Every day billions of fast moving particles (meteoroids) impact the Earth's upper atmosphere to create a spectacular phenomenon called meteor. Many of these meteoroids have sufficient energy to produce high-density plasmas in the E-region ionosphere. Small meteoroids with the size much less than a grain of sand are believed to be the dominant source of extraterrestrial material in the Earth's atmosphere. Rare big meteoroids can be seen by naked eye, but much more frequent small meteoroids are often invisible even to sensitive optical instruments. Such invisible meteoroids can only be detected by radars. The radar-transmitted electromagnetic waves can be scattered from the dense plasma formed by a meteoroid and the received signals contain important information about the meteoroid and surrounding atmosphere. However, despite the frequency and importance of meteors, we have a limited understanding of meteor plasma dynamics and the radio wave scattering characteristics. This restricts our ability to utilize the abundant information that radars generate about meteors and to understand their effects on the atmosphere.
       The completed project research further developed the field of meteor plasma physics with the main objective to improve our ability to interpret the results of radar measurements. The accurate quantitative interpretation of these measurements is needed for finding key meteoroid characteristics, such as the material composition and structure, meteoroid mass, etc. The project researchers modeled the evolution and spatial structure of the meteor plasma in order to provide the radar observers with the physics-based tool for reliable interpretation of future radar observations. The project results will help answer a number of important scientific and practical questions including: (1) How do meteor plasmas evolve from their initial ablation and ionization through the early-stage kinetic expansion to their later-stage diffusion and turbulence? (2) What characteristics of the meteor plasma influence radar head echoes? (3) Can more accurate theoretical and computational models improve researchers quantitative understanding of radio wave scattering? (4) How do large-scale atmospheric inhomogeneities and neutral wind shears modify the evolution of the long-lived plasma trail produced by the meteoroid? Answering these questions should lead to progress in understanding highly collisional plasma physics, meteors and will provide better interpretations of measurements made by radar.
       During the reported last period of six months the researchers mostly wrapped up the project findings to prepare last publications and smoothly transition to a related research funded by a new NSF core aeronomy grant. During the preceding project period, the researchers obtained a number of important results. Among those is the physics-based theory that produces analytic expressions describing the detailed structure of the near-meteoroid plasma responsible for forming the radar head-echo signals. The analytic results have been confirmed by recent supercomputer simulations. The new model should be used as a basis for accurate quantitative interpretation of radar measurements in order to help calculate meteoroid and atmosphere parameters from radar head-echo observations.
       The project research progress and results have been published in peer-reviewed journals (7 papers) and presented in multiple conferences. The results have also been disseminated through discussions within the corresponding research community.
       The project research has had an important educational aspect. Graduate (2) and undergraduate (6) students (among those were 4 women) have been involved in various stages of the project research. During their work, the students acquired a number of skills that should help them in their future academic and research activities. One of the two graduate students has successfully defended his Ph.D. dissertation based, to a large extent, on this project research.

Last Modified: 08/08/2019
Modified by: Yakov S Dimant