INTERNAL GRAVITY WAVE PROPAGATION : ILLUSTRATE VARIOUS FEATURES OF WAVE MOTION AND TURBULENCE IN A STATICALLY STABLE SALT STRATIFICATION

  1. Create a salt stratification in a tall shallow box (see salt stratification maker).  Use 20% (strong) salt solution in the salt chamber.
  2. Fill slowly, letting fresh in first.  Cylinder should be in position while filling.
  3. Wait for stratification to smooth out (overnight).
  4. Wheel into class.  Be careful not to bumb stratification too much.
  5. Attach drive motor to power supply.
  6. Visualization is by shadowgraph.  Shine projector through the flat side of the tank then onto a wall.  The white light projector uses a box slide to crop the beam.  Position the projector as far away from the tank as possible (i.e. make it like a point source).  The tank should be far enough away from a white wall to permit students to see both the tank and the image on the wall.
  7. Start with a slow small amplitude oscillation.  Compare beam angle with prediction.  Change frequency, not change in beam angle.
  8. Drag cylinder horizontally to see lee wave formation or blocking.

 

Tank with drive motor and cylinder at mid depth.

Close up of drive motor.  Hook suspension string closest to axis for weak waves.  Also, high frequency up down motion will generate turbulence and collapse near the cylinder.

Drive motor power supply.  Start with a low voltage (low frequency) oscillation.

Picture of the beaming.  

Picture of trapping, when forcing frequency is higher than Brunt Vaisala frequency ( root (g*delrho/rho*H)).

MOVIES:

  1. QUASI LINEAR WAVE PROPAGATION
  2. TOWING THROUGH A STRATIFIED FLUID:  LEE WAVES - (FOLLOWED BY INADVERTENT RISE OF OBSTACLE AND COLLAPSE OF STRATIFICATION INTO A LAYERED SYSTEM    (BIG SCREEN)

SALT STRATIFICATION GENERATOR


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2000.  John Hart, University of Colorado