This project is to refine and implement a recently developed technique for estimating the altitude profile of neutral winds in the equatorial mesosphere/lower thermosphere between 85-115 km from high-resolution radar observations of non-specular meteor trails. This effort will utilize incoherent scatter radar (ISR) observations of velocities, deceleration, and change in deceleration of meteoroids acquired from Jicamarca Radio Observatory (JRO) in Peru. The project will include an evaluation of new radar transmission modes for routine wind determination, which will be used to assemble a database of wind estimates. The measurements in turn will be used to create more realistic simulations of meteor trail evolution using a massively parallel, multi-dimensional hybrid numerical code developed over the past several years by the Principle Investigator as well as used to improve neutral density estimates between 80 and 120 km. The simulations and meteor observations will be used to address broad questions regarding the nature of radar scatter from the meteor plasma. This effort will involve participation by multiple graduate and undergraduate students over three institutions.
Every day billions of particles impact the Earth's upper atmosphere with sufficient energy to create high-density plasma trails in the E-region ionosphere at altitiudes 90-120 km. For the last 50 years, optics and radars have characterized these meteor plasmas in order to infer properties of the meteoroids (speed, direction of origin, size) and the atmosphere in which they disintigrate (winds and temperatures). In the last decade, the aeronomy research community has made dramatic improvements in understanding the observational characteristics of radar meteors and their underlying physics. They have improved the measurements both of the meteors and the atmosphere they travel through. The objective of this project was to further develop this field in two directions: (1) improve high-resolution atmospheric measurements made with radar meteor observations and (2) to better understand and model meteor physics. Meteor physics plays an important role in many areas of space science and aeronomy. Aeronomers need to know the amount and location of meteoric material deposited in the Earth's atmosphere. Current estimates of the total amount deposited range between 1,600 and 170,000 tons per year but this wide range makes atmospheric modeling ambiguous. Aeronomers also need better estimates of meteoroid composition in order to understand the effects of metals such as Na and Fe on upper atmospheric chemistry. Since 1991, four satellites were seriously damaged by meteoroids; the shuttle's windows have been hit by over 20 meteoroids with enough energy to require replacement; and the Hubble telescope has received more than 5000 meteoroid impacts. A more accurate picture of the distribution of particle orbits and masses would help not only spacecraft designers but solar system scientists who model the outer solar system and its evolution based on the material observed near the Earth. Researchers have been using meteor radars for decades to infer neutral wind velocities in the lower thermosphere (LT). The reported project has developed a technique to dramatically improve the altitude and temporal resolution of LT wind measurements. The research group has used simulations, theory, and observations to improve our understanding of meteor trail dynamics and radar measurements. This has led to a deeper understanding of meteor physics and to improved techniques for interpreting radar meteor measurements. Intellectual merit of the proposed activity. The proposed research has refined the newly developed technique of using non-specular meteor echoes to track winds in the 85-115km altitude range. Using the data from Jicamarca Radio Observatory (JRO) in Peru and ARPA Long-Range Tracking and Instrumentation Radar (ALTAIR) in Kwajalein Pacific island, this technique has allowed obtaining the collection of the highest resolution remotely detected wind measurements ever made. It helped answer the questions: (1) How do winds and wind shears evolve through the course of the night and over the period of a year? (2) What radar configuration and modes gives the highest resolution temporal and spatial atmospheric measurements? (3) What is the best way to make wind measurements using a lower power mode at JRO? The second component of this research will complement the first and encompass a broad investigation of meteor observations, theory and simulations. This has led to a significant progress in understanding meteor physics as related to the following questions: (1) How do meteor plasmas evolve from their initial ablation and ionization through their earlystage kinetic expansion and thermalization, and into their later stage diffusion and turbulence? (2) Can we build analytical and/or simulation based models of each of these stages to generate quantitative estimates of meteor and atmospheric characteristics? (3) What radiowave scattering characteristics do we expect during each of these stages? (4) Can we establish a link between meteor sources and specific meteoroid properties such as mass? Broader impacts resulting from the proposed activity. In addition to developing the tools necessary to address the questions described above, this group has further developed simulators capable of modeling collisional plasma physical processes extending from the sub-microsecond to the second time-scale and the mm to km length-scale. They have collaborated with other research groups to apply this simulator to a variety of plasma and space physics problems and will continue to do so. This group has trained Dr. Elizabeth Bass (Fucetola), now a research member at Lincoln Laboratory and continued training graduate and undergraduate students. This group has a strong record of giving undergraduates their first research positions and three undergraduate students are currently assisting them.
