Thursday, 1 March 2007

Probable fragment of subheliac arc

On February 20 there were a lot of cirrus shreds in the foehn area of a strong northern low pressure area. Already in the morning there appeared unusually bright sundogs and a circumzenithal arc of the same brightness in these cirrus shreds. Later also a Parry arc appeared together with parts of the parhelic circle and very bright 120°-parhelia which had an accentuated reddish rim. At 11.50 CET, another arc seemed to form above the left 120°-sundog which stayed at its position for about 10 minutes while the cirrus clouds kept moving on. As the simulation for a sun elevation of 24° shows, the position of that arc fragment is identical to the subheliac arc.

By Claudia Hinz


  1. Did you try stacking? That way the arc would've been easier to identify as the cloud movement would smoothen the cloud features.

  2. Unfortunately, I have only a very bad Stack because the original pictures weren't congruent. For building a tripod, unfortunately, it was far too stormy.

    The Stack is made from 10 pictures which were taken within 10 min. But the two arcs have somehow an easy moving in this :o(

    Best wishes

  3. Here once again the link:

  4. To me the stack does not look too bad as far as 120 parhelion and parhelic circle are concerned. But it looks bad for the subhelic arc.

    But there is something else here. The upper part of the parhelic circle / 120 parhelion seems to have a reddish hue. Does anybody see it, or is it just my imagination? I thought I saw it in all the photos that Cladia sent some time ago of this display.

    We have paid attention to this effect also in some Finnish photos.

  5. yes, I've seen the reddish and later bluish rim also with naked eye.