Asymptotic theory of ion conic distributions

Abstract

The formation of ion conics is discussed in terms of a model which permits an asymptotic determination of the ion distribution function. This model is applicable to a class of observed ion conic events where the ion energization is attributable to lower hybrid wave activity. A two‐stage process is considered wherein the upward moving component of the ambient ion population is first subjected to a region of weak turbulence and is then allowed to drift adiabatically up the geomagnetic field. Identification of the ratio of ion thermal speed to mean wave speed as a small parameter leads to a uniformly valid solution of the quasilinear diffusion equation. The resulting analytic form for the ion conic is then available for further analytic work. Implications and limitations of the model will be discussed.