Physical Effects of the Yushu Meteoroid: 1.

The purpose of this article was to evaluate the mechanical, optical, and gasdynamic effects that accompanied the passage and explosion of the Yushu meteoroid. The explosion occurred over a sparsely populated area, Qinghai Province (Tibetan Plateau, People's Republic of China). According to NASA, the initial kinetic energy of the celestial body was approximately 9.5 kt TNT or 40 TJ. Approximately 4.9 TJ, i.e., 12.25% of the initial kinetic energy of the body, was converted into the energy of the light flash. The projections of the velocity of the meteoroid are as follows: vx = –2.6 km/s, vy = 5.9 km/s, and vz = –12.1 km/s. They are used to estimate the angle of inclination of the trajectory to the horizon, which is approximately 5°. Using the explosion height of 35.5 km and the inclination angle, the density of the matter is estimated to be close to that of an ordinary chondrite (approximately 3.5 t/m3). Knowledge of the kinetic energy and velocity allows us to calculate the mass of the meteoroid (432 t) and its characteristic size (6.2 m). The energy of the processes, as well as mechanical, optical, and gasdynamic effects of the celestial body, are analyzed. The main release of energy accompanying the deceleration of fragments of the body destroyed at a dynamic pressure of ~1 MPa took place in a 17.2 km long area at a height of approximately 35 km. A quasi-continuous fragmentation and a power law of the distribution of the mass of the fragments are assumed. The main parameters of ballistic and explosive shock waves are estimated. With a Mach number of 45, the radius of the ballistic shock wave was approximately 280 m, and the fundamental period was 2.6 s, which increased from 9.5 to 30.1 s due to dispersion as the distance traveled by the wave increased from 50 to 5000 km. The radius of the cylindrical and spherical explosion waves was approximately 0.8 and 2 km, respectively, and the fundamental period was 7.5 and 18.8 s. This period increased from 21.1 to 66.7 s as the distance increased from 50 to 5000 km. Near the meteoroid terminal point, the relative overpressure was maximal. It decreased with decreasing height, and increased with increasing height until approximately 120–150 km, where it reached ~10–20 percent and then decreased to a few percent. The absolute value of the overpressure for the spherical wave was maximal near the explosion height, then it decreased as the height decreased to 15 km, then increased again. At the epicenter of the explosion, it was approximately 310 Pa for a cylindrical wave or ~48.5 Pa for a spherical wave, which is insufficient to damage ground objects. With increasing height, the overpressure decreased from many tens of pascals to micropascals. The average power of a light flash with a duration of approximately 1.26 s was 3.9 TW, the power flux density near the fireball, more precisely, a 3.4 km long cone with a diameter of 18.6 m, was 19.5 MW/m2. The surface temperature was close to 4300 K and the Wien wavelength was 6.7 × 10–7 m. [ABSTRACT FROM AUTHOR]