OceanographyLesson 1 of 1 in the course Tides and waves

Internal Waves: Stratification, Wave Dynamics, and Oceanic Effects

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

This lesson introduces internal waves and explains the density layering that allows them to exist. Understanding stratification and buoyancy helps explain why waves can travel inside water or air, often much more slowly than waves at a surface.

An internal wave is a gravity wave that oscillates within a fluid rather than at the boundary between a fluid and another medium, such as the ocean surface. The fluid must be stratified: its density must vary with depth or height. Temperature and salinity differences can create density layers in water; changes in temperature can also stratify the atmosphere.

All flashcards

What is an internal wave?
A gravity wave that oscillates within a fluid rather than at its outer boundary; it requires density stratification.
What is reduced gravity?
An effective gravitational acceleration representing buoyancy across a density interface; for two layers, g′=gρ2−ρ1ρ2+ρ1g'=g\frac{\rho_2-\rho_1}{\rho_2+\rho_1}.
What is the buoyancy frequency?
The characteristic oscillation frequency of a vertically displaced parcel in a continuously stratified fluid.
What is an internal soliton?
A large-amplitude interfacial wave, also called an internal solitary wave.
What is the Boussinesq approximation?
A model that neglects small density variations in most terms but retains them in the buoyancy force.

Quiz questions

  1. In the simple two-layer interfacial-wave model, what dispersion relation connects angular frequency ω\omega, reduced gravity g′g', and horizontal wavenumber kk?Answer: ω2=g′k\omega^2=g'k
  2. What does the Boussinesq approximation assume about density variations in a stratified fluid?Answer: They are neglected in most terms but retained in the buoyancy force.
  3. For internal waves, what does group velocity describe?Answer: The motion of a wave packet and the direction of energy propagation.
  4. Why can a boat experience dead water while crossing a relatively fresh surface layer?Answer: Energy transferred to an internal-wave wake creates strong resistance.
  5. How can an approaching internal wave steepen into an internal bore near shore?Answer: Bottom friction slows water near the seabed, making the wave asymmetric and steepening its face.

Based on the Wikipedia article Internal wave, licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.

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