Metallic deposition by meteor ablation in the upper mesosphere and lower thermosphere is quantified by lidar observations of meteor trails, and the relationship between the quantified meteoric deposition and long-lifetime metallic layers is explored. The required observations are accomplished with upgraded resonant lidar systems at the Arecibo Observatory. The extant potassium resonant lidar system is first modified to sample every lidar return pulse, improving temporal resolution within the beam to 35 ms and altitude resolution to 150 m in the upper mesosphere. Following that upgrade, including development and application of real-time signal processing algorithms, the Fe, Ca, Ca+, and Na lidar systems are also upgraded. The ratios of meteor tail metals to metallic content in sporadic layers is used to improve our understanding of the dynamic and chemical processes that lead to metallic layering in the atmospheric region. The meteor trail metallic deposition rate is also used to calculate direct metallic deposition to the atmosphere on a global scale.
The modeling efforts developed in part through this grant have shown that the global distribution of the meteoric input function in the upper atmosphere is non uniform and is dependent on the detectability of a particular orbital family with respect to geographical location. Initial analysis of lidar observations has detected several meteor trails. These trail events were studied to understand the detection characteristics and improve the meteor search algorithm. The detection of trails using lidar provides insight on the meteoroid ablation process through which metallic atoms are deposited in mesosphere and lower thermosphere. Supported through this grant we have also shown that the meteoroid differential ablation is responsible for short scale temporal and spatial features in the observed meteor head echo SNR detected by High Power and Large Aperture radars, which had been unexplained until now. These results indicate that differential ablation is the main mass loss mechanism. Additionally, we have undertaken on the analysis of D-region spectra to study the presence of meteoric smoke in the Mesosphere and Lower Thermosphere atmospheric region. Our results have shown to be consistent with results of past observations. It was found that the hourly, day-to-day and seasonal variability of the smoke particle size is constant at tropical latitudes. The analysis shows close correlation between the seasonal variabilities of meteoric input function and MSP properties. Finally supported through this grant, a graduate student obtained his PhD at the department of Aerospace Engineering of the University of Colorado in 2008. A second undergraduate student was supported with this grant and perform his undergraduate senior thesis at the Department of applied Physics of the University of Colorado. With the results of this research he received a Summa Cum Laude degree and the Research Excellence Award at the graduation ceremony.
