Meteoroid sputtering, high-altitude radar and optical meteors, and sources for lower-thermospheric metals

J. D. Mathews, B. Gao, V. Kesaraju, S. Raizada

    Research output: Chapter in Book/Report/Conference proceedingConference contribution

    4 Scopus citations

    Abstract

    Observations of radar and optical meteors at altitudes above the ablation-defined meteor zone point to a 'new' sputtering source of high-altitude metals while also yielding clues to the radio science of radar meteors. That high-altitude radar meteors (HARMs) are visible at altitudes of up ∼180 km using the 50 MHz Jicamarca Radio Observatory (JRO) implies that a significant fraction of the directly-sputtered meteoroid material is ionized as the collisional mean free path (MFP) at these altitudes is many tens of meters. Also, that high-altitude klB FAI (Field-Aligned Irregularity) trail-echoes are observed in association with HARM head-echoes offers insight into the meteor-associated plasma processes as well as the radar scattering mechanism. In particular, HARMs reveal the onset, as the meteoroid enters the upper atmosphere, of radar scattering which must be from the minimum, radar detectible, electron production. The maximum Radar backscattering Cross-Section (RCS) from N electrons, σBS = 4πν2eN2, is the result of totally coherent scattering from N, equally illuminated and closely spaced, electrons where re, is the classical electron radius. An estimate for N is given. Overall, this approach yields a direct, physics-based path linking the RCS of observed head- and trail-echoes to the meteoroid sputtering process and to the ion atmospheric 'capture' process whereby the head-echo 'plasma' is embedded into the atmosphere. In addition, recent lidar observations of atomic Fe, Na, and K at altitudes well above the traditional meteor zone violate the usual assumptions regarding thermospheric metals and form an instructive complication to the above 'simple meteoroid' scenario as many meteoroids appear to be fragmenting at high altitudes. This 'cold fragmentation' likely points to complex 'dirty-ice' and 'dust-ball' meteoroids comprised of small, dense grains weakly bound together by more volatile substances. These meteoroids may disperse into an extended 'coma' that presents a more complex and larger surface area atmospheric-interaction region. We briefly discuss sputtering, the impact energies needed for onset of sputtering, sputtering yield, and the observational evidence available for interpretation of meteoroid sputtering as a source of aeronomically interesting metals above the classical meteor zone. We further suggest that a thermospheric 'reservoir' of nanometer-sized dust play an important aeronomic role.

    Original languageEnglish (US)
    Title of host publication2017 32nd General Assembly and Scientific Symposium of the International Union of Radio Science, URSI GASS 2017
    PublisherInstitute of Electrical and Electronics Engineers Inc.
    Pages1-4
    Number of pages4
    ISBN (Electronic)9789082598704
    DOIs
    StatePublished - Nov 10 2017
    Event32nd General Assembly and Scientific Symposium of the International Union of Radio Science, URSI GASS 2017 - Montreal, Canada
    Duration: Aug 19 2017Aug 26 2017

    Publication series

    Name2017 32nd General Assembly and Scientific Symposium of the International Union of Radio Science, URSI GASS 2017
    Volume2017-January

    Other

    Other32nd General Assembly and Scientific Symposium of the International Union of Radio Science, URSI GASS 2017
    CountryCanada
    CityMontreal
    Period8/19/178/26/17

    All Science Journal Classification (ASJC) codes

    • Computer Networks and Communications
    • Instrumentation
    • Radiation

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