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

研究人员将对在中层/低热层(MLT)大气区域发现的钙/钙+金属层的来源和化学进行迄今为止最全面的研究。这种陨石物种的中性和离子状态都很少被研究，并具有两个独特的性质：1)与陨石成分相比，大气中非常缺乏钙；2)与高层大气中其他陨石金属相比，Ca+/Ca的离子中性比高得多(约一个数量级)。这种行为可能与高速微流星流有关，因为钙是最难熔的陨石成分之一。这项研究将涉及观察和建模。观测将包括使用430 MHz非相干散射雷达(ISR)的流星头回波雷达观测以及使用激光雷达的Ca、Ca+和K金属密度观测，所有这些都在波多黎各的阿雷西博天文台进行。理论工作将涉及改进现有的微流星输入函数(MIF)模型。这一综合模型包括太阳系流星体种群、大气层进入和消融机制，从而能够估计上层大气中亚毫克质量范围内的陨石质量沉积的地理、季节和日变化。这些结果还将与英国一个合作小组正在进行的关于钙和钙离子相关反应的主要实验室研究进行比较。大气测量、实验室实验和模型的结合将首次允许描述在阿雷西博观察到的零星钙层形成的完整图景。这项研究将丰富阿雷西博天文台和世界各地科学家之间的现有合作。这一结果将是三名学生博士论文工作的关键部分。来自当地大学和技术学院的一些人数不足的本科生和研究生以及农村大学的学生将参与这项工作的各个阶段，设计和实施与阿雷西博激光雷达活动有关的小型工程项目。最后，该系统收集的所有数据将通过阿雷西博天文台和雪松数据库档案向公众开放。

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.