What was it?

Matthew Drews saw this ice halo display in New Brunswick, New Jersey May 14,2013. The US east coast had extensive halo displays that day.

At top: is a bright circular halo that persisted for several hours.

The lower image shows a faint but huge colourful halo beneath the sun and close to the horizon.




What are they?

The first reaction to a halo circling the sun is that it is a 22° halo produced from randomly oriented hexagonal ice crystals. It looks circular doesn't it? The large halo beneath the sun might then be a rare 46° halo fragment (improbable) or a circumhorizon arc from plate crystals.

However, the lower halo appears to curve up strongly from the horizon making it less likely to be a circumhorizon arc which is always parallel to the horizon. The enhanced view (below) shows the curvature. But beware of camera distortions - it could be a circumscribed halo!

An infralateral arc from horizontal column crystals curves upwards. But in that event, there ishould be an oval inner halo around the sun - a circumscribed halo generated by rays through the same crystals. There could also be a superimposed circular 22° halo.

Comparison with an added circle (below left) shows that the inner halo was in fact oval (to the extent one believes a camera lens without star field calibration) and severe enhancement shows a faint high sun parhelic circle.  A HaloSim ray tracing for the solar elevation of 68° gives weight to the interpretation....

      ... A circumscribed halo, probably an infralateral arc, a parhelic circle from horizontal column crystal and possibly also a 22° halo.

But then the plot thickens.. .. see below.

The topmost image was taken at 12:55 EDT with the sun was 68° high.

Later on - and coincidentally - Michael Lee took images of the display from within a mile of Matthew Drews' position.   These images became available after the above analysis.

How the sky changes!  At left is the scene at ~14:15 - 14:30 with the sun now lower at 62-59°.

The circumscribed halo has become more oval and inside it is the 22° halo. Perhaps there is a trace of cloud iridescence near the sun.

The lower image clearly shows a parhelic circle.

At these lower sun altitudes any infralateral or circumhorizon arcs would be fading fast as the rays forming them would be increasingly internally reflected within the crystals.




When the sun is high the 22° halo and circumscribed halos are not easy to tell apart. Take plenty of images and be sure that the camera clock is accurate.  Keep the image EXIF data.

Look for a hint of two halos at 3 and 9 o'clock from the sun. Look for brightening at 12 and 6 o'clock.

The circumscribed halo tends to have more saturated colours and tapers off more sharply away from the sun.
Atmospheric
Optics
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Grotesque enhancement - levels, unsharp mask, embossing - just manages to show a high-sun parhelic circle.
A clear parhelic circle.
The halo is not circular. At the sun elevation of 68° the circumscribed halo is easily mistaken for a circular halo. The higher the sun, the more a circumscribed halo approaches a circle.
The lower arc is strongly curved and therefore not a circumhorizon arc. However, be wary of a camera image because of possible distortion. Measure the arc's distance above the horizon visually.
A colour separation technique clearly highlights the circumscribed halo and inner 22° halo. The parhelic circle disappears because it has no colour.