Plasma instabilities in meteor trails:linear theory

Ablation of micrometeoroids between 70 and 130 km altitude in the atmosphere creates plasma columns with densities exceeding the ambient ionospheric electron density by many orders of magnitude. Density gradients at the edges of these trails can create ambipolar electric fields with amplitudes in excess of 100 mV/m. These fields combine with diamagnetic drifts to drive electrons at speeds exceeding 2 km/s. The fields and gradients also initiate Farley-Buneman and gradient-drift instabilities. These create field-aligned plasma density irregularities which evolve into turbulent structures detectable by radars with a large power-aperture product, such as those found at Jicamarca, Arecibo, and Kwajalein. This paper presents a theory of meteor trail instabilities using both fluid and kinetic methods. In particular, it discusses the origin of the driving electric field, the resulting electron drifts, and the linear plasma instabilities of meteor trails. It shows that though the ambipolar electric field changes amplitude and even direction as a function of altitude, the electrons always drift in the positive ∇n × B direction, where n is the density and B the geomagnetic field. The linear stability analysis predicts that instabilities develop within a limited range of altitudes with the following observational consequences: (1) nonspecular meteor trail echoes will be field-aligned; (2) nonspecular echoes will return from a limited range of altitudes compared with the range over which the head echo reflection indicates the presence of plasma columns; and (3) anomalous cross-field diffusion will occur only within this limited altitude range with consequences for calculating diffusion rates and temperatures with both specular and nonspecular radars

Modelling high-power large-aperture radar meteor trails

Despite decades of research, many questions remain about the global flux of meteoroids at Earth, their influence on the atmosphere, and their use as upper atmospheric diagnostics. We see high-power large-aperture (HPLA) radar observations of meteor phenomena called head echoes and non-specular trails as a valuable tool for answering these questions. In the past we conducted plasma simulations demonstrating that meteor trails are unstable to growth of Farley-Buneman gradient-drift (FBGD) waves that become turbulent and generate large B-field aligned irregularities (FAI). These FAI result in reflections called non-specular meteor trails. Using these and other results, we have developed a model that follows meteor evolution from ablation and ionization through the creation of radar head echoes and non-specular trail reflections. This paper presents results from this model, showing that we can reproduce many aspects of these large radar observations, such as the general altitude profile of head echoes and non-specular trails. Additionally we show that trail polarization due to E-fields or neutral winds causes a noticeable trail feature as well as may be responsible for trails lasting longer than about 1 s. We also demonstrate how such a model is a valuable tool for deriving meteoroid properties such as flux, mass, and velocity. Finally, such a model could also provide some composition information, and diagnose the atmosphere and ionosphere where meteors produce their trails

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat Mission: A Pathfinder for a New Measurement of Earth\u27s Radiation Budget

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) mission is a 3U CubeSat pathfinder for a constellation to measure the Earth’s radiation imbalance (ERI), which is the single most important quantity for predicting the course of climate change over the next century. RAVAN will demonstrate a small, accurate radiometer that measures top-of-the-atmosphere Earth-leaving fluxes of total and solar-reflected radiation. RAVAN demonstrates two key enabling technologies. The first is the use of vertically aligned carbon nanotubes (VACNTs) as a radiometer absorber. VACNT forests are some of the blackest materials known and have an extremely flat spectral response over a wide wavelength range. The second key technology is a gallium fixed-point black body calibration source, which serves as a stable and repeatable reference to track the long-term degradation of the sensor. Absolute calibration is maintained by regular solar and deep space views. The RAVAN payload will fly on a 3U CubeSat that combines stellar attitude determination, sub-degree pointing, and both UHF and Globalstar communication. RAVAN will help enable the development of an Earth radiation budget constellation mission that can provide the measurements needed for superior predictions of future climate change