THEORY OF LARGE-SCALE STRATIFICATION IN COMETARY PLASMA TAILS

We study the successive development of ion-acoustic and filamentation instabilities of solar wind in cometary plasma tails to clarify the me chanism of formation of the ray structure. For the case in which ion-a coustic turbulence is important, we estimate the effective frequency o f electron scattering from ion-acoustic oscillations (v(eff)). We cons truct a linear theory of filamentation instability for the nondissipat ive (v(eff) = 0) and dissipative (v(eff) not-equal 0) cases. We show t hat filaments of considerably larger spatial scales are formed in the latter case. We carry out numerical modeling of the process of combini ng of filaments at the nonlinear stage of instability, and we establis h that their maximum size corresponds approximately to the maximum pos sible wavelength obtained in the linear theory, i.e., 5 . 10(3) - 10(4 ) km. We suggest a possible scenario, for large-scale plasma stratific ation in cometary plasma tails.