drift electrons would therefore move eastward instead of westward. In
the vicinity of the boundary, this would tend to cause a decrease of
ion density.
Furthermore, the ccmbination of decrease in atmospheric
density with height and the conservation of mass would result in a
greater downward velocity of air molecules at higher altitudes than
at lower levels. The ions that are moved eastward by the descending
air would be swept eway more rapidly at higher than at lower levels,
and the effective height of the F2 layer might even be lowered. Tie
ionosphere recorder would not, therefore, register the large apparent
increase in height that would be observed ‘directly below the rising
heated air mass. Of course, turbulence near the boundary, and
tpiling up" of ions would complicate the picture.
The above discussion is offered as an explanation of the events
following Shot 4. The yield of this shot was smaller, which would
have resulted in a smaller volume of heated air. Furthermore, because
of the later date, seasonal changes in upper atmosphere winds might
have caused a different horizontal distribution of blast-wave energy.
The net result may have been that, for this shot, the ionosphere recorder was located outside of the boundary of the heated air mass,
hence no pronounced change in the height of the F2 layer occurred.
(The large apparent increases in level observed at about plus one hour
appear to have been due to a horizontal motion of the point of ree~
flection as described in Section 3.3.3, and may have been the early
stages of the wave motion which gave rise to the distant effects de=
scribed in Section 3.4.)
In the case of Shot 5, the occurrence of a G condition (see
Section 3.3.4) made it impossible to obtain a complete picture of the
F2elayer phenomena.
Another mechanism which may be of importance in explaining the
results is the "cyclone" action due to the rising air mass.
Air
moving in horizontally to replace the ascending air would be deflected
by the Coriolis force caused by the earth's rotation, and a counterclockwise whirl would result in the northern hemisphere, just as in
the case of an ordinary tropical or extratropical cyclone. The winds
of this whirl would have a northwardly directed component east of the
shot point (where one of tke ionosphere recorders was located). This
component would lie along the earth's magnetic field, and, inasmuch
as electrons can be moved freely parallel to the field, the F2-layer
ions would tend to move northwards and downwards. This may be the
mechanism by means of which the F2-layer conditicns return to normal
(i.e., F2-layer ionization is moved in from the south by this process).
This would explain the occurrence of the lower of the two maxima de-=
scribed in Section 3.3.1 (see also Fig. 3.12) and would also explain
the gradual descent of the F2 layer as conditions return to normal,
From the above discussion, it is obvious that the F2-leyer
phenomena that follow a large atomic blast are quite complicated and
probably cannot be com letely explained with the limited data available.
Data covering a wider range of distances and azimuths would be ree
guired in order to obtain a complete picture,
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SECRET