METEOROLOGICAL EFFECTS 43 



after the end of the test series confirmed earlier speculations concerning the poleward drift or 

 mixing of equatorial stratospheric injections. In both fallout and ground-level air, higher con- 

 centrations were observed in north temperate latitudes than in tropical or southern latitudes. 

 An area of particular importance in understanding global fallout is the distribution and 

 movement of debris in the high atmosphere. Unfortunately, sampling in the stratosphere is 

 difficult. Many more measurements are needed to further our understanding of stratosphere 

 circulations and stratospheric-tropospheric exchange phenomena. However, significant prog- 

 ress has been made. Balloon sampling of particulates over one southern and three northern 

 hemisphere stations iip to altitudes of 90,000 feet has given a gross picture of concentrations 

 of fission products in the stratosphere, although the technical difficulties render the results 

 somewhat uncertain. Data from a similar program to collect C'^ from the stratosphere have 

 also been reported. In addition, the lower stratosphere has been systematically probed by air- 

 craft; the resulting data, in conjunction with that from balloons, has made it possible to esti- 

 mate the fission-product content of the stratosphere. 



IV. Analysis and Interpretation 



The observations mentioned above, together with earlier data, have given us the follow- 

 ing broad picture of world-wide fallout: 



1. The non-uniform distribution of Sr'° fallout, suggested in 1956, has been confirmed 

 and the principal features are shown by the solid curve in figure 1. (This curve is based on 

 the 1958 soil results, corrected to a common date, November 1, 1958, by means of observed 

 precipitation and fallout data.) There is a maximum in the 40°-50°N latitude band, a sug- 

 gestion of a secondary maximum in the same latitudes of the southern hemisphere, and minima 

 in the equatorial and polar regions. A similar pattern exists in the specific activity of Sr"", the 

 amount of Sr" fallout per unit area per inch of rain. 



2. The concentration of Sr'" in the air and in precipitation exhibits a seasonal trend in 

 the temperate zones, the highest values being observed in the spring and the lowest in the fall. 

 This trend has been marked in the United States and in western Europe, and is somewhat more 

 nebulous in the southern hemisphere and elsewhere in the northern hemisphere. 



3. An analysis of short-lived fission products and estimates of the production of tropo- 

 spheric debris indicates that 90% or more of the long-lived fallout originates from the strato- 

 sphere. Possible exceptions are in the areas downwind of test sites. Soil data in the United 

 States suggest an influence from the Nevada Test Site for several hundred miles in the down- 

 wind direction. 



4. All stratospheric measurements of fission products and C" indicate a non-uniform 

 distribution of contaminants, both on a hemispheric basis and in smaller scale terms. In mid- 

 1958, the northern hemisphere stratosphere contained about two to three times as much 

 debris as the southern hemisphere stratosphere because of more testing in the northern hemi- 

 sphere. Inhomogeneities are found in each hemisphere. 



5. Non-local fallout, both tropospheric and stratospheric (intermediate and delayed), is 

 deposited primarily by precipitation. Most observations suggest that on the average dry fallout 

 is of the order of 10% or less of the total deposition. 



6. While the average specific activity of Sr™ is observed to be reasonably constant in the 

 same climatic region, it is higher in arid regions than in rainy areas at the same latitude. 



Some progress has been made in the past few years in determining the residence time of 



