QBO

Creating waves from above

In the actual stratosphere, waves are transmitted from the lower boundary layers. In Plum and MacEwan's experiments as well, waves are created from the base of the water tank. This is, however, quite a difficult thing to do.

On the other hand, the structure of the water tank is a lot simpler if you create waves on the surface of the water, and it is easier to deal with problems that may occur during the experiments.

Internal gravity waves are vertically symmetrical, so the same thing happens if you create waves on the surface.

Dealing with bubbles.

If you carry out an experiment over a long period of time, thousands and thousands of bubbles form in the water tank. If you mix in just a little detergent when you are creating the stratified layers, you can prevent to a great extent the attachment of bubbles.

However, depending on the type of detergent, it can cloud the water, or become clouded at certain salt densities.

Neutral flotation.

In this experiment we need to create neutral flotation matched to the specific gravity each layer of saltwater. We tried many and varied materials, but in the end the best combination was a mixture of glue for a hot melt gun (a gun-shaped tool that melts and ejects glue), and moldable resin (resin that becomes soft when you heat it with warm water).

The glue of a hot melt gun is lighter than water, and the moldable resin is heavier, so you can create plastics of all different specific gravities by softening the two materials in hot water and kneading them together.

To shape the resulting plastic, you first roll it into a cylindrical shape like the hot melt gun glue, fit it to a gun which has had its temperature lowered using a transformer, and eject it from the gun, creating a long soft thread of something like thick spaghetti. You can then cut it into lengths, roll it into balls while it is still hot and voila, you have a collection of neutral floats.

Measuring the density gradient

In this experiment, the vertical density gradient is important, and unless the density gradient near the surface where the waves are created is correctly formed, the experiment won't work. Here we used a laser to check the density gradient.

If you shoot a laser beam horizontally into the stratified fluid, the line of light will bend downwards. If you place a mirror vertically inside the water tank, and reflect the laser off it, the light will pass through the water twice, and thus bend further than it would otherwise. By measuring the distance the laser has bent, you can measure the density gradient without touching the water.