The observed characteristics of radio-echoes from overdense meteor trains

Observational data relating to the duration of radio-echoes from overdense meteor trains are presented and discussed, with particular reference to the differences between daytime and night-time conditions. Experimental distributions of echo-duration for different meteor showers observed at various radio frequencies have been collected from several sources. When interpreted in terms of duration distribution theory (which, as developed here, represents an important revision of previous theories) these data are shown to be consistent with the assumption that free electrons are removed by an apparent three-body attachment mechanism, at a rate which is approximately three times higher at night than during the day. The absolute rates which emerge from this analysis depend on the exact meteor ionization model adopted, but for the most probable range of models our values are found to be lower than those obtained by other workers by an order of magnitude. The duration of echoes from bright meteors associated with the Quadrantid shower has been observed to increase considerably some 30 min after sunrise in the meteor region. This phenomenon is associated with a decrease in the mean range of the echoes. The results indicate that deionization is particularly rapid below ?80 km at night, and may no longer appear as a three-body attachment in this region.

It is shown that the observed echo characteristics cannot be satisfactorily explained in terms of the well-known processes of direct recombination or simple attachment to atmospheric molecules, indicating that a much more complex ion-chemistry is required.