"O. Sami Saydjari" wrote in message
...
This question is a question on physcial phenomena, NOT on regulation (so
I am starting a new thread).

As I understand it, icing happens between +2C and -10C. Assuming this
is correct, I have three questions.


MOST icing occurs between 0C and -10C but icing has been shown to occur
at -40C. Icing in cumulus clouds virtually always extends below -10C.and
often to below -20C


(a) Does that mean one is relatively safe if the surface temperature is
below -10C (and there is no temperature inversion, meaning that the
temperature is known to decrease as one goes up in altitude)?


Ice is less likely to be a problem than if it was 0C at the surface but,
again, icing can occur at temperatures much lower than -10C particularly in
clouds with vertical movement (cumulus).
..
(b) Is icing from 0C to +2C a possibility only when your aircraft skin
is colder than 0C (probably because you are descending from altitude)?
Or is there some other condition where this is possible?

This was the conventional thiinking buy a recent NASA study was unable to
document ANY ice formation above 0C.

(c) I have been told that icing is possible from -10C to 0C because
water sometimes get "super-cooled" (which I assume means that water gets
below freezing, but does not form ice for some reason). Is that right?
If so, under what atmospheric conditions does water get super-cooled?

If you do a search on supercooling you will find a lot of info. Basically
water almost NEVER cools to 0C and then starts crystalizing. It usually
cools to -7C before crystalizing starts. Once the crystalization starts the
temperature increases as the latent heat is released and when the last water
freeezes the temp is at 0C again. You can verify this with a glass of
water.and a thermometer. This assumes that the water is still. It the
water is turbulent then the temperature will go even lower before
crystalization starts.

Mike
MU-2