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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