A Model for Thermal Radiation from the Tunguska Airburst
Christopher O. Johnston, Eric C. Stern
Icarus
Available online 7 February 2019
“Highlights
• Radiative heating to the ground from the Tunguska event modeled
• Applies recently-developed computational fluid dynamic and radiation models
• Optically-thick shock layer and near wake minimize details of object fragmentation and ablation
• Matching simulated radiant burn area with that measured suggests object diameter between 60 and 90 m”
“This paper develops a model for simulating the radiative flux reaching the ground originating from a meteor shock-layer and wake. The area of radiant burn measured for the Tunguska event provides a test case for the developed model. This model applies recently developed computational fluid dynamic simulations, which include the impact of ablation and radiation on the shock-layer flowfield, and ray-tracing radiation transport with atmospheric absorption. The impact of the meteor view angle is shown to significantly impact the radiative flux. Looking at the meteor along the flight path (head-on) results in lower radiative heating because it reduces the wake field of view, where the large radiating wake is shown to provide a significant contribution to the radiative flux (when viewed from the side). The impact of ablation on the ground radiative flux is negligible because the ablation products are limited to the optically-thick core of the wake. The resulting simulated radiative flux values are correlated as a function of velocity, altitude, view angle, and meteoroid radius. This correlation is then applied to potential Tunguska entry trajectories to provide a simulated ground heating footprint. Comparing this simulated footprint with the measured radiant burn area provides a metric for assessing unknown Tunguska entry parameters. Using this approach, the initial radius resulting in good agreement with the measured radiant burn footprint was found for a range of maximum debris cloud radii, entry angles, and velocities. The resulting optimal initial radii were between 30 and 45 m for the entire range of cases considered. This provides a valuable constraint on initial radius for complementary Tunguska studies, such as blast-wave simulations that aim to reproduce the tree-fall pattern.”
