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Discontinuous rainbow

This is an older observation (from last year). I made it at the Langmuir Laboratory for Atmospheric Research on a mountaintop in central New Mexico, USA at about 10,500 feet altitude above MSL.

The photos look to the east-northeast. The rainbow occurs in a storm that is receding and drifting to the east and has just passed Sawmill Canyon in the foreground. The mountain ridge on the photo is called Timber Ridge, and most of the heavier rainfall is on the other side of that. The much finer, mist-like droplets near the trailing end of the storm are still falling in the canyon and create a rainbow that has a smaller radius and is a little wider than an ‘ordinary’ bow that occurs in larger raindrops. The effect is very obvious but requires a fairly specific landscape setting to be seen.

The photos were taken on July 27, 2009 using a Nikon D700 camera. Times below are local time (MDT).

Photo 1: The effect is just beginning to occur. 18:37:50 pm, 36 mm focal length, ISO 800, 1/160 sec at f/6.3.

Photo 2: Effect strongest. 18:43:17 pm, 38 mm focal length, 800 ISO, 1/250 sec at f/8.

Photo 3: The rainbow in canyon is disappearing and still shows a discontinuity. Also note that the ‘foot’ of the rainbow beyond the canyon is not following the circle but appears to kink – i.e. the radius is getting larger at lower altitude – maybe due to drops coalescing and increasing in size as they fall? 18:45:11 pm, 48 mm focal length, 200 ISO, 1/125 sec at f/5.6.

All three photos have not been cropped, modified or enhanced in any way.

Posted by Harald Edens

Strange Rainbow

Reinhard Nitze observed at Barsinghausen (Niedersachsen, Germany) on the morning of July 7, 2007 a strange rainbow produced by a passing shower. Owing to the low solar elevation it had a predominantly reddish colour. When he saw the photos he remarked on the strange step change in brightness, colour saturation, radius and width near the left-hand base of the bow (photo with unsharp mask). The change is marked on the photo by an arrow and is not an artefact because it is present on other images (1 2 3). The upper part of bow is considerably brighter and more strongly coloured although blues are weak and violet is completely absent. This is not easy to explain. A cloud might be shadowing the weaker part of the bow but that does not explain the width or radius change. Smaller drop sizes in the lower region might be responsible and could be obscuring rays from larger raindrops further away. Effects of reflected light bows can be ruled out because no water was nearby. Somewhat similar unusual rainbows were imaged by the Japanese observer Yuji Ayatsuka.