Waves and Tides Flashcards
Density defined by…
Temperature and salinity
Nansen bottle
Used for collecting ocean water samples at various depths. It consists of a cylindrical container that sinks vertically through the water column when deployed from a research vessel. Once triggered at a desired depth, the bottle snaps shut, trapping the water sample inside. This sample can then be analyzed in the laboratory for parameters like temperature, salinity, nutrients, and biological content.
Wave frequency (f)
= 1/T (time period)
Wave slope=
wave height/wavelength
= H/ λ
Wave height=
2 λ
Orbits of water-parcel in shallow water
Ellipsoids - clockwise
Parcel of water in deep water
Round- clockwise
Fetch
refers to the distance over which wind blows uninterrupted across the surface of ocean It plays a crucial role in determining the characteristics of waves, influencing their height, length, and energy. Longer fetch distances = in larger and more energetic waves, while shorter fetch distances= smaller waves.
Short waves
Travel slower than long waves
Outside the fetch where waves sort out each other according to speed
Dispersion
Wave generation
Not wind friction associated with laminar flow
Laminar flow
Smooth, orderly flow pattern characterized by fluid moving in parallel layers with minimal mixing between them. Fluid particles follow predictable paths, with each layer of fluid flowing at a constant velocity. This type of flow occurs at low velocities and in situations where there is little disturbance or obstruction to the flow.
Wavelength spectrum at source
- Large range of wavelengths
- Chaotic
Wavelength spectrum at far field
- Smaller range of wavelengths
Long wavelengths
What happens as swell moves from deep ocean to shallow water?
The wave speed changes from the deep water to the shallow water condition: speed becomes controlled not by wavelength but water depth
As waves approach the shore
Wave speed decreases as water depth decreases
Consequences of waves approaching shore:
- Amplitude increases
- Direction of travel changes due to refraction
Huygens Principle
Every point on a wave-front may be considered a source of secondary spherical wavelets. New wavefront defined by tangential to all surfaces
Sin(i)/ Sin(e)=
cd/ca
As water gets shallower:
Shorter wavelength and larger height
As amplitude increases
Shape of wave changes from sine wave to trochoid
Trochoid wave
Sharper peak and smoother trough
Trochoid
The line traced by a point on the radius of a rolling cylinder
When happens to centrifugal force when the distance from the spin axis decreases ?
Centrifugal force increases
What causes tides?
Gravitational attraction of the Moon and Sun
What happens to gravity when the distance separating the attracting masses increases?
Gravity decreases
Centrifugal force
The outward force experience by an object moving in a curved path or rotating around a center point
Luni-solar tides
= the result of the combined gravitational forces exerted by both the Moon and the Sun on Earth’s oceans. These tides occur due to the gravitational attraction between the Earth and these celestial bodies.
When the gravitational forces of the Moon and the Sun align, such as during full or new moons when they are in syzygy (aligned with Earth), their combined influence leads to enhanced tidal effects known as spring tides. Conversely, when the gravitational forces of the Moon and the Sun counteract each other, such as during the Moon’s first and third quarters, the tidal range is reduced, resulting in neap tides.
Effect of the solid earth being springy
Squashes and stretches in response to tide generating forces
Free periods for elastic oscillation
Represent the natural frequencies at which an elastic system vibrates when disturbed and allowed to move freely
Amphidromic points
Locations where there are no tidal amplitude
Which direction are tides in Northern hemisphere deflected due to coriolis effect?
Right- produces a higher tide on the southern margin
Which direction are tides in the Southern hemisphere deflected due to Coriolis effect?
Left- tides rotate counterclockwise around high tides
Why does Coriolis effect lead to deflection of tides?
Water is forced to move away from the direction of the gravitational pull of the Moon and the Sun.Difference in eastward velocity
