On shock waves and the role of hyperthermal chemistry in the early diffusion of overdense meteor trains

Abstract

Studies of meteor trails have until now been limited to relatively simple models, with the trail often being treated as a conducting cylinder, and the head (if considered at all) treated as a ball of ionized gas. In this article, we bring the experience gleaned in other fields to the domain of meteor studies, and adapt this prior knowledge to give a much clearer view of the microscale physics and chemistry involved in meteortrail formation, with particular emphasis on the first 100 or so milliseconds of the trail formation. We discuss and examine the combined physico-chemical effects of meteor-generated and ablationally amplified cylindrical shock waves which appear in the ambient atmosphere immediately surrounding the meteor train, as well as the associated hyperthermal chemistry on the boundaries of the high temperature postadiabatically expanding meteor train. We demonstrate that the cylindrical shock waves produced by overdense meteors are sufficiently strong to dissociate molecules in the ambient atmosphere when it is heated to temperatures in the vicinity of 6,000 K, which substantially alters the considerations of the chemical processes in and around the meteor train. We demonstrate that some ambient O 2 , along with O 2 that comes from the shock dissociation of O 3 , survives the passage of the cylindrical shock wave, and these constituents react thermally with meteor metal ions, thereby subsequently removing electrons from the overdense meteor train boundary through fast, temperature independent, dissociative recombination governed by the second Damköhler number. Possible implications for trail diffusion and lifetimes are discussed.

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

“…Smaller fragments are incapable of generating strong shockwaves necessary for the dissociation of atmospheric species that contribute to NO production (e.g., [Silber et al, 2018a]). That is primarily because the flow filed associated with small fragments rapidly rarefies and almost instantaneously thermalizes behind the particle [Silber et al, 2017]. Thus, as mentioned earlier, small and rapidly decelerating fragments will have a negligible contribution to the overall NO production.…”

“…The sizes represent the extra-terrestrial objects capable of generating a shock wave given appropriate conditions (see the Introduction section). Additionally, the chosen sizes are within the group of the smallest shock-forming meteoroids that impact the Earth's atmosphere, and incidentally are also the most frequent [Drolshagen et al, 2017, Silber et al, 2017. Moreover, the dimensions given are consistent with the size of fragments that would result from a disruption episode during a meteoroid flight through the atmosphere.…”

“…The code is suitable for simulating supersonic and hypersonic flows because it can solve the Navier-Stokes equations written in the conservative form, which minimizes the numerical errors when discontinuities (shock waves) appear. Furthermore, it has been used extensively in similar studies [Niculescu et al, 2016;Silber et al, 2017;Niculescu et al, 2018]. Since ANSYS is proprietary, the inner workings of this code will be omitted here.…”

“…This rapid energy conversion process also results in heating and a range of subsequent physico-chemical processes in the local atmosphere [e.g., Silber et al, 2018b]. Moreover, the hypersonic centimetre-sized or larger extraterrestrial objects generate strong shock waves [Silber et al, 2018b, Silber et al, 2017, which may influence not only fragmentation Shuvalov, 1996, Artemieva andShuvalov, 2001] but also the rate and type of ablation [Bronshten, 1983, Silber et al, 2018b.…”

“…Such processes that take place at extreme temperature (e.g. Berezhnoy and Borovička, 2010) produce large quantities of NO and other NOX products, destroy local ozone and have a capacity to strongly modify the ambient atmospheric region [e.g., Menees and Park, 1976, Park and Menees, 1978, Berezhnoy and Borovička, 2010, Silber et al, 2017Silber et al, 2018a). Similarly, the chemistry of the thermalized meteor trails and their interaction with the ambient atmosphere have been studied extensively (e.g., Baggaley, 1978, Baggaley, 1979, Plane, 2012, Plane et al, 2015Plane, 2003, Jenniskens, 2004, Whalley et al, 2011.…”