Waves and Oceanic Circulation Flashcards
Name the four general types of wave from lowest wavelength to highest
Wind waves - storm swell - storm surge - tsunami
What are Capillary waves
A wave travelling along the phase boundary of a fluid - dynamics are dominated by the effects of surface tension. These are ripples with a small wavelength.
What is a gravity capillary wave?
Influenced by both the effects of surface tension and gravity as well as fluid inertia.
How can wind waves be generated
The coalescence of capillary waves caused by the boundary forces from the wind - frictional transfer of energy
What is Jeffreys’s Sheltering Theory?
Airflow sparates from wave crest and creates back eddy sheltered region of low wind speed and pressure on the leeward slope and a high pressure region in the windward slope.
What does the concept of Jeffrey’s theory do the wave?
Adds height and energy to the wave
How is seastate measured?
Beaufort Scale
What is the motion of water in a wind generated wave - how does it change with depth?
Ellipsoid Orbital motion - diameter of motion decreases with depth
How to calculate wave speed?
Wave speed = Frequency*Length
What happens to waves approaching the shore?
When L = 1/2H friction between wave and seabed occurs - transfer of kinetic to potential energy. Wave height rises and will break when unstable.
Three kinds of breaking wave
Spilling, plunging, surging
What is a Rogue wave
A wave that is much larger/steeper than significant wave height
What is the return period of a 30m rogue wave?
10,000 yrs
What sort of energy can a rogue wave deliver?
100tons/sq m
Cause of rogue waves?
Much speculation however aided by wind against prevailing current
Three waves observation methods
By eye (sea state); Data buoys - (noaa.gov); satellite data
What does kinetic energy in waves refer to?
Wave speed
What does potential energy in waves refer too?
Wave height
What is an XBT probe? What is it used for?
The Expendable Bathythermograph. To obtain information of the temperature structure of the ocean to 1500m; falls at a known rate - plot temperature as a function of depth
What is a Sofar float and what is it used for?
Sounding, fixing and ranging float. To measure and track oceanic currents - they send out acoustic pulses and moored listening stations record location of float from sound signals (need two or three hydrophones to fix float position)
What equation can explain the driving momentum of wind driven current?
Mass*velocity
What are current decays?
Friction and work
What is the impact of Coriolis on sfc wind driven current vertical energy transfer?
Sfc wind driven current deflects to 30degrees - deflection continues through water column
What are oceanic gyres
Mass semi permanent movement of water that move heat energy and impact oceanic life
What are the five major gyres
Indian ocean gyre; North Atlantic Gyre; North Pacific Gyre; South Atlantic Gyre; South Pacific Gyre
Describe a subtropical gyre
The center is high pressure and circulation in clockwise N.Hemisphere. High pressure due to westerly winds on N.side of the gyre - cause frictional surface currents toward the centre
How are subtropical gyre western boundary currents intensified
Build up of water in centre of gyre from convergent flow of water; due to Coriolis is returned poleward to intensify the WBC. Flow is enforced by Pgf
What gyre does the Gulf Stream Belong to?
Gulf stream is the intensified WBC of the N.Atlantic gyre
What is the conservation of vorticity?
The angular momentum of any isolated spinning body is conserved - in vast interior of the ocean flow is nearly frictionless and vorticity is conserved - conservative flow
Give an example of oceanic circulation caused by density changes
Outflow of warm saline water from the Mediterranean - sinks to 100m in Atlantic then flows north and rises - this is indicated in salinity levels to the west of the Uk
What is an oceanic front?
A boundary of water masses of different densities. There can be temperature fronts and salinity fronts depending on which is the determining factor
Implications of an oceanic front
Important for the distribution of life but are very complex acoustic areas
What is a baroclinic atmosphere?
One where density depends both on temperature and pressure - unlike a barotropic zone where it only relies on pressure
Where are baroclinic and barotropic atmospheres found on earth?
Baroclinic - Mid-latitudes/polar regions; Barotropic - Tropics, (central latitudes).
What flow features can be found at oceanic front boundaries?
Eddies and quasi-geostrophic flow on density slope
How and where are eddies formed
They are a product of baroclinic instability at the density boundary (front)
What types of eddies are there
Cold/warm core; Divergent/convergent
Eddy characteristics
Warm less common than cold, (1:2) ~80km diameter - inverted cone shape
What is the significance of equatorial eddies?
Possible transfer of energy and water between hemispheres.
How is the swirling current of an eddy generated?
Reverse current formed from frictional forces when passing an obstacle such as density boundary (front).
What are meddies?
The warm and saline outflow from the mediterranean sea - eddies called meddies form in the process. (this is the density circulation that sinks the med water 1000m deep and travels N to affect W.UK salinity) V.large and persistent features
What are tidal eddies?
These are a product of tidal convergence and shear and are much smaller in scale than others
What are the impact roles of eddies?
Energy, heat, salt and nutrient transfer. Energy can be compared to a thunderstorm. Transfers water volume between hemispheres
Eddies and modelling?
WOCE - map ocean circulaton - observing, modelling and remote sensing of satellites and buoys.
