All three Lowitz arcs ~ A rare ice halo display seen by Hans Nienhuis on September 29, '10.  

"I was driving along the A12 near the town of Ede, The Netherlands. For the whole day there had been cirrostratus all over the sky, sometimes with a glimpse of one of the two sundogs. Nothing special seemed to happen - just a display with sundogs as seen so often before.

But just before half past five, when I looked up towards the sun again, the left sundog started to grow rapidly. Finally it became one of the brightest sundogs of this whole year. A few minutes later the sundog started to decay. But right next to it something else had appeared.

Lowitz arcs? There was no sign of the 22 halo at all and right between the sundog and the sun, there was a kind of a 'gap' in the bows. Then right in front of the car there started a traffic jam. This was the first time ever that I was glad of a traffic jam. It gave me enough time to find my camera and to take some pictures through the car windows before it was too late!"

Images ©Hans Nienhuis, shown with permission.

The first publicly reported photographs of Lowitz arcs were taken as recently as the 1990s. Until then, and even afterwards, the arcs' existence was in doubt.

There are three Lowitz arcs, 'upper', 'middle' and 'lower' but usually only the upper and/or lower arcs are seen extending from a sundog.

Images like this one showing all three arcs are comparatively rare.

Lowitz arcs are thought to arise when plate crystals take up different rotational orientations about a near horizontal axis passing through two opposite hexagonal prism vertices. There are then three possible ray paths between faces inclined at 60°. These give the three arcs.

The model is not fully satisfactory and often has difficulty in reproducing the finer details of a display.

The HaloSim ray tracing here (for red rays only) needed unusually thick plates (c/a at least 0.3) and some non regular hexagons to generate a bright enough middle arc.

The lower Lowitz is clear in this image


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