- 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

Ocean Waves & Sea-State Forecasting Flashcards by Megan Stackhouse

Define currents

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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What is a key role of currents?

Play a key role in warm water transport poleward, cold water transport equatorward

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What are currents largely driven by?

Subtropical Highs

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Describe the track of global surface winds

Progress Equatorward => poleward E of the E coast
Transported Equatorward W of W coast
=> cools by upwelling

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

push

direction

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Coriolis force deflects the water to the ____ at the ____

right

surface

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

45 deg

right

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PGF in the ocean is commonly dependent on ____

The depth of the ocean

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What influence does PGF have in the ocean?

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

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Ocean currents ___ the ____ of global oceans

contort

topography

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Where does a max of ocean dynamic topography exist?

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

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Sub-Surface Currents are driven by what two things?

Continental boundary effects

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

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What are some examples of Continental boundary effects?

large scale upwelling

- downwelling

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What are some examples of Thermohaline effects?

sinking of cold and salty water
rising of fresh and warm water
(is driven by topography)

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What are 4 examples that demonstrate the complexity of currents?

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

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What is an important local current feature?

Gulf Stream Loop Current

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

Creates local maximum in water temperature

- is an important energy source for tropical storms

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Name two effects of coastal winds

1) Upwelling

2) Downwelling

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Name two effects of tides

1) lunar and solar effects

2) Ebb and flood

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Upwelling is _____ escape

Mass

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Name 4 impacts of currents

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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What are three factors in Wave Formation?

1) Wind strength
2) Fetch
3) Duration

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

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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_____ energy of air creates _____ energy in the water

Kinetic

Potential

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What is the equation for Kinetic energy?

1/2 m(air) * V^2

What is the equation for Potential energy?

m(water) * g * H

There is a ______ between wave height and velocity squared

proportionality

What is the equation for wave height?

H (ft) = 0.02 * V^2

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

- wave shape - steepness - wind drag/shadowing

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

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

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

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

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

theoretical | unperturbed

______ have far more incipient wave activity

shorelines

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

grow faster | less distance

The equations for fetch are not useful for ___ or _____

lakes | bays

Wave breaking tends to occur in ____ water

shallow

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

extended | largest

Biggest waves form in ____ moving storms

slow

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

fast-moving | brief windstorms

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

Time (hrs) = 6.4 * wind^(1/3) (kts) | = 12.3 * H^(1/6) (ft)

Waves are seldom _____ and are best understood ______

uniform | statistically

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

periodic waves | Fourier series

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

rho-g term

What is the significant wave height?

The average waves in the upper one-third of waves to be encountered Hs (ft) = 0.02 * Wind^2 (kts)

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

periods or lengths

______ is the most often-used wave forecasting parameter

significant wave height

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

larger waves

Average wave height is ____% of significant wave height

62%

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

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

wave lengths

Why are distant storms evidenced by long period swells?

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

______ interaction occurs between waves

Nonlinear | constructive and destructive interference

____ affects the speed of waves

gravity

______ _______ is how waves dissipate energy

wave dispersion

Real ocean waves come from _____ swells

superimposed

What are two characteristics of superimposed swells?

1) they are rarely regular and orderly | 2) they are more like oscillating hillocks

Define a rogue wave

height estimate > twice the Hs

When will a wave break?

If its height is approximately 10% of its length

What is the equation for wave length?

L = 0.15 * wind^2 (kts)

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

80%

What are 4 dangerous wave situations?

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

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

superimpose

Define dynamic fetch and group (energy) velocity

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

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

one-half 0.6 times wave "sets"

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

Dynamic Fetch

Dynamic Fetch requires what?

relatively slow moving lows

Describe the process of ocean waves with currents

1. ) wind opposing current; growth faster | 2. ) water piles up much faster, wave height builds quickly, and the waves are steep

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

sooner | grow faster

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

H = 0.020 * wind^2 * (fetch/Ffds)^(1/2) | = .011 * wind^(4/3) * fetch^(1/2) (nm)

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

Time (hrs) = H (ft)

_____ waves form on ____ ____ density discontinuities

Internal | sub-surface

Internal waves ____ wave drag on surface ships

Increase

What is a source of Ocean Wave Climatology?

European Center for Medium Range Forecasting

Describe the European Center for Medium Range Forecasting

- 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

Describe Wave Watch III

- 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

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

wave data assimilation

How often doe the Wave Watch III run?

Every 6 hours out to 6 days

What effect does friction have on the geostrophic wind?

- Forces in Balance - Slows the wind - Reduces Coriolis Force - Wind "pulled" toward lower pressure

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

reduced 30% | backed 30 degrees

Ocean Waves & Sea-State Forecasting Flashcards

(79 cards)