tropical winds from 20,000: feet or 30,000 feet up to the tropopause at 55,000 feet are highly variable, but over a period of several .davs carry material.to the east or west, but at a differentspeed than the underlying layer. The result is larze shear between these layers - an important effect because it causes great horizontal Julietta: inbbilanentl aide stretching which in turn exposes large areas to the diffusive action of atmospheric turbulence. The rate of dilution by diffusion, therefore, proceeds much faster than would be the case with no Stretching. An elongation of the clouds originating from the continental tests also occurs since there is a change of wind speed with elevation but the effect is not as dramatic as in the Facific. In some of the earlier Pacific tests there was evidence ' that the cloud extended from North America to Asia within. a few days after the burst. Second, the tropical precipitation is in the form of showers instead of large areas of continuous rain mre typical of the ‘United States. It would be very instructive to determine the . effect of the showery type of rainfall on the gummed paper collec‘ions ° The height of atomic debris affects the resulting deposition: ‘pattern. Tests at the Nevada Proving Grounds rarely penetrate “«, heaabasietiit aporeciably into the stratosphere whereas both the MIKE and KING tests did and the mushroom from MIKE is believed to have been ‘entirely within the stratosphere. It is believed by most meteoro- dogists that vertical diffusion in the stratcsphere is appreciably slower than in the troposphere although no quantitative dava is avallable. If that is true and if the important vertical trans- ‘part is the consequence of vertical diffusion, then the vertical transport within the stratosphere would be considerably slower than the transport through the troposphere. The consequence of the great height of the IVY clouds, therefore, might be to deposit their debris later than previous atomic clouds and thus produce more uniform fallout, since there is more time for horizontal diffusion to operate. -