Bent Glitter Path

Glitter paths usually come straight. This unusual bent one was captured off the Norwegian Coast by David Lynch, co-author of Color & Light in Nature (Now back in print! Available here).
©David Lynch, shown with permission.


David Lynch writes: "Glitter is that bright patch of sunlight (or moonlight) reflected on water.   It can take various forms depending on the wave slopes and sun elevation, but in almost all cases the glitter is symmetric about a vertical line running down its axis.

From time to time, however, the glitter appears “bent”, with part of it offset from the vertical.  Such features are the result of waves whose transverse profiles (left-right relative to vertical) are asymmetric.

One possible way is to have a field of short wavelength glitter-producing waves overtaken by a long wavelength wave. This causes the short-wavelength waves to be tilted one way or the other on average. As a result, the wave slope distribution is shifted in one direction, thereby shifting the glitter sideways. This is the case at left where the long bow wave of a ship moves into a field of glitter.

Another way to produce asymmetric wave slopes is with wind action. Wind blowing across water will produce all wavelengths of waves, starting with short waves (capillary waves—“cat’s paws”) and building up to longer wavelengths as time goes on.

To simulate bent glitter, David Dearborn and I wrote a computer program that predicts the shape of glitter for an arbitrary wave slope distribution and sun elevation.   By skewing the waves in the foreground, we were able to produce bent glitter that resembles the image at top."

The work, plus other new glitter findings, is published in:
Lynch, D. K., D.S.P. Dearborn, J.A. Lock “Glitter and Glints on Water”, Applied Optics, 50, F39-F49 (2011)

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Glitter paths are the collective glints of sunlight reflected from the curved and ever changing surface of wavy water.

That description belies their considerable subtleties. Under many conditions the reflected light forms caustic sheets. As wave motion sweeps a sheet across the eye it sees a bright flash on the water surface. The flash then splits into two spots that dance around until they eventually find one another and recombine in another flash. All that can be too fast for the eye to follow and then we see the dance of the spots as one of many closed loops. A comparatively recent branch of pure mathematics ‘catastrophe theory’ has many applications to the descriptions of caustics and water glint effects.