li, METEOROLOGICAL FORCES L. B. Smith Presiding (A) Atmospheric Traces Above 100,000 Feet L. Machta*¥ and R.J. List U.S. Weather Bureau Introduction The design of an effective and useful high-altitude sampling system for probing the atmosphere at levels from 100, 000 to 200, 000 feet is dependent upon a knowledge of the constituents to be sampled and upon reasonable estimates of the concentrations to be expected. The constituents to be sampled may be radioactive or stable. Radioactive Isotopes A summary of the radioisotopes of interest to be expected from 100, 000 feet and their expected concentrations at this time are given in Table 1. Certain of the isotopes are present only as the result of natural processes, cosmic ray bombardment of the atmosphere (5-35, Be-7 and P-32), or products of natural radioelements in the earth's crust (Pb-210); others are the result of artificial production in nuclear reactions (Sr-90, Cs-137 and Rh-102), while C-14, H-3 and Na-22 are present from both natural and artificial sources. The results of some recent lower stratospheric measurements of several of these isotopes, which form the basis of the estimated concentrations, will be discussed briefly, together with some indication of what we might expect to learn from measurements at higher altitudes. Carbon-14, C-14 has been measured in the stratosphere by balloon collection for several years, sults for April-September 1955 are shown in Figure 1, in terms of excess over natural background. The re- The units are 10° C-14 atoms per gram of air and are This background value is assumed to be 73 x 10° atoms/gm. numbers in parentheses refer to the number of observations.) (The In view of the long half-life, the background can be considered constant throughout the atmosphere. Since at the time of the collections virtually the only source of artificial C-14 was the Marshall islands (11°N), the observations tend to support the view that contaminants move poleward and downward in the northern hemisphere stratosphere (evidence in the southern hemisphere is less convincing). equator at 90, 000 feet, when compared with other latitudes, The lower values over the indicate either a rising motion in the tropical stratosphere or an initial injection at altitudes above the highest level sampled. Because of the large yield de- vices and uncertain cloud height information in the Castle and Ivy series, the latter possibility cannot be discounted. It may be that subsequent tests (excluding Teak and Orange) did not reach to these altitudes. I should be pointed out that not enough C-14 data is available to determine whether the poleward and downward movement is due to a circulation or to a mixing process. *Speaker presenting the paper. 295