)? SHALLOW (depth < /20) or DEEP water wave (depth > λ ~ 20 000 km depth ave ocean ~ 4 km depth ~ λ /5000 Consequence : all ocean bottoms feel effects of tides F d • Forced wave C = 1600 km/h (at Equator) GEO 1111 – Introduction to Earth Systems Lecture 16 Classification of waves according to wave-forming and restoring FORCES - have the longest period at these time - tides are shallow - ocean waves- ocean floor will feel the passage of the wave
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Types of tides How many high tides are to be expected in a period of 24hrs? Semi-diurnal tides: 2 high tides and 2 low tides / day But also … Diurnal tides: 1 high tide and 1 low tide / day Mixed tides: semi-diurnal signal modulated by a diurnal signal. Why? GEO 1111 – Introduction to Earth Systems Lecture 16 - in a perfect world...
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Types of tides M f id l b l i i d b l d d f i i b Mvt of tidal bulges impaired by landmasses and friction at ocean bottom break up into cells rotate around a point (amphidromic point - AP) • AP AP GEO 1111 – Introduction to Earth Systems Lecture 16 different cells - that go around the dot
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Types of tides
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