Detection of Meteoric Dust in the Earth's Upper Mesosphere

In 1983 a series of small rockets were launched from the Poker Flat Rocket Range near Fairbanks, Alaska to study what has come to be called polar mesospheric summer echoes (PMSE). Very intense VHF radar returns from the region had been reported by Balsley and co-workers using the Poker Flat Radar. The purpose of the experiment was to understand the scattering mechanisms and to this end simple nosetip Langmuir probes were flown on Super Arcas rockets. We report here on a fortuitous simultaneous radar and rocket detection of what seems to be a meteor trail produced over the Poker Flat Rocket Range. The two data sets are mutually consistent and taken together suggest some very interesting properties for the trails of large meteors. Most notable is the evidence that the ablated material has coagulated into particles the order of 50 nm in radius. This estimate is based primarily on the fall speed deduced from both the Doppler shift of the VHF radar signal and the time rate of change of the target as it fell through the beam. In addition the very existence of the radar target, the extremely sharp edges of the trail, and the existence of electron density structures inside the trail more than an order of magnitude smaller than the Kolmogorov microscale, all require large charged aerosols and a very high Schmidt number. Curiously the environment leading to PMSE is very similar to the properties of a large meteor trail some minutes after it is formed. In the former case ice particles grow and become charged by the plasma and, when more than half the charge is tied up on the ice, the plasma diffusion coefficient becomes so small that structure can be supported at VHF scattering scales. In the late-time meteor case large aerosols coagulate and tie up both natural charge in the plasma and the original meteor trail electrons. Following the work of Rosinski and Snow [1961] and Hunten et al. [1980] we conclude that the incident meteor was the order of 50-100 g and would have had a visual magnitude of about -4. Such a meteor is not uncommon but it is remarkable indeed to have had the opportunity to study its evolution with radar and particularly with rocket instrumentation. Two experimental techniques are discussed which could be used to test the conclusions of this report and, if verified, to further study large charged mesospheric aerosols.
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