FY
)
RESTOREAIPA —Gneagbetamtt@s6 —
-
Explanation of Trajectories
Trajectories are dram for parcels originating at the following pressure levels:
This report on the visible clouds could end with the descriptions of the clouds
at the end of three hours, since after that time there are no records of the clouds
840, 700, 500, 300, and 200 millibars. These levels are at approximtely 5,000; 10,000;
sidering the obvious question of what happenc to the airborne radioactive material
after the clouds disappeared from the Eniwstok area, The charts which follow show
are transmitted over worldwide mpteorological networks; and since tha heighta of these
pressure surfaces are necessary for estimations cf upper wind conditions, the computations
having been seen.
20,000; 30,0003; and 40,000 feet, respectively.
However, the report would seem unfinished if {t ended without con-
of trajectories are facilitated if these levels are used. By noting combinations af trajectories at these "standard" levels some idea of the trajectories for intermediate levels
de obtainable; however, a study of the 25,000 foot trajectory for YOKE Day showed that it
wos quite differant than either the 20,000 or the 30,000 foot trajectory. It wis not possible to do any trajectory work at a1] above 40,000 feet because cuteide of the Eniwetok
how the cloud shapes in the preceding diagrams titled
may have been acted on by the upper winds, and they give some in-
dication of the manner in which the cloud mterial 1a essumed to have been spread over
thousands of square miles,
area there ware no upper wind data above that altitude, Two sete af upper air charts
drawn from observational data collected and analyzed on « 12 hour basia were used daily
in trajectory computations,
Operational requirements for the long range deteotion program made it necessury
to produce estimates of how the radioactive materials of the bomb olouds were transported through the atmosphere and to mike day to day forecasts of where the material
was likely:to.go, With present day knowledge and the available facilities for analysis,
The trajectories presented here are based on the data which were available te the
Staff Meteorologist. Consequently, for the Marshal? Island area, these charts are thought
it was necessary to consider the atomic clouds as a set of points which wore carried
along at constant levels by the winds. The paths of these points are called trajectories; and on the lines representing these paths, the arrowheads indicate the locations
of the points at 24 hour intervala, A trajectory analysis assumes that the cloud consisted of parcels which were gaseous In nature and which did not change elevation.
Actually, the cloude contained a high percentage of solid particles which continued to
fall cut as the cloud was transported; and the rate that the solide settled cut is
unknown. It is not possible to determine at what altitude the material was at any
particular tims.
to be more accurate than any other similor charts; but they are less waluable as distance
increases from the test sites, As the distance increased from Eniwetck there waa an attenuation of the amount of meteorological data received.
All of the soundings from the
concentration of upper air stations operating in the Marshall Taland area for the) needa
of the' Task Force were available aboard the 0.8.5, Ut. McKinley; but these data, expept
the soundings from Kwajalein, were not tranamitted to unite outside of the Marshall
islands,
Also, it is false to consider the clouds as sete of points since
the horizontal dimensians of the clouds is important in determining how tho clouds
The structure of tho atmosphere over the Marshall Islands during the season of the
were acted upon. By the time the clouds had travelled across the Pacific, they had
bean affected by a miltitude of diffusion processes. The altitude of the cloud mte-
SANDSTONE Operation and its effects in producing somewhat similar trajectories are worthy
of note, During thio perlod, easterly winds, the trades, are no
found from the
surface to approximtely 15,
or 20,000 feat. At about that elevation there is a
rial was changed by large-scale vertical turbulence such as is found in cumvjo-forn
clouds; and the clouds nere spread out over such a large area as to be dispersed by
the eddy-diffusion effects of high or low pressure systems such as are shown on weather
transitionul region of variable winds,
nesterlies prevail to the otratosphere,
Above 20,000 feet the wind is westerly, and
Generally speaking, this caused the material
below 20,000 feet to apread toward the Southwest Pacifis or the Philippines and the
material above 20,000 feet to spread toward Mexico or the United States, Such an upper
mape,
Another feature of a trajectory analysis which is wfevorable is that meteorological
theory indicates that an air parcel, or clad aaterial which is moving as a gas, moves
wind structure is normal for the Marshall Island area during sesson when the trade winds
predominate, 4 study, not included in this report, we nade of the trajectory patterns
not at a constant elevation, or at a constant pressure level, tut om *isentropic® surfaces, Isentropic surfaces are defined aa surfaces of constant “potential temperature,"
and such a surface varies in altitude depending on the preaswe-temperature choracter-
jatios of the atmosphere,
The data for these pressure surfaces
for alr parcels originating over Eniwetok daily for a period of 30 days begdaning on
Murch 22, 1948, and ending on April 20, 1948, This study sbowed that parcels originating
over Eniretck at altitudes from 5,000 to 10,000 feet normally moved wostward and passed
This means that the gaseous cloud material prokably uwderwent
over the Philippine Islands within two weeks, Parcels at 20,000 feet did not move cansistently in any particular direction, In this transitional sone, some of them moved to
merked changes in elevation as constant potential temperatures were maintoined. It also
maens that the wind patterns for large areas on istentropio surfaces my be somewhat dif-
the east, some weat, and a few moved into the southern hemisphere where upper air data
Were unavailable. The 30,000 and 40,000 foot trajectories invariably moved sastward,
normally passing south of Hawaii, and reached Mexico within six to aight days after their
ferent than on constant level or constant pressure surfaces. (The movement, of the
clouds on isentropic surfaces is the subject of a ourrent investigntion under the direc-
tion of Dr. R. Wexler of the U, S. Weather Bursa.)
origin at Eniwetok,
The effecta of the trajectories on the testa days were to stretch out the aloud
material to the wast and to the east in a band which continually increased in length.
If no foll out is considered, the cloud may be assumad to be « ribbon~Liks atructure
Because of so many false assumptions, it would seem that trajectory studies are
useless; but when used operationally in long range detection, trajectory analyses gave
remarkably successful results. For thie reason, and because constant level or constant
pressure analyses are a)] that are available to date, these charts are included here.
which was slanted downvard from east to west. That is, the clouds even after several
days mintained smpes similar to those show in the vertical projections on the
preceding pares,
AAED AtomiesEneryyACh1946 Sueckernliineeeutsyiuensnpeaimanint
-43-
.