0018933 best defined for Koa where it circulated -over: the afort foriatleast ** aday. For Koa and Walnutthe altitude of the layer coincided quite closely with the top of the cloud, whereas for Oak it was some 20,000 feet below the top which was blown off rapidly by the strong casterly winds, } Since the B-57D samples were taken from this stratum in each case, the criterion of sampling from a region which would not be receiving fallout from any other source was easily satisfied, Some altitude data taken in part from the wind and- _ temperature tables in Appendix E are giveninthe Table 2..2: TABLE 2.2 Approximate Altitude in Feet Koa Walnut Oak Tr opopause 57, 000 54,000 50,000 Light & Variable Layer 60,000 i 55,000 55,000 Cloud Top, Expected* 72,000 72,000 99,000 Cloud Top, Observed 65,000 61,000 70,000 - 75,000 Sampling Flights 60, 300 56,500 56, 300 * (Reference 59) The suitability of the wind structures for fallout sampling elong height lines can be most readily visualized by reference to the plan view, wind velocity hodographs at shot tlme which are reproduced in Figures 2.9, 2,10 .