waves, tides, ENSO

Tides

Longest of all ocean waves, caused by the gravitational force of the moon, sun and motion of earth, wavelength of tides half the circumference of earth, forced waves as they are never free of the forces that cause them

Equilibrium theory of tides

If the planet is not moving, gravity will pull it into the sun,
Planet moving, inertia keeps it in a straight line,
In a stable orbit, gravity, and inertia together cause a fixed travel path

Moon orbiting the earth

Rotates around a common center of mass around 1650 km beneath earth’s surface

Movement of the moon and earth generate…

Strong tractive force, caused bulges that oppose and face the moon. inertia and gravity create two tidal bulges

Tides result from…

Between gravitational attraction and inertia, forces exceed eachother at different points causing two tidal bulges, forces only balanced at the center of earth

Semi-diurnal tide

Twice per lunar day, a lunar day is earth rotating on its axis and the moon orbiting the earth, dragging the tidal bulges around it

Moons orbit is at an angle to the …

Equatorial plane

Diurnal

Once per lunar day

Spring tides

At new and full moons the solar and lunar tides reinforce each other making spring tides, highest high and lowest lows

Neap tides

At first and third-quarter moons, the sun earth and moon form a right angle, lowest high and highest low

Equilibrium theory of tides

Combination of the gravitational force of the moon and sun, plus the motion of earth and motion relative to each other

Dynamic theory of tides

Characteristics of ocean tides based on celestial mechanics and the physics of fluid motion

Amphidromic points

Nodes at the center of ocean basins, no tide points

Three main types of tides

Mixed tide= LA, California
Diurnal tide= Mobile, Alabama
Semidiurnal tide= Cape Cod, Massachusetts

Antartic bottom water

Very dense cold water, Sits on the bottom, fresh water is frozen causing brine rejection creating very salty water, Antarctic winds cause cold water

North Atlantic deep water

Loses heat due to conduction, becomes sufficiently dense that it sinks, spreads at about 3000-4000m when becoming neutrally buoyant

Mediterranean outflow

Sea has huge amounts of evaporation creating very salty warm water, Cascades out at 1000m and will not settles due to water temp, very little circulation due to Gilbralter sill preventing lots of inflow

Thermohaline circulation

Driven by differences in salinity and Temp, deep flow can return via upwelling and mixing, time >150000 years

Tao array

Automaous monitoring system to sense El Nino effects

Tritium

No natural sources, radio isotopes, added in 1980 -1970 due to weapons development and testing, shows downwelling and circulation

La nina effects

Stronger trade winds, exaggeration of normal

El nino conditions

west to east convection currents, cold and upwelling in west, trade wind either weaken or switch direction, warm phase, El Nino southern oscillation

Normal years

East pacific cold and Upwelling, downwelling in west, east to west convection currents, transverse convection currents, western pacific warm, no Coriolis force

El Nino effects

Rainfall in east when usually dry, drought in west, Nz colder winter

La nina effects in NZ

Light winds, extreme warming of upper ocean, marine heatwaves, drought

Progressive waves

Waves of moving energy where the wave moves in one direction, move energy not mass

Wavelength

Horizontal distance between two wave crests. after one period a wave moves 1 wavelength

Period

Time required for a crest a point A to reach point B

Speed of a wave equation

Crest speed= wavelength/period

What factors influence wind wave development

Wind strength: wind must be moving faster than the wave crest for energy transfer
Wind duration: winds the blow for a short time will not generate large waves
Fetch: uninterrupted distance where the wind blows without changing direction

Where are the largest waves

Drakes passage, near infinite fetch, no interrupting land, longest storms and winds

Wave dispersion

Longer wave lengths travel faster than shorter ones, causes separation of waves based on lengths

Tsunami generation sources

Underwater and terrestrial landslides, volcanic eruptions or collapse, meteor strike, vertical movement of seafloor due to earthquakes

What are tsunamis

SHALLOW WATER WAVES