Speaker
Description
Meteoric ablation is the main source of the metal layers in the mesosphere and lower thermosphere (MLT). Simultaneous observations of different metals in individual meteor trails can reveal how meteoroids ablate and how the trails evolve. We present a statistical study of 385 meteor trail events detected simultaneously by Na and K resonance lidars at sao jose dos campos on 174 nights between February 2018 and June 2023. For each event we derived the peak altitude, peak density, and column abundance of both metals. The trails occurred between 80 and 97 km (median 87.1 km). The Na and K signatures were co-located, confirming a common meteoric origin. Most events lasted less than one minute, but one trail on 10 March 2020 persisted for 37 minutes at 83 km. Na and K column abundances were strongly correlated (Spearman ρ = 0.75). The Na/K column ratio had a median of 8.4 (interquartile range 5.7–12.6) and was independent of altitude. This ratio is below the chondritic value and far below that of the background metal layers, suggesting differential ablation and/or rapid chemical processing of Na in fresh trails. Na trails were systematically broader than K trails (median FWHM ratio 1.29), indicating differences in diffusion or chemical loss between the two metals. Events with higher ratios were concentrated in April and May (median 14.0, versus 7.7 in other months). We discuss these results and their implications for meteoric input to the MLT metal layers.