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Oceans II Surface Currents Heat Variations Latitude • Depends on angle sunlight hits surface – Sunlight at polar latitudes covers wider area; therefore, less heat – At equator, sunlight covers less area; more heat Heat Transfer • Heat is transferred from equator to poles – Air Circulation – Ocean currents Origin of Currents • Ocean surface currents are wind driven • Air movement due to less dense air rising and more dense air sinking • Horizontal air flow along Earth’s surface is wind • Air circulating in this manner is convection currents Wind Movement Non-rotating Earth • Simple wind pattern – Warm air rises at equator, flows toward poles – Air cools at poles, sinks, and flows toward equator • Winds named by direction from which they blow – North-blowing winds = southerly winds – South-blowing winds = northerly winds Wind Movement Rotating Earth • At equator, warm air rises – Zone of low pressure – Clouds and precipitation – Reaches troposphere and moves poleward – As it spreads, it cools • 30° N&S, cool air sinks – Area of high pressure – Dry conditions – Location of world deserts • 60° N&S, air masses meet – Form Polar Front – Air masses rise, diverge and sink @ 90° and 30° N&S Wind Movement • At equator, warm air rises, condenses and precipitates • At 30° and 90°, cool air sinks • Air that sinks does not flow back in a straight north-south path – it curves (Coriolis Effect) Rotation on a Globe • Buffalo and Quito located on same line of longitude (79ºW) • Both cities circles the globe in one day (360º/24 hours = 15º/1 hour) • Quito has larger circumference; thus, travels farther • Quito needs to travel faster than Buffalo Apparent Deflection • Hypothetical war game • If a cannonball is shot north from Quito • It will travel a straight path • But, because Earth is rotating east to west • The cannonball appears to veer to the right in Northern Hemisphere • This is the Coriolis Effect Wind Movement Coriolis Effect • Deflected winds due to movement over spinning object – Produce wind bands • In Northern Hemisphere: – Winds are deflected to the right – Travel clockwise around high P • In Southern Hemisphere: – Winds are deflected to the left – Travel counter-clockwise around high P Assume water-covered Earth Surface Current Circulation Waves • Transport energy over a body of water Wave Terminology Still water Height line • • • • • Still water line – level of ocean if it were flat w/o waves Crest – highest part of wave Trough – lowest part of wave Wave height (H) – vertical distance between crest and trough Amplitude – distance between crest and still water line – ½ the wave height • Wavelength (L) – horizontal distance from each crest or each trough – Or any point with the same successive point • Steepness = Height (H)/length (L) Wave Parameters • Period (T) – the time it takes for two successive waves to pass a particular point • Frequency (f) – the # of waves that pass a particular point in any given time period Deep Water Wave Motion • Waves transmit energy, not water mass • Water particles move in orbits • Diameter of orbits decrease with depth • Particle motion ceases at ½ wavelength Shallow Water Waves 1. Swell feels bottom at depth < ½ wavelength 2. Wave crest peaks and wave slows 3. Orbits progressively flatten at depth 4. Wave height (H) increases and wavelength (L) decreases 5. Wave breaks when H/L ratio > 1/7 6. Just above seafloor particles move in back-and-forth motion Breaking Waves Tsunami Characteristics • Energy passes through entire water column • Long periods (T) – T = 10-20 min. • Small Height (H) – H = 1-2 m • long wavelengths (L) – L = 100-200 km • Shallow water wave • Deep wave base • Travel at great speeds – c = 200 m/s Tsunami Crest and Trough