sen
yaare
| During its rapid initial ascent the ball contracted horizontally and became trans
formed into a fiery and exceedingly turbulent columnar cloud, losing its quasi-spherical
form soon after the ascent began. | thought | saw a small secondary explosion in the
fiery column at this time, but other observers do not confirm this. I removed the goggles
immediately ofter this secondary detonation.
A Ly
The *doughnut* or ‘smoke ting was then formed, without much slockening in the
rate of ascent, | estimated that the mushroom cloud reached the tropopause within H
plus 3 minutes. Its vertical deceleration after 2 minutes was very rapid and was accompanied by a tremendous lateral spreading many times faster than that seen in A-
bomb clouds. It appeared as if the cloud “’splashed"” ogainst the tropopause.
The stem passed into the head of the cloud and moved upward with it from the
time the latter was first formed. At first the stem wos relatively natrow. being not more
than I mile in diometer and perfectly vertical, it seemed fo be very turbulent but was
not marked spirally as are some A-bomb stems. The turbulent appearance soon vanished
and the stem expandedJaterally to a diameter of 10 miles. At maximum and before deformation. if presented a'very smooth appearance like a pile of inverted saucers of
different diameters, stacked one upon the other. The only natural cloud resembling the
stem af this time is the vertically stocked alfocumulus lenticularis seen over and near
high mountains during foehn periods. | have seen clouds like the stem over the Sierras
in California, and the Southern Alps in New Zealand and | have seen photographs taken
in Sardinia of similar structures associated with the Alps. There is no doubt in my mind
that the smooth stem is a surround formed about the nar-ow turbulent initial stem by
condensation in atside air taking part in the vortex:ring circulation. The smooth out-
lines indicate that this part of the ci:culation is non-tu:bulent streamline motion and
that the various ’’saucers”’ are the sesult of variations in moisture content in the atmos-
pheric layers partaking in the motion upward through the middle of the vortex ring. It
may be assumedthat the rapid lateral extension of the initial stem is an index of the
rate of entrainnent of outside air into the vortex ring system, if so, the rate must be
many orders of mogitude greater than that in any p:evious detonation. At the point
where the stem joined the head several large skirts formed toward the end of the ascent. Their presence suggested a highly saturated atmospheric laye: af about
30000 feet.
In contrast to the broad stem the head remained turbulent. It still presented a
cumuliform structure-at H plus 45 minutes. By this time however, parts of it were
being transformed into altocumulus and other parts (at the same level but on the opposite side of this cloud) into cirrus. After compaving notes with other observers. 1
om convinced that the mushroom cloud remained below the tropopause throughout the
period of its expansion and thereafter. This is not to say that the entire cloud was
18.
ERESTRICTEDEDAL
Y
MIGENER
S15z35
-
“rt