john cop wrote:
Thank you. Makes sense.

In my little experience, the icing was ferocious within, in seemed,
the top 10 ft of the cloud (it was probably more like 100 to 500 but
who knows – it was 20 years ago and I wasn't taking notes at the
time). I always assumed that it was the sun heating the vapor,
droplets, whatever, and forcing them to a higher altitude so they were
a very nearly at their super cooled limit. The dividing line between
ferocious and minimal icing conditions was sharp and very pronounced
during the decent which suggested to me, that sun heating (energy
transfer, if you prefer) was the cause or at least a significant
contributing factor.

The reason that the top portion of a cloud may produce the most icing...
is that the cloud's formation process has resulted in the most liquid
water near the top.

The formation of most clouds is the result of lift, and as air lifts it
cools at a very substantial rate. When the dewpoint is reached, the
condensation occurs. As the air lifts more, the air becomes colder and
has less capability to support water vapour... hence more
condensation. If the air near the top of the cloud was lifted the
furthest, then that is the air where the most liquid has been condensed.

The fact that the sun may heat the top of the cloud a little, actually
works against icing. By raising the temperature slightly, the air can
support more vapour, and some of the liquid will evaporate.



--
God grant me the serenity to accept the things I cannot change, the
courage to change the things I can, and the wisdom to know the difference.
--- Serenity Prayer