Post on 17-Dec-2015
Currents, Waves, & TidesHighways in the Sea
What forces are responsible for currents? Wind: transfers energy through friction on
surface; causes currents and waves Sea level: steeper slope=greater pressure
gradient=drives a larger, faster current Water density: greater density in one area
causes pressure gradient to drive a current below the surface
Causes of Currents
What influences the direction and nature of these currents?- Ocean boundaries force currents in various
directions; - Trade winds and the westerlies account
for most of the wind’s energy that drives currents
Causes of Currents
How do Western Boundary Currents differ from Eastern Boundary Currents?- Eastern Currents: carry cool water towards
equator; tend to be wide and shallow; not common to have eddies spin off these currents
- Western Currents: much stronger; western intensification: Coriolis effect is a major contributor; Trade winds also contribute to the strong western currents
Western VS Eastern
Wind-driven currents that flow vertically Upwelling: upward vertical current that
brings deep water to the surface Downwelling: downward vertical current
that pushes surface water deep into the ocean
What kind of biological effect does this have?-nutrients to shallow waters and to deeper waters-weather patterns
Upwellings & Downwellings
Buildup of warm water in the Central and Eastern Equatorial Pacific
Tremendously affects world weather patterns
El Niño = warm surface current in equatorial eastern Pacific that occurs periodically around Christmastime
El Nino
Powerful upwellings bring deep cooler waters to the surface
This colder than normal condition is called La Nina (opposite of El Nino)
Scientists still trying to determine what exactly causes these warm and cold phases
La Nina
The interconnected flow of currents that redistribute heat
Earth’s “air conditioner” Moderates the world’s climateOcean Conveyor Belt Animation:http://bcs.whfreeman.com/thelifewire/content/chp58/5802003.html
Ocean Conveyor Belt
1. Drogue: float that determines the drift of currents2. Argo Float: float that transmits data to satellites 3. Various Flow Meters: measure and record current
speed and direction (Eulerian study method)4. Doppler Acoustic Current Meter: determines
current direction and speed5. Flotsam method: accidental opportunities to study
currents; ships losing cargo that wash up on beaches and can improve computer models of currents
How do we study currents?
Waves & Tides
What is a wave?-Transmission of energy through matter; matter moves back and forth or rotates, but then returns to its original position Three types of progressive waves:1) Longitudinal: when matter moves back and forth in same
direction energy travels2) Transverse: motion of matter is perpendicular to the
direction in which the whole wave is moving3) Orbital: transmit through fluids only; main waves that
concern us with respect to the ocean; energy moves fluid in a circular motion
Anatomy of a Wave
Wavelength: measured as horizontal distance between identical points on two waves; crest to crest
Crest: highest point above the avg water level Trough: lowest point Height: vertical distance from the trough to the crest Period: time it takes for the same spot on two waves
to pass a single point Frequency: number of waves that pass a fixed point
in one second
Wave Terms:
Disturbing forces (cause waves):1. Winds (most common)2. Changes in gravity3. Seismic activity: eartquakes and volcanic eruptions
(tsunamis) Restoring forces (resist waves):1. Gravity (main force here for large waves)2. Coriolis Effect: good for resisting tides3. Surface tension: resists surface distrubances in
tiny waves
Forces that Cause Waves
Deepwater Waves:- Occur in water that is deeper than half their wavelength- No interaction with the bottom floor can change any
wave characteristics- The orbital motion progression is also unaffected Shallow-water Waves:- Occur in water that is shallower than one-fourth the
wavelength- Bottom creates a drag that affects the orbital motion- Flattens the circular motion Both can exist at the same time!
Deep Waves VS Shallow Waves
Refraction: bending of light rays; bend the ocean waves as well when waves begin to approach the ocean shore at an angle
Diffraction: occurs when waves pass an obstacle, like a jetty; energy shift within a wave, allowing a new wave pattern to form
Reflection: occurs when waves hit an abrupt obstacle that is nearly perpendicular in the water, like a sea wall; in this case, the wave retains much of its energy and bounces back towards open waters
Refraction, Diffraction, Deflection
What causes a storm surge?- This is a destructive wave that forms when high
winds push water against the shore, where it piles up What causes seiches?- This is a form of standing wave that can be destructive;
result from a strong wind that pushes the water level up on one side of a lake or basin
What causes tsunamis? -results from sudden water displacement caused by a landslide, an iceberg falling into sea from a glacier, a volcanic eruption, or an earthquake (most common)
Destructive Waves
TIDES
Tides: variations in the ocean’s level Result from the gravitational pull of the moon and
(to a lesser degree) the sun They pull the ocean into a huge wave with a wave
length the size of an ocean basin Sun and moon create two bulges on opposite sides
of the Earth; position of the sun and moon change slowly, causing the bulge to rotate around the Earth
As a coastline rotates into the bulge, the tide rises; as it rotates out, the tide falls
What causes Tides?
The imperfect sphere of the Earth The season Time of the month The shape of the ocean basin Coriolis effect
What influences besides lunar and solar gravity affect the tides?
Diurnal: single high and low tide that occurs daily in certain locations; Gulf of Mexico
Semidiurnal: have two roughly equal high and low tides daily; happens on east coast of US
Mixed: consists of two unequal high and low tides daily; happens in Pacific coast of the US
Types of tides: vary with location
The influence of the moon on the tides is about twice the influence of the sun
1) Spring Tides: when the sun and the moon are aligned on the same side of Earth (new moon) AND when the sun and moon are aligned on opposite sides of Earth (full moon)
2) Neap Tides: when the sun’s gravitation pulls to the side of the moon’s tidal bulge and tends to raise low tides and lower the high tide
Sun, Moon, and Types of Tides