eee 0018933 mately équalto the diameter of the cloud, The wind structure described in the preceding section on the formation of the light and variable layer also leads to isolation of the 55,000 foot height line along the eastern periphery of the fallout curtain. This situa- tion is advantageous for height line sampling since the aircraft may proceed westward from a position east of the fallout area and collect the first fallout encountered, The samples should contain 55, 000-foot fallout alone,uncon- taminated by material from the rest of the cloud, Other types of wind structure will probably not be as favorable for height line sampling and the fallout collected is likely to contain particles originating from different levels in the cloud. As one proceeds outward from ground zero along a height line, the particle size of the fallout decreases and the time of arrival increases, However, low altitude sampling at a given location should provide a sample containing particles of relatively uniform size.*® Hence, by making a series of collections along a height line at different distances from the shot point, advantage can be taken of particle size separation by natural fallout processes, The WB-50 operations were arranged to utilize this situation to obtain a set of samples suitable for an investigation of size-dependent * Used synonomously with falling rate. SAN BR L Xo FRE 38 “a” 38