372
MACHTA
10
3
=p
No)
‘»
5
.
6
Fig. 2—Estimated upper tropothe Sept. 1, 1961, U.S.S.R. test.
Shading indicates dates of first
appearance
air filters.
of debris on surface
D,
©
6
7-8
spheric trajectory of debris from
‘
iN
9-10
|
3°
72—\
7 °¢
9-10
eo
°
eete
fe ot
.
Ss
GROSS BETA
NETWORK
ePTIME OF ARRIVAL
IN SEPTEMBER 1961
5-6
C= 7-8
(1D 9-10
lay of several days between the predicted arrival at 30,000 ft and at
ground level. This delay results, inour opinion, from time to mix down-
ward or for particulates to settle out.
The literature contains innumerable examples of trajectories of
nuclear clouds obtained by many techniques. Of these methods the ap-
plication of isentropic analysis is one of the two most valuable improvements over past Weather Bureau procedures. Isentropic analysis
permits the tracking of air parcels undergoing adiabatic vertical motions, A dramatic case in which the isentropic trajectories appear to
explain better the observations of ground-level air concentrations has
been given by Reiter.‘ In the mean, the isentropic surfaces slope downward from north to south in the troposphere; thus trajectories moving
southward will be brought closer to the ground or man’s environment,
whereas those moving northward rise away from the ground.
A second, less important, improvement is the computation of tra-
jectories by an electronic computer rather than by hand. An illustration
of a computer forecast currently in operational usage by the Weather
Bureau appears in Fig. 3 with starting points at the Nevada Test Site
(NTS). In practice, it is felt that the additional wind information and
knowledge of local topographic conditions permit meteorologists at NTS
to start computation of the trajectories more correctly than can be done
by machine, After 6 hr the machine trajectories are used as the basis
for continuing the forecasts to 30 hr. Figure 4, taken from the Weather
Bureau analysis of trajectories for STROBE (the use of constant-level