The effect of ionic processes on the characteristics of radio-echoes from meteor trains

Abstract

The effect on meteoric ionization of known ionic reactions of possible relevance has been assessed. It is shown that oxidation of positive meteoric ions by molecular oxygen and ozone, and the formation of nitride ions, followed in each case by dissociative recombination, can give rise to a pseudo-three-body attachment, which for reasonable ozone concentrations in the meteor region is sufficiently rapid to explain observed deionization. The difference between daytime and night-time rates is attributable to the diurnal variation of ozone. It is also shown that direct recombination with meteoric ions (whether hydrated or not) is too slow to be important, and that positive atmospheric ion-molecules, which are capable of participating in rapid recombination, are probably never formed in significant numbers. True attachment and associated negative ion processes are found to be generally unimportant in meteor trains, except possibly below ~80 km at night, where significant attachment, leading eventually to the formation of complex radicle ions, is feasible. The reversal of this ionization over the sunrise period, due to various detachment processes, could influence the detailed transition from night to daytime conditions. A comparison of the observed changes in integrated duration of echoes from Quadrantid shower meteors over the sunrise period with theoretical expectation confirms that the “attachment” rates previously obtained by the authors (see below) are of the correct order of magnitude. Reasons for the discrepancies between these rates and the higher rates found by other workers are discussed. Quantitively, we may conclude that the maximum ionization of a 5th magnitude meteor travelling at 40 km s −1 occurs between 90 and 95 km, and hence that the apparent attachment rate at a reference height of 95 km most probably lies in the range 0.0003–0.001 s −1 during the day, and 0.001–0.003 s −1 during the night. Ozone height profiles consistent with these conclusions are proposed for day and night conditions. The suggested ozone concentrations lie within the range of previously measured values, and the profile shapes are in good qualitative agreement with the predictions of photochemical theory.