roswell

134 JOURNAL OF METEOROLOGY VOLUME 5
from the desert set in, the balloon maintained an alti-
tude of 9200 ± 150ft.
.1\n explanation as to why the ballast release func-
tioned at 9000 ft, although it was set to operate at
12,000 ft, is plain from the following data. The air in
the diaphragm was sealed off on the dawn ascent at
12,000 ft, where the pressure was 657 mb and the
temperature 9C. However, by the time the balloon
passed through this level during the slow descent, the
instrument temperature was 19C. This means that
the pressure of the air trapped inside the diaphragm
was higher than it was at time of seal-off.
For the ballast valve to function, the balloon had to
descend to a pressure which would be greater by about
3 mb than the pressure of the trapped air at its now
higher temperature. Of course, there was little ventila-
tion past the instrument, and therefore the instrument
temperature was about 25C above the ambient tem-
perature after the sun had risen.
The automatic ballast valve operates. when the
volume inside the sealed diaphragm becomes slightly
less than the volume at seal-off. Denoting the altitude
at which it can operate by the subscript h, the pressure
divided by the temperature at this altitude will equal
the pressure at the seal-off altitude divided by the
trapped-air temperature at the time of seal-off; in
this case
p, =657mb
T, = 9C = 282A
T,. = 39C = 312A,
where the subscripts refers to seal-off. Thus the pres-
sure at altitude h is given by
p,. = p,TA/T, = 727 mb.
This pressure, at which ballast release will begin, cor-
responds to an altitude of 9000 ft, which is the ob-
served altitude maintained by the balloon for nearly
4! hours, until the radiosonde tracking signal was lost.
The theodolite lost the balloon in clouds earlier and
the airplane observer never succeeded in seeing it, so
the balloon may have remained for a considerably
longer period at this altitude. Eleven hours after be-
ginning the ascent, the balloon was reported to have
been seen over Albuquerque, New Mexico, and about
26 hours later a report was made from Pueblo,
Colorado, which seemed to indicate that the balloon
was still in the air at that time. The meteorological
situation and wind data for that area at the time of
flight support the contention that the latter observa-
tions were of the same balloon.
The next flight consisted of an assembly of various
balloons, as follows:
One 15-ft diameter 0.008-inch polyethylene balloon,
Six 7-ft diameter General Mills 0.001-inch poly-
thene balloons,
Two 350-gm meteorological balloons for stadia
measurements.
The single balloon had a measured diffusion loss of
lift of 4 grams per hour. The General Mills balloons
were observed to lose lift at the rate of about 100
grams per hour per balloon.
Three of the 7-ft balloons were inverted and deflated
shortly after launching, due to differences in the rates
of rise of the various balloons in the cluster. Therefore,
the altitude reached was not high enough to effect
seal-off. (It is for this reason that the minimum pres-
sure switch wa,s developed for use in later flights.)
Fig. 9 shows the elevation and plan views of the
track of this flight. The train leveled off at 16,500 ft.
The diffusion loss of lift of the remaining balloons wa..
approximately 300 grams per hour. The ballast valve
used had an unusually high rate of static leakage
which had been measured before release and found to
be 310 grams per hour. Thus fortuitously, the loss of
lift was compensated by ballast leakage. This nearly
~·r----r--~----r---~---r--~----r---~---r--~----r---~---r--~----~--.----.--~--~
r
I -- Ballool flooli'}' a/
!,.
i
l (
I5..
IIILIA6
ils ~ling
c~n's. •.,.isllhP6; ,_ s«Jillcil~ -- Balloon floolin on
\
""' '"'" LOCAL Tllll
FIG. 6. Idealized time-altitude curves for various balloon-control systems.
' ' '
\
\
\ \
\ \