CEDAR: An Observational and Theoretical Study of the Climatology of the Ca/Ca+ Layer in the MLT at Arecibo and Its Relation to the Sporadic Micrometeor Flux

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The investigators will conduct the most comprehensive study to date of the origin and chemistry of the Ca/Ca+ metallic layer found in the Mesosphere/Lower Thermosphere (MLT) atmospheric region. Both the neutral and ionic states of this meteoric specie have been rarely studied and are characterized by two unique properties: 1) a very significant lack of Ca in the atmosphere when compared with meteorite composition; and 2) the ion-neutral ratio is much higher (by about an order of magnitude) for Ca+/Ca than those measured for other meteoric metals in the upper atmosphere. This behavior may be connected to a high velocity micrometeor flux, since Ca is among the most refractory of the meteoritic constituents. The study will involve observations and modeling. The observations will include meteor head-echo radar observations using the 430 MHz incoherent scatter radar (ISR) and Ca, Ca+, and K metallic densities using lidars, all at the Arecibo Observatory in Puerto Rico. The theoretical effort will involve the improvement of existing models of the Micrometeor Input Function (MIF). This comprehensive model includes solar system meteoroid populations, atmospheric entry and ablation mechanisms, which allow for the estimation of the geographical, seasonal, and diurnal variability of the meteoric mass deposition in the upper atmosphere of particles in the sub-milligram mass range. The results will also be compared with major laboratory studies of the pertinent reactions of Ca and Ca+, which are being conducted by a collaborating group in the U. K. The combination of atmospheric measurements, laboratory experiments, and models will, for the first time, allow a description of the full picture of the formation of sporadic calcium layers observed at Arecibo. This research will enrich existing collaborations between the Arecibo Observatory and scientists around the world. The results will be a crucial part of the PhD dissertation work of three students. A number of underrepresented undergraduate and graduate students from local universities and technical institutes, as well as REU students, will be involved in various phases of this effort, designing and implementing small engineering projects related to the lidar activities at Arecibo. Finally, all of the data collected with this system will be made publicly available through the Arecibo Observatory and CEDAR database archives.