. sHts Is there any experirental evidence on the marnitude of diffusion coefficient? RATP? No, there have been some estimates of diffusion coeffic made from the clouds. ante lr. Nachta, of the Weather Bureaag has done some work on this, but these diffusion coefficients Bn free atzosphere are extremely rough estimates. the This one, 0°, was chosen because this would give us a scale of motion malier than the cloud and therefore not tear it up, but it was biggest one that would give such a motion. If we go te larger diffusion coefficient the seale of the motion is gping to be big enough to tear this cloud into little whiseps pieces. We didn’t want that te happen on this xodel. We have gone all the way back to Richardson's collection ef K val which he mede in 19°76. 8, I don't think anybody holds a brief for those today, .We went on to this andmade a rough integration of the amount of raterial that was under the 6.4 Kilomete? at different tizes, level At one hour the gradient is steep (Figure 2) and you would expect very little in there. Sy stout thr hours you are just beginning to get appreciable amcants in therg, you would provably got sone rain-cut but we would have hed te|have another line kere to make some sort of a calculation. 6 hours we have made a calculation Atlabout. and assuming 100% ecafenging over a small area of just about one-half a square nile we fwould have gotten a dose rate on the ground of abcat 70 nilircer per hour. scavenging. If this diffusion had gone along and we had 10@ Now let us go back to Yr. Greenfleldk pis os aetepant o¥id.et it on here so that ‘ . can look at it. o iI This represents % os, SY