Parker's model prediction of an unbounded solution for the supersonic solar wind plasma (SWP) requires a subsonic origin at the solar surface. The transition to supersonic SWP flow is well understood by analogy with the de Laval nozzle. The basic physics, however, of the self-consistent solar surface emission of subsonic SWP is still not very clear. We propose a theoretical model based on a gravito-electrostatic plasma sheath (GES) to investigate the surface emission mechanism of the quasi-neutral SWP. The basic equations for the interior steady state description are solved numerically as an initial-value problem under spherical geometry. A bounded solution for the solar self-gravity distribution is found to exist, meaning that a global quasi-hydrostatic equilibrium is formed at some distance from the heliocentric origin. This defines the solar surface boundary in our model, which lies at radius $ 3.5 (in units of the Jeans length). A minimum speed of $3.0 cm s À1 , corresponding to Mach number $10 À7 , is obtained at this location. Consequently, a subsonic origin of the solar interior plasma flowing radially outward becomes a physical reality. Our model requires a mean electron temperature T e $ 10 7 K (=1 keV) for the numerical results to match the standard solar values. The boundary is found to be negatively biased, with a normalized value of the electrostatic potential s $ À1 (=1 kV ). It is conjectured that our model provides an interesting new physical basis for understanding the collective dynamical coupling processes of solar interior and exterior ( heliosphere) regions through local, as well as global, modes of GES-induced collective waves, instabilities, and oscillations.

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It is recently discussed that a plasma system with drifting ions at near the acoustic phase speed becomes susceptible to weak but finite electron inertial delay effect. In such plasma condition, the linear normal modes of acoustic oscillations undergo resonant linear growth. Such situation exists naturally in transonic zones of boundary plasma layers. The present contribution considers this as a specific case to describe the possible role of an external source driving on the usual ion acoustic soliton solution in the unstable region of the transonic zone assumed to have finite extension. A driven Korteweg-de Vries equation is obtained that is not exactly integrable. It is shown by numerical analysis that the usual acoustic soliton solution exists only for infinitely long wavelength source perturbation. For short wavelength (but within the limit of the long wavelength approximation) source perturbations interesting solutions of single unit of localized oscillatory shock-like structure are obtained. Possible physical interpretations of the results are included in the text.Ã Bharat is an ancient country and is also known as India in recent times.

The pulsational mode of gravitational collapse (PMGC) in a hydrostatically bounded dust molecular cloud is responsible for the evolution of tremendous amount of energy during star formation. The source of free energy for this gravito-electrostatic instability lies in the associated self-gravity of the dispersed phase of relatively huge dust grains of solid matter over the gaseous phase of background plasma. The nonlinear stability of the same PMGC in an infinite dusty plasma model (plane geometry approximation for large wavelength fluctuation in the absence of curvature effects) is studied in a hydrostatic kind of homogeneous equilibrium configuration. By the standard reductive perturbation technique, a Korteweg-de Vries (KdV) equation for investigating the nonlinear evolution of the lowest order perturbed self-gravitational potential is developed in a time-stationary (steady-state) form, which is studied analytically as well as numerically. Different nonlinear structures (soliton-like and soliton chain-like) are found to exist in different situations. Astrophysical situations, relevant to it, are briefly discussed.

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