CEDAR: Meteor Plasmas--Theory, Simulations and Observations

每年有数以千计的陨石物质进入地球上层大气层，大多以比一粒沙子还小的流星体的形式存在。它们进入大气层会导致颗粒加热和烧蚀，留下热气和等离子体的痕迹。光学仪器只能探测较大的流星；雷达可以探测更小的粒子，比其他所有技术都能进行更多的测量。流星雷达是一种观测流星轨迹的仪器，几十年来一直被用来测量中层顶附近和较低热层中的风。为了更好地了解流星的演化和观测，研究人员正在重点回答流星物理学中的四个长期存在的问题：(1)流星等离子体是如何从产生到扩散到大气中的？(2)是否有可能通过解析或通过模拟对流星演化的每个阶段进行建模，以生成对流星特征的定量估计？(3)流星穿过大气层时的无线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进对流星的雷达测量，从而更好地估计较低热层的风和温度。这项研究还将能够评估大气中的陨石物质沉积在哪里以及沉积了什么物质。目前对大气输入总量的估计极不确定。这些估计在大气建模、太阳系演化理论的形成和测试以及航天器设计中都是有用的。该研究团队是世界上唯一一个有能力从第一性原理模拟流星演化，并从等离子体理论和散射角度分析流星雷达数据的团队。在过去工作的基础上，研究人员将开发一种全面处理磁化和碰撞电离层中流星扩散的方法。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第二时间尺度以及从毫米到几十米长度的碰撞等离子体物理过程。建模和模拟研究将包括多种离子物种的处理、电动效应、散射效应，以及可能受到大的中性风影响的现实E区的影响。这些模型和理论解释将应用于从Jicamara、Altair、阿米西里、米尔斯通山、阿雷西博、Sondrestrom和EISCAT等不同雷达获得的观测数据。这项调查支持一名博士后学者和一名研究生参与；两名本科生通常也参与其中。通过这个项目，他们将在观测、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。计划与其他研究小组进行国际和国内合作，并将为学生的参与和进步提供更多机会。

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.