England February 9, 2001
England February 9, 2001 - Yorkshire, Lancashire and the Midlands saw bright displays. Ray Martin took this montage from Sutton Coldfield a few miles north of Birmingham. Comparison with a South Pole display of the identical solar altitude shows the same major halos and that spectacular halos can be seen in the UK. Horizontal column crystals formed most of the halos with very bright supralateral and infralateral arcs, an almost blinding upper tangent arc and a hint of a diffuse Wegener arc. The aircraft trail was above the halo-forming ice crystal layer and casts a shadow downwards onto it. A matching HaloSim simulation below identifies the halos. Images ©Ray Martin, shown with permission.
HaloSim ray tracing for a solar elevation of 22.5°.   Crystals: 76% columns 1° tilt dispersion c/a=1.2, 10% random columns c/a=2, 5% plates 2° tilt disp c/a=0.1, 6% plates 6° tilt disp c/a=0.1, 3% Parry 1° tilt c/a=2.   Very few Parry crystals are needed to make the arc, Parry orientations seem appear very improbable but, conversely, Parry rays are very efficient at halo formation.   256 colour levels, 30 million rays.