HR: 08:30h
AN: U21E-03 INVITED    [Abstracts]
TI: Computational Modeling of Low-Altitude Airbursts
AU: * Boslough, M
EM: mbboslo@sandia.gov
AF: Sandia National Laboratories, PO Box 5800 MS 0370, Albuquerque, NM 87185-0370,
AB: New simulations of airbursts in the Earth's lower atmosphere from hypervelocity asteroid impacts suggest that a re-evaluation of the impact hazard is necessary to properly account for the enhanced damage potential relative to point-source approximations. The intent of these simulations was to explore the phenomenology associated with low-altitude airbursts and to determine whether the altitude of maximum energy deposition can be used as a reasonable estimate of the equivalent height of a point explosion. The simulations suggest that this not a good approximation, because the center of mass of an exploding projectile is transported downward in the form of a high-temperature jet of expanding gas. The jet descends by a significant fraction of the burst altitude before its velocity becomes subsonic. The time scale of this descent is similar to the time scale of the explosion itself, so the jet simultaneously couples both its translational and its radial kinetic energy to the atmosphere. Because of this downward flow, larger blast waves and stronger thermal radiation pulses are felt at the surface than would be predicted for a nuclear explosion of the same yield at the same height. For impacts with a kinetic energy above some threshold, the hot jet of vaporized projectile (the descending "fireball") makes contact with the Earth's surface, where it expands radially. During the time of radial expansion, the fireball can maintain temperatures well above the melting temperature of silicate minerals, and its radial velocity can exceed the sound speed in air. Surface materials can ablate by radiative/convective melting under these conditions, and then quench rapidly to form glass after the fireball cools and recedes. One possible example of an airburst glass is the Libyan Desert Glass of western Egypt. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000.
DE: 5420 Impact phenomena, cratering (6022, 8136)
SC: Union [U]
MN: 2007 Fall Meeting