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):
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?