Discontinuous Rainbow in Front of Ridge

There have already been observed discontinuous rainbows above a ridge for several times. (For example by H. Edens and C. Hinz). Explanations range from an optical illusion via burst raindrops up to the assumption that there are only large flattened raindrops in front of the ridge which reduce the radius.

This is why during my latest observation on June 16, 2011, on Mt. Wendelstein (1838 m), I made the effort to also watching the raindrops. During my observation, there were wind gusts of up to 34 m/sec (122 km/h). In addition, on (my) mountain slope, there were heavy turbulences making the large raindrops come from all directions, even upwards the steep northern slope. These were most deformed of all, some had the shape of vertical ellipses, and some were even almost triangular. Unfortunately, due to the storm I was unable to take valid photographs of the raindrops.

From Physical Review Letters (DOI: 10.1103/PhysRevLett. 101.234501) I learned that raindrops of a diameter of about 1 cm and making 3 rotations per second take a triangular shape. Such kind of rotations must have occurred on my mountain as well as on the neighbouring one where the rainbow appeared.

I am sure that such deformations alter the diameter of the rainbow causing those breaks. Does someone have the occasion to simulate rainbows on such raindrops?

Author: Claudia Hinz, Brannenburg, Germany

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