Olga P. Verkhoglyadova

Three-dimensional model of ray structure formation in cometary plasma tails

Abstract The theoretical model of large-scale ray structure formation proposed in a preceding paper (Verkhoglyadova et al., Lett. Russ. Astro. J. , 19 , 823–869, 1993) resides in filamentation instability development due to the solar wind flow partially penetrating into the cometary plasma tail. In order to study a real form of the filaments and instability development in space a study of the proposed mechanism in three dimensions is made. Cometary plasma ions and those of the solar wind seem to be collisionless, otherwise collisions of electrons dealing with scattering on ion-acoustic oscillations are characterized by effective collision frequency. The cometary plasma filaments, which are observed as bright rays, are formed due to instability development and take the form of cylindrical plasma fibers with the thickness determined by cometary plasma parameters and those of the solar wind. Under some assumptions we obtain the characteristic length which may be thought of as the maximum ray size. We evaluate the number of rays within one lobe of cometary plasma tail which varies at a range of 2–30 rays. The observational evolution of the ray structure is discussed.

Paraboloidal model for formation of plasma envelopes and ray structures in the cometary ionosphere

Abstract A three-dimensional model of the large-scale stratification of the cometary ionosphere is studied. A physical mechanism for the development of filamentation instability is proposed. The study is carried out in terms of linear magnetohydrodynamics in the paraboloidal geometry of the cometary ionosphere. This model enables the formation of both paraboloidal envelopes covering the cometary head and ray system in the tail to be studied. A numerical simulation of the nonlinear processes by the CIC method is made. Shape, thickness and formation time of these plasma structures are discussed. Formation processes are simulated for different physical parameters.