Home
  OpticsPOD
  What's New 
  Rays & Shadows
  Water Droplets
  Rainbows
  Ice Halos
    Contents
    Crystals
     Crystals & Halos 
     Columns & Plates
     Orientations
        Plate
        Column
        Parry
        Lowitz     
        
Random     
     Face numbers
     Real Crystals
     Diamond Dust
     Pyramidal
    Frequent Halos
    Infrequent Halos
    Multiple Displays
    Other Worlds
    Observing Halos
    HaloSim
  High Atmosphere
  Links & Resources
  Search - Index






 
123456789012345678


   Randomly Oriented Crystals





 

Circular halos are most facilely explained by positing randomly oriented ice crystals.

But why do aerodynamic forces, otherwise so remarkably effective, not orient them? Equidimensional column crystals would in principle be randomly oriented but they are not found in any significant numbers in displays showing good circular halos.

However, total randomness is not essential, poorly aligned crystals – ones with large tilts from their equilibrium orientations, can produce circular halos. Very large columns can have poor orientations.

Column clusters might also sometimes be responsible.

Rays passing through column side faces with wedge angles of 60° give a 22° circular halo when the crystals are poorly oriented. Rays traversing a side face and an end face – wedge angle 90° - produce the very rare 46° halo. Supralateral arcs are more frequent and often mistaken for the former.
    

   22° halo  46 and 22° and other
 halos.