We're probably going to deep. The air is cold. The air coming down from the helicopter is full of moisture and condensation nuclei. Ice fog forms.
The main reason why ice fog forms from water vapour created by human activities, is because when its cold enough for ice fog to form there is hardly any water in the air. Survival in arctic conditions has the same hydration concerns as desert survival.
The helicopter's engines produce the water vapour based on how much fuel is being used, or how high the power demand is. It's hard to say for certain, but I think the helicopter is producing some ice fog on approach to the area, but doesn't produce a large amount until it tries to lift the slung load. Condensation nuclei are readily available from the exhaust.
One clue that there is some ice fog already is the "light pillar" is commonly associated with ice fog, however this could also be a lens effect.
We've spent the last week with temperatures below -30C and with Wind Corrected Temperatures of less than -40C (occasionally below -50C). I drove to work in ice fog that reduced visibility well below 100m at times (I know this because I couldn't see the traffic lights when I was first one stopped at the intersection).
Today we're up to -22C and my 6 and 8 year old are keen to spend the whole day snowboarding. You get used to it.
Matthew.
Last edited by Matthew Parsons; 2nd Feb 2008 at 21:05.