Abstract
Abstract. Studies of transitionally dense meteor trails using radars which employ specularly reflecting interferometric techniques are used to show that measurable high-temperature chemistry exists at timescales of a few tenths of a second after the formation of these trails. This is a process which is distinct from the ambient-temperature chemistry that is already known to exist at timescales of tens of seconds and longer in long-lived trails. As a consequence, these transitionally dense trails have smaller lifetimes than might be expected if diffusion were the only mechanism for reducing the mean trail electron density. The process has been studied with four SKiYMET radars at latitudes varying from 10 to 75° N, over a period of more than 10 years, 24 h per day. In this paper we present the best parameters to use to represent this behaviour and demonstrate the characteristics of the temporal and latitudinal variability in these parameters. The seasonal, day–night and latitudinal variations correlate reasonably closely with the corresponding variations of ozone in the upper mesosphere. Possible reasons for these effects are discussed, but further investigations of any causative relation are still the subject of ongoing studies.
Highlights
Radar studies of meteor trails provide valuable information both about the meteors that cause them and the environment in which they ablate
In time the trail expands and the mean electron density is reduced, eventually allowing penetration of the radio waves. These latter class of meteor trails, termed “overdense”, represent a relatively small, but not negligible, percentage of meteors detected by backscatter meteor radars
Small bumps and dips are allowed, provided they are not too excessive. This means that underdense meteors, transitionally dense and even some overdense meteors can in principle be identified by the system
Summary
Radar studies of meteor trails provide valuable information both about the meteors that cause them and the environment in which they ablate. In time the trail expands and the mean electron density is reduced, eventually allowing penetration of the radio waves These latter class of meteor trails, termed “overdense”, represent a relatively small, but not negligible, percentage of meteors detected by backscatter meteor radars. These long-lived meteor trails seen with forward-scatter radars are known to be depleted by ozone chemistry in their final stages This process takes place at temperatures close to the ambient temperature, the meteor trail having substantially cooled by this time. Exothermic chemical reactions between ozone (as the controlling neutral mesospheric gas) and meteor metal ions, followed by dissociative recombination, play a primary role in removal of electrons (Reactions R1–R2 below) from the thermalized overdense meteor trains (Baggaley, 1979).
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