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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
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•
•
•
•
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