Atmospheric
Optics
Halos at Whistler, BC, Canada
Fiona Gidden captured these halos on Blackcomb Mountain Christmas Day, �14 using her iPhone .
All images ©Fiona Gidden, shown with permission
The halos as ray traced with HaloSim. The below horizon halos are often seen from ski-slopes.
The sharp
suncave
Parry arc
Unusual features of this diamond dust display:
46° halo – The coloured halo near the circumzenithal arc is a 46° halo. The more common supralateral arc always touches the CZA. The 46° halo only approaches it at sun altitudes between 15 and 27°. Here the sun is only 12° high.
Two Parry arcs – The sun altitude is again influential. When the sun is close to the horizon the sunvex Parry is very close to the upper tangent arc and the suncave parry is very weak indeed. As the sun climbs the sunvex arc separates from the UTA. At 14° it is roughly tangent to the now dominant suncave Parry. 2° higher and the sunvex Parry is just a faint smudge. Try it in HaloSim. Note the sharpness of the suncave Parry.
Moilanen arc – Is it there? Possibly. It is often seen in ski-slope displays when the crystals nucleate downwind of snow blowers. We are uncertain about how the Moilanen forms.
