Subsun Streaks?

Robert Goren was travelling from Florida to Atlanta when he saw a host of above horizon and subhorizon halos.

Here we have a subsun and to the right a subparhelion.
The puzzle is the arc curving upwards and rightwards from the subsun.

Subsuns are direct reflections of the sun by millions of horizontal plate ice crystals. When almost perfectly horizontal the subsun can resemble the sun itself. More usually, the crystals wobble slightly and the sun image is vertically elongated. When the wobbles are large the subsun transforms into a lower sun pillar.

Curved streaks from subsuns have been seen and photographed previously but they remain unexplained.

A possibility is plate crystals become temporarily tilted in the airstream perturbed by the aircraft. The difficulty with that explanation is that in some images the distance of the glinting crystals can be measured from the length of their streak, the camera shutter speed and the aircraft's speed. The distances are 40-60m, farther than the wing length of the airplane. Robert Goren's arc shows no streaks during the 1/1250s exposure but the absence of any glints suggests that the ice crystals responsible were at some distance.

Beware of window scratches! They produce a similar effect. Try to take many images, moving the camera relative to the window between them.

Image ©Robert Goren, shown with permission.

About - Submit Optics Picture of the Day Galleries Previous Next Today Subscribe to Features on RSS Feed
Subsun rays. Reflections from the upper and lower hexagonal faces of horizontal plate crystals.