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Ocean Atmosphere > Waves and Oceanic Circulation > Flashcards

Waves and Oceanic Circulation Flashcards

1
Q

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

A

Wind waves - storm swell - storm surge - tsunami

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2
Q

What are Capillary waves

A

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.

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3
Q

What is a gravity capillary wave?

A

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

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4
Q

How can wind waves be generated

A

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

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5
Q

What is Jeffreys’s Sheltering Theory?

A

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.

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6
Q

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

A

Adds height and energy to the wave

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7
Q

How is seastate measured?

A

Beaufort Scale

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8
Q

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

A

Ellipsoid Orbital motion - diameter of motion decreases with depth

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9
Q

How to calculate wave speed?

A

Wave speed = Frequency*Length

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10
Q

What happens to waves approaching the shore?

A

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

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11
Q

Three kinds of breaking wave

A

Spilling, plunging, surging

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12
Q

What is a Rogue wave

A

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

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13
Q

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

A

10,000 yrs

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14
Q

What sort of energy can a rogue wave deliver?

A

100tons/sq m

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15
Q

Cause of rogue waves?

A

Much speculation however aided by wind against prevailing current

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16
Q

Three waves observation methods

A

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

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17
Q

What does kinetic energy in waves refer to?

A

Wave speed

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18
Q

What does potential energy in waves refer too?

A

Wave height

19
Q

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

A

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

20
Q

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

A

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)

21
Q

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

A

Mass*velocity

22
Q

What are current decays?

A

Friction and work

23
Q

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

A

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

24
Q

What are oceanic gyres

A

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

25
Q

What are the five major gyres

A

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

26
Q

Describe a subtropical gyre

A

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

27
Q

How are subtropical gyre western boundary currents intensified

A

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

28
Q

What gyre does the Gulf Stream Belong to?

A

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

29
Q

What is the conservation of vorticity?

A

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

30
Q

Give an example of oceanic circulation caused by density changes

A

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

31
Q

What is an oceanic front?

A

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

32
Q

Implications of an oceanic front

A

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

33
Q

What is a baroclinic atmosphere?

A

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

34
Q

Where are baroclinic and barotropic atmospheres found on earth?

A

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

35
Q

What flow features can be found at oceanic front boundaries?

A

Eddies and quasi-geostrophic flow on density slope

36
Q

How and where are eddies formed

A

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

37
Q

What types of eddies are there

A

Cold/warm core; Divergent/convergent

38
Q

Eddy characteristics

A

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

39
Q

What is the significance of equatorial eddies?

A

Possible transfer of energy and water between hemispheres.

40
Q

How is the swirling current of an eddy generated?

A

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

41
Q

What are meddies?

A

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

42
Q

What are tidal eddies?

A

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

43
Q

What are the impact roles of eddies?

A

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

44
Q

Eddies and modelling?

A

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

Ocean Atmosphere (11 decks)

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