I
|
following IVY Mike and CASTLE 1 and 2 was not observed after Shots
4 and 5. ‘(Shot 3 was too small to cause such a rise and dets ob=
tained t'rom Shot 6 were insufficient).
The results obtained from -
=
the IVY shot are therefore still the best available upon which to
base an explanation of the rising F2 layer.
Continued study of the data obtained from the IVY snot has led
to the conclusion that the results cannot be explained by as simle
a mechanism as was assumd in the IVY report (see Section 4.1 of
Reference 1). In that report, a simplified model of the ionosphere
was used as a basis and computations were made which indicated that
a vertical motion of the Felayer electrons could occur at aout a
twentieth of the velocity of the convection current caused by the
_
thermal effects of the blast. Since the IVY revort was written, howe
ever, a series of three papers (Reference 4) uas been published in
:
which a complete theory of ionization drift is outlined. These papers
include detailed computations of both vertical and horizontal drift
of ions caused by air currents, for various values of the dip angle
of the earth's magnetic field, and for various altitudes above the
earth's surface.
Reference 4 includes the effect of Hall conductivity,.
which was not included in tha simplified treatment of the IVY report,
In that report, jt was pointed out that a vertical current of air at
the magnetic equator cannot cause an appreciable vertical drift of
Feelayer ions.
According to the nore complete theory of Reference
4) nowever, a pronounced horizontal drift would occur, which would
be in the westward direction for an upwardly directed current of air.
In the light of this theory, it would appeer that the apparent rige
of the F2 layer was not an actual rise at a1]; the F2 layer only
appeared to be rising because ions were awept away horizontally at
successively higher levels by the ascending heated mass of air. The
tests did not, howaver, take place exactly at the magnetic equator,
the earth's magnetic field being tilted at an angle of about 13 de= ©
grees at the Pacific xsroving Ground. The rising air current, therefore, would have a small component of velocity along the earth's field
' and there would be sam rise due to this component, There would also ©
be a component directed toward the south, because the field tilts up~ward in that direction. The net effect would be that ions would
be moved in a southwesterly direction, with small vertical velocity
svperposed upon the horizontal motion. A411 of the observed phenomena
should be consistent with this picture, if it is correct. -
,
The horizontal extent of the phenomena would, of course, depend
upon the size of the heated air mass, ari this, in turn, would depend
upon the erergy released by the blast.
Furthermore, the distribution
of the blast-wave energy would depend upon the wind and temperature
structure of the atmosphere, and the volume affected would,* in ‘gen-
eral, not be symmetrical with respect to the source,
Should this
volume have a fairly sharp boundary (true for atomic clouds observed
near the earth's surface), tne horizontal extent of the phenomena
observed would also have a sharp boundary and, if the Ltonogphere
recorder were located just outside the boundary, a completely different sequence of events would be observed than if the recorder were
located nearer tothe shot point.
Outside the heated sir mass, for
example, there would be a downwardly directed current of air, and the
67
SECRET
Nee