Iron, calcium, and potassium atom densities in the trails of Leonids and other meteors: Strong evidence for differential ablation

We report on studies of the Fe, Ca, and K atom densities in the trails of m eteors. The measurements of the densities were taken simultaneously and in a common volume by three ground-based lidars. We report and analyze the dat a obtained during two nights of Leonid showers (1996 and 1998 November 16/1 7) and of one night five days after the 1998 Leonids. The lidar-observed tr ails of Leonids differ from those of other meteor showers in both their mea n altitude and in mean metal composition. The Leonid trails show a highly d epressed Ca/Fe abundance ratio in comparison to CI meteoritic composition. Our observations are interpreted with the help of a numerical model that de scribes the ablation processes occurring during the high-speed entry of met eoroids into the Earth's atmosphere. We conclude that for the lidar-observe d meteoroids, the ablation process occurs differentially for the three elem ents. This leads to a mixture of metals in the meteor trails, the compositi on of which is strongly altitude dependent and at any one altitude deviates significantly from a CI meteoritic composition. The model predicts differi ng altitudes and durations of trail observations for different showers, all owing us to tentatively assign the origin to the observed trails.