UK halo display

UK halo display 9th February 2001

	Photographs	Supralateral?	HALO site

       HALO3 simulation of the rare UK display.   The sun is below centre inside the bright circular 22° halo.
       30 million virtual light rays were traced through mathematical representations of the cloud ice crystals to
       make this view as would be photographed by a wide angle camera.

    Halos, produced by hexagonal shaped ice crystals in clouds, are visible once or twice a week on average.
    These are usually sundogs and fragments of a 22° radius circular halo around the sun.   In complex displays
    a whole variety of bright and colourful arcs spread across the sky including ones rarely seen.   In the UK
    these displays are few and far between but one was visible over the Midlands and Northern England on
    Friday 9th February .

The sightings of common and rare halo arcs were:

Observer	Location	Time	Arcs visible
Malcolm Garland	Sheffield	12.40 - 13.10	1 2 4 5 6 7 8
Malcolm Goldsmith	Prestwich, Manchester	10.30 &13.30	2 10
Judith Proctor	Leicestershire	- 1330	1 2 3 5 10 11
Gill Smith	Ashberry near Rievaulx Abbey, Yorkshire	13.30 - 14.00	1 2 3 4 5 7 9
Bruce Thomas	Castleford near Pontefract, Yorkshire		1 2 3 4 5 7 8 9 10
Ant Veal et.al.	Birmingham	11.45 - 12.40	1 2 3 4 5 9 10
Tony Young	Derby	12.00 - 13.15	1 2 4 5 6 7

The halos:

Key	Name	Cloud crystals
1	22° halo	poorly oriented crystals	Weak in display
2	22° sundogs (parhelia)	hexagonal plates
3	Circumzenithal arc	plates
4	Upper tangent arc	horizontal columns	Extremely bright and coloured
5	Parhelic circle	plates & columns
6	Sun pillar	plates & columns	Not often seen when the sun is so high. Probably made by the large numbers of column crystals.
7	46° halo	poorly oriented	Rare and colourful halo - see supralateral arc.
8	120° parhelia	plates	Produced by multiple reflections inside plate crystals.
9	Parry arc	Parry columns	Rare halo first seen by Parry in 1820 while icebound in the Arctic.
10	Supralateral arc	columns	The sun was 18 to 22° high and these altitudes it can be difficult to distinguish between partial supralateral arcs and 46° halo fragments. Crystals capable of generating each were present but the hexagonal columns which generate supralateral arcs were most abundant.
11	Infralateral arc	columns	Coloured arcs beneath the parhelic circle at this solar elevation. Produced by the reverse ray paths through column crystals to those which create supralateral arcs.