Waves and Oceanic Circulation

Question 1

Name the four general types of wave from lowest wavelength to highest

Answer 1

Wind waves - storm swell - storm surge - tsunami

Question 2

What are Capillary waves

Answer 2

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.

Question 3

What is a gravity capillary wave?

Answer 3

Influenced by both the effects of surface tension and gravity as well as fluid inertia.

Question 4

How can wind waves be generated

Answer 4

The coalescence of capillary waves caused by the boundary forces from the wind - frictional transfer of energy

Question 5

What is Jeffreys’s Sheltering Theory?

Answer 5

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.

Question 6

What does the concept of Jeffrey’s theory do the wave?

Answer 6

Adds height and energy to the wave

Question 7

How is seastate measured?

Answer 7

Beaufort Scale

Question 8

What is the motion of water in a wind generated wave - how does it change with depth?

Answer 8

Ellipsoid Orbital motion - diameter of motion decreases with depth

Question 9

How to calculate wave speed?

Answer 9

Wave speed = Frequency*Length

Question 10

What happens to waves approaching the shore?

Answer 10

When L = 1/2H friction between wave and seabed occurs - transfer of kinetic to potential energy. Wave height rises and will break when unstable.

Question 11

Three kinds of breaking wave

Answer 11

Spilling, plunging, surging

Question 12

What is a Rogue wave

Answer 12

A wave that is much larger/steeper than significant wave height

Question 13

What is the return period of a 30m rogue wave?

Answer 13

10,000 yrs

Question 14

What sort of energy can a rogue wave deliver?

Answer 14

100tons/sq m

Question 15

Cause of rogue waves?

Answer 15

Much speculation however aided by wind against prevailing current

Question 16

Three waves observation methods

Answer 16

By eye (sea state); Data buoys - (noaa.gov); satellite data

Question 17

What does kinetic energy in waves refer to?

Answer 17

Wave speed

Question 18

What does potential energy in waves refer too?

Answer 18

Wave height

Question 19

What is an XBT probe? What is it used for?

Answer 19

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

Question 20

What is a Sofar float and what is it used for?

Answer 20

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)

Question 21

What equation can explain the driving momentum of wind driven current?

Answer 21

Mass*velocity

Question 22

What are current decays?

Answer 22

Friction and work

Question 23

What is the impact of Coriolis on sfc wind driven current vertical energy transfer?

Answer 23

Sfc wind driven current deflects to 30degrees - deflection continues through water column

Question 24

What are oceanic gyres

Answer 24

Mass semi permanent movement of water that move heat energy and impact oceanic life

Question 25

What are the five major gyres

Answer 25

Indian ocean gyre; North Atlantic Gyre; North Pacific Gyre; South Atlantic Gyre; South Pacific Gyre

Question 26

Describe a subtropical gyre

Answer 26

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

Question 27

How are subtropical gyre western boundary currents intensified

Answer 27

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

Question 28

What gyre does the Gulf Stream Belong to?

Answer 28

Gulf stream is the intensified WBC of the N.Atlantic gyre

Question 29

What is the conservation of vorticity?

Answer 29

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

Question 30

Give an example of oceanic circulation caused by density changes

Answer 30

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

Question 31

What is an oceanic front?

Answer 31

A boundary of water masses of different densities. There can be temperature fronts and salinity fronts depending on which is the determining factor

Question 32

Implications of an oceanic front

Answer 32

Important for the distribution of life but are very complex acoustic areas

Question 33

What is a baroclinic atmosphere?

Answer 33

One where density depends both on temperature and pressure - unlike a barotropic zone where it only relies on pressure

Question 34

Where are baroclinic and barotropic atmospheres found on earth?

Answer 34

Baroclinic - Mid-latitudes/polar regions; Barotropic - Tropics, (central latitudes).

Question 35

What flow features can be found at oceanic front boundaries?

Answer 35

Eddies and quasi-geostrophic flow on density slope

Question 36

How and where are eddies formed

Answer 36

They are a product of baroclinic instability at the density boundary (front)

Question 37

What types of eddies are there

Answer 37

Cold/warm core; Divergent/convergent

Question 38

Eddy characteristics

Answer 38

Warm less common than cold, (1:2) ~80km diameter - inverted cone shape

Question 39

What is the significance of equatorial eddies?

Answer 39

Possible transfer of energy and water between hemispheres.

Question 40

How is the swirling current of an eddy generated?

Answer 40

Reverse current formed from frictional forces when passing an obstacle such as density boundary (front).

Question 41

What are meddies?

Answer 41

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

Question 42

What are tidal eddies?

Answer 42

These are a product of tidal convergence and shear and are much smaller in scale than others

Question 43

What are the impact roles of eddies?

Answer 43

Energy, heat, salt and nutrient transfer. Energy can be compared to a thunderstorm. Transfers water volume between hemispheres

Question 44

Eddies and modelling?

Answer 44

WOCE - map ocean circulaton - observing, modelling and remote sensing of satellites and buoys.