CHAPTER 8 INTERACTION OF SIMULTANEOUS SURFACE BURSTS Circumstances have arisen leading to concern over how the effects of multiple bursts would differ from those of single bursts. For example, multiple reentry vehicles, row-charge atomic demolition munitions, and barrages from nuclear artillery provide scenarios for the occurrence of multiple bursts nearly simultaneous and space, , in time The United States has no experience with multiple bursts in the atmosphere. Under the Limited Nuclear Test Ban Treaty, the only recourse is to theoretical analysis and laboratory modeling. Theoretical analysis is both mathematically and computationally difficult, involving aerodynamic and thermodynamic modeling of complex flow fields and interacting forces in time and space. Laboratory modeling, while of some use in confirming theoretical analysis, suffers from experimental difficulties and inadequate representation of real-world phenomena. An essential element for theoretical analysis of possible multipleburst interactions is a vortex model of the rising nuclear-debris cloud. Work in this area is being performed by Major Dan Matuska at the Air Force Weapons Laboratory (AFWL), using the Shell Oil code, Dr. wil Lia Layson at Science Applications, Incorporated, using LADUST, WEDUST, £ DUSTEN, and VORDUM models, and Dr. Timothy Fohl, formerly at Mt. Auburn Research Associates (MARA), using a buoyant vortex ring model. As yet, very little work has been reported on the actual interactions between the rising nuclear-debris clouds from multiple bursts. Independent efforts in this area have been performed by MARA and are being performed by AFWL., Preliminary results from MARA for simultaneous, space-separated, equal-sized nuclear bursts on the same horizontal surface indicate that the bursts will interact if separated by an injtial center-to-center distance of less than five fireball diameters. This interaction results in the clouds merging to form a single cloud which will rise to a stabilization height that is markedly less than the stabilization height to be expected from the individual clouds if they had not interacted. A MARA example for the side-by-side collision of two 13.5 MT clouds indicatesa center height of the combined cloud of 14-19 km, whereas the center height of a single cloud would be ~ 25 Im. The results so far are necessarily preliminary and leave unanswered, even on a model scale, questions of bursts of non-equal yields, or not- quite-simultaneous bursts, or bursts not at the same height, or combinations of these. The results do indicate how far apart bursts must be to be -considered independent and non-interacting. For purposes of making hypothetical-attack studies, the Subcommittee recommends that megaton bursts more than 700 w/3 ge apart (7000 ft for 1 MI) be treated as 27