rT TTT TTT 10! T_T TTT SOLID SYMBOLS, INSTANTANEOUS &TT-TTTTTTN $375 K,, CMe/SEC OPEN SYMBOLS, CONTINUOUS a 4x 10° aan < 4 MZ ~ » —— a S 10°! L 1 | itty Lt} purty 10! 107 Lt tity 10° TRAVEL PERIOD, HR Fig. 5— Values’ of the coefficients of horizontal eddy diffusion based upon observations for periods of greater than 1 hr. In practice, it is difficult to distinguish between spread due to horizontal mixing and that due to shear and vertical diffusion. Figure 7 illustrates two cases in which the width of the peak concentration of nuclear debris from Operation Ranger along a line perpendicular to the mean flow appears to be related to the directional shear of the wind. ® Thus, in the upper part of Fig. 7, all the trajectories from the first nu- clear cloud passed the 95°W meridian between 38°N (at 9000 ft) and 39.5°N (at 12,000 ft). Only one filter paper lying in this latitude range located the peak, This is a case of small directional shear. In the lower part of Figure 7, the fifth cloud was intercepted over the Gulf of Mexico at 82°W. At 15,000 ft the trajectory crossed the flight line at about