Physics of meteor generated shock waves in the Earth’s atmosphere – A review

Abstract

Shock waves and the associated phenomena generated by strongly ablating meteoroids with sizes greater than a few millimeters in the lower transitional flow regime of the Earth's atmosphere are the least explored aspect of meteor science. In this paper, we present a comprehensive review of literature covering meteor generated shock wave phenomena, from the aspect of both meteor science and hypersonic gas dynamics. The primary emphasis of this review is placed on the mechanisms and dynamics of the meteor shock waves. We discuss key aspects of both shock generation and propagation, including the great importance of the hydrodynamic shielding that develops around the meteoroid. In addition to this in-depth review, the discussion is extended to an overview of meteoroid fragmentation, followed by airburst type events associated with large, deep penetrating meteoroids. This class of objects has a significant potential to cause extensive material damage and even human casualties on the ground, and as such is of great interest to the planetary defense community. To date, no comprehensive model exists that accurately describes the flow field and shock wave formation of a strongly ablating meteoroid in the non-continuum flow regime. Thus, we briefly present the current state of numerical models that describe the comparatively slower flow of air over non-ablating bodies in the rarefied regime. In respect to the elusive nature of meteor generated shock wave detection, we also discuss relevant aspects and applications of meteor radar and infrasound studies as tools that can be utilized to study meteor shock waves and related phenomena. In particular, infrasound data can provide energy release estimates of meteoroids entering the Earth's atmosphere. We conclude with a summary of unresolved questions in the domain of meteor generated shock waves; topics which should be a focus of future investigations in the field.

Verification of the Flow Regimes Based on High-fidelity Observations of Bright Meteors

“…The consideration of varying γ is best suited for numerical models, although some modeling studies did apply γ = 1.4 and found that the main dependences of the vapour (hydrodynamic shielding) parameters, and consequently the temperature and density jumps, are the size and the altitude of the meteoroid (see Popova et al 2000 and Section 1.2). Also, the consideration of an ablating centimeter-sized meteoroid entering at velocities up to 73 km/s is very different and profoundly more complex than, for example, a much larger re-entry vehicle at significantly lower velocities (e.g., 7 km/s) (see Silber et al 2018b for discussion).…”

Production of nitric oxide by a fragmenting bolide: An exploratory numerical study

“…Second, the numerical models best describe the motion and physical and chemical behaviour of hypersonic objects at lower velocities. For a detailed discussion about the challenges in numerically modeling meteoroids, the reader is referred to [Silber et al, 2018b].…”

“…However, it should be noted that the actual flow field of a strongly ablating meteoroid at higher velocities is much larger than the characteristic object size (e.g., see [Silber et al, 2018b, Silber et al, 2018a). Consequently, the fragment sizes were chosen to satisfy the flow field requirements corresponding to the continuous flow regime [Silber et al, 2018b].…”

“…However, it should be noted that the actual flow field of a strongly ablating meteoroid at higher velocities is much larger than the characteristic object size (e.g., see [Silber et al, 2018b, Silber et al, 2018a). Consequently, the fragment sizes were chosen to satisfy the flow field requirements corresponding to the continuous flow regime [Silber et al, 2018b]. For the purpose of simplifying the computational approach in this exploratory study, we also neglect the compositional effect of the parent and fragmented objects and assume no appreciable size or mass loss in the studied velocity regime and the altitude interval.…”

The challenges in hypervelocity microphysics research on meteoroid impacts into the atmosphere

“…Meteoroids collide with the Earth's atmosphere on a daily basis. On average, meteoroids cumulatively deposit about 5 to 300 tons of material per day (Plane, 2012;Silber, Boslough, Hocking, Gritsevich, & Whitaker, 2018), mostly into our atmosphere and only a tiny amount to the Earth's surface in a form of meteorite falls. Meteors have been an integral part of astronomy since ancient times as they are easily observed with the naked eye.…”