Circulation Considerations Recent observations > of the stratospheric distribution of wi85 and Rh stratospheric circulation and mixing processes. 102 . . shed considerable light on The w'8 activity, injected at several levels in the lower equatorial stratosphere from the spring 1958 Hardtack tests at 11 degrees north latitude, provides evidence against a Brewer-Dobson! 8 s 9 type of organized meridional circulation. From about September 1958 to the 1 most recent observations, the maximum W 85 concentration has persisted in the equatorial stratosphere at U-2 aircraft ceilings of about 20 kilometers. is shown in Figure 3. A typical latitude profile at this level, based on HASP data’? The stratospheric distribution of wi indicates that debris in the lower equatorial stratosphere mixes downward toward middle latitudes into both hemispheres mainly by the process of turbulent diffusion. The distribution of wi85 at levels above 20 kilometers has not been assessed, The Rn? activity which was injected to great heights at about 16 degrees north latitude over Johnston 7 . . . Island in August 1958 shows a very different pattern of mixing and distribution. A typical latitude profile for nn02 following its buildup in the lower stratosphere is given in Figure 3, Debris from high-altitude sources 102 apparently mixes downward into the low stratosphere selectively at higher latitudes during winter. The Rh data indicate very limited horizontal or vertical mixing into or through the lower equatorial stratosphere, The observed levels of rn? in the lower stratosphere indicate that most of the Teak and Orange debris is still present in higher layers of the stratosphere over both hemispheres, For clouds in the equatorial stratosphere at heights greater than the main wi85 source, it is expected that, with increasing altitude, the mixing pattern will shift from that observed for wi 8 to that exhibited by rn? Thus the 1959 spring peak observed for wi8 in Bedford rains® may reflect a Rhi0? type behavior for the highest altitude portion of the multiple w)85 source. exhibited a pn ?? hike behavior. Similarly, the Ivy and Castle clouds apparently Figure 4 indicates the apparent variation in the Castle component of gr?? fallout during 1956 based on the isotope-ratio data interpretation of Peirson, 21 analysis are discussed elsewhere. 22 Uncertainties in the Peirson It is indicated that, at the higher levels of the equatorial stratosphere, the dominant transport pattern involves horizontal mixing to higher latitudes followed by downward mixing into the lower stratosphere at high latitudes in winter. Subsequent mixing into the troposphere follows the pattern 5, 6,15 for Soviet tests. Thus the spring peak contribution of fallout from equatorial tests would appear to involve an altitude effect. Summary and Conclusions The evidence against an organized stratospheric circulation of the Brewer-Dobson type is convincing. It is also evident that the Teak and Orange debris, and possibly a large portion of the debris from Ivy, Castle, and other multimegaton test events, was injected into the stratosphere above aircraft ceilings and past balloonsampling levels and may still reside there. Material balance estimates are too unreliable for estimating the residual contamination burden of the high stratosphere. Neither sedimentation nor organized circulation appear to be effective in the downward transport of high-altitude debris. There appears to be no alternative to the direct experimental investigation of residual contamination by high-altitude sampling. 82 Evaluation of the distribution of contamination in the high stratosphere will contribute