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Synoptic Met II => Final Exam > Ocean Waves & Sea-State Forecasting > Flashcards

Ocean Waves & Sea-State Forecasting Flashcards

1
Q

Define currents

A
  • Movement of water in the main water bodies of the earth
  • Affected by cold and warm sources
  • Modified by Coriolis Force
  • Conform to Continental boundaries
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2
Q

What is a key role of currents?

A
  • Play a key role in warm water transport poleward, cold water transport equatorward
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3
Q

What are currents largely driven by?

A

Subtropical Highs

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4
Q

Describe the track of global surface winds

A
  • Progress Equatorward => poleward E of the E coast
  • Transported Equatorward W of W coast
    => cools by upwelling
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5
Q

Winds and wind stress ___ water initially in the ____ of the wind

A

push

direction

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6
Q

Coriolis force deflects the water to the ____ at the ____

A

right

surface

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7
Q

Net current is about ___ deg to the ____ of the wind

A

45 deg

right

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8
Q

PGF in the ocean is commonly dependent on ____

A

The depth of the ocean

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9
Q

What influence does PGF have in the ocean?

A

The balance between water pressure and Coriolis force aligns the current closer to the wind direction

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10
Q

Ocean currents ___ the ____ of global oceans

A

contort

topography

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11
Q

Where does a max of ocean dynamic topography exist?

A

Off the E coast of Asia (due to location of warmest water)

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12
Q

Sub-Surface Currents are driven by what two things?

A
  • Continental boundary effects

- Thermohaline effects (sinking of cold and salty water; rising of fresh and warm water)

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13
Q

What are some examples of Continental boundary effects?

A
  • large scale upwelling

- downwelling

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14
Q

What are some examples of Thermohaline effects?

A
  • sinking of cold and salty water
  • rising of fresh and warm water
  • (is driven by topography)
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15
Q

What are 4 examples that demonstrate the complexity of currents?

A

1) Sharp gradients and current shear
2) Current acceleration by gap flow
3) Warm clockwise eddy
4) cool counterclockwise eddy

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16
Q

What is an important local current feature?

A

Gulf Stream Loop Current

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17
Q

What is the important role of the Gulf Stream Loop Current?

A
  • Creates local maximum in water temperature

- is an important energy source for tropical storms

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18
Q

Name two effects of coastal winds

A

1) Upwelling

2) Downwelling

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19
Q

Name two effects of tides

A

1) lunar and solar effects

2) Ebb and flood

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20
Q

Upwelling is _____ escape

A

Mass

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21
Q

Name 4 impacts of currents

A

1) Heat transport and enhancement of ocean storms
2) Enhanced ocean waves when winds are opposed
3) Coastal water cooling/warming (low clouds, fog, convection)
4) Ship routing decisions

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22
Q

What are three factors in Wave Formation?

A

1) Wind strength
2) Fetch
3) Duration

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23
Q

Describe the 3-step process of ocean wave formation by WIND

A

1) Microscopic capillary waves
2) Slight ripples are pushed upward by wind
3) Wave height increases based on speed and duration

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24
Q

_____ energy of air creates _____ energy in the water

A

Kinetic

Potential

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25
Q

What is the equation for Kinetic energy?

A

1/2 m(air) * V^2

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26
Q

What is the equation for Potential energy?

A

m(water) * g * H

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27
Q

There is a ______ between wave height and velocity squared

A

proportionality

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28
Q

What is the equation for wave height?

A

H (ft) = 0.02 * V^2

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29
Q

What are other factors that affect energy transfer when creating potential energy in the water?

A
  • wave shape
  • steepness
  • wind drag/shadowing
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30
Q

What is the equation for fetch to attain a fully developed sea (FDS)?

A

Fetch (nm) = 3.17 * Wind^(4/3) (kts)

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31
Q

What is the equation for fetch for a Significant Wave height (H) (ft)?

A

Fetch for H (nm) = 43 * H^(2/3)

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32
Q

The equations for fetch are _____ and assume a totally ______ sea

A

theoretical

unperturbed

33
Q

______ have far more incipient wave activity

A

shorelines

34
Q

Because shorelines have more incipient wave activity, the result is that waves grow _____, and require ____ distance to grow

A

grow faster

less distance

35
Q

The equations for fetch are not useful for ___ or _____

A

lakes

bays

36
Q

Wave breaking tends to occur in ____ water

A

shallow

37
Q

With duration, the wind over a particular patch of water must blow for an _____ period to generate _____ waves

A

extended

largest

38
Q

Biggest waves form in ____ moving storms

A

slow

39
Q

____ moving or ____ windstorms (squalls) don’t linger long enough to generate significant wavese

A

fast-moving

brief windstorms

40
Q

What is the equation for wind duration for a fully developed sea?

A

Time (hrs) = 6.4 * wind^(1/3) (kts)

= 12.3 * H^(1/6) (ft)

41
Q

Waves are seldom _____ and are best understood ______

A

uniform

statistically

42
Q

Any water perturbation is made up of several ____ waves (i.e.: _____ series)

A

periodic waves

Fourier series

43
Q

To calculate energy/unit area, we really need a ____ term

A

rho-g term

44
Q

What is the significant wave height?

A

The average waves in the upper one-third of waves to be encountered

Hs (ft) = 0.02 * Wind^2 (kts)

45
Q

A wave system is also a group of waves of various ____ or _____

A

periods or lengths

46
Q

______ is the most often-used wave forecasting parameter

A

significant wave height

47
Q

Hs is useful for mariners because it favors the _____ waves that might be encountered allowing for better preparation

A

larger waves

48
Q

Average wave height is ____% of significant wave height

A

62%

49
Q

There is a ____% chance of getting a wave twice as high as the Hs

A

1%

50
Q

A typical ocean wave is made up of a series of individual ____ ____

A

wave lengths

51
Q

Why are distant storms evidenced by long period swells?

A

Once formed the wave starts to disperse with the longer wave lengths traveling faster

52
Q

______ interaction occurs between waves

A

Nonlinear

constructive and destructive interference

53
Q

____ affects the speed of waves

A

gravity

54
Q

______ _______ is how waves dissipate energy

A

wave dispersion

55
Q

Real ocean waves come from _____ swells

A

superimposed

56
Q

What are two characteristics of superimposed swells?

A

1) they are rarely regular and orderly

2) they are more like oscillating hillocks

57
Q

Define a rogue wave

A

height estimate > twice the Hs

58
Q

When will a wave break?

A

If its height is approximately 10% of its length

59
Q

What is the equation for wave length?

A

L = 0.15 * wind^2 (kts)

60
Q

Near shore, waves break if H > ___% depth (h)

A

80%

61
Q

What are 4 dangerous wave situations?

A

1) strong slow-moving lows
2) lows moving at certain speeds
3) currents with wave motion opposed
4) waves near land - breaking

62
Q

With a slow-moving low, waves _____ for maximum threat

A

superimpose

63
Q

Define dynamic fetch and group (energy) velocity

A

Two or more wave lengths combine, each moving at a different velocity
=> With constructive and destructive interference

64
Q

Dynamic fetch and group (energy) velocity forms a wave packet that moves at ______ the average speed of the waves, or ____ times the wind speed.

This forms wave ___ for surfing

A

one-half
0.6 times

wave “sets”

65
Q

If a storm moves at a speed, then energy maximum will stay in wave generation zone for many hours. This is called ____

A

Dynamic Fetch

66
Q

Dynamic Fetch requires what?

A

relatively slow moving lows

67
Q

Describe the process of ocean waves with currents

A
  1. ) wind opposing current; growth faster

2. ) water piles up much faster, wave height builds quickly, and the waves are steep

68
Q

On a lake or bay, waves happen ____ and grow ____

A

sooner

grow faster

69
Q

What is the equation for wave height on a lake or bay?

A

H = 0.020 * wind^2 * (fetch/Ffds)^(1/2)

= .011 * wind^(4/3) * fetch^(1/2) (nm)

70
Q

What is the equation for wind duration for fully developed waves?

A

Time (hrs) = H (ft)

71
Q

_____ waves form on ____ ____ density discontinuities

A

Internal

sub-surface

72
Q

Internal waves ____ wave drag on surface ships

A

Increase

73
Q

What is a source of Ocean Wave Climatology?

A

European Center for Medium Range Forecasting

74
Q

Describe the European Center for Medium Range Forecasting

A
  • Mean and standard deviation of significant wave height, and also wave period
  • Based on 45 years of ship reports and wave model
  • Is Global
  • and by month
75
Q

Describe Wave Watch III

A
  • used by both FNMOC and NCEP
  • Driven by Global and Regional forecast models
  • solves spectral balance equations for wave frequencies for a number of propagation directions
  • takes into account currents, refraction, breaking, and ice coverage
76
Q

Wave Watch III has no _____ ____ _____, but uses 12-hr wave forecast from previous run

A

wave data assimilation

77
Q

How often doe the Wave Watch III run?

A

Every 6 hours out to 6 days

78
Q

What effect does friction have on the geostrophic wind?

A
  • Forces in Balance
  • Slows the wind
  • Reduces Coriolis Force
  • Wind “pulled” toward lower pressure
79
Q

Wind is reduced by ___% and backed ___ degrees due to friction

A

reduced 30%

backed 30 degrees

Synoptic Met II => Final Exam (6 decks)

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