CEDAR: Meteor Plasmas--Theory, Simulations and Observations

每年都有数千吨的流星物质进入地球的高层大气，其中大部分是比一粒沙子还小的流星体。 它们进入大气层导致粒子加热和烧蚀，留下热气体和等离子体的痕迹。 光学仪器只能探测到大的流星;雷达可以探测到小得多的粒子，比所有其他技术都能解释更多的测量结果。 流星雷达是观测流星轨迹的仪器，几十年来一直用于测量中层顶附近和低热层的风。 为了更好地理解流星演化和观测，研究人员正集中精力回答流星物理学中四个长期存在的问题：（1）流星等离子体从产生到扩散到大气中是如何演化的？ (2)是否有可能通过分析或模拟对流星演变的每一阶段进行建模，以便对流星的特征作出定量估计？ (3)流星在穿越大气层时的电波散射特性是什么？ (4)从流星雷达数据中可以可靠地提取哪些信息？ 这些问题与高层大气科学高度相关，因为它们的分辨率将改善流星的雷达测量，从而更好地估计低热层的风和温度。 这项研究还将有助于评估在大气层中沉积的流星物质的位置和种类。 目前对流星输入总量的估计极不确定。 这些估计在大气建模、制定和测试太阳系演化理论以及航天器设计中很有用。 该研究小组是世界上唯一一个有能力从基本原理模拟流星演变并从等离子体理论和散射方面分析流星雷达数据的研究小组。 在过去工作的基础上，研究人员将制定一个完整的处理流星扩散在磁化和碰撞电离层。 将开发的大规模并行多维流体/动力学模拟器将能够模拟从微秒到秒的时间尺度和从毫米到几十米的长度尺度的碰撞等离子体物理过程。建模和模拟研究将包括多个离子种类的治疗，电动效应，散射效应，和一个现实的E区，可能会受到大中性风的影响。 模型和理论解释将通过应用于从各种雷达，包括Jicamarca，ALTAIR，AMISR，Millstone Hill，Arecibo，Sondrestrom和EISCAT获得的观测进行练习。 调查支持参与博士后学者和研究生，两名本科生也通常参与。 通过这个项目，他们将在观察，数据分析和解释，理论计算和数值模拟方面接受广泛的培训。 与其他研究小组的国际和国内合作计划，并将为学生参与和进步提供进一步的机会。

Every year thousands of tons of meteoric material enter the Earth's upper atmosphere, mostly in the form of meteoroids smaller than a grain of sand. Their entry into the atmosphere causes the particles to heat and ablate leaving trails of hot gas and plasma. Optical instruments can detect only large meteors; radars can detect much smaller particles and account for more measurements than all other techniques. Meteor radars, instruments which observe the meteor trails, have been used for decades to measure the winds near the mesopause and in the lower thermosphere. To enable better understanding of meteor evolution and observations, the investigators are focusing on answering four long-standing questions in meteor physics: (1) how do meteor plasmas evolve from creation until diffusion into the atmosphere? (2) is it possible to model, analytically or via simulations, each stage of meteor evolution to generate quantitative estimates of meteor characteristics? (3) what are the radiowave scattering characteristics during the meteors' passage through the atmosphere? (4) what information can be reliably extracted from meteor radar data? These questions are highly relevant to upper atmospheric science since their resolution will improve radar measurements of meteors leading to better estimates of the winds and temperatures in the lower thermosphere. The research will also enable evaluation of where and what meteoric material is being deposited into the atmosphere. Current estimates of total meteoric input are extremely uncertain. These estimates are useful in atmospheric modeling, in formulating and testing theories of solar system evolution, and in spacecraft design. The research team is the only one in the world with the ability to simulate meteor evolution from first principles and to analyze meteor radar data in terms of plasma theory and scattering. Building on past work, the investigators will develop a full treatment of meteor diffusion in a magnetized and collisional ionosphere. The massively parallel multi-dimensional fluid/kinetic simulators to be developed will be capable of modeling collisional plasma physics processes extending from the microsecond to the second time scale and from the millimeter to tens of meters length scale. The modeling and simulations studies will include treatment of multiple ion species, electrodynamic effects, scattering effects, and the effects of a realistic E region which may be subject to large neutral winds. The models and theoretical interpretations will be exercised through application to observations obtained from various radars including Jicamarca, ALTAIR, AMISR, Millstone Hill, Arecibo, Sondrestrom, and EISCAT. The investigation supports participation by a postdoctoral scholar and a graduate student; two undergraduate students are also typically involved. Through this project, they will receive extensive training in observing, data analysis and interpretation, theoretical calculations, and numerical modeling. International and domestic collaborations with other research groups are planned and will provide further opportunities for student involvement and advancement.