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 × 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.