Rates of Rise of the Atomic Clouds
The curves which are titled as the rates of rise of the atomic clouds combine
the graphs of the elevation angles of the tops of the primary parts of the atonic clouds
(see pages 11, 13, and 15 of Appendix I) with borizontal distances. These curves show
approximately the time when the cloud reached a particular altitude and moy be used to
Caleulate how fast the clouds were rising at any particular tims, These curves are considered to be useful in planning aircraft operations or scientific work when atomic
clouda are expected.
The altitude of the clouds at esch minute ws found by simple trigometric
methods; however, the horisonte] distances used in these calculations were not easily
determined. If the types of date available for calculations are reviewed, it will be
seen that the elevation and asimith angles, the upper winds, the hoipht of the tropo=pause, and the approximate times the clouds reached maximm altitudes, are the only
known factors. Unfortunately, the angles are from uhat must be assumed to be a single
theodolite station. With the available data, it is impossible to fix the positions of
the top of the clouds in apace with the exception of the locations of the XRAY and YORE
day clouds at the times whan these clouds my be apsumad to Inve reached the tropopause.
Other values for horizontal distances mist be arrived at by sethods shich appear to be
most reasonable,
the elevation angle curwe is believed to represent the most probable slovation anglea
for the top of the cloud and the solid line represents the elevation angles of the edge
of the cloud. This lower elevation angle gives a reasonable looking rate of rise curve.
The angle 24.5 degrees does not,
as in the case of the XRAI day cloud, there seemed to be little horizontal
aovement during the first few minutes. The distance of the test site waa 15 ailes,
so it has been ressoned that the cloud was at this distance during the first four
ainutes, After the fourth mimte, it wae assumed that the cloud moved 1n e etreight
line, but at warying distances each minute depending on the azimuth angles.
Different methods have been used for each of the three clouds, and these
sethods will be explained below as each cloud is discussed,
It may be noted that the curves are dashed at low clevationa,
the atomic clonia were rapidly
YOKE DAY <—the sketches of the top of the clond show that it begen to spread
out into an anvil form ebout 12 minutes after H-hour. The height of the tropopause was
between 55 and 5% thousand feet, so it 1s aseused that the cloud reached 56,000 feet or
an altitude of 9.2 miles at that time, Examination of the graph for the elevation angle
{see page 13, Appendix I) shows how the elevation angle of 23,5 degrees was obtained.
It 1s thought that this elewation angle is more reasonable than the 24,5 degree angle
ebtained directly, The shape of the claud was auch that it was impossible to sight an
the true top of the cloud and it 1s assumed thet the theodolites were sighted on the
noar edge. The elevation angles of the top of the cloud and the near edge would have
approached equality as the cloud moved away from the observer. The dashed section of
To obtain what seens to be the best possible approxisations of the horigenta] distances, the triangular diagrem shown above the rate of rise curve ms constructed. This diagram bas been drawn to acale by means of points representing the
test site, the horizontal distance of the cloud at the tine that it reached its
This is because
ing as well as rising when they wero first farwed.
highest point, and the atimuth angles of the center of the cloud top. The horizontal
distences wara obtained by noting the lengths of the azimuth angle linea for each
ainute,
Theodolite data are not believed to be reliable until] after the Nrast minute,
-_
XRAY DAY= ron skstches of the cloud showing the formtion of the plum, it
ZEBRA DAY=— the atomic cloud on ZEBRA day did not reech the tropopause and
seems that the atomic cloud reached the trepopause and stopped rising about twelve and
one half ainutes after B-hour. The height of the tropopause on this day ms about
56,000 fest or 9,2 miles, With the elevation angle of 26.0°, this puts the cloud at a
horisontal distance of 18.9 siles. The distance of the test site was 17 miles and since
the cloud wea acted on by easterly and then westerly winds, the azimuth angles of tha
olond show Littles or no change in the firet three mimtes. Therefore, it 1s assumed
for this reason it is difficult to fix the horiaonteal distance of the top of the cloud
at the time that it reached fits highest alevation. Al) that is known are the azimrth
angles and the distance of the test site, Fortunately, the upper winds were such that
the path of the rising cloud would have much the same even though the rates of rise
might hawe waried considerably. By means of the triangular diagram shown above the
curve, it may be seen that the most probable position of the cloud top at the time
minute until the clond reached the tropopause, it 1s assumed that the horizontal motion
wes wmifors and in a straight line. This means that the horizontal distance is assuned
to be increasing at the rate of .2 mi/min during the time that the cloud ms rising. It
believed that the nature of the upper winds was such that the actual action ws more
that the curve drew gives a reasonably accurate representation of
winds could oot have carried the cloud far enough north for it to have been as far as
twelve miles away, and the winds were too strong to have only carried the cloud to a
distance of 10 miles, The beet estimate of distances which can be obtained is Ll miles,
and this is the diutance which bas been used to determine the position of the cloud top
at each minute. The behavior of the ZEBRA day cloud was wunusuel in that it rose to
about 28,000 feet in eight minutes and then « finger of the cloud rose out of the primary macs for an additional 5000 feet. There were two rates of rise, one for the primary mise and one for the cloud projection. The usimuth angles for toe primary mse
tave been obtained from pages 27 of Appandix I but the asisuth angles for the fingerlike projection have heen abtaiged fram the cloud sketches,
.
From the third
that 1¢ reached highest elevation 1s somewhere between 10 and 12 miles.
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that the top of the aloud ws still at 17 miles at the third minute.
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The upper