Feb. 2 1953 RDDN | active material left behind the "wake" of the ascending vortex-ring. Compared with the scale distance (ground to tropopause, about 55,000 feet) the fireball is not large and the bomb material and heated gases have a chance to form a structure, the mushroom top, that has a relatively long life. It is quite otherwise with MIKE shot. the fir: ball diameter is now an appreciable fraction of the scale distance, its top, at form ation extends into the middle troposphere and its energy content is huge. It is quick - transformed into a fiery colum (I called this the primary stem) which immediately pene trates the tropopause and does not come into equilibrium with its environment until it has reached 134,000 feet or, as I suspect, greater heights. Probably no ring vortex is formed, but only a "plume" which later hangs and is deformed in the stratosphere. In that region it probably becomes very stable in stratification and has a long life-tistor The greater energy of this fiery cataract sets up a secondary circulation in the surrounding atmosphere below the tropopause. Huge volumes of outside air are entrained in this circulation, comparable now in size, though not in intensity, to an incipient typhoon. The sudden formation of the thick secondary stem and its streamlined features indicate that it and the mushroom top consist of condensed water from air outside the primary stem, constituting a circulation induced by the latter. In the mushre there are other materials beside air and water vapor of course. Coral fragments ané condensed steam from the ocean ere probably swept up initially ani later heavy bomb particles may fall from above or be incorporated in other ways. A very elementary calculation, however, shows that the mushroom consists of material that could not possibly heave all come from these sources or from the original bomb material. It is precisely because the mushroom cloud is not primary, but is the visible part of a secondary circulation, that it is confined to the troposphere; this ompiains also why, it appears to advance so rapidly in a lateral direction. The operational implications of this hypothesis are interesting. The dangerous part of the total Cloud will be in the stratosphere, but here the column should be reaSonably narrow. An aircraft flying above the tropopause ought to be able to avoid too close proximity to the plume, provided appropriate parachutes are developed for the dro There remains the hazard frem the mushroom, which under certain conditions could be gre chiefly through secondary contamination. If the above hypothesis is sound, the best operational level for the drop aircraft would probably be 65,000 or 70,000 feet. This being difficult to achieve at present, it would probably not be serious if the aircraft was overtaken by the lower edge of the mushroom at, say, 30 miles and 40,000 feet, for if the hypothesis holds, the major concentration of contaminants outside the primary stem and plums, would be in the mushroom just below the tropopause, I presume you heve information on this, As you can see, the evidence upon which the report was based is simply that which any observer of MIKE shot could collect. In the light of your more detailed knowledge you should not put too much weight on it. I Have seen no photographs and am relying en tirely on memory of the events, a notoriously unreliable proceeding. However, the theo: retical reasons for believing thet MIKE was altogether a different and new geophysical phenomenon are well founded, Sincerely yours, ' /e/ CLARENCE E, PALMER. Professor of Geophysics CEP: ehm x . i, we 8 ee 03-5352