UK halo display 9th February 2001            
 
                                                Photographs         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   
    Gill Smith Ashberry near Rievaulx Abbey, Yorkshire      13.30 - 14.00       1 2 3 4 5    7    9
    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.