Originally Posted by
double_barrel
I would appreciate some help to understand the physics of icing risks.
A couple of good articles here:
Supercooled liquid water and airframe icing
Cloud liquid water content, drop sizes, and number of droplets
I read that the icing zone is +2C to -20C and that low clouds represent a greater icing risk than high clouds.
I take that to mean that only liquid water striking an airframe colder than 0C will form ice. Is that correct? Otherwise why does the icing risk disappear at temps below -20C?
In essence, yes.
And that the reason that high clouds are low risk is simply the assumption that they are in air temps below -20?
It's a bit more than that. As you'll see from the second article, the liquid water content in a cloud depends on the cloud
base temperature.
And does it follow from that, that even with very high tops which you cannot get above, an IFR flight, that didn't have a descend option, would be better to stay in cloud but climb into lower temps?
Usually yes, though note the strong peak in LWC around minus 6 or 7 degC.