REPORT OF THE 

 COMMITTEE ON METEOROLOGICAL ASPECTS 



I. Preface 



This report is intended as a supplement to the Committee's 1956 Summary Report and deals 

 with a problem which has received our major attention and which has been a matter of intense 

 public concern for the past few years — the meteorological aspects of world-wide fallout. This 

 does not imply that significant progress has not been made with other problems or that other 

 phases are less important. For example, considerable experimental and theoretical effort has 

 been expended on the problems associated with gaseous and particulate effluents from nuclear 

 reactors, and it is felt that these problems will become increasingly important with the rapid 

 development of nuclear technology. Also, some very recent work using natural radionuclides 

 as atmospheric tracers has opened new avenues for meteorological research. New proposals 

 involving the use of nuclear explosives for weather modification and research have been ad- 

 vanced recently. These proposals should be carefully studied, both for their technical feasibil- 

 ity in accomplishing the desired results and for side effects such as further contaminating the 

 atmosphere. The present state of knowledge does not seem to warrant the use of nuclear ex- 

 plosions for meteorological purposes. Finally, although there has been much speculation 

 about the influence of atomic testing on weather, there still appears to be no additional evi- 

 dence suggesting a cause and effect relationship. 



II. Introduction to the Fallout Problem 



The detonation of a nuclear device normally results in the release of radioactive isotopes 

 into the atmosphere. Of greatest concern in the problem of world-wide fallout are the longer- 

 lived fission products, particularly strontium-90 (Sr"") with a radioactive half-life of 28 years, 

 and cesium-137 (Cs"') with a 27-year half-life. Attention has also been directed to carbon- 

 14 (C^), a 5,600-year half-life radioisotope which both occurs naturally and results from 

 nuclear detonations. 



The airborne radioactive particles from an atomic explosion are normally classified, ac- 

 cording to their history, into three categories: local, intermediate, and delayed. Local fallout 

 consists principally of the larger particles that are deposited in the vicinity of the burst and 

 does not significantly influence the world-wide patterns. The fraction of the radioactivity 

 produced which falls out locally varies from virtually none in the case of air bursts high above 

 the ground to almost all in the case of ground surface or subsurface bursts. Intermediate 

 fallout comprises that debris which remains airborne on the average for several weeks and is 

 composed primarily of particles left in the troposphere after the nuclear cloud has stabilized. 

 The troposphere is the layer of air extending from the earth's surface to about 35,000 feet in 

 temperate and polar regions and to about 55,000 feet in tropical areas. The troposphere con- 

 tains our everyday weather, clouds, and precipitation. Tropospheric debris is deposited in the 



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