I have found this specific image here (Loong found out that it is the Soviet Joe 4 test of the 400 kiloton RDS-6 warhead at the Semipalatinsk test site on August 12, 1953):
Also an impressive Youtube Video of the same explosion
As you see, an inverted trumpet cloud is forming around
the rising mushroom stem. I have never seen this strange
picture before.
My educated guess is that the mushroom is rising through
a layer of supersaturated air (which cannot form clouds
normally because of missing seeds provided now by the explosion),
causing fog which is pushed evenly outside by the high air
pressure inside the stem.
- Is there a name for the phenomenon of the trumpet cloud?
- Is my explanation correct and if not, what is the cause
of the trumpet?
Best Answer
This is called a 'skirt' or 'bell' and it is indeed a condensation effect: humid air is entrained by the rising column, and water then condenses out as the pressure falls. These droplets, if they get big enough fast enough, then fall with respect to the rising air, resulting in these skirts.
Condensation phenomena are fairly common with nuclear (and other large) explosions.
This is covered in the Wikipedia article.