Upshot-Knothole Test Series
Nuclear Test ENCORE
Detonated: 8 May 1953
Time: 1530 GMT
TYPE OF DETONATION: Airdrop
ALTITUDE OF DETONATION: 740 m (above ground)
REPORTED YIELD: 27 kilotons
RADIOIODINE (I-131) PRODUCED: 3.9 x 10E6 Curies.
STABILIZED CLOUD HEIGHT: Top 12.5 km, msl
Base 8.8 km, msl
MEASUREMENTS AVAILABLE FROM GROUND-LEVEL COLLECTORS: Yes
RADIOIODINE IN COUNTIES WITHOUT GROUND-LEVEL COLLECTORS
ESTIMATED BY: AIPC method
CLOSE-IN FALLOUT PATTERN AVAILABLE: No
Trajectory and Fallout Characteristics
Upshot-Knothole, ENCORE
Close-In Fallout
No Close-In Fallout data have been located for this test.
Town Data Base
No Town Data Base estimates were made for this test.
County Data Base
No County Data Base fallout estimates were made for this test.
Upper-Air Trajectories
The three highest trajectories started to the northeast but they diverged
widely after leaving Utah because of large directional and speed shears
beginning late in the first day of detonation (Fig.UK/8/T). At detonation time,
upper winds over NTS were very strong from the southwest being over 50 m s-1 at
9.2 km, 87 m s-1 at 10.7 km and 74 m s-1 at 11.8 km. The 11.8 km trajectory,
speeding to the east-northeast, reached southern Minnesota late on the first day
of detonation, turned to the southeast while accelerating and left the U.S. over
the Georgia coast in the middle of the second day. The 9.2 km trajectory moved
to the northeast across Wyoming and exited the U.S. into Canada over central
North Dakota late on the first day. Turning to the southeast, it reentered the
U.S. early on the third day (1200 GMT, 11 May to 1200 GMT, 12 May) over Lake
Ontario moving to the south. It continued southward over eastern Virginia and
exited the U.S. over the coast of South Carolina. The 5.6 km trajectory took a
path across Utah to the northeast, curved to the left and exited the U.S. into
Canada over eastern Montana, early on the second day, while moving slowly to the
north.
The much slower 3.0 km trajectory took up a wave pattern to the east
reaching eastern Kansas at the middle of the third day. There it turned to the
northeast and accelerated, crossed the southern tip of Lake Michigan, then left
the eastern border of Maine at the end of the fourth day. Much of the U.S. was
covered by the envelope described by these trajectories.
Radioactive iodine (I-131) was widely distributed over the United States
after this test (Fig.UK/8/F) possibly due to the widely-divergent trajectories
as shown in Fig.UK/8/T. Even though this was a powerful explosion, gummed film
(GF) observations indicated most of the depositions were light. This is
consistent with an airdrop explosion. The exceptions were a few moderate to
heavy amounts in eastern Montana and northwestern North Dakota. Only the far
west states and the southeast coast received no fallout.
The only significant recorded fallout (medium heavy) on the first day
occurred in northwest North Dakota rain. It was associated with the debris
cloud segment stretched between the 5.6 and 9.2 km trajectories. On the second
day, light, mostly wet, depositions appeared in the central and north-central
U.S. (east of the Rocky Mountains) with moderate amounts (wet) in
southeast Montana and (again) northwest North Dakota. These depositions were at
actual locations of GF sites; areas between them undoubtedly received fallout
also. List (1954) states that the 5.6 and 9.2 km trajectories also carried
fallout into southern Canada on this day. No fallout appeared beneath the track
of the 11.8 km trajectory that moved southeastward from Wisconsin to Georgia in
the first half of the day. Light wet depositions continued in the central U.S.
on the third day (1200 GMT, 10 May to 1200 GMT, 11 May) and dry depositions
began in the southeastern New England states. Some light, wet fallout occurred
in south-central U.S. on the fourth day and light depositions spread in the
northeast into western New York State and eastern Maine. The northeastern
depositions may have resulted from westerly winds at lower levels carrying
radioactive debris from beneath the 9.1 km trajectory that had passed from north
to south across the eastern states on the third day. Light wet fallout appeared
also in southeast Montana on the third and fourth days without any trajectory
associations. On the fifth day, the only depositions were in the northeast, New
England and south-central U.S. to the Gulf Coast. Strong shears caused by
the greatly diverse trajectories undoubtedly contributed to the wide
distribution of fallout following this test.
REFERENCES
List, R. J., 1954: The transport of atomic debris from Operation Upshot-
Knothole. U.S. Atomic Commission, NYO-4602 (del); U.S. Weather Bureau,
Washington, D. C.
Figure UK/8/T. Estimated trajectories, at several altitudes, of the radioactive cloud resulting
from the test ENCORE of 8 May 1953. Numbers indicate the position of each
trajectory at 0000 GMT for several days following the explosion.
Figure UK/8/F.
Table UK/8/GF (Part 1). Estimates of I-131 daily deposition derived from gummed-film results and associated
precipitation indices for the shot ENCORE detonated 5/ 8/1953.
. Dep = daily deposition of I-131 per unit area of ground (nCi per sq m)
. Pi = precipitation index
Site State Month and day
________________________________________________________________________
5/ 8 5/ 9 5/10 5/11 5/12 5/13
Dep Pi Dep Pi Dep Pi Dep Pi Dep Pi Dep Pi
ABILENE TX 0 1 0 1 1 2 NA 1 3 3 0 1
ALBANY NY 0 1 0 1 15 2 13 2 4 5 3 7
ALBUQUERQUE NM 1 1 0 1 0 1 0 1 0 1 0 1
ALPENA MI 0 1 1 1 1 1 0 1 0 1 0 1
AMARILLO TX 1 1 5 1 0 1 3 1 1 3 0 1
ATLANTA GA 0 1 0 1 0 1 0 1 0 1 0 1
BALTIMORE MD 0 1 0 1 0 1 0 1 0 1 5 5
BILLINGS MT 0 1 81 3 20 4 36 6 2 1 0 1
BINGHAMTON NY 0 1 0 1 0 1 0 1 1 2 1 5
BOISE ID 0 1 0 1 0 1 0 1 0 1 0 1
BOSTON MA 0 1 0 1 1 1 0 1 0 1 0 1
BUFFALO NY 0 1 0 1 0 1 13 3 1 2 0 1
BUTTE MT 0 1 18 1 0 1 0 1 0 1 0 1
CARIBOU ME 0 1 0 1 0 1 3 5 1 1 2 6
CASPER WY 3 2 12 5 0 1 0 1 0 1 0 1
CHARLESTON SC 0 1 0 1 0 1 0 1 0 1 0 1
CHEYENNE WY 0 1 1 2 1 2 1 2 0 1 0 1
CHICAGO IL NA 1 NA 1 NA 1 NA 1 NA 1 NA 1
COLO SPRINGS CO 1 1 1 2 1 2 1 5 0 1 0 1
CONCORDIA KS 0 1 8 5 1 1 2 4 1 3 2 1
CORPUS CRIS. TX NA 1 NA 1 NA 1 NA 1 1 2 NA 1
DALLAS TX 0 1 1 2 2 6 6 4 8 6 2 6
DANSVILLE NY 0 1 0 1 0 1 2 1 0 1 0 1
DEL RIO TX 0 1 0 1 0 1 1 2 0 1 0 1
DENVER CO 1 1 4 4 4 4 0 1 0 1 0 1
DES MOINES IA 0 1 3 2 6 6 1 1 0 1 0 1
DETROIT MI 0 1 0 1 0 1 2 4 4 5 0 1
DUNKIRK NY 0 1 0 1 0 1 1 2 2 6 1 5
EAST PORT ME 0 1 0 1 0 1 0 1 3 2 10 6
ELKO NV 0 1 0 1 0 1 0 1 0 1 0 1
ELY NV 0 1 0 1 0 1 0 1 0 1 0 1
EUREKA CA 0 1 0 1 0 1 0 1 0 1 1 4
FARGO ND 0 1 4 5 2 6 0 1 0 1 0 1
____________________
NA = not available
1 Table UK/8/GF (continued)
Site State Month and day
________________________________________________________________________
5/ 8 5/ 9 5/10 5/11 5/12 5/13
Dep Pi Dep Pi Dep Pi Dep Pi Dep Pi Dep Pi
FLAGSTAFF AZ 0 1 1 2 0 1 1 2 0 1 0 1
FORT SMITH AK 0 1 2 4 0 1 NA 1 NA 1 1 2
FRESNO CA 0 1 0 1 0 1 0 1 0 1 0 1
GOODLAND KS 0 1 2 1 10 6 0 1 0 1 0 1
GRAND JNC CO 2 1 1 3 NA 1 0 1 0 1 0 1
GRAND RAPIDS MI 0 1 0 1 0 1 0 1 2 6 0 1
GREEN BAY WI 0 1 1 2 0 1 0 1 0 1 0 1
HELENA MT 0 1 0 1 0 1 0 1 0 1 0 1
HURON SD 0 1 4 5 NA 1 0 1 0 1 0 1
JACKSON MS 0 1 0 1 1 2 0 1 5 5 1 4
JACKSONVILLE FL 0 1 0 1 0 1 0 1 0 1 0 1
KALISPELL MT 0 1 0 1 0 1 0 1 0 1 0 1
KANSAS CITY MO 0 1 0 1 2 4 0 1 0 1 0 1
KNOXVILLE TN NA 1 NA 1 NA 1 NA 1 NA 1 0 1
LAS VEGAS NV 1 1 1 1 1 1 0 1 0 1 0 1
LOS ANGELES CA 0 1 0 1 0 1 0 1 0 1 0 1
LOUISVILLE KY 0 1 0 1 0 1 1 5 2 3 NA 1
LYNCHBURG VA 0 1 0 1 0 1 0 1 0 1 4 1
MARQUETTE MI 0 1 3 3 0 1 0 1 0 1 0 1
MEDFORD OR 0 1 0 1 0 1 0 1 0 1 0 1
MEMPHIS TN 0 1 0 1 28 6 15 7 10 6 1 2
MIAMI FL 0 1 0 1 0 1 0 1 0 1 0 1
MILFORD UT 3 5 1 4 0 1 0 1 0 1 0 1
MILWAUKEE WI 0 1 0 1 0 1 0 1 0 1 0 1
MINNEAPOLIS MN 0 1 1 1 NA 1 0 1 0 1 0 1
MOBILE AL 0 1 0 1 0 1 0 1 0 1 0 1
MONTGOMERY AL 0 1 0 1 0 1 0 1 0 1 0 1
NASHVILLE TN 0 1 0 1 0 1 1 2 0 1 3 5
NEW HAVEN CT 0 1 0 1 0 1 7 1 0 1 1 3
NEW ORLEANS LA 0 1 0 1 0 1 0 1 3 3 2 3
NEW YORK AEC NY NA 1 NA 1 NA 1 NA 1 NA 1 NA 1
PHILADELPHIA PA 0 1 0 1 0 1 1 1 1 2 2 6
PHOENIX AZ 0 1 1 1 1 1 0 1 0 1 0 1
PITTSBURGH PA 0 1 0 1 0 1 1 3 3 5 0 1
____________________
NA = not available
1 Table UK/8/GF (continued)
Site State Month and day
________________________________________________________________________
5/ 8 5/ 9 5/10 5/11 5/12 5/13
Dep Pi Dep Pi Dep Pi Dep Pi Dep Pi Dep Pi
POCATELLO ID 1 3 1 4 0 1 0 1 0 1 0 1
PORT ARTHUR TX 0 1 0 1 3 5 0 1 15 7 NA 1
PORTLAND OR 0 1 0 1 0 1 0 1 0 1 0 1
PROVIDENCE RI 0 1 0 1 2 1 18 1 0 1 0 1
PUEBLO CO 1 1 1 2 1 3 1 5 0 1 0 1
RAPID CITY SD 8 5 8 5 NA 1 0 1 0 1 0 1
RATON NM 1 1 5 1 1 1 1 2 0 1 0 1
RENO NV 0 1 0 1 0 1 0 1 0 1 0 1
ROCHESTER NY 0 1 0 1 0 1 1 3 NA 1 1 3
ROCK SPRINGS WY 2 4 1 4 NA 1 0 1 0 1 0 1
ROSWELL NM 2 1 18 1 3 1 0 1 14 1 3 1
SACRAMENTO CA 0 1 0 1 0 1 0 1 0 1 0 1
SALT LAKE UT 2 4 0 1 0 1 0 1 0 1 0 1
SAN DIEGO CA 0 1 0 1 0 1 0 1 0 1 0 1
SAN FRAN. CA 0 1 0 1 0 1 8 1 0 1 0 1
SCOTTSBLUFF NB 1 1 4 1 1 2 0 1 0 1 0 1
SEATTLE WA 0 1 0 1 0 1 0 1 0 1 0 1
SPOKANE WA 0 1 0 1 0 1 0 1 0 1 0 1
ST. LOUIS MO 0 1 0 1 0 1 0 1 1 5 1 5
SYRACUSE NY 0 1 0 1 0 1 1 4 0 1 0 1
TEXARKANA AK 0 1 0 1 4 5 18 7 8 6 4 6
TUCSON AZ NA 1 NA 1 NA 1 NA 1 NA 1 NA 1
WASHINGTON DC NA 1 NA 1 NA 1 NA 1 NA 1 NA 1
WATERTOWN NY 0 1 0 1 0 1 1 4 3 5 0 1
WICHITA KS 0 1 6 6 1 1 2 6 0 1 0 1
WILLISTON ND 136 6 45 7 0 1 1 5 0 1 0 1
WINNEMUCCA NV 0 1 0 1 0 1 0 1 0 1 0 1
YUMA AZ 0 1 0 1 0 1 0 1 0 1 0 1
____________________
NA = not available
Table UK/8/GF (Part 2). Estimates of I-131 daily deposition derived from gummed-film results and associated
precipitation indices for the shot ENCORE detonated 5/ 8/1953.
. Dep = daily deposition of I-131 per unit area of ground (nCi per sq m)
. Pi = precipitation index
Site State Month and day
________________________________________________________________________
5/14 5/15 5/16 5/17 5/18 5/19
Dep Pi Dep Pi Dep Pi Dep Pi Dep Pi Dep Pi
ABILENE TX 0 1 0 1 0 1 0 1 0 1 0 1
ALBANY NY 1 3 4 6 0 1 0 1 1 4 1 1
ALBUQUERQUE NM 0 1 0 1 0 1 0 1 0 1 0 1
ALPENA MI 0 1 1 1 0 1 2 6 0 1 0 1
AMARILLO TX 0 1 0 1 0 1 0 1 0 1 0 1
ATLANTA GA 0 1 0 1 0 1 0 1 0 1 0 1
BALTIMORE MD 1 5 0 1 0 1 0 1 0 1 0 1
BILLINGS MT 1 2 3 1 1 1 0 1 0 1 0 1
BINGHAMTON NY 1 5 0 1 2 6 0 1 0 1 0 1
BOISE ID 0 1 0 1 0 1 0 1 0 1 0 1
BOSTON MA 0 1 0 1 0 1 0 1 0 1 0 1
BUFFALO NY 4 6 0 1 0 1 0 1 0 1 0 1
BUTTE MT 0 1 0 1 0 1 0 1 0 1 0 1
CARIBOU ME 0 1 4 6 0 1 0 1 0 1 0 1
CASPER WY 0 1 0 1 0 1 0 1 0 1 0 1
CHARLESTON SC 0 1 0 1 0 1 0 1 0 1 0 1
CHEYENNE WY 1 2 1 5 0 1 0 1 0 1 0 1
CHICAGO IL NA 1 NA 1 NA 1 NA 1 NA 1 NA 1
COLO SPRINGS CO 0 1 4 6 0 1 0 1 0 1 0 1
CONCORDIA KS 0 1 0 1 0 1 0 1 0 1 0 1
CORPUS CRIS. TX 2 6 NA 1 NA 1 NA 1 NA 1 NA 1
DALLAS TX 1 4 3 7 0 1 0 1 0 1 0 1
DANSVILLE NY 0 1 0 1 0 1 0 1 0 1 0 1
DEL RIO TX 0 1 0 1 0 1 0 1 0 1 0 1
DENVER CO 0 1 0 1 0 1 0 1 0 1 0 1
DES MOINES IA 0 1 0 1 0 1 0 1 0 1 0 1
DETROIT MI 0 1 0 1 0 1 0 1 0 1 0 1
DUNKIRK NY 1 5 0 1 0 1 0 1 0 1 0 1
EAST PORT ME 0 1 0 1 0 1 0 1 0 1 0 1
ELKO NV 0 1 1 3 0 1 1 5 0 1 0 1
ELY NV 0 1 0 1 1 4 0 1 0 1 0 1
EUREKA CA 0 1 0 1 0 1 0 1 0 1 0 1
FARGO ND 0 1 0 1 0 1 0 1 0 1 0 1
____________________
NA = not available
1 Table UK/8/GF (continued)
Site State Month and day
________________________________________________________________________
5/14 5/15 5/16 5/17 5/18 5/19
Dep Pi Dep Pi Dep Pi Dep Pi Dep Pi Dep Pi
FLAGSTAFF AZ 0 1 0 1 0 1 0 1 0 1 0 1
FORT SMITH AK 0 1 0 1 0 1 0 1 0 1 0 1
FRESNO CA 0 1 0 1 0 1 0 1 0 1 0 1
GOODLAND KS 0 1 2 6 0 1 0 1 0 1 0 1
GRAND JNC CO 0 1 0 1 0 1 0 1 0 1 0 1
GRAND RAPIDS MI 0 1 0 1 0 1 0 1 0 1 0 1
GREEN BAY WI 0 1 0 1 0 1 0 1 0 1 0 1
HELENA MT 0 1 0 1 0 1 0 1 0 1 0 1
HURON SD 0 1 0 1 0 1 0 1 0 1 0 1
JACKSON MS 4 6 12 7 16 6 3 7 0 1 0 1
JACKSONVILLE FL 0 1 0 1 0 1 0 1 0 1 0 1
KALISPELL MT 0 1 0 1 0 1 0 1 0 1 0 1
KANSAS CITY MO 0 1 0 1 0 1 0 1 0 1 0 1
KNOXVILLE TN 3 5 NA 1 NA 1 NA 1 NA 1 NA 1
LAS VEGAS NV 0 1 0 1 0 1 0 1 0 1 0 1
LOS ANGELES CA 0 1 0 1 0 1 0 1 0 1 0 1
LOUISVILLE KY 2 6 0 1 2 6 2 6 0 1 0 1
LYNCHBURG VA 0 1 0 1 0 1 0 1 4 6 3 7
MARQUETTE MI 0 1 0 1 0 1 0 1 0 1 0 1
MEDFORD OR 0 1 0 1 0 1 0 1 0 1 0 1
MEMPHIS TN 6 7 3 7 0 1 0 1 0 1 0 1
MIAMI FL 0 1 2 1 2 1 4 1 0 1 0 1
MILFORD UT 0 1 1 2 3 4 0 1 0 1 0 1
MILWAUKEE WI 0 1 0 1 0 1 0 1 0 1 0 1
MINNEAPOLIS MN 0 1 0 1 0 1 0 1 0 1 0 1
MOBILE AL 0 1 0 1 0 1 0 1 0 1 0 1
MONTGOMERY AL 0 1 0 1 0 1 0 1 0 1 0 1
NASHVILLE TN 2 6 NA 1 12 7 0 1 0 1 0 1
NEW HAVEN CT NA 1 NA 1 0 1 0 1 0 1 0 1
NEW ORLEANS LA 2 6 1 3 1 2 0 1 4 5 0 1
NEW YORK AEC NY 6 6 1 2 NA 1 NA 1 NA 1 NA 1
PHILADELPHIA PA 3 5 1 3 0 1 0 1 0 1 0 1
PHOENIX AZ 0 1 0 1 0 1 0 1 0 1 0 1
PITTSBURGH PA 1 5 0 1 0 1 2 6 0 1 0 1
____________________
NA = not available
1 Table UK/8/GF (continued)
Site State Month and day
________________________________________________________________________
5/14 5/15 5/16 5/17 5/18 5/19
Dep Pi Dep Pi Dep Pi Dep Pi Dep Pi Dep Pi
POCATELLO ID 0 1 0 1 0 1 0 1 0 1 0 1
PORT ARTHUR TX 6 6 2 6 NA 1 0 1 0 1 0 1
PORTLAND OR 0 1 0 1 0 1 0 1 0 1 0 1
PROVIDENCE RI 0 1 0 1 0 1 0 1 0 1 0 1
PUEBLO CO 0 1 1 4 0 1 0 1 0 1 0 1
RAPID CITY SD 0 1 0 1 0 1 0 1 0 1 0 1
RATON NM 0 1 0 1 0 1 0 1 0 1 0 1
RENO NV 0 1 0 1 0 1 0 1 0 1 0 1
ROCHESTER NY 0 1 0 1 0 1 0 1 0 1 0 1
ROCK SPRINGS WY 0 1 0 1 0 1 0 1 0 1 0 1
ROSWELL NM 1 5 1 5 2 1 0 1 0 1 0 1
SACRAMENTO CA 0 1 0 1 0 1 0 1 0 1 0 1
SALT LAKE UT 0 1 0 1 0 1 0 1 0 1 0 1
SAN DIEGO CA 0 1 0 1 0 1 0 1 0 1 0 1
SAN FRAN. CA 0 1 0 1 0 1 0 1 0 1 0 1
SCOTTSBLUFF NB 0 1 0 1 0 1 0 1 0 1 0 1
SEATTLE WA 0 1 0 1 0 1 0 1 0 1 0 1
SPOKANE WA 0 1 0 1 0 1 0 1 0 1 0 1
ST. LOUIS MO 0 1 0 1 0 1 0 1 0 1 0 1
SYRACUSE NY 0 1 0 1 0 1 0 1 0 1 0 1
TEXARKANA AK 0 1 0 1 0 1 0 1 0 1 0 1
TUCSON AZ NA 1 NA 1 NA 1 NA 1 NA 1 NA 1
WASHINGTON DC NA 1 NA 1 NA 1 NA 1 NA 1 NA 1
WATERTOWN NY 2 6 0 1 0 1 0 1 0 1 0 1
WICHITA KS 0 1 0 1 0 1 0 1 0 1 0 1
WILLISTON ND 0 1 0 1 0 1 0 1 0 1 0 1
WINNEMUCCA NV 1 5 0 1 0 1 0 1 0 1 0 1
YUMA AZ 0 1 0 1 0 1 0 1 0 1 0 1
____________________
NA = not available
Figure UK/8/CD.